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Should You Be Periodizing Your Carbohydrate Intake?

Dr. Jeffrey Sankoff on whether periodizing your carbohydrate intake will improve perfromance

Should You Be Periodizing Your Carbohydrate Intake?

Dr. Jeffrey Sankoff is an emergency room physician, triathlete, coach, and host of the TriDoc podcast. He breaks down the latest in multisport science to help keep you educated, healthy, and fast!

In the never-ending search for a competitive edge, Dave Brailsford’s Sky cycling team led the way in finding small things that would give their riders incremental benefits that when summed could mean significant differences. This strategy of so-called ‘marginal gains’ was to become the stuff of legend during the 2010’s and was thought to be instrumental in the team’s successes at grand tours throughout the decade.

  • Everything from clothing to tire pressure to bed sheets to training regimens was subject to scrutiny and tweaking to find every possible watt. 

  • Of course, nutrition was also investigated, and working together with physiologists and sports scientists, Team Sky developed a program based on some novel theoretical premises. 

Brailsford posited that while our bodies work best with carbohydrates as their principal fuel source, over long days in the saddle and especially over long events like the Giro or the Tour, there would be times when our muscles would invariably need to rely on alternate fuels like fatty acids or ketones. Physiologists had long known that it was possible to train our bodies to better utilize those fuel sources under certain conditions and now Brailsford had his scientists embark on a program to leverage that. 

  • Initial results were promising and Sky’s ‘carbohydrate periodization’ looked to be a winning strategy that other teams soon adopted. But a recently published study co-authored by none other than the coach of Tour De France winner Tadej Pogacar has once again thrown it into question. 

What then is the truth?

The short answer: Carbs are king - our bodies love this fuel source and do best with it. The various fueling strategies designed to ‘fat-adapt’ our cells do not seem to improve performance.

The long answer: Our bodies are well-designed to metabolize different kinds of fuels for different needs. At low intensities, our cells can make use of fatty acids and ketones because burning those fuels does not produce large amounts of adenosine triphosphate (ATP) and at lower efforts, we don’t need as much.

  • But at higher intensity when large amounts of ATP are needed, there is no substitute for carbohydrates as a fuel source since proportionally, so much more can be generated per gram of fuel.

Is there a way to augment metabolism by fat-adaptation?

Many coaches and nutrition scientists have wondered if there might be a way to enhance ATP production by training our cells to make use of fats and ketones at higher levels of effort. This is what is referred to as fat adaptation. There are a few ways to do this:

Keto Diet

First, an athlete can restrict carbohydrate intake in what is often referred to as a keto diet. Keto diets are high in fats and protein but very low in carbohydrates. Ketone bodies are formed in abundance in this diet and are metabolized along with fatty acids as a fuel source. There is evidence that keto diets do lead to improved fat metabolism by cells but all studies to date have shown that endurance performance is impaired.

Intermittent Fasting

Intermittent fasting is another means by which fat adaptation can occur. Here athletes still take in near normal amounts of carbohydrates but they do so in a restricted window of time during the day. As a result, most training is done in a fasted state. Intermittent fasting has been shown to be an effective means of weight loss but again has been shown to be detrimental to endurance performance.

Periodization of Carbohydrate Intake

This is the final method by which fat adaptation can be done and this is the method trialed by Team Sky. In this method, athletes take in normal amounts of carbohydrates, but only at certain times of the day. Most commonly, endurance work is performed late in the day or the evening. Afterwards refueling is done with protein and fat only, no carbohydrate. Athletes then sleep in a low glycogen state. When they wake, they again fuel without carbohydrates before exercising while still in a low glycogen state.

Does fat adaptation work?

In 2016 a compelling study was released on triathletes who underwent this kind of sleep-low fueling strategy while training in comparison to a group who fueled in a more traditional way. After three weeks, the group in the ‘sleep-low’ group were found to have a significantly improved 10k run time that was three minutes faster than the control group. In addition, cycling was felt to be easier and this group had slightly more weight loss.

  • Unfortunately, no study since then has been able to reproduce these results and several have been done demonstrating no benefits to this fueling strategy.

One particularly vocal critic of the sleep-low strategy was Iñigo San-Millan. Dr. San-Millan is the coach of 2020 Tour de France winner Tadej Pogacar and the co-author of a recent paper that looked at this question.

In this study, two groups of cyclists underwent a five-week training regimen in which one group followed the sleep-low nutritional plan while the other followed a more traditional high carbohydrate-at-all-times diet. Both groups consumed similar amounts of calories and carbohydrates, only the timing differed.

  • At the end of the study, there was some biochemical evidence that the experimental group was metabolizing fats better than the control group but not during intense exercise. Furthermore, in every respect that mattered, specifically, all the metrics related to performance, there were no differences observed whatsoever.

Finally, unlike in the study on triathletes, in this study, there were no differences between the groups concerning weight or body fat changes over the five weeks.

This is just the latest study to throw the fat-adaptation strategy into question and in my mind, I see no compelling reason for anyone to choose it over a traditional high-carbohydrate nutrition plan. Give the body what the body wants!

Train hard, train healthy.

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