Caballero B. (ed.) Encyclopaedia of Food Science, Food Technology and Nutrition. Ten-Volume Set

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Authentic

0022 Food that is authentic, traditional or natural and has not

been adulterated in production, processing or storage,

including the use of genetically modified organisms or

their derivatives.

Consistently, research into consumers’ attitudes

shows that the main perceptions of organic food are

linked to phrases such as ‘no chemicals/additives/

pesticides,’‘natural’ and ‘healthy.’ Although there is

an increasing range of processed organic foods being

produced, these processes are themselves bound by

standards for organic production. According to the

IFOAM Basic Standards, the general principles of

organic food processing and handling are that: ‘any

handling and processing of organic products should

be optimized to maintain the quality and integrity of

the product.’ Furthermore, the processing methods

should ensure that: ‘the vital quality of an organic

ingredient should be maintained throughout each

step of its processing.’

0023 Measuring authenticity is almost impossible be-

cause it relates to such a large extent to individual

consumer preferences. However, issues like the avoid-

ance of most agrochemicals, the fact that organic

food aspires to be locally produced, and the generally

reduced processing appeals to a substantial part of the

food market. The fact that organic food is also free of

genetically modified (GM) food also meshes well with

consumer preferences in Europe and beyond. More

generally, the less processed nature of most organic

food helps fulfill the needs of those consumers who

are consciously trying to move away from the highly

processed foods that became a dominant part of the

industry in the 1980s and 1990s.

Functional

0024 How appropriate food is to its specific purpose – i.e.,

food that produces, stores, or cooks well. ‘Functionality’

is also used by food scientists and technologists to de-

scribe ingredients that blend well, or which have a good

shelf-life.

Concern about the world’s diminishing biological di-

versity (or biodiversity) has been growing in recent

years. Although biodiversity loss tends to be linked in

people’s minds with threats to rainforests or to rare

animals like giant pandas, genetic diversity is also

being lost within food production. This loss inevit-

ably affects our choice of the variety of food and the

functionality of crops produced.

0025 Loss of variety means loss of potential to adapt to

different conditions. A distinction between organic

and conventional agriculture is that in the former,

encouragement of greater variety is an important

part of the overall system, because reduced reliance

on agrochemicals to change conditions in the soil

means that the plants must themselves be better

adapted to local conditions. Organic standards en-

courage the expansion of varieties grown to gain

benefit from those suited to particular growing con-

ditions. For example, conventional wheat grown in

an organic system will show a distinct reduction in

protein content, whereas selection of a variety suit-

able for the particular conditions on the farm can

allow baking-quality wheat to be grown.

0026This encouragement of diverse species use is

threatened by the general reduction in crop diversity.

A survey of some 75 crop species, carried out by the

Rural Advancement Fund International, found that

about 97% of the varieties given on old US Depart-

ment of Agriculture lists are now extinct (assuming

that varieties that are not stored in US seed banks are

probably extinct). This loss is not unique to the USA,

for example, indigenous wheat, rice, and sorghum

varieties have virtually disappeared from many

centers of diversity in areas of Europe, the Middle

East, Africa, and Asia. Of the 2500 or so apple var-

ieties that have been grown in the UK, just nine now

dominate the retail outlets. Within the EC, this ero-

sion of diversity in crops has become legally obliga-

tory with the introduction of a common catalogue.

Varieties not listed are seen as inferior and cannot

be legally sold by seed companies.

0027Organic growing conditions can also contribute to

the functionality of food. A review of research on

storage degradation by the Soil Association shows

that organic crops can have better storage quality

and postharvest behavior than nonorganically

grown produce. Organic plant production is charac-

terized by a relatively low level of nutrient supply

compared to conventional crops. This leads to earlier

completion of vegetative growth and an early onset of

maturity, which may contribute to a longer shelf-life.

Respiration rates and enzyme activity, which can also

result in lower storage losses, also tend to be lower

in organically farmed foods.

Biological

0028How food interacts with the body’s functioning. This

includes both negative and positive interactions, such

as the detrimental effects of some food additives on

allergies and beneficial effects of foods in stimulating

immunity to disease. The concept also refers to the

pharmacological qualities of foods and herbs.

Many consumers feel that organic food can have

positive effects on health and this is a major reason

for purchase. A comprehensive review of over 400

published papers by the Soil Association of existing

research on the differences between organically and

4274 ORGANICALLY FARMED FOOD

nonorganically grown foods has revealed significant

differences to key areas of food quality important to

the promotion of good health – food safety, nutri-

tional content, and the observed health effects of

organic food. The review notes that, while there has

been little research carried out on humans, a number

of feeding trials on animals have shown significant

improvements in the growth, reproductive health,

and recovery from illness of animals fed organically

produced food.

0029 Reproductive health is seen as a particularly sensi-

tive indicator of environmental conditions and has

been the focus of some research into the effects of

organic food on health. It is known that occupational

exposure to pesticides can impair reproductive health

and it is hypothesized that long-term low-dose expos-

ure to residues through food intake may also have

adverse effects, so food with less pesticide residues

might be expected to have beneficial results. In the

mid-1990s, two small studies in Denmark indicated

that semen quality was improved among consumers

of organic food and this gained worldwide publicity –

however, a larger study could not confirm these

results. Several feeding experiments have also been

carried out, but over a range of studies of mice, rats,

pigeons, rabbits, and hens the reproductive effects of

diet have shown no clear trend. In feed experiments

with mice and rats the share of stillborn animals and

animals that died shortly after birth was significantly

higher in litters fed on conventionally produced feed.

0030 The routine use of antibiotics in intensive farming

has been linked to the development of ‘superbugs’

resistant to antibiotics used to combat human illness.

As organic standards only allow the use of antibiotics

in animals to cure specific problems, it is reasonable

to suggest that an organic diet will reduce the build-

up of antibiotic residues.

Nutritional

0031 How food contributes to a balanced diet. This recog-

nizes individual food values, such as vitamins, protein,

and trace elements, and undesirable elements such as fats

and sugar and nitrate and sodium, which in large

amounts can be harmful.

Public concern about the presence of pesticide resi-

dues, additives, and nitrates in food is the reason

many consumers purchase organically produced

food. The organic sector has, however, been careful

to stress to consumers that, given the state of the

environment, and the presence of pesticide residues

in soils, air pollution from spray drift, and industrial

pollution, no food production method can guarantee

a 100% chemical-free crop. There is however

evidence that organic foods do have lower levels of

pesticide residues than comparable conventional

crops, although these results should not be overesti-

mated given the small number of studies.

0032Concern has also been expressed over increasing

nitrate intake from dietary sources, notably from the

consumption of vegetables, although the possible

health impacts of this remain the subject of debate.

There is considerable variation in the levels of nitrate

in foods, and in the consumption patterns of different

foodstuffs amongst people; for example, the nitrate

content of leafy vegetables is generally higher in

winter. Comparative studies on farming systems and

the related accumulation of nitrate in vegetables have

been the subject of several research projects in recent

years. In the UK, trials showed significantly lower

levels of nitrate accumulation when using composted

farmyard manure compared to the use of the soluble

compound fertilizer – although fertilization with

either type of material did lead to an increase in the

level of nitrate in the plants. This trend is confirmed

over a range of research studies (the Soil Association

reviewed 16 studies, of which 14 showed a trend

toward significantly lower nitrate contents in organ-

ically grown food), with nitrate content of conven-

tional produce as opposed to organic production

being particularly high in nitrophilic leaf, root, and

tuber vegetables.

0033The presence or absence of harmful or potentially

harmful substances in food only represents one aspect

of the nutrition equation, as our food is made up of a

range of nutrients such as vitamins and minerals. The

Soil Association reviewed 99 papers that compared the

nutritional quality of organically and conventionally

grown crops. These studies were assessed for validity

in terms of agricultural practice and scientific analysis.

Of those studies deemed valid, the Soil Association

concluded that vitamin C and dry-matter contents

are higher, on average, in organically grown crops.

Mineral contents were also higher, on average, in or-

ganically grown crops, although the small number and

heterogeneous nature of the studies included mean

that more research is needed to confirm this finding.

Research also indicates a clear long-term decline in the

trace mineral content of fruit and vegetables, but to

understand the reason for this the influence of farming

practices requires further investigation.

0034As well as having effects on individual elements of

crops, the choice of an organic diet may also have an

effect on overall dietary habits. A survey of the diet of

UK organic consumers concluded that those commit-

ted to the consumption of organic food have a differ-

ent diet from the average consumer – a diet that is

more in line with the productive capacity of the

organic system. By collecting detailed diet diaries

and comparing them with data from the Office of

ORGANICALLY FARMED FOOD 4275

Population Censuses and Surveys, organic consumers

showed a significant swing towards the consumption

of fruit and vegetables, with a reduction in the protein

food ‘centerpieces.’ Protein consumption was less

dependent on meat, being derived from other sources.

Staples showed a greater diversity, with a greater

intake of pasta, grains, and cereals, with less concen-

tration on potatoes. The survey data also showed an

increased consumption of fibrous foods and a de-

creased consumption of animal-based as well as

sweet and fatty foods.

Sensual

0035 Food which appeals to the senses; the industry uses the

term ‘organoleptic’ to refer to sensual quality of food,

i.e. its look (esthetic appeal), taste, feel (as in mouth

feel), smell, and sound.

The determination of whether organic food tastes

better than food produced from other forms of pro-

duction has been the subject of considerable research.

Although it is widely believed by consumers that

organically farmed food tastes better than the alter-

natives, there is no conclusive scientific evidence to

prove this. Partly this is due to individual preferences

in taste, which makes the determination of quality

through taste alone totally subjective, and is compli-

cated by a whole range of regional factors, such as

soils and climate, which make direct comparisons

between growing systems difficult (unless trial plots

are extremely well matched). The Soil Association

also suggests that other influences on taste could be

the higher water content in conventionally grown

food diluting its flavor, different choices of cultivars,

and the fact that organic produce has sometimes been

shown to have higher natural sugar content, which

may be perceived as a better or worse taste,

depending on the product.

0036 Review of feeding experiments with animals has

however drawn one unexpected, and so far unex-

plained, conclusion. When given the choice, animals

almost always prefer organic produce to convention-

ally produced feed.

Ethical

0037 This concept has four related but distinct meanings:

environmental (the effects on our environment of food

production methods); social (the conditions in which

food producers are treated – on the farm, in the factory,

on the shop floor); ethical (the morality of the way

specific foods are produced – for example, the condi-

tions of animals raised for meat); and political (the

effects of the food industry on specific countries).

Research into consumer preferences suggests that

there has been a shift in emphasis amongst purchasers

of organic food in the last decade, away from people

primarily driven by personal health concerns to those

with a wider interest in the environmental and social

impacts of the food that they buy.

0038There is a large literature describing the environ-

mental problems of conventional agriculture and the

benefits of organic agriculture. For example, long-

term research projects have accumulated substantial

evidence that organic systems are beneficial to bio-

diversity. An overview of research findings from 23 of

these projects by the Soil Association concluded that

in most studies there were important differences be-

tween the biodiversity on organic and conventional

farms, with generally greater levels of both abun-

dance and diversity of species on organic farms. On

average, the research found five times as many wild

plants in arable fields and 57% more species, 25%

more birds at the field edge, and 44% more species in

fields in the autumn and winter, and three times as

many nonpest butterflies in crop areas.

0039In a review of the environmental impacts of organic

farming in 18 European countries, an assessment of a

series of environmental indicators found that organic

farming has more floral and faunal diversity than

conventional farms, tends to conserve soil fertility

and system stability better and on a per-hectare scale

has between 40 and 60% lower CO

emissions and is

likely to have lower emissions of N

O, CH

, and

0040Sociological data comparing organic and conven-

tional farming systems are not so well advanced. The

IFOAM began a project on data collection and farm

system comparison in 1997 and has developed a

methodology which collects data on 13 indicators

that provide information on subjects such as produc-

tion of main and byproducts, recycling, male and

female hired and own labor, financial results, energy

consumption and production, water use, family ex-

penditure, and education. The methodology is now

being tested in Guatemala, India, and Nicaragua.

Results to date have shown that self-reliance, which

is defined as a percentage of output value that is

consumed on the farm, is higher in the organic farms.

Conclusions

0041Many of the issues described above are not limited to

organic production: for example, fresh food is avail-

able at the farm gate from many conventional farms

and there is a growing fair-trade movement that in-

sures equitable returns for food produced in develop-

ing countries. However, organic farming is the only

system where all such issues are addressed together

and within a legal framework through the organic

standards, insuring that consumers can be reasonably

4276 ORGANICALLY FARMED FOOD

confident that a ‘package’ of health, environmental,

and social issues has been addressed in the production

of the organic food that they purchase. When pro-

vided with the whole picture, across a range of issues

such as those given above, there does seem to be suffi-

cient research to conclude that organically farmed

food does have some unique characteristics.

See also: Antibiotics and Drugs: Uses in Food

Production; Food and Agriculture Organization of the

United Nations; Legislation: Codex; Quality Assurance

and Quality Control; World Health Organization

Further Reading

Alfo

ldi T, Lockeretz W and Niggli U (2000) Proceedings of

the 13th International IFOAM Scientific Conference.

Germany: IFOAM.

Azzeez G (2000) The Biodiversity Benefits of Organic

Farming. Bristol, UK: Soil Association.

Finesilver T (1989) Comparison of Food Quality of Organ-

ically versus Conventionally Grown Plant Foods.

Ecological Agriculture Projects. Quebec, Canada:

McGill University.

Gold M (2000) Organically Produced Foods: Nutritive

Content. Special Reference Briefs Series no. SRB 2000–

03. Beltsville, USA: Alternative Farming Systems Infor-

mation Center, National Agricultural Library, US

Department of Agriculture.

Heaton S (2001) Organic Farming, Food Quality and

Human Health: A Review of the Evidence. Bristol, UK:

Soil Association.

Lampkin N (1990) Organic Farming. Ipswich, UK:

Farming Press.

Pretty JN, Brett C, Gee D et al. (2000) An assessment of

the total external costs of UK agriculture. Agricultural

Systems 65(2): 113–136.

Stolze M, Piorr A, Ha

ring A and Dabbert S (2000) The

Environmental Impacts of Organic Farming in Europe.

Organic Farming in Europe: Economics and Policy,

vol. 6. Hohenheim, Germany: University of Hohenheim.

Woese K, Lange D, Boess C and Bo

gl K-W (1997) A com-

parison of organically and conventionally grown foods –

results of a review of the relevant literature. Journal of

the Science of Food and Agriculture 74: 281–293.

Woodward L, Stolton S and Dudley N (1992) Food Qual-

ity: Concepts and Methodology. Hamstead Marshall,

Berkshire, UK: Elm Farm Research Centre.

Organoleptic Evaluation See Sensory Evaluation: Sensory Characteristics of Human Foods; Food

Acceptability and Sensory Evaluation; Practical Considerations; Sensory Difference Testing; Sensory Rating and

Scoring Methods; Descriptive Analysis; Appearance; Texture; Aroma; Taste

Osmosis See Membrane Techniques: Principles of Reverse Osmosis; Applications of Reverse Osmosis;

Principles of Ultrafiltration; Applications of Ultrafiltration

Osteomalacia See Rickets and Osteomalacia

ORGANICALLY FARMED FOOD 4277

OSTEOPOROSIS

J J B Anderson, University of North Carolina,

Chapel Hill, NC, USA

Background

0001 Osteoporosis is considered a chronic multifactorial

disease because many variables contribute to the de-

velopment of low bone mass and low bone mineral

density accompanied by an increased risk of fracture.

This disease usually occurs in late adulthood,

following the menopause in women, and a decade

or so later in men, but it may appear rarely earlier in

life depending on the status of reproductive steroid

hormones.

0002 Both hereditary and environmental factors con-

tribute to the multifactorial nature of this disease.

Individual differences in constitutional factors as

well as lifestyle/environmental determinants influ-

ence bone. In terms of lifestyle, both regular physical

activities and a healthy diet remain two of the more

important contributors to bone health and the main-

tenance of its functions into late life. The major func-

tion, sound ambulation, needs to be preserved as long

as possible through exercise and diet. When calcium

intake is not adequate, the adaptational role of the

calcium regulatory system operates in an attempt to

preserve skeletal structure for its functional uses. If the

adaptation is not sufficient, bone deterioration, i.e.,

loss of both mass and density, will lead to fragility

fractures. These and related topics are covered in this

paper. (Although drugs that help conserve bone are

widely used today, this review focuses on dietary risk

factors and nutritional therapies.)

Bone Structure

0003 Bone tissue consists of two types within the same

specific bone, e.g., a vertebra of the spinal column:

trabecular (cancellous) and cortical (compact). Trab-

ecular tissue is the more metabolically active because

it has about eight to 10 times more total surface area

than cortical tissue, and these surfaces are all largely

covered by bone cells that are responsible for new

bone formation and old bone resorption (degrad-

ation). In the body of a vertebra most of the bone

tissue is trabecular, but near the surfaces of the entire

vertebra, cortical bone predominates. Therefore, each

specific bone or organ contains both types of bone

tissue but typically in different locations within the

bone. For example, long bones, such as the femur,

contain much more trabecular tissue at either end

near the hip joint or knee joint and a much greater

proportion of cortical bone in the shaft that connects

the two ends. This distinction is important because

most of the fractures of the bones (organs) occur

where more metabolically active trabecular bone

tissue exists.

Bone Gain and Bone Loss through the Life

Cycle

0004In early life, during the growth periods of the skel-

eton, bone acquisition through bone formation dom-

inates. This phase represents the making of the

skeletal model, i.e., modeling, and it typically ends

by 16–18 years in females and 18–22 years in males.

Modeling is characterized by greater formation than

resorption and results in a net gain of bone mass or

bone mineral content (BMC) by the end of the growth

phase. Modeling is completed at the end of linear

growth. In remodeling of the skeleton, resorption of

bone equals formation; so, the net amount of bone

mass remains fairly constant, though some modest

gain may still occur until the mid-20s or beyond.

During the beginning of the remodeling, the increase

in pubertal hormones is responsible for the cessation

of growth in length, or height increase. At this time,

bone mineral density (BMD) attains a maximum

value that becomes the ‘healthy norm’ for an individ-

ual for the rest of their life. (In the definitions of

osteopenia and osteoporosis, the healthy means of a

population of 20–29-year-old males or females are

taken as the standard values for determining osteo-

porosis late in life (see below.)

0005In late life, i.e., after the menopause in women and

a decade or so later in men, imbalances in the remod-

eling of the skeleton result in bone losses, so that

reductions in both BMC and BMD occur. The loss

of estrogens after the menopause and probably the

later decline of androgens by men contribute to the

increase in resorption, the reduction of formation, or

both. The increase in resorption is triggered by in-

creased activity of osteoclasts, and the decline in for-

mation is directly related to decreased activity of

osteoblasts. An increase in bone turnover, i.e., in-

creased rates of resorption and formation with re-

sorption dominating formation, greatly accelerates

the rate of bone loss. Most individuals are slow

or moderate losers of bone, whereas only a small

fraction are ‘fast losers.’ Bone turnover is assessed

by measurement of chemical markers of degraded

matrix proteins, such as collagen, resulting from

4278 OSTEOPOROSIS

bone resorption and of hormones, especially parathy-

roid hormone, involved in calcium homeostasis.

0006 The changes in the skeleton over the life cycle

reflect early-life gains and late-life losses. When the

losses become sufficient to deteriorate to the state of

osteoporosis, an individual becomes at risk of fragil-

ity fractures of bones such as the vertebrae and prox-

imal femurs (hips). The hip fractures are the most

severe and debilitating, and many individuals never

recover.

Measurement of BMC and BMD

0007 BMC and BMD are measured today using a tech-

nique called dual energy X-radiographic analysis

(DXA). Osteopenia, or too little bone, is followed

by osteoporosis, or even greater bone loss, which

places an individual at great risk of a fracture. Quan-

titative definitions of osteopenia and osteoporosis

have been established by the World Health Organiza-

tion as follows: osteopenia is between minus 1 and

2.5 standard deviations (SDs) below the 20–29-year-

old mean values for women or men; and osteoporosis

is greater than 2.5 SDs below the 20–29-year-old

means. (These values of individuals at any adult age

compared with means of healthy young adults are

known as T-scores.) According to this definition, a

postmenopausal 60-year-old woman with 3.0 SDs

below the mean at different skeletal measurement

sites does not necessarily have any clinically diag-

nosed fracture, but she is likely to have one over the

next few years without any drug (or drug and diet)

therapy.

0008 In addition to the DXA determination of bone

status, biochemical markers may also be used to

assess the severity of bone turnover and the potential

risk of fracture. Therefore, both clinical observations,

e.g., loss of height and pain in the lower back, and

biochemical marker data may increase the diagnostic

significance of DXA measurements that classify an

individual in the osteoporotic range or > 2.5 SDs

below the healthy means.

Types of Osteoporosis

0009 Type I osteoporosis uses the postmenopausal woman

as the prototype, although men also rarely may suffer

from the abrupt loss of sex steroids that impact

greatly on the retention of bone tissue. Type II osteo-

porosis is age-related and typically occurs in both

genders in the later decades of life; the causation of

Type II is poorly understood, but it accelerates when

the musculoskeletal system functions decline.

0010 Although, for simplicity, only two types of osteo-

porosis are defined here, other variants clearly exist.

One that is of increasing importance is corticosteroid-

induced osteoporosis because of the widespread use

of prednisone and related drugs in therapy of diseases

other than osteoporosis. This type of osteoporosis

is called secondary. Other drugs may also induce

secondary osteoporosis.

Nondietary Risk Factors for Osteoporosis

0011Several nondietary risk factors – all potentially ad-

verse or harmful – have been identified that promote

the loss of bone and the onset of fractures. Seven

environmental/lifestyle factors are listed here:

0012thinness with low LBM;

0013cigarette smoking;

0014excessive alcohol consumption;

0015insufficient physical activity;

0016drugs – over-the-counter and prescription;

0017decline of sensory perceptions;

0018falls.

0019Each of these factors has a risk associated with it,

but when two or three exist together at the same time,

the risk of an osteoporotic fracture may increase ex-

ponentially rather than additively. For example, the

small-framed older postmenopausal woman who

smokes a pack of cigarettes a day, drinks two or

three servings of alcohol a day, and who has little

physical activity in her daily life will typically be at

great risk of an early hip fracture, i.e., by age 70 years

or younger. When the old-old, i.e., greater than 80,

suffer declines of acuity of their senses, such as vision

and equilibrium, or take medications that result in the

same effects, they are much more likely to fall and

break their hip.

0020The most important of these adverse factors, in

general, may be the decline in regular physical activity

that results in the loss of lean body mass (LBM),

characterized by declines in muscle strength and

tone, because bone loss follows closely the loss of

LBM.

0021Many elderly take several drugs, i.e., polyphar-

macy, and some of them become confused or have

difficulty maintaining equilibrium. Each of these

factors may contribute to falls and consequent hip

fractures.

Dietary Risk Factors

0022In addition to adverse environmental/lifestyle factors,

numerous dietary factors may also have adverse

effects on skeletal tissue. These deleterious factors

are thought to operate throughout the life cycle, not

just during late life. The major variables are given

here, but this list is not exhaustive:

OSTEOPOROSIS 4279

.0023 low calcium;

0024 high phosphorus;

0025 low vitamin D;

0026 high-animal protein and acid load;

0027 high-sodium snacks;

0028 vegetarian diet;

0029 poor diet in general.

0030 The most common dietary problem associated with

the development of osteoporosis has been an inad-

equate consumption of calcium, at least among

Caucasians in Western nations, including pediatric

populations. Low calcium intakes in these nations

are typically accompanied by high phosphate con-

sumption because of both the ingestion of naturally

occurring phosphorus in foods, especially animal

proteins, and phosphorus from food fortification.

Phosphorus fortification is fairly common in West-

ern nations because of the widespread use of pro-

cessed foods – foods modified with the many

applications that utilize phosphate salts of one

type or another. Cola-type soft drink beverages

also fit in this category, although, technically, they

are not foods. The net result of consuming phos-

phate-rich foods may be a low calcium (Ca) to high

phosphate (P) intake that is worsened when individ-

uals consume little milk or cheese in their usual

diets.

0031 If the Ca:P ratio declines to approximately 1 to 4,

the serum parathyroid hormone (PTH) concentration

becomes elevated (but remains within the normal

range). A constantly elevated PTH leads to bone loss

and a gradual decline in BMD that eventually be-

comes osteoporosis. How many years bone takes to

get into the osteoporotic range, according to WHO

definitions, is not clear, but a long-term dietary pat-

tern of low calcium–high phosphate may even con-

tribute to low bone mass in females before they reach

20 years of age, if fractures among girls and pubertal

females are a valid index of low bone mass.

0032 Coupled with limited skin exposure to vitamin D-

promoting sunlight, a low intake of vitamin D from

foods, especially fortified dairy products in the USA

and various deep-sea fish species in much of the

world, is now considered a risk factor for low bone

mass. The mechanism for this condition is not entirely

clear, but a low circulating concentration of 25-hydro-

xyvitamin D is linked with both a decline in intestinal

calcium absorption and an increase in bone turnover

with a resultant loss of bone.

0033 A usual high-animal protein intake has been

reported by some investigators to contribute to

bone loss and an increase in risk for osteoporosis.

The mechanism is considered to reside in the increased

production of acids, i.e., phosphoric and sulfuric,

from the degradation of phosphorus- and sulfur-

containing amino acids that are considerably greater

in animal than plant proteins, such as those derived

from soy. The net effect is an increased loss of calcium

ions in urine. This loss has been shown acutely and in

short-term experiments, but it has not been estab-

lished in long-term studies.

0034High-sodium snack foods have become very popu-

lar in Western nations, and they contribute additional

sodium to an already high intake that derives from so

many foods processed with sodium or salt. Calcium

renal losses increase on high-sodium intakes because

the kidneys favor sodium reabsorption at the expense

of calcium ions. The net loss of calcium comes from

bone, and therefore a loss of bone mass may be asso-

ciated with excessive consumption of sodium-rich

snack foods.

0035Vegetarian diets may also compromise bone health

through a number of possible mechanisms, but the

low calcium and vitamin D intakes from a vegan

dietary pattern may be largely responsible for lower

bone mass among vegetarians.

0036Finally, a poor diet, especially one based on a

limited intake of fruits and vegetables, may be defi-

cient in other bone-essential nutrients, such as mag-

nesium, vitamin K, zinc, antioxidant nutrients, and

probably a dozen others. Any one or a combination of

these deficits may inhibit efficient bone formation.

Adverse effects include loss of protection against oxi-

dants, and poor regulation of acid–base balance, thus

impacting bone as a major buffering store. Whatever

the mechanisms may be, bone health requires a wide

variety of nutrients that are best supplied by a varied

diet consisting of the recommended numbers of

servings of foods each day.

Adaptation to Low Calcium Intakes

0037Several adaptations to dietary intakes occur after

each meal in healthy individuals; a number of these

adaptations directly affect calcium homeostasis by

impacting on serum PTH and 1,25-dihydroxyvitamin

D concentrations. For example, a low calcium intake,

especially when coupled with a high phosphate con-

sumption pattern, stimulates PTH secretion via a cal-

cium sensor on the membranes of parathyroid gland

cells. Elevated PTH, in turn, stimulates the removal of

calcium from bone (see above).

0038In addition, a low calcium intake stimulates the

vitamin D regulatory mechanism by increasing the

renal production of the hormonal form of vitamin

D, i.e., 1,25-dihydroxyvitamin D, which leads to an

increase in intestinal calcium absorption and bone

utilization of calcium. The potential problem in

older women, and perhaps men, is that the intestinal

4280 OSTEOPOROSIS

adaptation declines, and less calcium can be absorbed

with the hormonal stimulus.

0039 Finally, excessive, continuous PTH secretion that

may develop late in life with a low Ca:high P ratio

diet and low circulating 25-hydroxyvitamin D con-

centration contributes to bone loss almost across the

24 h of a day. It is now recognized that a persistent

and continuous treatment with PTH causes signifi-

cant bone loss, whereas a discontinuous treatment

with PTH, i.e., once daily or once weekly, increases

bone mass and density by stimulating osteoblasts to

make new bone tissue. Thus, any type of low calcium

intake that generates a continuous secretion and ele-

vation of PTH in blood will have serious negative

consequences on the maintenance of bone, especially

of trabecular bone tissue.

Dietary Prevention and Treatment – Foods

and Supplements

0040 The principles of both primary and secondary preven-

tion of osteoporosis are similar: increase calcium in

the diet through foods and supplements to 1000 mg

or more per day in order to suppress PTH secretion

(see above), and assure that individuals obtain suffi-

cient amounts of vitamin D through both foods and

supplements: a dosage of 800 IU or more is recom-

mended. Sunshine exposure is also encouraged,

depending on geographic latitude and time of the

year. Finally, a healthy diet containing virtually all

nutrients from foods makes sense from a nutritional

perspective. For the elderly, a daily supplement that

contains a wide range of nutrients at recommended

intake levels is both safe and inexpensive. The current

dietary reference intakes should be used to guide

consumers in maintaining appropriate amounts of

nutrients each day (1997–2001).

Public Health Implications and

Conclusions

0041 Since the incidence and prevalence of osteoporosis

are increasing as our populations are aging, greater

expenditures are anticipated for direct care of hip

fracture patients and then their subsequent rehabili-

tation. Many victims will not survive the first post-

fracture year. Preventive strategies, either primary or

secondary, that are cheap and effective, must be iden-

tified and implemented. Improving the diet may be

one of the most easily modifiable approaches for the

prevention of osteoporosis, but of course, if individ-

uals cannot ambulate, the dietary changes will have

little impact with regard to osteoporosis. Walking and

maintaining activities of daily living by the elderly

are critical for the prevention of osteoporosis. Any

type of minimal exercise program should also yield

some benefit to the retention of musculoskeletal

function.

See also: Bone; Calcium: Properties and Determination;

Physiology; Cholecalciferol: Properties and

Determination; Physiology; Hormones: Thyroid

Hormones; Smoking, Diet, and Health; Sodium:

Properties and Determination; Physiology

Further Reading

Anderson JJB (1999) Plant-based diets and bone health:

Nutritional implications. American Journal of Clinical

Nutrition 70: 539S–542S.

Anderson JJB, Sell ML, Garner SC and Calvo MS (2001)

Phosphorus. In: Russell R and Bowman B (eds) Present

Knowledge in Nutrition, 8th edn. Washington, DC: ILSI

Press.

Committee on Nutrition (1999) Calcium requirements of

infants, children, and adolescents. Pediatrics 104:

1153–1157.

Dietary Reference Intakes (DRIs) (1997–2001) Several

Reports Including: Institute of Medicine (IOM), Food

and Nutrition Board. Dietary Reference Intakes for

Calcium, Phosphorus, Magnesium, Vitamin D, and

Fluoride. Washington, DC: National Academy Press.

Goulding A, Cannan R, Williams SM et al. (1998) Bone

mineral density in girls with forearm fractures. Journal

of Bone and Mineral Research 13: 143–148.

New SA, Robins SP, Campbell MK et al. (2000) Dietary

influences on bone mass and bone metabolism: Further

evidence of a positive link between fruit and vegetable

consumption and bone health? American Journal of

Clinical Nutrition 71: 142–151.

Wyshak G (2000) Teenaged girls, carbonated beverage con-

sumption, and bone fractures. Archives of Pediatrics and

Adolescent Medicine 154: 610–613.

OSTEOPOROSIS 4281

OXALATES

S C Morrison, New Zealand Institute for Crop and Food

Research, Lincoln, Canterbury, New Zealand

G P Savage, Lincoln University, Canterbury,

New Zealand

Introduction

0001 Oxalic acid and its salts occur as end products of

metabolism in a number of plant tissues. When

these plants are eaten they may have an adverse effect

on mineral bioavailability because oxalates bind

calcium and other minerals. While oxalic acid is a

normal end product of mammalian metabolism, the

consumption of additional oxalic acid may cause

stone formation in the urinary tract when it is

excreted in the urine. The mean daily intake of oxal-

ate in the diet in the UK has been calculated to be 70–

150 mg; tea, rhubarb, spinach, and beet are common

high oxalate-containing foods. Soaking and cooking

foodstuffs high in oxalate will reduce the oxalate

content by leaching.

0002 The consumption of high-oxalate foods is more

likely to pose health problems in those who have an

unbalanced diet or those with intestinal malfunction.

A diet high in oxalate and low in essential minerals,

such as calcium and iron, is not recommended.

Vegans and lactose-intolerant persons may have a

high-oxalate and low-calcium diet unless their diet

is supplemented. Vegetarians who consume greater

amounts of vegetables will have a higher intake of

oxalates, which may reduce calcium availability. This

may be an increased risk factor for women, who

require greater amounts of calcium in the diet. Per-

sons with an increased absorption rate of oxalate are

advised to avoid or eat fewer high-oxalate foods to

prevent kidney stone formation. In healthy individ-

uals, the occasional consumption of high-oxalate

foods as part of a balanced diet does not pose any

particular problem.

Oxalates in Plants

0003 Oxalate can be found in small amounts in many plants.

Oxalate-rich foods are usually minor components in

human diets but are present in higher quantities in

seasonal diets in certain areas of the world (particu-

larly in the tropics) as a component of grains, tubers,

nuts, vegetables, and fruits. The highest levels of

oxalates are found in the foods listed in Table 1.

0004 In general, oxalate content is highest in the leaves,

then in the seeds, and lowest in the stems. Reports

show that the stems or stalks of plants, such as

amaranth, rhubarb, spinach, and beet, contain sig-

nificantly lower levels of oxalates than the leaves. In

the buckwheat family (e.g., rhubarb, sorrel), there is

almost twice as much oxalic acid in the leaves as in

the stalk. However, in the goosefoot family (e.g., beet,

spinach), oxalic acid is more abundant in the stalk

than in the petiole of the leaf. It must be noted that the

leaves of rhubarb are rarely eaten and therefore the

oxalate content of its leaves is of no concern in human

nutrition.

0005Oxalic acid concentration tends to be higher in

plants than in meats, which may be considered oxal-

ate-free when planning low-oxalate diets. Meats,

fats, and dairy products contain very low levels of

oxalates.

0006The levels of oxalates in fungi are low when com-

pared to the levels found in spinach and rhubarb. The

giant mushroom (Tricholoma giganteum), a large,

edible fungi, is reported to contain 89 mg 100 g

1

dry weight (DW) oxalic acid while tropical species

of mushrooms, including termite and ear mushrooms,

contain between 80 and 220 mg oxalate 100 g

1

DW.

0007High oxalate levels in tropical plants are of some

concern. Taro (Colocasia esculenta) and sweet potato

(Ipomoea batatas) were reported to contain 278–

574 mg 100 g

1

fresh weight (FW) and 470 mg

100 g

1

, respectively. Total oxalate levels in yam

(Dioscorea alata) tubers were reported in the range

486–781 mg 100 g

1

DW, but may not be of nutri-

tional concern since 50–75% of the oxalates were

present in the water-soluble form and therefore may

leach out during cooking. Oca or New Zealand yam

(Oxalis tuberosa Mol.) contains 80–221 mg 100 g

1

FW soluble oxalate. Higher levels of oxalates are

usually found in the leaves and highest concentrations

of oxalate have been found in the skin of these

tropical root crops. Peanut greens, commonly con-

sumed in tropical climates, are reported to contain

407 mg 100 g

1

. Coriander leaf (Coriandrum sati-

vum) contains 1268 mg 100 g

1

; horsegram (Macro-

tyloma uniflorum) and santhi (Boernavia diffusa)

contain 508 mg 100 g

1

and 3800 mg 100 g

1

re-

spectively. Nuts such as peanuts, pecans, and cashews

are relatively high in oxalates. Sesame seeds have

been reported to contain high quantities of oxalate,

ranging from 350 to 1750 mg 100 g

1

FW.

0008Beverages with a high-oxalate concentration

include Indian black tea, cocoa drinks, Ovaltine,

cola, and certain types of beer.

0009The oxalic acid content is variable within some

species; some cultivars of spinach (Universal, Winter

4282 OXALATES

Giant) contain 400–600 mg 100 g

1

, while others

range from 700 to 900 mg 100 g

1

. Oxalic acid ac-

cumulates in plants, especially during dry condi-

tions. A study comparing two cultivars of spinach,

Magic (cv. summer) and Lead (cv. autumn),

revealed that the summer cultivar contained greater

amounts of oxalate (740 mg 100 g

1

FW) than the

autumn cultivar (560 mg 100 g

1

FW). Oxalate con-

tent has been reported to increase as the plant ages

and becomes overripe. The proportion of oxalic

acid in the leaves of the goosefoot family can

double during ripening. However, in tomatoes, ox-

alic acid content has been reported to decrease

during ripening.

Absorption and Metabolism in Mammals

0010 Calcium can combine with oxalate to form calcium

oxalate in the intestinal lumen, making the calcium

unavailable for absorption; calcium oxalate is then

excreted in the feces. Free or soluble oxalate is

absorbed by passive diffusion in the colon in humans;

comparative studies between healthy individuals and

those with ileostomies indicate that the colon is the

principal site for oxalate absorption. However, it

is suggested that the small intestine may be the

major absorptive site rather than the colon. The

absorption of oxalates from individual foods varies

depending on their dietary conditions and source; in

general, the absorption is quite limited. It has been

estimated that 2–5% of administered oxalate is

absorbed in humans. Experiments have shown that

more oxalate is absorbed when consumed while

fasting (12%) compared to only 7% oxalate absorp-

tion when consumed with a normal diet. The percent-

age of oxalate absorption varied markedly from 1%

for rhubarb and spinach to 22% from tea, but gener-

ally absorption was higher at low doses.

0011 Oxalate is an end product of ascorbate, glyoxylate,

and glycine metabolism in mammals. Thirty-three to

fifty percent of urinary oxalate is derived from ascor-

bate, 40% from glycine and 6–33% from minor

metabolic pathways and dietary oxalate; dietary

oxalate appears to account for only 10–15% of

excreted oxalates.

Chemical Properties and Toxic Effects

0012Oxalic acid forms water-soluble salts with Na

and NH

ions; it also binds with Ca

2þ

,Fe

2þ

,and

2þ

, rendering these minerals unavailable to

animals. However, Zn

2þ

appears to be relatively un-

affected. Calcium oxalate (Ca(COO)

) is insoluble at

a neutral or alkaline pH, but freely dissolves in acid.

0013Ingestion of 4–5 g of oxalate is the minimum dose

capable of causing death in an adult, but reports have

shown that 10–15 g is the usual amount required to

cause fatalities. Oxalic acid ingestion results in corro-

sion of the mouth and gastrointestinal tract, gastric

hemorrhage, renal failure, and hematuria. Other as-

sociated problems include low plasma calcium, which

may cause convulsions and high plasma oxalates.

Most fatalities from oxalate poisoning are apparently

due to the removal of calcium ions from the serum by

precipitation. High levels of oxalate may interfere

with carbohydrate metabolism, particularly by suc-

cinic dehydrogenase inhibition; this may be a signifi-

cant factor in death from oxalate toxicity induced in

animals grazing pastures containing high levels of

Halogeton glomeratus. Halogeton (H. glomeratus)

and wood sorrel (Oxalis cernua) are high in oxalates

and are known to cause injury to grazing cattle and

sheep.

0014Although garden sorrel is a herb and not normally

consumed in large quantities, there has been one

report of fatal oxalate poisoning after a man con-

sumed an estimated 6–8 g oxalate in vegetable soup

containing 500 g sorrel. Both fatal and nonfatal

poisoning by rhubarb leaves is thought to be caused

by toxic anthraquinone glycosides rather than

oxalates. Experiments involving the consumption of

more than 30–35 g day

1

of cocoa, a high-oxalate

foodstuff, by eight women provoked symptoms of

intoxication including loss of appetite, nausea, and

headaches. However, cocoa contains theobromine

(1500–2500 mg 100 g

1

) and tannic acid (4000–

6000 mg 100 g

1

), both of which are more toxic

than the oxalic acid present (500–700 mg 100 g

1

There appears to be a great deal of confusion as to

what was responsible for these poisonings and it

would be unwise to assume that only one factor was

responsible.

tbl0001 Table 1 Common foods exhibiting high levels of oxalates

Spinach Beet Rhubarb

Swiss chard Yam, oca, sweet potato Gooseberries, strawberries

Kale Peanuts, pecans Black tea

Purslane Soybean Cocoa, chocolate, Ovaltine

Collards Wheat germ, wheat bran Cola

Mustard and turnip greens Sorrel, parsley, amaranth Beer

OXALATES 4283