Nutrition: A Very Short Introduction (Very Short Introductions) by David Bender

Author:David Bender [Bender, David]
Language: eng
Format: epub, mobi
Publisher: Oxford University Press
Published: 2014-05-05T00:00:00+00:00

How we gather evidence linking diet and health

Different types of epidemiological study can give information about diet and health. The first clues often come from looking at changes in diet over the past 100 or so years, coupled with changes in the pattern of disease. Such studies suggest that, in parallel with the increase in atherosclerosis, cardiovascular disease, and cancer, there have been increases in the total amount of fat and sugar consumed, with a reduction in starch and dietary fibre. A considerably greater proportion of the fat consumed is animal fat, which is largely saturated. One obvious problem with this comparison is that people now live longer now than they did 100 years ago. This is partly because the diseases associated with under-nutrition are now rare in developed countries, and partly because many infectious diseases that were common killers can now be treated with antibiotics and anti-viral drugs. The provision of clean drinking water and effective management of sewage have also been important factors.

A great deal can be learnt from studying people who have migrated from one country to another, and comparing their patterns of disease, and their diets, with relatives who have remained in the mother country. Similarly, we can look at patterns of disease in different countries—for example, there is a 100-fold difference in the incidence of breast and prostate cancer between West Africa and the USA. Are there any differences in diet that might explain this? Vegetables form a large part of the traditional Japanese and Chinese diets, as does fish in Japan and near the coast in China. The oestrogen-like compounds in soya products may explain the lower incidence of breast and prostate cancer in China and Japan compared with that in Western countries. The traditional Mediterranean diet, rich in fruits and vegetables, with more fish and seafood than meat, and moderate wine consumption is associated with considerably lower incidence of cardiovascular disease than Northern Europe.

Many studies have shown that there is a significant international correlation between fat intake and breast cancer. Such studies assume that the data on food availability in different countries are comparable. The main problem here is that diet is only one of many factors that differ between different countries, and many other lifestyle and environmental factors may also be important. More detailed international correlation studies involve taking blood samples for laboratory studies. The Seven Countries study, which started in the 1950s and has continued to the present, first established that elevated serum cholesterol was a major factor in atherosclerosis and coronary heart disease.

At a more individual level, we can look at people with a given disease and compare them with people who are free from the disease, but matched for age, sex, lifestyle, and as many other factors as possible. This is a case-control study. It gives better information than international correlation studies, and in many studies we also have information not only on diet but also on results from laboratory tests to measure individual nutrients and markers of nutritional status in blood and urine samples.

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