The Effect Of A Vegetarian Diet On Performance

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Vegetarian dietary practices have been associated with many health benefits, including reduced death rates from ischemic heart disease, diabetes, and certain forms of cancer,2,5-8 and decreased risk of obesity, dyslipidemia and hypertension.2,9-11 Vegetarians, compared with non-vegetarians, typically have a higher intake of fruit and vegetables, dietary fiber, antioxidant nutrients, phytochemicals, and folic acid, with a lower intake of saturated fat and cholesterol,12-15 each of which has been related to decreased risk of chronic disease.16-21

The question of whether the multiple benefits of vegetarian dietary practices extend to enhanced physical fitness and performance has been explored since early in the 20th century.2-4 A few simple studies conducted prior to 1910 reported augmented muscular endurance (e.g., holding arms out horizontally, deep knee bends, and leg raises) in vegetarian vs. non-vegetarian subjects, but these results have not been confirmed in subsequent research.2-4

Modern-day research comparing physical fitness performance in vegetarians and non-vegetarians began in the 1970s. Cotes et al.22 compared thigh muscle width, pulmonary function measures, and the cardiorespira-tory response to submaximal cycle ergometry exercise in 14 vegan and 86 non-vegetarian women. Ventilation responses during rest or exercise did not differ between the groups, and thigh muscle width was similar. The authors concluded that the lack of animal protein did not impair the physiological response to submaximal exercise.

Meyer et al.23 studied the effect of a vegetarian diet on running performance (5- to 8-kilometer test runs). The subjects completed the runs before and after being on the diet for 2 weeks, and then again 2 weeks after returning to a non-vegetarian diet. No significant differences were found between the trials, suggesting that the vegetarian diet had neither a beneficial nor detrimental effect on aerobic endurance.

Physical fitness, anthropometric, and metabolic parameters were compared by Hanne et al.24 in 49 vegetarian and 49 non-vegetarian male and female Israeli athletes who were matched for age, sex, body size, and athletic activities. No significant differences were found between groups for pulmonary function, aerobic and anaerobic capacity, arm and leg circumferences, hand grip and back strength, hemoglobin, and total serum protein. The authors concluded that the specific influence of the vegetarian diet on physical performance is confounded by several factors, including the type of vegetarian diet ingested, the training regimen, and other lifestyle practices.

Twenty-one overweight females were fed a lacto-ovo-vegetarian diet for 5 weeks, with all meals prepared, weighed and served in a research kitchen.25 Half of the subjects were randomized to a walk/jog exercise program (five 45-minute sessions each week at an intensity of 60% VO2max), while the other half remained sedentary. Submaximal and maximal car-diorespiratory measures improved significantly in those who exercised, but no improvement was seen in the women who consumed the vegetarian diet without exercise. In other words, the vegetarian diet alone is an insufficient stimulus to improve physical performance unless accompanied by a regular exercise training program.

Snyder et al.26 studied two groups of female runners who were matched for age, weight, and distance run per week. One group regularly consumed a semi-vegetarian diet (< 100 grams red meat per week), while the other group ingested a diet that included red meat. No significant difference in maximal aerobic capacity was found between the two groups.

A series of papers has been published on 110 runners who competed in a 1000-km race conducted over a 20-day period in West Germany.27-29 Before and during the race, 60 of the runners consumed a conventional Western diet, and 50 consumed a lacto-ovo-vegetarian diet. During the race, diets for both groups were formulated to ensure a similar intake of carbohydrate for both groups (~ 60% total energy). Diet had no effect on the performance of the runners. Half of each group finished the 20-day race, the order of finishers was not influenced by the diet, and the average running time for the vegetarian runners was not significantly different from the non-vegetarians. (See Figure 12.1).

Nineteen long-term (mean of 46 years) vegetarian and 12 non-vegetarian, healthy, physically active elderly women (mean age of 71 years) were compared on a variety of hematological, anthropometric, and metabolic factors.30 Although the vegetarian subjects had significantly lower blood glucose and cholesterol levels, no differences between groups were found for submaximal and maximal cardiorespiratory and electrocardio-graphic parameters measured during graded treadmill testing. The authors

CUVegetarian Diet CHOmnivorous Diet

114.3

116.5

Percent Finishing

114.3

116.5

Total Time (h)

Percent Finishing

Total Time (h)

Figure 12.1 With a similar intake of carbohydrate (~ 60% total energy), the proportion of finishers and performance time following a 1000-km, 20-day race were not significantly different between vegetarian and non-vegetarian

concluded that a long-term vegetarian diet may be associated with several benefits, but these do not include greater cardiorespiratory fitness.

Two papers have been published on a study of eight well-trained male athletes in Denmark who consumed either a lacto-ovo-vegetarian or non-vegetarian diet for 6 weeks (cross-over design).31,32 Both diets consisted of 57% total energy as carbohydrates, 14% protein, and 29% fat. Maximal aerobic capacity, aerobic endurance time to exhaustion, muscle glycogen levels, and isometric strength were unaffected by changes in the diet. This study demonstrated that when macronutrient intake is held constant, switching between a vegetarian and non-vegetarian diet should not be expected to have an influence on exercise performance.

Animal product intake was measured and related to VO2max in a group of 80 women who varied widely in age, body mass, maximal aerobic power, and meat intake (1.1 to 31.6 meat exchanges per day).33 Maximal aerobic power was not related to meat intake, an animal product index, or dietary cholesterol. Multiple regression analysis, using models to control for age and body composition, failed to alter these findings.

Together, these studies indicate that the vegetarian diet, even when practiced for several decades, is neither beneficial nor detrimental to cardiorespiratory endurance, especially when carbohydrate intake, age, training status, body weight, and other confounders are controlled for. Endurance exercise performance is strongly related to genetic factors, training regimens, and carbohydrate intake.1 The inclusion or avoidance of meat in the dietary patterns of endurance athletes is not an important issue, especially when contrasted to the dominating influence of these three factors.

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