I make no secret of my carnivorous ways, and was interested to read of a study which found that supplementing children's diets with meat enhanced their growth and led to improved performance in problem-solving and intelligence tests. If nothing else, this study highlights the fact that a diet devoid of animal-derived foods may fall short in some nutrients required for healthy development. There is also evidence that even a diet which includes eggs and dairy products may fail to supply adequate levels of key nutrients. This week, I thought I'd examine the potential deficiencies of vegan and vegetarian diets, and suggest ways to beef them up.

The growth-augmenting effects meat appears to have may relate to the protein it provides. While the importance of protein seems to have slipped off the nutritional agenda over the past decade or two, this dietary element provides building blocks (amino acids) that can be reassembled into body components including bone and soft tissues. Higher levels of protein intake are associated with enhanced height and lean weight in children.

Amino acids come in 22 types, 10 of which must be supplied by the diet for optimal growth. The full spectrum of these 'essential amino acids' is found more readily in animal foods. Those on a vegan diet will improve their chances of getting enough of these by eating a wide range of protein-rich foods such as beans, lentils, tofu, nuts and seeds. Vegetarians can also find quality protein in such dairy products as milk, cheese and yogurt.

Another good source of protein for vegetarians is eggs, which offer vitamin B12 and iron. Vegans are prone to iron deficiency, and may need to eat such foods rich in this mineral, including cocoa, prunes, raisins, seeds and nuts. Vitamin B12 deficiency is a common consequence of a vegan diet (it is only rarely found in plant foods), so supplementation with B12 is generally advised.

In practice, I recommend vegans get their B12 from a multivitamin and mineral supplement which contains other nutrients that tend to be deficient in a vegan diet, including vitamin B2, zinc and iodine. For vegans and vegetarians alike, the taking of a multi-nutrient supplement offers a 'nutritional safety net'. Kids' Complete Complex and Kids' Complete Capsules are available from BioCare (0121 433 3727). Countering potential nutritional deficiencies through diet and supplements can help ensure vegan and vegetarian children don't suffer growing pains.

· To order Natural Health for Kids by Dr John Briffa for £16.14 (including 5% discount and free UK p&p), call the Observer book service on 0870 836 0885, or go to www.observer.co.uk/bookshop

Nutrition news:

Cocoa is well known to contain substances called flavanols, the consumption of which has been associated with a reduced risk of heart disease. In a recent study, Argentinian researchers assessed the effects of consuming flavanol-containing chocolate on a range of health parameters including blood pressure, and blood levels of cholesterol and uric acid (higher levels of which are associated with an increased risk of heart disease). Each of the individuals in the study was asked to eat 105g of chocolate each day for two weeks. At the end of the study, chocolate eating was found to bring about meaningful reductions in blood pressure, cholesterol and uric acid.

The authors of this study, which was published this month in the journal Clinical and Developmental Immunology, believed that the flavanols contained in chocolate are likely to have been a significant factor in these improvements. Those who are looking to get health benefits from chocolate should opt for dark chocolate, as this is richer in flavanols (and other nutrients) and lower in sugar than milk-chocolate varieties.