By Maria Muccioli and Ross Wollen
Do you need carbohydrates to optimize athletic performance? Or can athletes with diabetes do even better when they fuel their bodies with protein and fat?
By now it’s clear that the low-carb approach to diabetes has largely gained clinical acceptance, for people with both type 2 and type 1 diabetes (T1D). But some questions remain about when carbohydrate restriction is and isn’t appropriate.
One of those big questions: athletics. It’s long been conventional wisdom that athletes – whether elite professionals or weekend warriors – absolutely need carbs to fuel performance. But when you’ve got diabetes, “carb loading” the night before a big race is a tricky proposition.
At this year’s ADA Scientific Sessions, two experts went head-to-head in a debate on “Carbohydrate Intake and Its Impact on Athletics and Health.”
Read on to hear what happened – and who, in our opinion, won the debate.
The Case for a High-Carb Diet
In his presentation titled “High/Normal Carbohydrate Intake Optimizes Performance and Glycemia,” James P. Morton, PhD argued in favor of a normal-to-high carbohydrate approach for athletic performance and blood glucose management. Morton is a professor of exercise metabolism at Liverpool John Moores University.
Morton focused his talk on the importance of fueling high-energy expenditure for elite athletes, such as those on multi-week bicycle races. He presented some data showing that people who consumed a high-carb load were able to exercise for longer periods of time than those who consumed a placebo solution. Morton pointed out that for professionals, even tiny differences can make the difference between victory and defeat.
As an example, Morton presented a case study of Tour de France winner Chris Froome. In 2018, Froome made a very dramatic comeback on the 19th day of a multi-week cycling race. He ate an incredible amount of carbohydrates that day and the day previous, which Morton believes contributed significantly to his victory.
How do carbs fuel performance? The primary explanation centers around the availability of glycogen (branched glucose molecules) in the liver and muscle. The higher the glycogen levels, the more glucose is readily available to power activity. Morton also presented evidence that those who eat high-carb delay the point at which they begin burning fat for energy, and claimed that delaying this crossover point was important for top performance in endurance athletes.
In addition, Morton cited personal testimonies from some elite endurance athletes, such as audio of interviews from his podcast, claiming that support of high-carb for athletic performance is “unanimous.”
Unfortunately, little of this presentation had much to do with the unique challenges of athletes with diabetes. And for that matter, its focus on truly elite professionals may be of limited relevance to even the most avid part-time athletes. Morton has never worked directly with athletes with type 1 diabetes, but referred to the opinions of his “friend and colleague” Sam Scott, PhD, a researcher at Novo Nordisk. Scott has plenty of firsthand experience with high-performing diabetic athletes: he works with Novo Nordisk’s inspiring all-diabetes pro cycling team.
Morton invited the audience to read Scott’s recent publication concerning type 1 diabetes, carbohydrate intake, and athletic performance. In that paper, Scott concludes that low-carb diets “represent an effective strategy to improve glycaemic control and metabolic health in people with T1D,” but that their effect on athletic performance is basically unknown:
Despite low carbohydrate training being one of the most widely debated topics amongst athletes, coaches and sport scientists, there is very little published research specific to athletes with T1D.
Some evidence suggests that people with type 1 diabetes might especially benefit from “train low” strategies – basically, limiting carbohydrate intake during regular training, and increasing carb consumption for competitions. Beyond that, however, there simply isn’t enough evidence to make concrete claims.
Leaning on his experience with non-diabetic athletes, Morton concluded:
Regardless of whether you have normal glycemic responses or you have type 1 diabetes, the principle of ensuring high carbohydrate availability should always be upheld, because carbohydrate will certainly make you go faster.
The Case for a Low-Carb Diet
In his presentation titled “Low Carbohydrate Intake Optimizes Performance and Glycemia”, Dominic D’Agostino, PhD argued that because low-carbohydrate diets are optimal for blood glucose control, they are therefore also optimal for athletic performance.
D’Agostino, a molecular pharmacologist, is something of a minor rock star in the keto community. He’s a frequent guest on podcasts and Youtube shows, and has a fair personal understanding of keto athletic achievement: he’s an impressive powerlifter to boot.
D’Agostino started by acknowledging that we do not really know the best level of carb intake for athletes. But in his telling, practices even among the elite are far from unanimous, with athletes experimenting with a variety of strategies, ranging broadly from carb restriction to carb loading.
Many athletes choose a low-carb diet because they like the way that it feels – some claim, for example, that keto results in more consistent energy throughout competition, making them much less likely to “bonk” or hit the wall. But for people with diabetes, the primary point in favor of a low-carb diet is the degree to which it optimizes glucose control.
A very low-carb or ketogenic diet doesn’t just steady blood sugar – it also appears to result in some measure of “hypoglycemic resilience”. This isn’t a small matter for diabetic athletes. Hypoglycemia during exercise or competition won’t just ruin athletic performance: it can be very dangerous.
Not only does ketosis protect against hypoglycemia, he explained, but recent research also shows additional benefits of ketosis, such as reduction of oxidative stress. D’Agostino also noted that increased fat utilization can lead to “glycogen sparing”, and that a low-carb diet does not cause glycogen depletion in the muscle. These features may confer additional athletic advantages.
While Morton’s presentation was largely founded on the assumption that athletes with diabetes are fundamentally like athletes without diabetes, D’Agostino emphasized a different principle:
Normal glycemia is optimal for health, performance and recovery.
Of course, normal blood glucose levels are very difficult to achieve for people with type 1 diabetes, especially during exercise. But the low-carb diet has been validated as perhaps the best method of doing so.
D’Agostino explained that his own thoughts on the subject were formed partially by the experience of his former Ph.D. student, Andrew Koutnik, who lives with type 1 diabetes. Initially, D’Agostino believed that type 1 diabetes was “the one condition that I thought you would want to stay away from low-carbohydrate nutrition,” but Koutnik’s success first convinced him otherwise.
I reached out to Koutnik, now a research scientist at Florida Institute for Human and Machine Cognition.
He stressed that most studies comparing high- and low-carb athletic results show mixed or neutral results; when there is a difference, the difference “is often of little meaningful impact to most individuals engaging in physical activity.”
Dr. Koutnik argues that any nutritional program that doesn’t consider glycemic control is missing the most important factor: “Very few will debate that poor health leads to poor performance. Additionally, few will debate that normoglycemia is likely to lead to better performance than hyper- or hypoglycemia.” Therefore, for the T1D athlete, performance is a “consequence” of health.
Who Won the Debate?
Here are our thoughts:
At a diabetes conference, the focus should remain on diabetes. Although Morton presented some evidence to support the performance benefits of high-carbohydrate intake in elite athletes without diabetes, it’s a mistake to assume that the same benefits would occur in athletes with diabetes, or that they wouldn’t be counterbalanced by the known downsides of high-carb consumption. Glycemic management is a huge issue during exercise, and both low and high blood sugars can have dramatic effects on performance.
Most of Morton’s talk also focused on elite endurance athletes. But what we learn from the best athletes on the planet may not be very useful for the rest of us.
In our opinion, D’Agostino showed a better understanding of the balancing act that athletes with diabetes (especially type 1 diabetes) need to perform.
Even if we accept that carb loading can provide a perceptible boost to serious athletes, we have to acknowledge that those carbs (and any accompanying insulin) also make it more likely for the athlete to experience hypo- or hyperglycemia, which can instantly ruin any sports outing. And the more predictable and stable your blood sugar, the more confident you can be, and the less mental space you’ll have to waste on monitoring and micromanaging glycemic changes. And if a ketogenic diet really does provide some protection against hypoglycemia, that’s just even more reason to choose a very low carb diet.
If you’re actually an elite athlete, maybe carbohydrates can help push you to the peak of performance. But maybe not – the scientific evidence is not overwhelming. For the rest of us, blood sugar control remains of paramount importance. It seems to me that a low-carbohydrate diet is more likely to deliver confident performances and strong athletic results.
What are your thoughts on this debate?