Recently, there has been an increasing interest in ‘clean-eating’, as well as plant-based, vegetarian and vegan diets. This interest is evident in both recreational and elite athletes, with various reasoning including ethical and environmental considerations, weight management and purported performance benefits.
Vegetarian and vegan diets should not be actively discouraged in members of the public. A Position Statement from the American Dietetic Association in 2009 stated that vegetarian and vegan diets represent a healthful and nutritionally adequate eating plan. The caveat to this, however, is that these diets, especially vegan eating, should be appropriately planned.
What are the proven benefits?
In athletes considering a switch to a vegetarian diet, detailed discussion regarding the reasons behind their decision is warranted and investigations including body composition analysis and monitoring of this following the switch can help to ensure that the required daily energy needs are fulfilled in this population.
What are the proven effects with respect to exercise?
Vegetarian diets tend to contain relatively large amounts of cereals, pulses, nuts, fruits and vegetables. They are, on average, higher in nutrient-rich carbohydrates, unsaturated fats, fibre and Magnesium and vitamins C and E, as well as certain phytochemicals that can encourage improved muscle refuelling and be beneficial during periods of strenuous training. With regard to protein, most vegetarian diets meet daily protein requirements, even in the raised required ranges recommended for individuals competing in high-level sports. Protein sources can include beans, nuts, tofu and wholegrains as well as meat substitutes.
What are the drawbacks to a vegetarian diet in exercising individuals?
Vegetarian diets tend to be lower in energy, protein and fat. A result of this is that vegetarian meals are often required to be of greater volume to meet nutritional demands. This is obviously further increased in athletes engaging in high levels of activity and a particular difficulty for travelling athletes in countries where a language barrier may make understanding the contents of their meals difficult.
Restricted availability of certain nutrients in a vegetarian diet include vitamins B12, B2 and D, as well as Calcium, Zinc and Iron, which is particularly important to consider in premenopausal female athletes, who are at risk of iron deficiency anaemia especially. Data collected in Australia suggests that prevalence of iron deficiency in the general population is 8% in women and 2% in men, which increases in active individuals to 27% in females and 5% in males. The prevalence in people of Aboriginal and Torres Strait Island descent is also increased (12-20%). The reason for this is that although the iron content of diets are similar in vegetarian and non-vegetarian individuals, the bioavailability of iron is decreased with the absence of haem-iron in vegetarian diets. Iron sources for vegetarians include cereals, legumes, eggs and green leafy vegetables. Those at risk for iron deficiency should be advised to increase vitamin C consumption to aid iron absorption and to avoid foods that impair uptake around meal times, such as tannins and tea, as well as medications such as antacids. Ferritin levels should be checked in those at risk and the current AIS recommendation is for iron supplementation should Ferritin levels be <30ng/ml.
People following a vegan diet have particularly low intakes of vitamin B12, which can put them at risk of a macrocytic anaemia. Plant-based foods do not contain adequate levels vitamin B12, so vegan athletes especially should be advised to ensure good intakes of dark-green vegetables; evidence to confidently suggest that tempeh contains adequate amounts of vitamin B12 is lacking. Vegetarian athletes should seek sources of this including dairy products, eggs, fortified foods or dietary supplementation. The same applies to calcium, where stress and pathological fractures can occur with deficiency states, but evidence suggests that a well-supported vegetarian diet has no increase in risk of stress fractures compared to omnivorous counterparts.
Another issue faced by the vegan diet is the reduced intake of long chain n-3 fatty acids. These can be also be found in eggs and dairy products, but tend to be reduced in the diets of vegetarians as well. Supplementation may have beneficial effects at preventing cardiovascular disease via reduction in platelet aggregation – although further research is required into this area.
A balanced vegetarian diet contains adequate nutrition to support health and growth during any point in the life cycle, with no significant differences in height or growth in vegetarian vs non-vegetarian children and adolescents. However, vegetarian athletes – especially children and adolescents, heavy endurance athletes and athletes focusing on increasing lean muscle mass – can struggle to meet daily energy and essential amino acid requirements and should be advised on how to meet these by a trained dietician. They should also be counselled regarding the incorporation of adequate protein at strategic meal times (e.g. post-exercise meal) to ensure optimal response to their training. Vegetarian athletes competing in maximal and sustained high intensity sport may have lower mean muscle creatine and carnosine (26%) levels than omnivorous athletes and may see benefit from supplementation of these.
There is little evidence to show that athletic performance differs greatly between vegetarians and non-vegetarians as long as diets are nutritionally adequate. Dieticians are an excellent resource to ensure that all nutritional needs are met, and recommending the use of a food diary to monitor average intake can be very beneficial. It is important to consider supplementation and the use of fortified foods to ensure that deficiency states do not occur, especially in those following a vegan diet. Clinicians should discuss the reasoning behind the choice in the diet and ensure that it is not a sign of disordered eating patterns. Evidence shows that an appropriately planned, dietician-endorsed vegetarian or vegan diet can provide adequate carbohydrate, fat and protein to support athletic performance, although further robust studies are required on the effects on elite athletes.