Fruit and vegetable consumption: impact on health

General benefits

There is clear and growing evidence for the protective effects of fruit and vegetables
against chronic diseases such as CHD and cancer. Eating at least five portions of fruit
and vegetables a day could reduce overall deaths from chronic diseases (such as heart
disease, stroke and cancer) by up to 20% (Khaw et al).

Increased consumption of fruit and vegetables can also have a positive impact on
other dietary goals, such as recommendations to increase fibre intake and reduce fat
intake (Stubbs et al and Cox et al). In addition, fruit and vegetables tend to be low in
calories and fat, and therefore, diets which contain plenty of fruit and vegetables can
help to reduce the risk of weight gain and obesity (and associated conditions such as
diabetes). Swopping fruit and vegetables for other snack foods may reduce intake of
foods high in fat and high in sugar. The place of fruit and vegetables within the whole
diet is shown in the plate diagram The Balance of Good Health.

Current consumption

The World Health Organisation (1991) and Committee on Medical Aspects of Food
and Nutrition Policy (1994 and 1998) recommend that people should eat at least 400g
(around 5 portions) of fruit and vegetables every day. A recent survey by the Food
Standards Agency found that 43% of adults are aware of this advice. In the UK,
average consumption is 3-4 portions per day (NFS 1998), though there are marked
differences between social groups - unskilled groups tend to eat around 50% less than
professional groups (NFS 1998 and NDNS 2000).

The Evidence for Cancer

It has been estimated that diet might contribute to the development of one third of all
cancers. COMA’s Working Group on Diet and Cancer concluded that, overall, the
evidence is moderately consistent that higher vegetable consumption would reduce
the risk of colorectal cancer, and that higher fruit and vegetable consumption would
reduce the risk of gastric cancer. There is weakly consistent evidence, based on fewer
data, that higher fruit and vegetable consumption would reduce the risk of breast
cancer. These cancers combined represent about 18% of the cancer burden in men
and about 30% of the cancer burden in women in the UK. Even a small reduction in
relative risk would have important public health benefits in terms of the absolute
numbers affected. The World Cancer Research Fund estimated that increasing fruit
and vegetable consumption could prevent 20% or more of all cases of cancer. As a
result, increasing fruit and vegetable consumption may be the second most important
strategy for cancer prevention after reducing smoking (and could save the NHS £72m
per annum (extrapolation from Day, 2000).

The evidence for cardiovascular disease

The results of a 1997 systematic review were consistent with a strong protective effect
of fruit and vegetables for stroke and a weaker protective effect on coronary heart
disease (Ness and Powles). The review found that 9 of 10 ecological studies, 2 of 3
case-control studies and 6 of 16 cohort studies showed fruit and vegetables (or
surrogate nutrients) to have a significant protective effect on coronary heart disease.
For stroke, 3 of 5 ecological studies, none (of one) case-control study and 6 of 8
cohort studies found a significant protective association with consumption of fruit and
vegetables or surrogate nutrients. Studies published since this review have also been
supportive of a protective effect. For example, a recent study among US health
professionals (Joshipura et al) found that each 1 portion per day increase in fruit and
vegetable intake was associated with a 4% lower risk of CHD and a 6% lower risk of
stroke, after controlling for other risk factors. Increased intake of fruit and vegetables
could save the NHS up to £200 m per annum (extrapolation from Day).

Vegetarians

Studies of vegetarians - who tend to have higher intakes of plant foods than non-
vegetarians - support the hypothesis that a diet higher in fruit and vegetables might
lower the risk of coronary heart disease and some cancers (Rimm et al). A pooled
analysis of the data from five large prospective studies found that vegetarians had a
24% lower mortality from ischaemic heart disease than non-vegetarians. Such studies
cannot provide conclusive evidence on the benefits of higher consumption, because
vegetarians may differ from non vegetarians in other ways – for example they may be
more active or less likely to smoke.

Protective substances in fruit and vegetables

There are many biologically plausible reasons why increased consumption of
vegetables and fruits might slow or prevent the onset of chronic diseases. A wide
variety of substances present in plant foods may play a role including carotenoids,
vitamin C, vitamin E, flavonoids and dietary fibre ( Jenkins et al and Lampe).

At almost every stage of the cancer process, identified phytochemicals (including
glucosinolates, phenols, coumarines, flavinoids and phytoestrogens) are known to be
able to alter the likelihood of carcinogenesis – occasionally in a way that enhances
risk but usually in a favourable direction. Most of the data for the observations on the
anticarcinogenic potential of all of these compounds have come from animal and
laboratory studies.

For cardiovascular disease, the main components in fruit and vegetables likely to
decrease the risk of disease are the antioxidants, which are capable of reducing the
oxidation of LDL cholesterol and folate which lowers plasma homocysteine levels
and hence reduces the strong risk factor for arteriosclerosis of the coronary, cerebral,
and peripheral arteries.

Dietary supplements of substances contained in fruit and vegetables

Although fruit and vegetables appear to have wide-ranging beneficial effects, this may
not be true for supplements of single nutrients or substances derived from them. For
example, a Finish study found that supplementation of beta carotene increased the risk
of lung cancer among smokers. As a result, COMA (1998) highlighted the need to
exercise caution in the use of high doses of purified supplements of other vitamins
and minerals as they cannot be assumed to be without risk.

References

Khaw (2001) Relation between plasma ascorbic acid and mortality in men and
women in EPIC-Norfolk prospective study: a prospective population study. Lancet
(357)

Stubbs, R. and A. Prentice, The effect of covertly manipulating the dietary fat to
carbohydrate ratio of isoenergetically dense diets on ad libitum food intakes in free
living humans. Proc Nut Soc, 1993. 52: p. 351A.

Cox, D.N., et al., Take Five, a nutrition education intervention to increase fruit and
vegetable intakes: impact on consumer choice and nutrient intakes. British Journal of
Nutrition, 1998. 80: p. 123-31.

WHO, Diet, nutrition and the prevention of chronic diseases. Technical Report Series
797, 1991, World Health Organisation: Geneva.

Department of Health, Nutritional Aspects of Cardiovascular Disease, 1994, The
Stationery Office: London.

Department of Health, Nutritional Aspects of the Development of Cancer, 1998, The
Stationery Office: London. p. 184-188.

National Food Survey 1998

National Diet and Nutrition Survey: 4-18 year olds (2000)

Food Standards Agency 2001

World Cancer Research Fund and A.I.f.C. Research, Food, Nutrition and the
Prevention of Cancer: a global perspective, . 1997, American Institute for Cancer
Research: Washington DC.

Day (2000)

Ness, A. and J. Powles, Fruit and vegetables, and cardiovascular disease: a review.
International Journal of Epidemiology, 1997. 26(1): p. 1-13.

Joshipura K.J. et al., The effect of fruit and vegetable intake on risk for coronary heart
disease. Ann Intern Med 2001. 134 p. 1106-1114.

Rimm, E., et al., Vegetarian diet: panacea for modern lifestyle disease. QJM, 1999.
275(6): p. 531-544.

Jenkins, D., et al., Effect of a diet high in vegetables, fruit, and nuts on serum lipids.
Metabolism: Clinical & Experimental, 1997. 46(5): p. 530-537.

Lampe, J., Health effects of vegetables and fruit: assessing mechanisms of action in
human experimental studies. American Journal of Clinical Nutrition, 1999. 70(3
Suppl): p. 475S-490S.

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