Posted: May 28, 2005

Science of Sport: Can Endurance Runners Be Vegetarians?

By Owen Anderson, Ph. D. (copyright © 2003-2005)

Many meat-eating athletes wonder whether a switch to a vegetarian diet might provide a performance boost, and there are logical reasons for such thinking. First, vegetarian diets tend to be high-carbohydrate regimens, which should lead to optimal glycogen storage in muscles. At the lofty intensities required for high-level training and serious competition, carbohydrate is the primary source of energy; when muscle-carbohydrate (glycogen) levels are too low, athletes experience fatigue and tend to perform poorly (1). Thus, a vegetarian diet may function as an "insurance policy" against insipid intramuscular carbohydrate storage and underachievement in races.

In addition, it is possible that vegetarian eating might enhance the recovery process following tough workouts and competitions. The reasoning goes this way: High-intensity or prolonged effort generates increased levels of "free radicals" within an athlete's body, potentially enhancing the breakdown of cell membranes, including the membranes which wrap around muscle cells (2). An athlete's own physiological systems can synthesize antioxidant enzymes to stem this free-radical onslaught, but an additional line of defense is provided via the consumption of antioxidant nutrients. Vegetarian diets revolve around fruits, vegetables, and whole grains - the kinds of food which are high in antioxidants. Thus, vegetarian eating may do a better job of protecting muscle cells during hard training, compared with dietary plans which are more biased toward meats.

Of course, the "coup-de-grace" pro-vegetarian argument in the running community relies on the fact that Kenyan distance runners, at least when they are "coming up," are basically lactoovovegetarians, depending on corn, beans, and the various fruits and vegetables found in Kenya, along with dabbles in milk and eggs, to fuel their achievements. Since the Kenyans perform better as a group than any other runners in the world, it would seem that vegetarian diets, or at least lactoovovegetarian ones, go hand-in-hand with top performances.

While those are rational and reasonable points, it should be noted that a meat-eating athlete's diet is not necessarily low in carbohydrate. Evidence now strongly suggests that an athlete who trains between 60 and 90 minutes per day should ingest about eight to 10 grams of carbohydrate per kilogram of body weight daily (approximately 3.6 to 4.5 grams of carbs per pound of body weight per day). Even an athlete who consumes a nightly T-bone steak is not prohibited from attaining such lofty carbohydrate heights; while the T-bone might take up room in the tummy which could be better filled with carrots, brown rice, and passion fruit, there is nothing about meat-eating per se which automatically produces a carbohydrate-consumption failure (the needed carbs could be ingested throughout the day, for example). Even an athlete whose diet is 70-percent carbohydrate has to fill that other 30 percent with something, after all. Take in a grandiose T-bone at every meal, and you've got a problem; take in meat in prudent amounts, and it is relatively easy to ingest adequate levels of carbs, too.

The Kenyan reliance on lactoovovegetarianism also provides rather shaky support for the idea that athletes should shun meat. After all, elite Kenyans increase their consumption of chicken, goat, and even beef after they have won a major race or two, with no noticeable fall-offs in performance.

Finally, although the story about vegetarian eating and muscle recovery is a nice one, there is no strong scientific evidence to support the tale. It would be nice for supporters of vegetarianism if there were some positive data here, because there is actually a laundry list of "knocks" against the practice of refraining from meat consumption during heavy training. For example, there is a concern that a vegetarian diet high in fiber and phytic acid (a compound found in whole grains) might actually reduce the absorption and availability of zinc, iron, and a few "trace" minerals. Fears have also been expressed that vegetarian diets tend to be too low in protein for athletes, and that female vegetarian competitors are at increased risk of impairment of menstrual function. Finally, there is a belief that vegetarianism gradually lowers muscle-creatine concentrations, thus diminishing the power outputs of vegetarian athletes during strenuous efforts.

What does science have to say about all of this? Are vegetarian diets good for performance - or bad? Does vegetarian eating enhance the health of athletes - or does it lead to potential problems?

Let's take a look at the performance side of these questions first. In a unique study, venerable exercise scientist Mel Williams examined the effect of a vegetarian diet on running performance, using 5- and 8-K test runs as the performance variables (3). The athletes in Mel's study completed their tests before and after a two-week vegetarian diet and then again two weeks following the resumption of a carnivore's diet. There were no differences in performance between the trials, suggesting that vegetarian eating was neither harmful nor beneficial for performance. However, two weeks is a particularly narrow "window" through which one might attempt to examine the potential performance benefits of vegetarian eating. Longer periods would certainly be necessary to understand how meat-free eating might alter the recovery process during strenuous training, for example.

In research which did proceed for a longer period of time, eight well-trained Danish athletes swallowed a Kenyan-style lactoovovegetarian diet for six weeks and then a meat-lovers' regimen for an additional six weeks (4). Both of these eating plans contained 57 percent of total calories as carbohydrate, 14 percent as protein, and 29 percent as fat. Interestingly enough, a plethora of variables - VO2max, endurance time to exhaustion, muscle-glycogen concentration, and muscular strength - were all unaffected by the changes in the athletes' diets.

In undoubtedly the most physically challenging of all the studies which have looked at the effects of vegetarian diets on performance, 110 runners competed in a 1000-K (one-million-meter) race carried out over a 20-day period (5). During the race (and also before it), 60 of the competitors ingested a conventional, meat-rich, "Western" diet, while 50 harriers took in lactoovovegetarian fare. During the race itself, both groups had a similar total intake of carbohydrate (60 percent of total calories). As it turned out, there was no connection between diet and performance in the race, with half of each group actually finishing the event and total performance time absolutely equivalent between groups.

So, the available research tells us that a vegetarian diet is neither beneficial nor detrimental to endurance performance (one caveat, of course, is that there have been no good long-term studies on this topic with serious athletes). There is a legitimate concern, however, that vegetarian practices might hurt high-power performances by lowering muscle-creatine levels.

Recall that creatine is found in large quantities in muscles, where it combines with phosphate to provide a significant source of "quick energy." High levels of muscle creatine ("phosphocreatine") have been linked with improved performance during high-intensity interval workouts (for example, five 30-second "reps" of very fast running, with one- to four-minute recoveries) (6). The estimated daily requirement for creatine is thought to be about two grams; a typical meat-eater gets about one gram from the animal muscle he/she ingests and probably synthesizes the other gram in his/her liver, kidneys, and pancreas. The vegetarian athlete, on the other hand, gets essentially no creatine in his/her diet, and there is strong evidence that his/her internal organs are not up to the task of creating two grams of creatine per day, leading to a situation in which vegetarian competitors are "low" on creatine. One study found that basal plasma creatine levels in vegetarian athletes were about 50-percent lower, compared with concentrations in meat-eating sportspersons (7).

In another investigation, 16 healthy men who normally consumed an omnivorous diet were placed on a lactoovovegetarian diet for 21 days, while 16 other men remained on the omnivorous regimen (8). Although the two groups had similar muscle-creatine levels at the beginning of the study, just three weeks of lactoovovegetarianism was enough to significantly reduce creatine concentrations in the meat-free group, compared with the omnivores. However, the good news was that when the two groups subsequently engaged in creatine supplementation (.3 grams of creatine per kilogram of body weight per day) for five days, the meat-free and meat-rich athletes ended up with exactly the same level of creatine in their muscles. In other words, vegetarian power athletes concerned about low intramuscular creatine levels can probably boost creatine to meat-loving levels with just five days of creatine supplementation.

In truth, while there is little doubt that vegetarians have less creatine in their muscles and plasma than omnivores do, there is actually little strong evidence that such creatine displacements put them at a major disadvantage, even in high-power competitions. In fact, one of the few pieces of research which has looked at this question (a randomized, double-blind study) found that creatine supplementation failed to have a uniquely positive effect on muscular power output in vegetarian athletes (9). The bottom line is that there is at present no strong reason for vegetarian athletes to be worried about losses of muscular power; if they are worried, they can simply stoke in creatine for five days and attain the same lofty levels enjoyed by the meat-rich crowd.

Other worries about vegetarianism also tend to fall by the wayside when inspected closely. Take the case of iron, for example (one argument is that since the "non-heme" iron found in plant foods is more poorly absorbed than the heme iron found in meat, an endurance-athlete's risk of developing anemia rises when he/she adopts a vegetarian diet; in line with this, a serious endurance athlete may already be at higher-than-usual risk of developing an iron deficiency because of exercise-induced iron losses (via sweat, urine, and feces), which exceed the losses associated with watching television or sitting around on the couch). In one scientific study, nine female runners who consumed a "modified-vegetarian diet" (with less than three ounces of meat per week) were compared with nine other female runners who ate red meat regularly (10). Dietary iron intake was actually the same for the two groups (about 14 mg per day), but the bioavailability of the ingested iron was about 50-percent greater in the meat-eating group (at least partially because of the presence of heme iron). Serum ferritin values were lower in the modified-vegetarian group, but the bottom line was that there was absolutely no difference between the groups in terms of ability to train or maximal aerobic capacity.

Blood ferritin was also lower in the vegetarian runners in the 1000-K race mentioned earlier in this article, but the vegetarian competitors fared just as well as their carnivorous peers. Bear in mind that reduced ferritin concentrations, although a potential warning sign, are not by themselves a bad thing. Running a race or hard workout with moderately low serum ferritin values is a bit like driving your car with less than a half-tank of gas; the car still operates in great fashion, and you can run PBs with less-than-half-full ferritin stores, as long as your blood hematocrit and hemoglobin are OK.

Furthermore, many studies of long-term vegetarian athletes report that iron status (as measured in blood, urine, and hair) is just fine (11). It is important to note that although inhibitors of iron absorption are present in plant foods (for example, phytates in grains and tannic acid in tea), plant products also possess compounds which stimulate iron absorption, including vitamin C and citric acid. As long as vegetarian athletes do not go to dietary extremes, it appears that their iron status will usually be adequate; iron-deficiency anemia is rare among vegetarian sportspeople (12).

Research has shown that very strenuous training leads to an uptick in urinary zinc excretion (13). This is potentially of concern to the serious vegetarian athlete, who already has a reduced bioavailability of dietary zinc and who may be losing more zinc, compared to the couch potato, in his/her feces and sweat. The good news is that most studies have failed to demonstrate impaired zinc status in vegetarian athletes; it is possible that the bodies of athletic vegetarians may be able to adapt by enhancing the absorption of zinc across the small-intestinal wall. This may not be true in adolescent vegetarian athletes, however, who actually have higher zinc requirements, compared with adults. One reasonable dietary practice for vegetarian athletes is to consume ample amounts of foods which are rich in zinc, including fortified breakfast cereals, legumes, nuts, and seeds. If you are a vegetarian and you decide to supplement your diet with zinc tablets, it is important not to take in more than 100 percent of the recommended dietary allowance (15 mg per day for men and 12 mg daily for women) - in order to avoid potentially negative interactions with the absorption of other nutrients, including iron (the same is true for iron supplementation, which in excess can interfere with zinc absorption). Doses of zinc only a few milligrams above the recommended intake, especially when ingested regularly over time, can also interfere with copper absorption and lower the body's total copper content, which may weaken the heart; high intakes of zinc may also diminish the concentration of protective HDL in the blood.

Protein is another concern for vegetarians, since plant foods can be considerably lower in protein, compared with meat. Research indicates that endurance athletes probably need to take in approximately 1.2 to 1.4 grams of protein per kilogram of body weight per day - and that strength athletes might need as much 1.4 to 1.8 grams per kilogram daily. While such intakes might seem rather expansive, they are actually fairly easy to meet when athletes - including vegetarians and meat-eaters - simply keep their protein intakes at around 15 percent of total calories (14). As Dr. David Nieman points out in an excellent review article (15), even totally vegan athletes can enjoy optimal protein intake by emphasizing the consumption of protein-rich plant foods, including legumes (beans and peas), nuts, seeds, and whole-grain products.

Straying away for a moment from performance to the topic of health, it is worthwhile noting that vegetarian eating has been linked with a variety of health benefits, including a lower risk of mortality from heart disease, diabetes, and certain forms of cancer (16), along with a reduced chance of developing abnormal blood-fat profiles, obesity, and high blood pressure (17). Interestingly enough, regular exercise is also associated with many of these same advantages. Is there any evidence that vegetarianism and regular training, when practiced together, produce greater health benefits than either factor taken alone? As you might expect, the evidence suggests that this is indeed the case. In two different studies, a combination of recurrent physical exertion and vegetarian eating produced lower mortality rates, compared with a vegetarian diet alone or exercise by itself (18 & 19). From a health perspective, it is hard to argue against combining regular physical training with a vegetarian eating pattern.

So what is the bottom line about vegetarian eating and athletic performance? As Dr. Nieman points out, the available evidence indicates that a vegetarian diet has neither a demonstrably positive nor significantly negative effect on physical capacity. Although vegetarian diets are definitely "endurance-athletes' diets," in the sense that they are high in carbohydrate, usually adequate in protein, and low in fat, it is possible for meat-eaters to consume just as much carbohydrate as vegetarians do; when this happens, meat-lovers and vegetarians perform in similar fashion during endurance activities. There has been some concern that vegetarian female athletes are at increased risk for menstrual dysfunction, but Nieman indicates that low energy intake, not vegetarian eating per se, is the actual culprit in this area. Finally, vegetarian athletes do not seem to be at higher risk for impaired nutrient status, either in terms of protein or various minerals. As Dr. Nieman concludes, "…a varied and well-planned vegetarian diet is compatible with successful athletic endeavor."

References

(1) "Substrate Utilization during Exercise in Active People," American Journal of Clinical Nutrition, Vol. 61 (Supplement), pp. 968S-979S, 1995
(2) "Oxidants and Antioxidants in Exercise," Journal of Applied Physiology, Vol. 79, pp. 675-686, 1995
(3) Nutritional Aspects of Human Physical and Athletic Performance. Springfield, IL: Charles C. Thomas Publisher, pp. 415-416, 1985
(4) "Serum Sex Hormones and Endurance Performance after a Lacto-Ovo-Vegetarian and a Mixed Diet," Medicine and Science in Sports and Exercise, Vol. 24, pp. 1290-1297, 1992
(5) "Nutrient Intake of Endurance Runners with Lacto-Ovo-Vegetarian Diet and Regular Western Diet," Z Ernahrungswiss, Vol. 33, pp. 217-229, 1994
(6) "Creatine and Its Application as An Ergogenic Aid," International Journal of Sport Nutrition, Vol. 5, pp. 94-101, 1995
(7) "Effect of Creatine Feeding on Maximal Exercise Performance in Vegetarians," European Journal of Applied Physiology, Vol. 82(4), pp. 321-325, 2000
(8) "Effect of Creatine Supplementation and a Lacto-Ovo-Vegetarian Diet on Muscle Creatine Concentration," International Journal of Sports Nutrition and Exercise Metabolism, Vol. 12(3), pp. 336-348, 2002
(9) "The Effect of Oral Creatine Supplementation on Torque Production in a Vegetarian and a Non-Vegetarian Population: A Double-Blind Study," Veg Nutr Int Journal, Volume 1, pp. 100-105, 1997
(10) "Influence of Dietary Iron Source on Measures of Iron Status among Female Runners," Medicine and Science in Sports and Exercise, Vol. 21(1), pp. 7-10, 1989
(11) "Iron Status of Vegetarians," American Journal of Clinical Nutrition, Vol. 59 (Supplement), pp. 1233S-1237S, 1994
(12) "Iron Deficiency in Distance Runners: A Reinvestigation Using 59Fe-Labelling and Non-Invasive Liver Iron Quantification," International Journal of Sports Medicine, Vol. 17, pp. 473-479, 1996
(13) "Trace Mineral Requirements for Athletes," International Journal of Sports Nutrition, Vol. 4, pp. 104-119, 1994
(14) "Do Athletes Need More Dietary Protein and Amino Acids?" International Journal of Sports Nutrition, Vol. 5, pp. S39-S61, 1995
(15) "Physical Fitness and Vegetarian Diets: Is There a Relation?" American Journal of Clinical Nutrition, Vol. 70 (Supplement), pp. 570S-575S, 1999
(16) "Vegetarianism, Dietary Fiber, and Mortality," American Journal of Clinical Nutrition, Vol. 36, pp. 873-877, 1982
(17) "Associations between Plasma-Lipid Concentration and Dietary, Lifestyle and Physical Factors in the Oxford Vegetarian Study," J Human Nutr Diet, Vol. 8, pp. 305-314, 1995
(18) "Effect of Risk Factor Values on Lifetime Risk of and Age at First Coronary Event. The Adventist Health Study," American Journal of Epidemiology, Vol. 142, pp. 746-758, 1995
(19) "Dietary and Lifestyle Determinants of Mortality among German Vegetarians," International Journal of Epidemiology, Vol. 22, pp. 228-236, 1993

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