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HDL, which is assembled in the plasma through the

action of LCAT (lecithin:cholesterol acyltransferase)

from hepatic or enteric nascent HDL, transports chol-

esterol from peripheral tissues to the liver and func-

tions as an acceptor/donor of apolipoproteins to

other lipoproteins (Figure 3). Among the lipoproteins

that transport endogenously synthesized lipids,

VLDLs are the principal source of triacylglycerols

for the tissues (50–55%).

0012 In the postprandial state, circulating chylomicrons

interact with HDL and acquire apolipoproteins E and

CII. Apolipoprotein CII activates the enzyme lipopro-

tein lipase in the capillary endothelium of adipose

tissue and skeletal muscle. The interaction between

the particle and the enzyme causes hydrolysis of

the triacylglycerols in the core of the chylomicron.

Repeated action of the lipases as the blood circulates

removes most of the triacylglycerols, and the resulting

particle (chylomicron remnant) is enriched in choles-

teryl esters, apo-B

, and apo-E. Apo-CII returns to

HDL. In the liver, specific remnant receptors are

activated by apo-E, and the remnants are taken into

the cell by endocytosis. Lysosomal hydrolysis in the

hepatocytes liberates fatty acids, cholesterol, and

amino acids. The overall result of the chylomicron

transport process is completed as dietary tria-

cylglycerols are delivered to peripheral tissues and

cholesterol to the liver.

0013 Lipids within the liver, formed by de novo synthesis

from carbohydrates (lipogenesis), chylomicron rem-

nants, and nonesterified fatty acids (NEFA) mobilized

from the adipose tissue, are incorporated into VLDL

particles and secreted into the blood stream during

the postabsorptive or fast period. The assembly and

secretion of hepatic VLDL is a complex process, and

the final particle is composed of a relatively rich core

of triacylglycerols with smaller amounts of choles-

teryl ester, surrounded by a monolayer of phospho-

lipids and cholesterol enclosed by apo-B

100

that

differs from the apo-B

secreted by the enterocytes.

In the hepatocytes, MTP plays a comparable role, as

in the enterocytes, in the assembly of triacylglycerides

with apo-B

100

. Secreted VLDL receives apo-CII and

apo-E from HDL and is acted upon by the lipoprotein

lipase in the same way as the chylomicrons. The

resultant lipoprotein of VLDL is an IDL. Some of

the IDL are catabolized in the liver through binding

to a specific receptor. The IDL particles that remain

in the plasma undergo transformation resulting in

the conversion to LDL. In this process, all the apoli-

poproteins are removed, with the exception of

apo-B

100

. LDL is almost entirely composed of cho-

lesteryl esters surrounded by apo-B

100

. LDL can be

further delipided, resulting in small dense LDL that

are more atherogenic. Circulating LDL delivers

cholesterol to hepatic and extrahepatic tissues, and

the process involves the interaction with a specific

receptor in the cell membrane (LDL receptors).

0014In the liver, cholesterol is converted to bile acids

or incorporated into the bile and excreted into the

intestine to facilitate lipid absorption. Hepatic chol-

esterol is also distributed to other tissues as it is

incorporated into VLDL. Circulating HDL capture

plasma unesterified cholesterol formed from cell

degradation and convert it to cholesteryl ester

through the action of LCAT. The cholesteryl ester

moves to the core of the particle. LCAT is activated

by apo-AI, the major apolipoprotein present in the

HDL (Figure 3). Major subclasses of HDL are desig-

nated HDL

and HDL

based on density. By the

action of LCAT, HDL

is produced from discoidal

HDL and HDL

from HDL

. HDL

also exchange

lipids with other lipoproteins (chylomicrons and

VLDL fractions) through the action of the enzyme

cholesterol ester:transfer protein (CEPT). Hepatic

lipase acts on IDL and HDL

-triacylglycerol and a

phospholipase on HDL

-phospholipid, which gener-

ates LDL and HDL

, respectively (Figure 3). These

reactions establish a cycle by which cholesterol is

removed and returned to peripheral tissues or is

disposed of by the liver.

See also: Cholecalciferol: Properties and Determination;

Physiology; Cholesterol: Absorption, Function, and

Metabolism; Coronary Heart Disease: Etiology and Risk

Factor; Fatty Acids: Properties; Metabolism; Dietary

Importance; Phospholipids: Properties and Occurrence;

Physiology; Retinol: Properties and Determination;

Physiology; Tocopherols: Properties and Determination;

Physiology; Triglycerides: Structures and Properties;

Characterization and Determination

Further Reading

Applebaum-Bowden D (1995) Lipases and lecithin:choles-

terol acyltransferase in the control of lipoprotein metab-

olism. Current Opinion in Lipidology 6: 130–135.

Gibbons GF, Islam K and Pease RJ (2000) Mobilization of

triacylglycerol stores. Biochimica et Biophysica Acta

1482: 37–57.

Hussain MM, Kedees MH, Singh K, Athar H and Jamali

NZ (2001) Signposts in the assembly of chylomicrons.

Frontiers in Bioscience 6: D320–D331.

Ros E (2000) Intestinal absorption of triglyceride and

cholesterol. Dietary and pharmacological inhibition

to reduce cardiovascular risk. Atherosclerosis 151:

357–379.

Spiller GA (ed.) (1996) Lipids in Human Nutrition. New

York: CRC Press.

Van Greevenbroek, MMJ and de Bruin TWA (1998)

Chylomicron synthesis by intestinal cells in vitro and

in vivo. Atherosclerosis 141: S9–S16.

2278 FATS/Digestion, Absorption, and Transport

Requirements

N M F Trugo and A G Torres, Universidade Federal

do Rio de Janeiro, Rio de Janeiro, Brazil

Background

0001 Dietary fat is a term used to designate the major

dietary lipids, triacylglycerols. Other dietary lipids

are the phospholipids, sterols, waxes, fat-soluble vita-

mins, carotenoids, and other minor compounds. Fats

are required in the human diet to provide energy and

essential fatty acids, and to improve the absorption of

fat-soluble vitamins, among other functions. They

can also enhance food palatability and influence

food texture.

0002 Determination of fat requirements as a basis for

recommendations is a complex issue owing to the

inherent characteristics of fat metabolism and its inter-

action with energy metabolism. Furthermore, recom-

mendations of desirable ranges of fat intake are

influenced by scientific controversies and changing

views on both the benefits and risks to human health

associated with fat intake. Recommendations may

also vary according to the dietary patterns and the

prevalence of diet-related noncommunicable diseases

in a determined population and in different physio-

logical situations throughout the life-cycle. Most of

the data available relating fat intake and health in the

general population come from studies in affluent soci-

eties and deal with the prevention of chronic diseases,

possibly caused by excessive fat intake. An adequate

level of fat intake in physiological periods of high and/

or special demands has also been of concern. During

early development, adequate fat provision will not

only influence fetal and infant nutrition but will also

have consequences on health in later life.

0003 In this chapter, fat requirements based on current

scientific knowledge and the accepted recommen-

dations regarding fat intake for the general adult

population, for pregnant and lactating women, and

for infants and young children will be specifically

addressed.

Fat Requirements for the General

Population

Dietary Fat and Energy

0004 Dietary fat intake world-wide is highly variable,

ranging from less than 10 to approximately 45%

of total energy, being highest among affluent societies.

Triacylglycerols present a high digestibility (approxi-

mately 95–99%) and the highest energy density

among macronutrients (approximately 9 kcal g

1

38 kJ g

1

). Since the metabolic fate of individual fatty

acids depends on dietary energy and on energy bal-

ance, the intake and requirements for fat and essential

fatty acids (EFA) are usually described as the percent-

age of energy in the diet (en%), rather than total

intake (g).

0005Since the contribution of dietary protein to energy

intake shows little variation, low-fat diets are associ-

ated with high carbohydrate intakes, and high fat

diets with low carbohydrate intakes. Although it is

generally assumed that a low fat intake helps to pre-

vent the development of chronic diseases, this may

not be necessarily true, since a consequent high intake

of carbohydrates can have specific metabolic effects

that, in the long term, may lead to chronic diseases,

such as type 2 diabetes. Therefore, a compromise

should be pursued, regarding an optimal ratio of fat

to carbohydrate in the diet. It is currently accepted

that dietary fat intake should be moderate: up to

30 en% for sedentary or overweight individuals or

up to 35 en% for lean, active individuals, to avoid or

minimize the occurrence of chronic diseases associ-

ated with high fat intakes. In contrast, fat intake

should not be lower than 15 en%, since low fat

intakes, common in developing countries especially

in rural areas, could limit energy intake and also

reduce the absorption of liposoluble vitamins and

essential fatty acids.

0006It has been hypothesized that high levels of dietary

fat could lead to obesity. Although it is generally

accepted that obesity is the result of a chronic positive

energy balance, the homeostatic mechanisms in-

volved in the regulation of energy metabolism

discriminate between energy substrates, at both the

cellular and whole-body levels. The metabolism of

protein and carbohydrates is strictly regulated in the

acute and long terms, possibly because of their rela-

tively small storage capacity. Fat, in contrast, has a

high storage capacity and is subjected to less efficient

homeostatic controls. Additionally, it has been well

demonstrated that healthy humans do not synthesize

fatty acids de novo in appreciable amounts, when

eating moderately low and appropriate amounts of

fat and carbohydrates, respectively. These evidences

lead to the suggestion that high fat intakes per se

could lead to net weight accretion and obesity.

However, an elevated fat consumption alone would

not lead to weight gain if not accompanied by a

positive energy balance. An elevated consumption of

fat is generally associated with high energy intakes,

possibly due to a phenomenon known as passive

overconsumption or simply due to the elevated

energy density of fat. A restriction of dietary fat

intake up to the level of 30 en% could help to reduce

FATS/Requirements 2279

energy intake and to improve health. However, fat

restriction should be accompanied by total energy

restriction and by an exercise plan if weight reduction

is to be attained.

Saturated and Unsaturated Fats

0007 The molecular structure of fatty acids will determine

their metabolic fate and effects from the cellular level

to the whole organism. Fatty acids vary in their chain

length, number, position, and geometric configuration

of double bonds, which are the main structural differ-

ences affecting fatty acid metabolism and, con-

sequently, requirements. Saturated fatty acids are

devoid of double bonds, whereas unsaturated fatty

acids may have one (monounsaturated) or more

(polyunsaturated) double bonds in their carbon

chain.

0008 Saturated fatty acids are high in animal fats and

palm and coconut oils, and their intake is associated

with some of the negative metabolic effects of fats,

especially those related to the development of

cardiovascular diseases (mainly atherosclerosis and

coronary heart disease). The critical links between

saturated fat consumption and cardiovascular dis-

eases are total blood cholesterol and low-density

lipoprotein (LDL)-cholesterol levels, and thrombosis.

Thrombosis is the major determinant of morbidity

and mortality from coronary heart disease, and may

be caused by elevated saturated fat in the diet.

Controlled trials demonstrated that the saturated fat

content, as well as the type of saturated fatty acids in

the diet, affect serum lipid and lipoprotein levels. The

consumption of saturated fatty acids, compared with

that of carbohydrates, leads to an increase in total

and LDL-bound cholesterol, and it is very likely that

high serum cholesterol levels may cause atheroscler-

osis and coronary heart disease. Therefore, saturated

fat intake should be restricted to less than 10 en%.

Saturated fatty acids are not equally atherogenic, lau-

ric (12:0), myristic (14:0), and palmitic (16:0) acids

seem to elevate LDL-cholesterol levels when com-

pared with carbohydrates, whereas fatty acids with

less than 12 carbon atoms (short and medium chain

fatty acids) and stearic acid (18:0) seem to have only

slight or no effects. These effects are justifiable by the

different metabolic fates of these saturated fatty

acids. Short-chain fatty acids seem to be oxidized

more efficiently than long-chain fatty acids, and

stearic acid is probably converted to oleic acid

(18:1n-9) very rapidly. Although there are differences

in the potency of lauric, myristic, and palmitic acids,

they are considered the major hypercholesterolemic

saturated fatty acids. In case of palmitic acid, its

position in the triacylglycerol molecule is also of

importance. When bound to the C-2 atom of the

glycerol molecule (as in pork lard), it is more

hypercholesterolemic than in the C-1 position (such

as in palm oil or cocoa butter). A reduction in total

saturated fat intake should lead to a decreased con-

sumption of the three aforementioned fatty acids

since they are usually the most abundant saturated

fatty acids in the diet.

0009Contrary to saturated fat intake, unsaturated fat

intake leads to a decrease in serum cholesterol and

LDL-cholesterol levels when substituting for carbo-

hydrates in the diet. The magnitude of this effect is

modest when compared with the cholesterol-raising

effect of saturated fat. When limiting the intake of

saturated fat up to 10 en%, unsaturated fat consump-

tion should increase. The number and position of

double bonds in unsaturated fatty acids will influence

their effects on serum lipids and lipoproteins levels.

The main polyunsaturated fatty acids (PUFA) in the

human diet are of the n-6 and n-3 series, and increas-

ing their intake up to a certain limit should have

beneficial effects on human health. However, PUFA

are susceptible to peroxidation and generation of

reactive oxygen species, which could increase the

susceptibility of LDL to oxidation, leading to an in-

creased risk of atherosclerosis, and are also involved

in the etiology of certain types of cancer. Therefore,

PUFA intake should not be higher than 10 en%.

0010Although the consumption of monounsaturated

fatty acids slightly decreases serum cholesterol and

LDL-cholesterol levels, they are generally considered

metabolically ‘neutral’ when compared with poly-

unsaturated and saturated fatty acids. Therefore,

monounsaturated fat intake should account for the

remaining of the energy intake contributed by fat,

which should correspond to more than 10 en%.

However, when the intake of cis-monounsaturated

fatty acids is elevated (18:1n-9/18:2n-6 ratio of

10:1), essential fatty acid deficiency may occur.

Essential Fatty Acids

0011Since animals, in contrast to vegetables, are incapable

of synthesizing fatty acids with double bonds at

positions n-6 or n-3, owing to a lack of D-12 and

D-15 desaturase activities, these compounds should

be present in the human diet. Linoleic (18:2n-6)

and a-linolenic (18:3n-3), considered essential for

humans, are the main fatty acids of the n-6 and n-3

series in the modern diet. Owing to the high intake of

vegetable oils, linoleic acid is present in the diet in

higher amounts than a-linolenic acid. PUFA are in-

corporated into cellular membranes where they pre-

sent structural functions. In addition, 18:2n-6 and

18:3n-3 are substrates for the synthesis of long-

chain polyunsaturated fatty acids with 20 or 22

carbon atoms (LCPUFA): arachidonic acid (20:4n-6;

2280 FATS/Requirements

ARA), dihomo-g-linolenic acid (20:3n-6), eicosa-

pentaenoic acid (20:5n-3; EPA), and docosahexae-

noic acid (22:6n-3; DHA). DHA has an important

structural role in the brain and retina, and the

LCPUFA with 20 carbon atoms are precursors for

the synthesis of eicosanoids, a group of important

signaling molecules.

0012 When EFA are not present in the diet in appropriate

amounts, deficiency will take place, and various

tissues and organs will be affected, owing to EFA

ubiquitous structural and regulatory functions. Al-

though its validity has already been questioned, the

tissue ratio of 20:3n-9 (Mead’s acid) to 20:4n-6

(triene/tetraene ratio) is still considered a sensitive

biochemical marker of essential fatty acid deficiency

and should be lower than 0.4 for the human. Mead’s

acid is the product of elongation and desaturation

of oleic acid, which is an important substrate for

elongases and desaturases only in the case of defi-

ciency of n-6 and n-3 fatty acids. Diets with 0.1–0.5

en% of linoleic acid are sufficient to normalize an

abnormally high triene/tetraene ratio, but for optimal

function of various tissues, much higher intakes of

18:2n-6 are necessary. The adequate level of linoleic

acid in the diet depends on the criteria used for its

determination. It has been recommended that linoleic

acid intake should be 1–2 en% to avoid clinical and

biochemical signs of EFA deficiency, whereas its

intake should be 3–5 en% for the prevention of

chronic diseases.

0013 a-Linolenic acid is much less efficient in the treat-

ment of EFA deficiency than linoleic acid, raising the

possibility that the former is a conditionally essential

nutrient. However, its essentiality for the develop-

ment and maintenance of normal functions in the

retina and brain has now been confirmed, although

the adequate level of intake has not yet been strictly

determined. It has been estimated that for adult men,

the consumption of 2 g day

1

of 18:3n-3 should pro-

vide 75–85% of the 350–400 mg day

1

requirement

of long-chain n-3 fatty acids (20:5n-3 and 22:6n-3).

The intake of approximately 1 en% or 3 g day

1

18:3n-3 and 800 mg of 20:5n-3 plus 22:6n-3 should

provide an adequate supply of n-3 fatty acids for

healthy adults.

0014 Fatty acids of the n-3 and n-6 series will compete

for the same enzymatic systems: acyl-transferases

for incorporation into membranes; elongases and

desaturases for LCPUFA synthesis; and lipoxygenase,

cycloxygenase and other enzymes for eicosanoid syn-

thesis. Therefore, the balance between tissue levels of

n-3 and n-6 fatty acids will depend on the balance

between dietary EFA. Although the optimal ratio of

n-6/n-3 in the diet has been set between 4:1 and 10:1,

scientific evidence is lacking to support ratios equal or

higher than 5:1. Furthermore, an adequate tissue

ratio of n-6 to n-3 is important to prevent coronary

heart disease and stroke, since n-6 fatty acids are

precursors of eicosanoids that stimulate platelet

aggregation and vasoconstriction, in contrast to

n-3 fatty acids, which are precursors of eicosanoids

that stimulate vasodilatation and are much less

aggregatory.

Isomeric Fatty Acids

0015The double bonds in fatty acids may present two

geometrical configurations: cis (the most common)

and trans. Trans fatty acids are formed during partial

hydrogenation of vegetable fats and oils, which are

widely used in the food industry for the production of

margarine, shortenings, frying fats, among other

products. Isomeric fatty acids formed through bio-

hydrogenation in the rumen may be naturally present

in meat, milk, and dairy products, which are enriched

in trans-11-octadecenoic acid (trans-11–18:1). The

main sources of total trans fatty acids in the Western

diet are the hydrogenated vegetable fats, which are

rich in octadecenoates with double bonds between D9

and D12.

0016The consumption of monoenes with a trans double

bond has long been associated with elevated total and

LDL-bound cholesterol in serum, and possibly with

reduced levels of high-density lipoprotein cholesterol.

In controlled trials in which the trans fatty acid intake

was increased, an increment in total and LDL-bound

cholesterol in serum occurred. It has also been

hypothesized that trans fatty acids are more potent

in eliciting such effects than saturated fatty acids.

However, this subject is still a matter of debate,

because the dietary levels that would lead to altered

serum lipid and lipoprotein levels are much higher

than that generally consumed. It is a consensus that

trans fatty acids intake should be kept low (up to

approximately 2 en%), but apparently, there is no

need for further limiting when the intake of total fat

and of essential and saturated fatty acids is appropri-

ate. However, it should be emphasized that con-

sumers of higher amounts of trans fatty acids may

present a higher risk of morbidity from cardio-

vascular diseases.

0017Other geometrical isomers of unsaturated fatty

acids are also present in foodstuffs, the conjugated

fatty acids, which are polyunsaturated fatty acids

with conjugated double bonds, i.e., double bonds

separated by two carbon atoms instead of three.

The main dietary sources of conjugated fatty acids

are meat and dairy products from ruminants, and the

most common are the octadecadienoic or conjugated

linoleic acids (CLA). Conjugated linoleic acids have

important biological effects that could be beneficial,

FATS/Requirements 2281

even when present in the diet at very low amounts

(1 en%). Effects of CLA range from a potent anti-

carcinogenic effect to changes in body composition

with reduction in the adipose tissue size. Advisable

and upper tolerable levels of intake for CLA have not

yet been defined, because of the scarce scientific data

concerning CLA consumption and its effects in

human subjects.

Fat Requirements During Pregnancy and

Lactation

Pregnant Women

0018 In the periconceptional period, maternal nutrition

is particularly important owing to its influence on

the physiological process of fat accretion during

pregnancy. Maternal fat stores are critical for placen-

tal development and embryonic cell division and dif-

ferentiation in the first trimester of pregnancy, for the

intense fetal growth during the third trimester, and

for the production of milk in early lactation. The

building up of adequate fat stores requires an increase

in energy and fat intakes during pregnancy. The

estimated additional energy for pregnant women

according to the WHO Report on Energy and Protein

Requirements (1985) is 300 kcal day

1

for the whole

pregnancy, with 30 en% as fat. Dietary energy from

fat should not be lower than 20% for women

of reproductive age, who might otherwise be ex-

posed to an insufficient supply of EFA and fat-soluble

vitamins.

0019 Owing to the demands of EFA for fetal, placental,

mammary gland, and uterine growth, and for the

increase in maternal blood volume, maternal EFA

intake during pregnancy should be increased from

3 to 4.5% of the total energy, and the ratio n-6/n-3

should be maintained at approximately 5:1.

0020 High consumption of fish and dietary supplemen-

tation with n-3 LCPUFA are associated with a modest

increase in the length of gestation and with reduced

incidence of low birth weight and prematurity, sug-

gesting that the dietary consumption of preformed

DHA could be advantageous.

0021 Placental transfer of ARA and DHA during preg-

nancy occurs preferentially in relation to other fatty

acids. This can be explained by the presence of a

plasma membrane fatty acid-binding protein that

presents the highest affinities and binding capacities

for both fatty acids, especially DHA. It seems that

elongation and desaturation of EFA in human pla-

centa are limited, and the fetus depends on the trans-

fer of ARA and DHA from maternal circulation.

There is a substantial increase of ARA and DHA in

fetal circulation, and fetal organs such as the liver and

brain incorporate large amounts of n-3 and n-6

LCPUFA into membrane phospholipids by the end

of the third trimester. Therefore, the preterm infant

will be endowed with a reduced provision of ARA

and DHA in utero, and will be at a disadvantage

concerning fat stores and membrane LCPUFA when

compared with term infants.

0022Prematurity and low birth weight are associated

with a high risk of neurodevelopmental disorders

and disabilities. An inadequate supply of ARA and

DHA during the period of rapid vascular and brain

growth could lead to membrane fragility, leakage and

breakdown, resulting in ARA peroxidation, vasocon-

striction, inflammation, and ischemia, which could

explain those disabilities. Fetal exposure to trans

fatty acids, which are transferred across the placenta,

has been related to low birth weight in premature

infants.

Lactating Women

0023The total fat content in human milk is highly variable

and is affected by several factors but is secreted

in adequate amounts to support infant growth and

development in a wide range of maternal nutritional

status, unless overt undernutrition is present. The

fatty acid composition of the triacylglycerols in

milk, however, is dependent on maternal fatty acid

intake, body stores, and endogenous synthesis. Gesta-

tional age, stage of lactation, nutritional status, and

genetic background may also influence the fatty acid

composition of human milk.

0024Saturated and monounsaturated fatty acids are

the major fatty acids in human milk, comprising ap-

proximately 83% (wt/wt) of the total fatty acids in

mature milk. In well-nourished mothers, approxi-

mately 11% (wt/wt) of fatty acids in human milk is

linoleic acid and 1% a-linolenic, while total n-6 and

n-3 LCPUFA account for 1.2 and 0.6%. Total PUFA

accounts for 6% of total energy in milk. PUFA

transfer from maternal circulation to milk and the

synthesis of LCPUFA from the EFA precursors are a

matter of concern, because of their importance for

infant growth, neurodevelopment, and visual func-

tion. Studies with lactating women using stable iso-

tope methodologies demonstrated that the major part

of PUFA in human milk is derived from maternal body

stores, which reflect long-term intake, and not from

direct dietary transfer. In women on omnivorous diets,

about 30 and 12%, respectively, of linoleic acid and

ARA secreted in milk were derived from the diet.

Endogenous synthesis from dietary linoleic acid

accounted for about 3–25% and 1–3% of dihomo-

g-linolenic acid and ARA in milk, respectively.

0025Assuming an appropriate weight gain during

pregnancy, an additional average energy allowance

2282 FATS/Requirements

of 500 kcal day

1

is recommended throughout lacta-

tion, according to WHO (1985). An additional ma-

ternal intake of 1–2% of energy in the form of EFA

(3–4 g day

1

) is recommended during the first 3

months of lactation, and thereafter a further increase

of up to 4% of energy (about 5 g day

1

) is required,

owing to depletion of maternal fat stores. An inverse

correlation between trans fatty acids and ARA and

DHA in plasma lipids has been reported in infants,

suggesting an impairment in LCPUFA synthesis and

metabolism. Therefore, maternal intake of trans fatty

acids is of concern when their intake is excessively

high or when EFA intake is low during pregnancy and

lactation.

Fat Requirements in Infancy and Early

Childhood

0026 Both the amount and quality of dietary fat can affect

child growth and development. Breast milk is the best

available source of dietary fat and fatty acids for

infants, providing between 50 and 60 en% as fat

and LCPUFA in adequate amounts for brain develop-

ment. The human infant should be preferentially

breast-fed, but when infant formulas are used, the

fatty acid composition should ideally correspond to

that of breast milk. Of special concern is the adequate

provision of LCPUFA to preterm infants who present

an insufficient intrauterine supply of these fatty acids.

0027 LCPUFA are required for adequate brain growth

and development. Their requirements are especially

high during the last trimester of pregnancy and in the

first months of life, when the brain is rapidly develop-

ing, and there is a significant deposition of DHA in

the central nervous system. The brain gray matter and

membranes of the retina present low deposition of

EFA but contain high amounts of LCPUFA, which

can be incorporated from plasma.

0028 Synthesis of LCPUFA was demonstrated in term

infants from the first week of life and even in very-

low-birth-weight infants through stable isotope meth-

odologies. However, the contribution of endogenous

synthesis to the total plasma LCPUFA pool is small.

The rate of ARA synthesis in term infants is low, and

it accounts for only about 6% of total ARA renewal

in plasma. Therefore, the term infant and especially

the preterm infant possibly do not synthesize enough

LCPUFA to attain their requirements for brain devel-

opment during the first few weeks after birth.

0029 Infants fed human milk, compared with infants

fed DHA-free formulas, present higher plasma con-

centrations of LCPUFA and also higher levels of

DHA in red blood cell phospholipids and in brain

cortex. Clinical trials in premature infants showed

beneficial effects of infant formulas enriched in ARA

and DHA, such as higher LCPUFA concentrations in

plasma, improvement of visual acuity and cognitive

abilities, without compromising growth and safety.

Several studies with healthy full-term infants indi-

cated that infants fed breast milk or DHA-supple-

mented formulas presented better visual resolution

acuity at 2 months and possibly at 4 months of age

than infants fed DHA-free formulas.

0030A WHO/FAO Expert Committee (1994) based its

recommendations for EFA and LCPUFA provision to

infants on the composition of breast milk from well-

nourished mothers, which provides both parent EFA

and their LCPUFA products in apparently adequate

amounts to fulfill infants’ requirements. The WHO/

FAO recommendations described below are similar to

those published in position papers of other national

and international expert committees.

0031Total EFA (n-6 plus n-3) should comprise 5–6 en%

(or 0.6–0.8 g kg

1

day

1

) and LCPUFA 0.8 en%. The

total n-6/n-3 ratio should be in the range of 5:1 to

15:1. To insure tissue proliferation, membrane

integrity, and eicosanoid formation, linoleic acid

should be supplied as a minimum of 1–4.5 en% or

0.5–0.6 g kg

1

day

1

, but its intake should be limited

to amounts lower than 10–12 en%, since its excess

impairs production of the n-3 LCPUFA. Arachidonic

acid could be considered conditionally essential

during early development, owing to its specific neural

and vascular functions, the role of its derived eicosa-

noids in cell regulation, and the interactions between

the n-3 and n-6 fatty acids series. In this regard, 40 mg

of ARA should be provided for the term infant,

whereas for the premature infant, the amount would

be 60–100 mg kg

1

day

1

, since, in these infants, a

low level of ARA is associated with low pre- and

postnatal growth.

0032Total n-3 fatty acids should amount to 70–150 mg

1

day

1

, and the intake of DHA should be 20 and

40 mg kg

1

day

1

for term and preterm infants, re-

spectively. The DHA/ARA ratio should be 1:1 to

1:2, since excess DHA impairs ARA metabolism.

Intake of a-linolenic acid should be approximately

1 en% in the absence of intake of EPA and DHA, or

0.5 en% when there is a supply of these LCPUFA,

although the bioequivalency of n-3 EFA and its

LCPUFA products has not yet been determined in

infants.

0033Regarding formulas for preterm babies, a mixture

of oleic acid and saturated fatty acids, with a predom-

inance of the former, could provide the required

energy from fat, since this mixture would possibly

meet the desirable criteria of digestibility and lack

of interference with essential fatty acid metabolism.

0034According to the FAO/WHO (1994) recommenda-

tions, during weaning and at least until 2 years of age,

FATS/Requirements 2283

a child’s diet should contain 30–40 en% as fat and

provide similar levels of EFA to those found in breast

milk. Special attention should be given to the comple-

mentary foods used in the weaning period in many

developing countries, where cereals or tuber-based

diets with a low energy density are used, resulting in

a drastic drop in energy intake. Low-fat diets with less

than 30 en% as fat have been associated with adverse

effects on child growth, but this might also have been

associated with a low intake of total energy and other

nutrients.

0035 The increase of the prevalence and severity of

obesity and type 2 diabetes mellitus in the pediatric

population is of particular concern, mainly in affluent

societies, which reinforces the need for appropri-

ate nutrition, including the quantity and quality of

dietary fat, not only in childhood but also in early

development.

See also: Atherosclerosis; Coronary Heart Disease:

Etiology and Risk Factor; Essential Fatty Acids; Fats:

Digestion, Absorption, and Transport; Fatty Acids:

Dietary Importance; Tr a n s -fatty Acids: Health Effects;

Infants: Nutritional Requirements; Lactation: Human

Milk: Composition and Nutritional Value

Further Reading

Al MDM, van Howelingen AC and Hornstra G (2000)

Long-chain polyunsaturated fatty acids, pregnancy and

pregnancy outcome. American Journal of Clinical

Nutrition 71 (supplement): 285S–291S.

Chapkin RS (2000) Reappraisal of the essential fatty acids.

In: Chow CK (ed.) Fatty Acids in Foods and their Health

Implications, 2nd edn, pp. 557–568. New York: Marcel

Dekker.

FAO/WHO (1994) Fats and Oils in Human Nutrition.

Report of a Joint Expert Consultation (19–26 October

1993). Rome: FAO.

Gibson RA and Makrides M (2000) n-3 Polyunsaturated

fatty acid requirements of term infants. American Jour-

nal of Clinical Nutrition 71 (supplement): 251S–255S.

Grundy SM (1999) The optimal ratio of fat-to-carbo-

hydrate in the diet. Annual Reviews of Nutrition 19:

325–341.

Jones PJH and Kubow S (1999) Lipids, sterols, and their

metabolites. In: Shils M, Olson JA

, Shike M and Ross

AC (eds) Modern Nutrition in Health and Disease, 9th

edn, pp. 67–94. Baltimore, MD: Williams & Wilkins.

Koletzko B (1999) Response to and range of acceptable fat

intakes in infants and children. European Journal of

Clinical Nutrition 53: S78–S83.

Pariza MW, Park Y and Cook ME (2000) Mechanisms of

action of conjugated linoleic acid: evidence and specula-

tion. Proceedings of the Society for Experimental Biol-

ogy and Medicine 223: 8–13.

SanGiovanni JP, Berkey CS, Dwyer JT and Colditz GA

(2000) Dietary essential fatty acids, long-chain

polyunsaturated fatty acids, and visual resolution acuity

in healthy fullterm infants: a systematic review. Early

Human Development 57: 165–188.

Sauerwald TU, Demmelmair H, Fidler N and Koletzko B

(2000) Polyunsaturated fatty acid supply with human

milk. Physiological aspects and in vivo studies of metab-

olism. Advances in Experimental Medicine and Biology

478: 261–270.

Uauy R and Hoffman DR (2000) Essential fat requirements

of preterm infants. American Journal of Clinical Nutri-

tion 71 (supplement): 245S–250S.

Vellas B, Chumlea WC and Lanzmann-Petithory D (eds)

(2001) Diet and cardiovascular diseases. Journal of

Nutrition Health & Aging 5: 129–204.

Fat Replacers

B G Swanson, Washington State University, Pullman,

WA, USA

Fat

0001Reducing dietary fat is a major, if not the primary,

dietary goal for many consumers. With encourage-

ment from health groups and government agencies,

the public is increasingly choosing foods and bever-

ages naturally low in fat, as well as new, revolution-

ary low-fat and nonfat foods and beverages.

The development and use of a wide variety of food

ingredients, known as fat replacers, are making many

low fat or nonfat foods possible.

0002Fat, protein, and carbohydrates are essential

components of the human diet. Fat is the most con-

centrated source of energy, contributing 38 kJ g

1

;

protein and carbohydrates contribute approximately

17 kJ g

1

to the diet. Some dietary fat is essential to

enable the body to function properly. Fat is respon-

sible for transporting fat-soluble vitamins A, D, E,

and K and is also a source of essential fatty acids

necessary for good health. (See Essential Fatty Acids.)

0003Most consumers enjoy the taste, texture, and

aroma fat gives to foods. Fat consumption, however,

is often considered too great by public health organ-

izations and nutritionists since a high intake of diet-

ary fat is associated with an increased risk for obesity,

some types of cancer, and possibly gall bladder dis-

ease. Epidemiological, clinical, and animal studies

provide strong and consistent evidence for a relation-

ship between saturated fat intake, high blood choles-

terol, and increased risk for coronary heart disease.

2284 FATS/Fat Replacers

0004 There are two primary types of fat replacers being

investigated: ‘energy-free fat substitutes’ and ‘energy-

reduced fat mimetics.’ Energy-free fat substitutes are

neither digested nor absorbed and therefore contrib-

ute no fat, calories, or cholesterol to the diet. Fat

substitutes are formulated and synthesized to exhibit

physical and cooking properties similar to fats or oils,

and are expected to replace some or all of the fat in

cooking, as well as in foods.

Fat Substitutes

0005 A group of compounds, called sucrose fatty acid

polyesters with the trade names ‘olestra 7’ or ‘olean

7,’ produced by Procter and Gamble Co., were ap-

proved for use in savory snacks by the United States

Food and Drug Administration (FDA) in 1996,

amidst great controversy regarding the potential

health benefits and risks. Recent consumer and indus-

try surveys suggest that the benefits of fat substitutes

far outweight the purported risks, and are being

favorably received by many consumers. Sucrose

polyester fatty acid mono- and di-esters are FDA-

approved emulsifiers at concentrations of less than

1% in food emulsions. (See Emulsifiers: Organic

Emulsifiers.)

0006 Carbohydrate (sucrose) fatty acid polyesters are

synthesized from fatty acid methyl esters and sugars

or sugar derivatives. Fatty acids available from many

triacylglycerol sources and sugars, such as sucrose,

glucose, raffinose, stachyose, and trehalose, as well

as sugar alcohols are combined, with the sugar as the

center and the esterified fatty acids extending away

from the sugar like spokes in a wheel. Sugars heavily

saturated (esterified) with fatty acids, such as hexa-,

hepta-, or octa-fatty acid esters of sucrose, are

not hydrolyzed by sterically and hydrophobically

hindered enzymes in human digestive tracts, are not

absorbed, and are poorly metabolized by colonic

microorganisms. The steric and hydrophobic hin-

drance of lipolytic enzymes is in response to the

many fatty acids esterified to sucrose, and the accom-

panying hydrophobic cloud surrounding the ester

bonds on the sucrose molecule. (See Carbohydrates:

Metabolism of Sugars; Triglycerides: Structures and

Properties.)

0007 Prior to petitioning the FDA for approval of olestra

7, Procter and Gamble evaluated olestra 7 in more

than 100 animal and 25 clinical studies involving

thousands of individuals with no observations of

mutagenic, teratogenic, or developmental responses.

Carbohydrate fatty acid polyesters exhibit organo-

leptic and physical properties similar to conventional

vegetable oils or animal fats (triacylglycerols), includ-

ing necessary heat stability for frying.

0008Structured lipids or medium-chain triacyglycerols

are being prescribed for treatment of patients

suffering from malabsorption symptoms, pancreatic

insufficiency, bile duct obstruction, steatorrhea, and

lipoproteinemia, and to bypass surgery patients and

infants requiring feeding formulas. Structured lipids

are generally triacylglycerols made up of two short to

medium-chain (< 12 carbon) fatty acids combined

with a single long chain (> 12 carbon) fatty acid.

Structured lipids provide the physical and functional

properties of fat while contributing approximately

one-half the calories or normal edible oils. ‘Caprenin

7’ and ‘Salatrim 7’ are structured lipids approved for

use as confectionary fats as well as for use in bakery

and filled dairy products in the USA.

0009Malonate esters, synthesized from malonic acid,

hexadecane, and fatty acids, were developed by

Frito-Lay, Inc. as a calorie-free substitute for high-

temperature frying applications. Feeding studies with

rats indicate that only trace concentrations are

absorbed, and the liver is the primary organ of distri-

bution and elimination.

0010Esterified propoxylated glycerol is similar to a

natural triglyceride, except that oxypropylene is in-

corporated between the glycerol and the fatty

acids. Short-term animal studies suggest that esteri-

fied propoxylated glycerol is safe and resistant to

hydrolysis.

0011Trialkoxytricarballate is also similar to natural tri-

glycerides with tricarballylic acid replacing the gly-

cerol and saturated or unsaturated alcohols replacing

the fatty acids. Animal studies indicate that trialkoxy-

tricarballates are not digested. Trialkoxytricarbal-

lates may be used to replace vegetable oil in cooking

applications as well as in food emulsions.

0012Polyorganosiloxane compounds are also noncalo-

ric, nonabsorbable liquid oils derived from silica that

are chemically inert and not toxic. The polysiloxanes

are stable, maintain viscosity over a wide temperature

range, are resistant to oxidation, hydrolysis, and deg-

radation, and are similar in solubility characteristics

to nonpolar lipids.

0013Jojoba oil and its derivatives have many applica-

tions as constituents of cosmetics and pharmaceut-

icals. Jojoba margarine and mayonnaise have been

shown to exhibit functional properties different than

controls, but perform acceptably in most food appli-

cations. Unfortunately, jojoba oil is sensitive to

hydrolysis by pancreatic lipases. The in vivo digest-

ibility of jojoba oil may be as much as 20%.

0014Other fat-based fat substitutes or replacers include

Dur-Lo, a vegetable oil mono- and diglyceride emul-

sifier manufactured by Durkee Industrial Foods

Corporation, which can replace all or part of the

shortening content in cake mixes, cookies, icings,

FATS/Fat Replacers 2285

and numerous vegetable oil-based dairy products

when emulsified with water. Mono- and di-glycerides

are considered generally recognized as safe (GRAS)

by the FDA. Emulsion systems using soybean oil or

milk fat can reduce fat and calories significantly by

replacing fat on a one-to-one basis, while utilizing less

fat and contributing fewer calories.

Fat Mimetics

0015 Fat mimetics are compounds that help replace the

mouthfeel of fats by contributing a greater viscosity

to the liquid phase in the mouth, but cannot substitute

for fats on a gram-for-gram basis. Fat mimetics do not

have the nonpolar chemical properties of fats and

cannot be used for frying applications because of

water concentration and heat lability.

0016 Fat mimetics are categorized as ‘protein-based,’

‘carbohydrate-’ or ‘starch-based’,or‘cellulose-

based.’ Many of the fat mimetics have been marketed

and are available in a wide variety of formulations as

salad dressings, frozen desserts, and baked goods.

0017‘Protein-based’ fat mimetics marketed under prod-

uct names Simplesse 7, Trailblazer 7, and Finesse 7

are structurally modified natural proteins derived

from milk or egg white. Simplesse is the initial

protein-based fat replacer prepared with a patented

heating and homogenization process of microparticu-

lation in which the proteins are aggregated into tiny,

round particles that create the creaminess and mouth-

feel of fat. Simplesse cannot be used in heated foods

because the protein will congeal and lose the creamy

mouthfeel. Traiblazer and Finesse are similar modi-

fied protein texturizers prepared with unique and

innovative combinations of heat, acidulation, and

homogenization of natural proteins, selected carbo-

hydrates, and water.

0018Carbohydrate- or starch-based fat mimetics are

formulated from GRAS oligo- or poly-saccharides

chemically extracted and prepared from hydrolyzed,

often modified, corn, potato, or tapioca starch. Many

calorie-reducing carbohydrate starch-based fat

mimetics are available for use as ingredients in low-

calorie or ‘lite’ foods.

tbl0001 Table 1 Selected applications and functions of fat replacing

Specific application Fat replacer General functions

Baked goods Lipid-based Emulsify, provide cohesiveness, tenderize, carry flavor, replace

shortening, prevent staling, prevent starch retrogadation,

condition dough

Carbohydrate-based Retain moisture, retard staling

Protein-based Texturize

Frying Lipid-based Texturize, provide flavor and crispiness, conduct heat

Salad dressing Lipid-based Emulsify, provide mouth feel, hold flavorants

Carbohydrate-based Increase viscosity, provide mouth feel, texturize

Protein-based Texturize, provide mouth feel

Frozen desserts Lipid-based Emulsify, texturize

Carbohydrate-based Increase viscosity, texturize, thicken

Protein-based Texturize, stabilize

Margarine, shortening, spreads, butter Lipid-based Provide spreadability, emulsify, provide flavor and plasticity

Carbohydrate-based Provide mouth feel

Protein-based Texturize

Confectionery Lipid-based Emulsify, texturize

Carbohydrate-based Provide mouth feel, texturize

Protein-based Provide mouth feel, texturize

Processed meat products Lipid-based Emulsify, texturize, provide mouthfeel

Carbohydrate-based Increase water-holding capacity, texturize, provide mouth feel

Protein-based Texturize, provide mouth feel, water-holding

Dairy products Lipid-based Provide flavor, body, mouth feel, and texture; stabilize, increase

overrun

Carbohydrate-based Increase viscosity, thicken, aid gelling, stabilize

Protein-based Stabilize, emulsify

Soups, sauces, gravies Lipid-based Provide mouth feel and lubricity

Carbohydrate-based Thicken, provide mouthfeel, texturize

Protein-based Texturize

Snack products Lipid-based Emulsify, provide flavor

Carbohydrate-based Texturize, aid formulation

Protein-based Texturize

Functions are in addition to fat replacement.

2286 FATS/Fat Replacers

0019 Carbohydrate-based fat mimetics are generally

digested and absorbed to some extent, contributing

19 kJ or less per gram of carbohydrate. Carbo-

hydrate-based mimetics taste bland, are soluble in

water, somewhat pH- and heat-stable, and, most im-

portantly, contribute a smooth, creamy texture and

mouthfeel of fat, as well as the spreadability and

appearance when replacing all or part of the fat in

natural or emulsified foods. General categories of

foods, potential fat replacers, and the functions of

the fat replacer in addition to fat replacement are

presented in Table 1.

0020 Cellulose-based fat mimetics contribute no calories

to the diet in contrast to the carbohydrate- or protein-

based fat mimetics. One cellulose-based fat mimetic

is Avicel, a blend of microcrystalline cellulose and

carboxymethyl cellulose. Cellulose-based fat mimetics

contribute a creamy mouthful and little taste to foods.

0021 With increasing evidence that fat consumption and

obesity are detrimental risk factors for chronic dis-

ease, and that reducing the intake of dietary fats and

oils will contribute to improved public health, the

demand of health conscious consumers for reduced

fat foods will continue. Despite medical opinion and

media attention to the benefits of reducing fat con-

sumption, many consumers find it difficult to make

long-term changes in their eating habits when taste

and enjoyment are compromised by reduction in

dietary fat. (See Obesity: Treatment.)

0022 Unique achievements in food science research and

technology are resulting in safe ingredients to replace

fats in foods. When limiting fats, calories, and sugars

in the diet, consumers need to satisfy their basic es-

sential nutritional needs. No fat replacer is a panacea,

and additional reduced fat and reduced calorie foods

will neither compensate for poor dietary habits nor

replace the need for moderation and good overall

nutrition. So, the consensus for the need to reduce

dietary fat is offset by the difficulty in identifying

alternative foods that encourage consumers to make

long-term dietary changes. Low-fat and low-calorie

foods and beverages formulated from ingredients that

replace hidden and obvious fats and oils can help to

maintain a healthy, nutritious diet.

See also: Bioavailability of Nutrients; Carbohydrates:

Digestion, Absorption, and Metabolism; Metabolism of

Sugars; Cholesterol: Role of Cholesterol in Heart

Disease; Emulsifiers: Organic Emulsifiers; Essential

Fatty Acids; Obesity: Treatment; Triglycerides:

Structures and Properties