Turning vegetarian was "trendy" in the 1980s and has since become more commonplace. But be it for health, religious, moral or taste reasons, the extent to which individuals truly go vegetarian is highly variable.

Research from the US shows that less than one percent of Americans are true vegetarians, that is, who never eat meat, fish or poultry although they may eat foods derived from animals such as dairy products and eggs. The number of vegans -people who avoid all animal-derived foods, including honey -is even smaller.

The healthiness of a vegetarian diet largely depends on the variety of foods consumed. Because vegetarian diets feature primarily plant foods, they tend to be richer in dietary fibre, carbohydrates and many vitamins and minerals.

Protein is a nutrient that many vegetarians worry about, but quite unnecessarily. While vegetarians typically eat less protein than non-vegetarians, their diets tend to meet or even exceed the recommended daily allowance for protein. And if they eat a variety of different plant foods -grains, nuts, seeds, legumes, vegetables and fruits -the quality of the protein is fine.

"In the past, we used to tell vegetarians to mix their plant foods at each meal", said Julie Howden, a nutritionist and executive director of the Singapore-based Asian Food Information Centre (AFIC). "This is because plant foods supply different types and amounts of amino acids, the building blocks of proteins. It was thought that you had to eat all of the amino acids at one meal to provide good quality protein. People were therefore taught to have rice with beans or cheese with bread."

"However, this approach is not necessary. Nutritionists now believe that eating a variety of plant foods every day is sufficient to meet one's protein requirements."

Vegetarian diets also enjoy a reputation for being low in fat and cholesterol. But this is true only if the intake of nuts and fats is kept low.

According to Ms Howden, "People on vegetarian diets would do well to heed the general advice about healthy eating: keep fat intake low. Choose polyunsaturated and monounsaturated fat spreads and oils and low fat dairy products."

There are a few nutrients which may be at-risk in a vegetarian diet. For people who exclude all sources of animal protein, including eggs and dairy products, deficiencies in iron, zinc, calcium and vitamin B12 are more likely. It is therefore important to seek nutritional counselling before embarking on such a diet.

"Nutritionists and doctors often see young women who have gone vegetarian for whatever reason and given up red meat," said Ms Howden. "As a result, they may become iron deficient or anaemic." Dietary sources of iron are needed to off-set iron losses through menstruation. Good plant sources of iron include dried beans, green leafy vegetables and dried fruits.

"Plant sources of iron are nowhere near as well absorbed as meat," said Ms Howden. "If people have given up animal products altogether, it is important they choose larger servings of iron-rich plant foods and eat them with a source of vitamin C such as a glass of orange juice."

Vitamin C helps the body to absorb iron. In some cases, an iron supplement may be required.

Vitamin B12 is another nutrient that may be at risk. Although the body only needs a very small amount of vitamin B12 and body stores can last for some years, nutritionists recommend that vegetarians who do not consume dairy products or eggs eat foods that have been fortified with vitamin B12 or take a vitamin supplement.

Compared to the general population, vegetarians appear to be at lower risk for heart disease, colon cancer, diabetes, obesity and high blood pressure. Not everyone however, believes it is necessary to eliminate meat for successful disease prevention.

"You can achieve many of the same types of health benefits with a diet that includes meat," said Ms Howden. "You just need to choose lean meats and remove any visible fat."

Even proponents of vegetarianism agree that it is hard to determine the extent that lifestyle impacts on the health statistics of vegetarians. Vegetarians are more likely to be health conscious -they tend to abstain from alcohol and smoking and to exercise regularly. It is these factors that experts agree exert a powerful health impact.

The bottom line is for those who have adopted vegetarian diets or are making gradual changes in that direction remains the same as with conventional diets: eat a wide variety of foods including plenty of whole grain products, vegetables, legumes and fruits and maintain a healthy lifestyle.

Vegetarian diets are healthful and nutritionally adequate when carefully planned. Consuming adequate amounts of iron and calcium is especially important. The following foods are good sources of these nutrients.

Iron: dried beans, spinach and other green leafy vegetables, dried fruit. To improve iron absorption, consume vitamin-C rich foods at the same time.

Calcium: Milk, yoghurt, cheese, calcium-fortified soy milk, calcium-fortified tofu, broccoli, green leafy vegetables.

Different types of vegetarian diets are characterised by the degree to which they exclude animal foods. Below are some diets most commonly thought of as vegetarian yet some people today call themselves vegetarian if they eat meat just occasionally.

• Pesco-vegetarian -include fish, dairy products and eggs.
• Lacto-ovo vegetarian -includes eggs and dairy products.
• Ovo-vegetarian -includes eggs.
• Vegan -excludes animal-derived foods of all types.