Should All Runners Now Eat McDonald’s All The Time?

McRunner’s marathon PR is not quite proof that “anything goes” in endurance nutrition.

Written by: Matt Fitzgerald

Joe D’Amico of Palatine, Illinois ran a new personal-best time of 2:36:14 at the Los Angeles Marathon on Sunday. D’Amico made a name for himself before the race by eating only McDonald’s food during the last 30 days of his training. McDonald’s is not considered to be the ideal diet for runners, or for anyone else, for that matter. Yet D’Amico was able to use it to fuel the best running performance of his life. What does this tell us?

It tells us that at least some athletes can get away with–at least for a while–eating a lot more crap than the sports nutrition establishment would have them believe they can.  There is actually no research demonstrating unequivocally that the performance or health of athletes who eat “too much” fat or sugar or other bad things is compromised compared to athletes who eat by the book.  But there is, in fact, some evidence to the contrary.  For example, studies have shown that physically active persons who maintain a normal bodyweight can get up to 50 percent of their daily calories from fat (the American College of Sports Medicine recommendation for athletes is no more than 35 percent) without exhibiting any of the adverse consequences (e.g. high cholesterol) that are associated with such a fatty diet in overweight, sedentary persons.

Athletic performance and health depend on our consuming enough but not too much of the various essential nutrients.  In American society, overconsumption is a far greater problem than under-consumption.  With a few key exceptions, vitamin and mineral deficiencies are relatively uncommon. But excess energy intake, in the form of carbohydrates, fats, and proteins, is very common.  We know this because excess energy turns into stored body fat, and two-thirds of American adults are overweight.

So, as long as an athlete maintains a normal body weight through training, what does he really have to worry about?  As trashy as it is, the average American diet seems to provide adequate amounts of most of the essential vitamins and minerals.  While it also provides too many calories, “too many” is defined by the effect of the daily calorie total on body composition; hence, by definition, the lean athlete is not consuming too many calories.

Nutrition experts who concede this point might still argue that athletes need to be careful not to get too many of their calories from sugar or saturated fat.  But they would have a hard time backing up this argument with scientific evidence.  For example, the biggest problems with sugar are that it is readily converted to storage fat and that it causes insulin spikes that can lead to insulin resistance over time.  However, competitive athletes are continually depleting their muscles of glycogen, so that dietary sugar is preferentially used to replenish these critical energy stores and is not converted to body fat.  And even when it is converted to body fat, this fat is used in the next workout, so it doesn’t accumulate.  In addition, exercise greatly increases insulin sensitivity, so insulin resistance is unlikely to become a problem for the sugar-loving athlete who maintains a lean body composition.

Among competitive endurance athletes, inadequate caloric intake is a more common problem than overeating. In many cases, the body responds to inadequate caloric intake during periods of heavy training not by shedding more and more weight but by reducing its metabolic rate and imposing fatigue during training to conserve weight.  These maladapatations to under-eating wreak havoc on performance.

A 1997 study by researchers at Xavier and Dayton universities provided evidence that the phenomenon is quite common in long-distance triathletes.  The subject pool was a group of triathletes preparing for the Hawaii Ironman.  At the beginning of the study, all of the athletes participated in a test sprint triathlon and their daily caloric intake and expenditure levels were estimated.  After completing the test race, the subjects met with the researchers to discuss ways of improving their diet for better performance.  On average, their daily caloric intake was increased by a massive 72 percent, with most of the extra calories coming from carbohydrate.  After four weeks, during which the subjects’ training was standardized, the sprint triathlon test was repeated.  On average, their performance improved by 8 percent.  While it’s possible that changes in fitness accounted for a portion of the improvement, it’s probable that improved fueling accounted for the bulk of it.

Exercise As Vitamin

Not only can many competitive endurance athletes consume more macronutrients (carbs, protein, fat) than are generally recommended without negative consequences, but they may also be able to consume less of at least some micronutrients (vitamins, minerals, antioxidants) than is widely believed.

There is a growing body of evidence that exercise stimulates certain physiological adaptations that mirror the benefits of consuming particular nutrients such as antioxidant vitamins. For this reason, athletes may need less of some nutrients than non-athletes, which would explain why athletes such as Joe D’Amico are able to thrive despite eating few fresh fruits and vegetables.

A 2009 study published in the journal Nutrition even showed that exercise can strengthen the body’s antioxidant defenses in a nutrient-poor diet, at least in laboratory animals. In this study, rats were fed either a normal diet or a diet deficient in vitamins and minerals for four months. After two months, half of the animals in either group were subjected to regular swimming exercise. The researchers measured levels of lipid peroxidation—a type of free radical damage—in all of the animals at various points. Predictably, they found that vitamin and mineral deficiency increased lipid peroxidation. Remarkably, however, exercise completely reversed this effect. Exercise also reduced lipid peroxidation in rats kept on a normal diet. The researchers concluded that “inadequate nutrition may enhance oxidative stress, and that intense chronic physical training may activate antioxidant defenses.”

The Catch

There may be one giant catch to the notion that hard-training endurance athletes can “get away with” eating a junky diet. The catch is that they may be able to get away with it only in the short term. Consider the case of American distance runner Anthony Famiglietti. Raised on a poor diet that included no fruits or vegetables aside from pizza sauce, Famiglietti continued to eat a trashy diet through college and well into adulthood. He survived entirely on fast food burgers and fries, pizza, and sweets. He claimed that he did not even know what broccoli tasted like. And he was proud of it. He boastfully included a segment entitled “World’s Worst Diet” in his self-produced DVD, Run Like Hell.

There seemed to be no reason to change. Famiglietti achieved stellar results despite his diet. He won three national championships, a World University Games gold medal and a Pan-Am Games bronze medal in the 3000m steeplechase. In 2006, at age 27, he had a career year, winning the USA 5km road title and setting personal best times in the 1500 (3:35.83), mile (3:55.71), and 10,000m (27:37.74).

But the very next year his body fell apart. After struggling to a fourth-place finish in the 2007 USA national championships steeplechase final, he simply shut down. For the next two weeks he could not even run a full mile without a walking break. It was then that he decided to finally find out what broccoli tastes like.

Famiglietti completely transformed his diet, along with other elements of his lifestyle. In 2008 he was back and better than ever.  He won the Olympic Trials steeplechase and set a new PR of 8:17.34 in the Olympic Games.

While he got away with eating the world’s worst diet for a while, Famiglietti could not get away with it for ever. But there are also athletes who cannot get away with eating an even moderately bad diet for any length of time. It seems that there is a good deal of genetically-based individual variation in the amount of garbage that athletes can tolerate in their diets. Thus, while you may have read this article as a license to eat whatever the hell you want, you might not be able to eat whatever the hell you want because of differences between your DNA and Joe D’Amico’s. Nor do I suggest you find out the hard way. We’re probably all better off eating the cleanest diet that satisfies our tastes and appetites.

[sgi:MattFitzgerald]

Check out Matt’s latest book, Racing Weight Quick Start Guide: A 4-Week Weight-Loss Plan for Endurance Athletes.