Meat vs veg: how does a vegetarian diet stack up?
Wednesday, 5 June 2013
By Surinder Baines, University of Newcastle
Ethical and environmental considerations are often the prompt for adopting a meat-free diet. But better health may also push some towards vegetarianism, with a new study showing vegetarians have a lower risk of premature death than their meat-eating counterparts.
The Journal of the American Medical Association (JAMA) study of more than 70,000 Seventh-day Adventists placed the participants into five groups: non-vegetarian, semi-vegetarian, pesco-vegetarian (includes seafood), lacto-ovo-vegetarian (includes dairy and egg products) and vegans.
Overall, the authors found a 12% reduction in premature death for the vegetarian groups, over a period of just under six years. The benefit was more pronounced for men, though the reason for this difference is not clear.
The researchers also reported the vegetarian groups were likely to be older, married, highly educated and tended to exercise more.
But there are a number of shortfalls to this study. The participants were only asked about their diets in an initial survey, so dietary patterns may have changed over time. It's also possible that some people in the vegetarian groups, including vegans, may have consumed some animal foods such as eggs, dairy, fish and meat.
Are vegetarians really healthier?
The JAMA study builds on a growing body of evidence that shows vegetarians have a lower risk of some chronic diseases such as hypertension (high blood pressure), heart disease and diabetes.
This may be because vegetarian diets are usually higher in fibre, antioxidants, and phytochemicals (natural compounds found in fruit and vegetables). They also tend to be lower in their content of animal fat, though some plant oils such as coconut oil and palm oil do contain saturated fats.
Many studies report that vegetarians are healthier than non-vegetarians because they have healthier lifestyles: they tend not to smoke, exclude or limit alcohol consumption, are more physically active and they usually have lower body mass index (BMI). But many of these have focused on specific groups such as Seventh-day Adventists, who tend to minimise behaviours which increase the risk of chronic disease.
Studies investigating the health and lifestyle of vegetarians and non-vegetarians in the wider community have also reported health benefits of a vegetarian diet.
The European Prospective Investigation into Cancer and Nutrition, or EPIC study – which investigates the relationships between diet, cancer and other chronic diseases in more than half a million European participants – found vegetarians tended to be healthier than meat eaters.
In March, for example, the UK arm of the EPIC study reported the risk of ischemic heart disease was 32% lower among the vegetarians. This was based on a study of 44,561 men and women over 11.6 years. Importantly, the researchers said the findings were not influenced by the participants' gender, age, BMI or smoking status.
Not all vegetarian diets are equal
Concerns have traditionally been raised about the health effects of severely restricting the consumption of foods of animal origin, especially meat. It was thought these diets may not be nutritionally adequate and therefore could impact on growth and development, especially among children and teenagers.
There is a risk that some vegetarian diets may not contain sufficient amounts of some nutrients required for optimal health, especially the more restrictive diets in which iron, zinc, vitamin B12 and some of the omega 3 fats are more likely to be low. But with careful planning, vegetarians can meet all their nutritional needs.
So, how much is enough?
The Nutrient Reference Values for Australia and New Zealand recently increased the recommended daily intake of iron and zinc for vegetarians, to 80% more iron and 50% more zinc than the current recommendations for non-vegetarians. This is because vegetarian diets have higher levels of constituents such as phytate, which can affect absorption of these minerals from the diet.
For iron, the recommended intake for vegetarians is 32 milligrams (mg) a day for women and 14 mg/day for men. This compares with 18mg/day for non-vegetarian women and 8mg/day for non-vegetarian men. Vegetarian sources of iron include fortified breakfast cereals, breads and soy drinks, firm tofu, legumes, nuts, seeds and brown rice.
Likewise for zinc, the recommended daily intake for vegetarians is 12 mg/day for women and 21 mg/day for men, compared with 8mg/day for non-vegetarian women and 14mg/day for non-vegetarian men. Good sources of zinc include whole-grain breads and cereals, rolled oats, nuts, seeds, legumes, brown rice and soy products.
The nutritional needs may be increased during growth and development and also during pregnancy and lactation. And in some cases, dietary supplements may be required.
Regardless of whether you follow a vegetarian diet, Australia's dietary guidelines recommend you consume a wide variety of foods each day, including plenty of vegetables, whole-grain foods (including legumes/beans, nuts and seeds) and low-fat dairy products.
And if you do eat meat, opt for lean varieties.
Surinder Baines was a co-author on several Medical Journal of Australia papers on vegetarian diets.