If you’re interested in the effects of diet and nutrition on endurance performance, you’ll be interested in a study that was just published in the Journal of Sports Medicine and Physical Fitness. Italian researchers recruited 40 student-athletes from the University of Bergamo and separated them into four groups. Two of the groups were made up of kickboxers, so we’ll ignore them. The other two were made up of runners, half of whom received nutritional counseling for three months while continuing to train normally, the other half of whom served as controls.

The runners receiving nutritional counseling were specifically instructed to bring their diet more in line with Mediterranean diet standards (which emphasize vegetables, fruits, herbs, nuts, beans, poultry, seafood, and dairy, roughly in this order). Before and after the three-month intervention, all of the athletes were subjected to various fitness tests. While both groups improved, the runners receiving nutritional counseling showed significantly greater improvements in VO₂max and body composition.

Why trust Professionals for Sports Nutrition Guidance?

Scientists are careful not to overgeneralize the conclusions they draw from individual studies, but I’m not a scientist, so I’m going to go ahead and do it. The lesson here, for me, is that if you improve your diet, you will probably run better, and that if you wish to improve your diet, your best move is put yourself in the hands of a credentialed sports nutrition expert with mainstream scientific training. Too many athletes who are motivated to improve their diet instead adopt fads such as ketogenic diets and intermittent fasting, and although some who go down this road end up satisfied with their results, it’s way riskier than the road I recommend.

Another advantage of the real experts is that they are full-service diet coaches, whereas their fraudulent competitors typically have just one limited shtick. In addition to supplying less risky (if also less sexy) dietary counsel, a legitimate sports nutritionist can help you customize the general principles of sound nutrition to your particular needs, preferences, and lifestyle, and help you solve special problems such as dialing in your race fueling.

I am reminded here of a 2014 study, conducted by researchers at Denmark’s Aalborg University, that is sort of the race-fueling equivalent of the general diet study I just described. In this one, 28 runners training for the Copenhagen Marathon were separated into two groups of equal ability based on their performance in a 10 km time trial. On race day, one group used their own “freely chosen nutritional strategy” while the other group applied a “scientifically based nutritional strategy,” consuming carbs on a schedule of 60 grams per hour, which prior research indicated was optimal for endurance performance. On average, the runners who executed their own freely chosen fueling plan took in 38 percent less carbohydrate during the race. They also finished an average of 10:55 or 4.7 percent slower than the runners of equal ability who fueled scientifically.

Scientifically based guidance on diet and fueling is best, and if you want it, your best move is to hire a credentialed sports nutrition expert—which is precisely what professional endurance athletes—who can’t afford to play games with their eating and fueling—do. A good example is the great Ethiopian runner Haile Gebrselassie, who, after a brilliant career on the track, moved up to the marathon, where he struggled at first (by his standards), winning only one of his first three attempts at 26.2 miles and falling short of his time goals. Realizing that his inability to tolerate large amounts of fluid and carb intake during longer events was holding him back, Gebrselassie sought help from world-renowned endurance sports nutrition researcher Asker Jeukendrup of the University of Birmingham (who wrote the foreword to my book The Endurance Diet, which I like to think makes up for my own lack of professional training in sports nutrition–oh, the irony!). In his next race, the 2007 Berlin Marathon, Geb consumed two liters of sports drink and water and six carbohydrate gels and broke the world record.

Given all of this, why would any athlete who cares about their performance seek nutritional guidance from any other kind of source? I think it happens for three reasons. First, most athletes—actually, all of them, I think—have been eating their whole lives, so they don’t see diet management as requiring any sort of special expertise. Heck it’s just food, right?

A second reason few athletes think to seek nutritional guidance from a credentialed sports nutrition expert is that their fraudulent competition has better marketing. Keto-friendly anti-vaxxer Ben Greenfield has books, a podcast, and a Twitter account with more than 73,000 followers. The typical sports dietitian just sits around waiting for the phone to ring. 

Reason number three (and there are probably others) is that there’s a sucker born every minute. The sad truth is that, if you give the typical athlete with a mediocre diet and love handles an option between eating fewer processed foods and adopting a sexy name-brand diet that’s promoted in spam emails and on “The Dr. Oz Show” and on the covers of glossy magazines in supermarket checkout aisles, odds are they will choose the latter. And get what they deserve!