Vegetarian Diets

This answer is brought to you by many of the Australian nutrition professionals who regularly contribute to a nutrition email discussion group.

Date of last revision: November 2011

The following series of questions and answers address various aspects of vegetarianism.

I have heard people say that they are 'vegetarian', yet some of these people eat poultry, others eat dairy products and/or eggs (but no meat or fish), while some eat nothing of animal origin. What does the term 'vegetarian' actually mean?

The word 'vegetarian' is not well-defined. It includes people with a wide range of attitudes and eating behaviours with respect to foods of animal origin.

Vegetarians all base their diets on foods of plant origin, but there are different levels of vegetarianism according to how much food derived from animals is also eaten. In Australia there are five major types of vegetarian:

A 'semi vegetarian' eats poultry and/or fish, dairy foods and eggs, but no red meat;

A 'lacto vegetarian' consumes dairy foods but no meat, poultry, fish or eggs;

A 'lacto-ovo vegetarian' includes dairy foods and eggs, but no meat, poultry or fish;

A 'pescetarian' includes fish and other seafood, but no meat or poultry (while eggs and/or dairy foods may or may not be eaten); and

A 'vegan' eats only foods of plant origin.

There are more extreme forms of vegetarianism. For example, 'fruitarians' eat nothing that required a living organism to be killed, restricting their diet to fruits, nuts, honey and olive oil. Similarly, the range of Zen Macrobiotic diets includes some that are as restrictive as that of the fruitarians. However, the five categories described above account for all but a very small minority of vegetarians in Australia (and in most of the remainder of the Western world as well).

Why do people adopt vegetarian diets?

The reasons for becoming a vegetarian are many and varied. Many people are vegetarians as a result of religious beliefs. In addition, semi vegetarians usually believe that red meat is harmful to health, particularly—but not exclusively—to heart health. Lacto and lacto-ovo vegetarians might add that there is a moral dimension, based on a belief that animals have the same right to live as we do. Because dairy foods and eggs can be collected without killing (or harming) the animals that provide them, lacto and lacto-ovo vegetarians might be justified in considering themselves more humane than meat eaters.

Vegans would almost certainly agree with the moral argument but would probably add that, unlike milk and eggs, plants contain no cholesterol and most plant foods have little 'saturated fat' (a type of fat that is associated with increased risk of heart disease). But it is worth noting that coconut oil and palm oil are exceptions, in that most of the fat from these plant foods is saturated.

The higher levels of many vitamins, fibre, antioxidants and other substances believed to be of nutritional benefit in foods of plant origin are also used as arguments for greater health benefits of vegetarian diets.

Many vegetarians believe that, in addition to health benefits and moral considerations, there is also reduced environmental degradation (i.e. increased sustainability) associated with vegetarianism. In some countries there are special reasons for considering adopting a vegetarian diet. For example, in the United Kingdom some people have become vegetarians following the advent of 'mad cow disease' (BSE), and the diagnosis of a similar disease in humans (variant CJD) believed to be acquired by eating beef infected with BSE.

Some teenagers, mostly girls, adopt a vegetarian diet because they think it will lead to weight loss. In a few cases, changing to an extreme vegetarian diet can be a smokescreen for an eating disorder. So although many girls follow a vegetarian diet, and only a small number develop an eating disorder, it is worth watching for any changes that lead to severely restricted total food intake.

How nutritious are vegetarian diets compared to the omnivorous diet?

There are at least two ways of approaching the question 'how nutritious is a particular diet?' First, it can be considered in terms of the 'completeness' of the diet (that is, does it provide all known essential nutrients in at least the minimum recommended quantities?). But it can also be addressed in terms of 'how much does the diet promote good health?' (i.e. how many components does it contain that are considered health-promoting compared to those associated with adverse health outcome?).

Considering the 'completeness' aspect first: Semi vegetarian, lacto vegetarian, and lacto-ovo vegetarian diets, when properly planned, have been consistently found to provide the full range of protein, essential fatty acids, vitamins, minerals and fibre necessary for optimal nutritional status. In this, they are approximately equivalent to properly planned omnivorous diets.

However, as they are often practised, these vegetarian diets can lead to low iron status. Vegetarian teenage girls and women of child-bearing age are particularly at risk of iron-deficiency anaemia because red meat is one the best dietary sources of iron. Proper planning can help ensure that adequate iron status is maintained when the diet does not contain red meat. For example, combining a source of vitamin C (such as fruit or fruit juice) with wheat-based cereal foods will increase the absorption of the iron available in the cereal. Eggs, legumes (a term that includes peas, beans, chickpeas, lentils, soy foods) and nuts are also significant sources of iron.

A well-planned vegan diet can meet all nutritional requirements. However, some who follow a vegan diet are at risk of developing B12 deficiency unless special effort is made to eat foods fortified with this vitamin, or a vitamin supplement is taken. Although any diet that fails to address healthy eating principles can be deficient in essential nutrients, vegans may need to be especially vigilant with their eating habits with regard to nutrients such as iron, calcium, zinc, iodine, selenium and omega-3 fats.

Vitamin B12 is found only in animal foods, and studies have shown that both vegetarians and vegans generally have lower levels of vitamin B12 than do omnivores.  While it can take many years to become deficient, anyone following a vegan diet who doesn’t include a reliable source of vitamin B12 is at risk of becoming deficient over time.  If you follow a vegan diet (or you are vegetarian but don’t eat many dairy foods or eggs) you should either take a vitamin B12 supplement or include foods fortified with vitamin B12 in your diet regularly (e.g. So Good soy milk, Marmite and some Sanitarium Veggie Delight products). This is particularly important for pregnant and breastfeeding women, to reduce the risk of deficiency in their babies.

Other nutrients at risk for vegans include protein, iron, zinc and calcium. Grain foods, legumes, potatoes, seeds and nuts are good sources of protein. Legumes, nuts and dried fruits are quite good sources of calcium, while legumes and seeds provide significant quantities of zinc.

From the point of view of promotion of good health, despite the greater risk of some vitamin deficiencies, it is fair to say that vegetarians in Western nations often eat a diet that is closer to the recommended pattern of food intake than their omnivorous relatives or neighbours. Vegetarian diets include higher intakes of cereal foods, vegetables (including legumes) and fruits—and therefore of dietary fibre—with lower intakes of fat (particularly saturated fat) and salt.

Fruitarian diets and those of some of the more extreme levels of the Macrobiotic diets are invariably nutritionally inadequate.

What about the relationship between vegetarian diets and health—is there any evidence for better (or worse) health outcomes compared to omnivorous diets?

There is a substantial body of evidence supporting the belief that vegetarians in Western countries experience significantly less cancer, less heart disease, fewer strokes, and generally live longer than omnivores.

However, it is also true that people who choose a particular diet for health reasons will probably also look after their health in other ways. For example, they are less likely to smoke, to abuse alcohol and other drugs, and are more likely to exercise for health and general fitness. It may be that these behaviours explain some of the health benefits associated with being vegetarian.

However, this argument does not explain the entire health benefit. It seems increasingly likely that higher intake of beneficial dietary factors—available only in foods of plant origin—also plays an important part in explaining the better overall health of vegetarians.

One 'natural experiment' being played out in the Western world exists in the form of a difference in diet between two groups of Seventh Day Adventists. Although members of this faith are advised not to eat meat, this is not binding. So Seventh Day Adventists divide rather neatly into two groups with apparently similar lifestyles, except that one group eat meat while members of the other group are strictly vegetarian. Studies have indicated that meat-eating Seventh Day Adventists have increased risk of heart disease, cancer, diabetes and arthritis compared to those who are strictly vegetarian. However, it is still not certain that this result is due only to the consumption of meat.

Much research is still needed to determine the optimal diet for health and longevity (living to a 'ripe old age'). Some nutritionists believe that a predominantly vegetarian diet, with low-moderate quantities of lean meat and moderate quantities of low- or reduced-fat dairy products will produce the best long-term health outcome. However, it is still true that strict vegetarianism (particularly the lacto and lacto-ovo varieties) is associated with better health outcome than an omnivorous diet.

Although the optimal dietary strategy for health and longevity has still not been determined, the emphasis today is on increasing intake of foods of plant origin—breads and cereals (preferably whole grain), vegetables (including  legumes) and fruits. If omnivores make this change at the expense of fatty meats, while continuing to eat moderate quantities of lean meat (including  red meat) and fish, an overall increase in health will almost certainly result.

I have heard that producing meat takes a greater area of land than producing plant foods. How much truth is there in this?

It is true that about seven hectares of land is required to produce the same quantity of protein from beef production as can be obtained from a hectare of wheat or rice. This is a powerful argument for less meat production from arable land when the world's population is increasing at a rate of about 80 million per annum, yet the quantity of fertile land is either static or reducing (because of salination, erosion, over-stocking, declining soil fertility and so on).

However, where the soil is of poor quality and/or rainfall is low, grains cannot be grown; such conditions are suitable only for meat production. For example, a significant proportion of the meat grown in Australia is grown in dry areas where the land would be of little value for anything else.

Perhaps the most efficient use of increasingly scarce (on a world scale) resources would involve replacing meat production with grain growing in those areas where this is possible, and retaining meat production where little else will grow. One consequence of this would be an overall reduction in meat consumption.


A book that is directed at the general public (and is of special value to teenage girls who have adopted a vegetarian diet) is:

'Healthy Vegetarian Eating' by Rosemary Stanton. Published by Allen and Unwin: 1997.


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