Do Athletes Need Carbs?

How accurate is the narrative that athletes need to fuel their training with carbohydrates?

I was having a discussion with a friend who wanted to “reduce his recovery time between sets (lifting).” His idea was that he would increase his muscle mass to increase the total available glycogen. Of course, I debated that glycogen can still be made without carbohydrate and there should be plenty floating around as long as you’re getting enough protein (via gluconeogenesis).

“… but that takes time and it’s fairly nondiscriminatory. It’ll break down myofibril protein as happily as fats or free protein. I’m thinking both can be circumvented with more available glycogen”; he said.

This was going nowhere fast, so I took to the research, which there was plenty of!

Dr. Tro fortunately did review in 2019 titled, “Do Athletes Need Carbs”. He refers to a 2012 study on gymnasts that a low carb diet caused no change in performance and improved body composition. Another study, 2018, with olympic lifters stated that the lifters on a low carb diet “did not lose training volume or load”, they did lose body mass (see below with triathletes), but 1RM didn’t change significantly (meaning strength-to-weight ratios actually improved!).

In 2017 endurance athletes saw improvements in peak power and body composition. In 2018 triathletes decreased fat mass without any changes to lean body mass and improved 45% PPO. I did point out to my friend that CrossFit athletes, for one, are really pushing recovery to the limit and certainly many are on low carb diets. A 2018 study saw them decrease fat mass without any compromise of weightlifting, running, or aerobic performance metrics. Furthermore, HIIT athletes were studied in 2018 (twice). One study saw them “increase ability to utilize fat over time, without any adverse effects on total time to exhaustion or on the graded exercise tests. The other study found that a “ketogenic diet did not affect performance of short duration, high intensity exercise.”

In addition to Dr. Tro’s article, there is more still information that “low muscle glycogen availability” does not compromise anabolic signaling ( r). This gives another view to the perspective that adding carbohydrates (or carbohydrates + protein) post-workout can aid recovery ( r, r, r, r).

That’s all well and good, but the point remains. Do we need glycogen to perform optimally in the first place? Everything Dr. Tro pointed out suggests that there’s no detriment to VLC (very low carb), but is there a performance benefit?

One study suggested that in some cases time to exhaustion increased, but that it decreased for others. The authors’ speculation was that this has to do with the training experience of the athlete. That is, more experienced athletes were less dependent on glycogen — they didn’t need the sugar to perform well. “To summarize, although some studies reported that repetitive low-glycogen training leads to improved performance compared with high glycogen ( r, r), extrapolating these findings to sports-specific performance should be done with prudence.”

So, now we’ve gotten a little more specific. I can tell you that while on a low carb (< 40g / day) diet for about 6 months, I experimented with 20–50g carbohydrates (dextrose) before jiu jitsu training. I couldn’t tell the difference. I didn’t have any negative effects, but there was no clear benefit either. Anyone who has spent any time in any combat sport will tell you that they require efficiency in all energy systems (aerobic, lactic-anaerobic, and alactic-anaerobic).

Though, this “target ketogenic” method is in contrast to research that found that found that centering carbohydrate intake around training and keeping it low the rest of the day improved performance (ala median power) ( r).

Confirming my friend’s suspicion, there was also at least one study that concluded that “fat may be unable to produce energy fast enough to meet the muscle demands of elite athletes” ( r). But, the same article concluded that “nevertheless, studies have found that low-carb diets can help prevent tiredness during prolonged exercise. They may also help you lose fat and improve health, without compromising low-to-moderate intensity exercise performance.”

Coming full circle then, what does the literature say about fat metabolism and ATP production? A meta-review from 2019, included more of the same — several studies that noted “no decrement” to a ketogenic diet. However, one study therein noted one group that saw a 3.3% increased in 1RM bench press, and another saw a 4.5% increase; both statistically significant ( r). That same review cited additional studies noting improvements in a 2000m run as well as 3 minute sprint and < 30 second sprint. “Available knowledge demonstrates no clear performance benefit to athletes following a KD, with some benefit shown mainly in short duration, vigorous-intensity tests, when weight loss was likely a confounding variable. While many of the trials provided no performance benefit, it is important to note that a KD often did not cause a performance decrement, particularly in recreationally trained athletes. Decreases in metabolic efficiency were common among trained athletes competing at >70% VO2max following acute adaptation.”

I think that sums it up pretty well. So, can you recover faster on a low carb diet? You almost certainly won’t see detriment from trying it and will likely see a host of other benefits including weight loss — thus improving strength-to-weight ratio. If your sole focus is sheer strength regardless of weight, then you’re still talking about an effort of < 30 seconds (e.g. a 1RM) where a low carb diet is shown to have benefits.

If you’re talking about recovery between sets, remember that when you start measuring rest you’re now in the territory of strength- endurance, not strength. Here there is even more evidence to the benefit of a low carb diet. This would be the 50% — 75% VO2max range. Again, if you’re focusing on reducing the refractory period between sets, you’re simply not going to be able to give 100% on each rep! True 100% efforts take significantly longer to recover from than the actual effort itself (e.g. on a 1RM you might be under load for 10 seconds and need to rest for several minutes before your next burn).