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LCHF athletes may need more protein, study shows

The effect of restricting carbs in an effort to become more fat-adapted may have a hidden side effect

Though many endurance athletes swear by a low-carbohydrate, high fat (LCHF) diet, recent research out of the University of Toronto shows a little-known side effect of low-carb training. The study, by Faculty of Kinesiology and Physical Education researchers Jenna Gillen and Daniel Moore, shows that endurance athletes who purposely restrict their carbohydrate consumption in order to train their bodies to become better fat-adapted may need more protein than athletes who consume more carbohydrate.

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The study was published in the November 2019 issue of Medicine & Science in Sports & Exercise. It observed eight male endurance athletes and how their bodies responded to training over two, two-day periods under conditions of low carbohydrate availability, and higher carbohydrate availability.

The study

On the first day of the low-carb trial, all the athletes consumed plenty of carbs (eight grams per kilogram of bodyweight), and in the evening they did a HIIT (high-intensity interval training) session. In the low-carb study, the group ate most of their carbohydrate before the evening HIIT session and almost none after the session and overnight (so as to minimize glycogen, or stored carbohydrate). The next morning, all participants did a hard 10K training run at 80 per cent of their max heartrate. Over the ensuing eight-hour recovery period, their protein metabolism was measured to determine their protein needs.


In the high-carb study, the group consumed less than half of their carbohydrate before the HIIT session, and the rest later the same evening, to maximize glycogen stores. The next day they did the hard 10K training run, and their carbohydrate and protein metabolism were measured during the recovery period.

What they found

In the low-carb trial (in which athletes ran fasted), the athletes burned 35 per cent less carbohydrate and 11 per cent more phenylalanine (the essential amino acid used to determine protein needs) during the recovery period than in the high-carb trial. This translates to an extra 1.2 grams per kilogram of bodyweight per day in extra protein required. And while the recommended protein consumption post-exercise is 0.25 grams per kilogram of bodyweight, the authors suggest increasing this to four grams per kilo, and eating it soon after exercising to maximize recovery.

One obvious question raised by the study concerns the definition of endurance training. A HIIT session followed by an early-morning hard tempo run may not align with most endurance athletes’ concept of what’s involved in endurance training, and it would be interesting to study the effect on protein metabolism of longer aerobic sessions done in high-carb and low-carb conditions.