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Question marks raised over the vegetarian diet

Posted Jan 07 2011 12:54am

Last week I wrote a piece which attempted to highlight the nutritional attributes of meat (and there are many). I appreciate that not everyone want to eat meat. Some don’t like to eat it, and some will not eat it on moral, ethical, animal welfare or religious grounds. Let me state here that I have no objection to any of this. I just think for those of us who do eat meat, it’s not a bad thing to know just how nutritious and potentially health-giving this food can be (despite what conventional nutritional wisdom may tell us).

I also believe that it’s not a bad thing for vegetarians to be aware that the omission of meat and fish from the diet can put them at risk of certain nutritional deficiencies. These were highlighted in a recent piece published in the journal Nutrition in Clinical Practice [1]. This piece specifically highlights the fact that vegetarian diets tend to be low in vitamin B12, vitamin D, omega-3 fatty acids, calcium, iron, and zinc. It also recommends the use of “supplements and fortified foods” to provide “a useful shield against deficiency”.

This piece goes on to claim, however, that vegetarians have reduced rates of death from ischemic heart disease; and decreased incidence of hypertension, stroke, type 2 diabetes, and certain cancers than do non-vegetarians. I hear these claims for vegetarian eating a lot, but do they stand up to scrutiny?

The idea that vegetarians enjoy a health advantage over more omnivorous eaters is based on the findings of ‘epidemiological’ studies. These studies may show an association between vegetarianism and improved health, but that does not mean the vegetarianism is causing the improved health. It is possible that any apparent benefits to health that appear to come from vegetarianism may come not from the absence of meat and fish from the diet, but from other factors associated with vegetarian living such as a reduced tendency to smoke and healthier exercise habits. These so-called ‘confounding’ factors need to be taken into consideration in order to make a fair assessment of the relative merits of vegetarian and non-vegetarian diets.

Some researchers have attempted to make a more accurate assessment of the benefits (or otherwise) of vegetarian eating by taking into account these confounding factors. In one study, researchers attempted to counteract any confounding factors by focusing only on individuals who shopped in health food stores. The idea here is that all of these individuals are generally ‘health-conscious’, whether they are vegetarian or not. This allows a fairer appraisal of the impact of vegetarian or non-vegetarian eating. This study found that compared to the general population, death rates in vegetarians and non-vegetarians were significantly lower than in the general population (which supports the notion that health food shoppers are a generally health-conscious bunch). However, overall risk of death in vegetarians and non-vegetarians the same [2].

In another study, vegetarians were asked to recruit their friends and family into the study. Doing this was thought to help ensure that all individuals in the study were similarly health-conscious. Again, this study found that vegetarians and non-vegetarians had risk of deaths lower than that of the general population. However, again, death rates for vegetarians and non-vegetarians were essentially the same [3].

And in another piece of research comparing vegetarians and non-vegetarians, quite detailed analysis of the dietary habits of some 56000 individuals was undertaken [4]. This study, yet again, found that the overall risk of death in vegetarians was not lower than in non-vegetarians.

And what of that claim about vegetarian diets being better for the heart? None of these studies found any evidence for this contention either.

So, the plain facts show that, overall, there is no broad health advantage to be had from eating a vegetarian diet. In other words, while individuals may be unkeen to eat flesh foods on moral, ethical and religious grounds, there does not appear to be a good argument for vegetarianism on grounds of health.

References:

1. Craig WJ. Nutrition concerns and health effects of vegetarian diets. Nutrition in Clinical Practice. 2010;25(6):613-20

2. Key TJA, et al. Dietary habits and mortality in 11000 vegetarians and health conscious people: results of a 17 year follow up. Br Med J 1996;313:775-9

3. Thorogood M, et al. Risk of death from cancer and ischemic heart disease in meat and non-meat eaters. BMJ 1994;308:1667-70

4. Davey GK, et al. EPIC-Oxford: lifestyle characteristics and nutrient intakes in a cohort of 33,883 meat-eaters and 31,546 non meat-eaters in the UK. Public Health Nutr 2003;6:259-68

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