Fitness Inventor

Q: How low can you cut your carbs before you lose power and reduce performance?

A: A new study seems to have established how low we can drop our carbs and still maintain our short-term power and strength output. This study looked at people who trained regularly and who normally ate about 250 grams of carbs per day (Note: Half the subjects were women, who have lower calorie and carb needs). The researchers tested them for handgrip strength, vertical jump, max bench press, max squat, maximum repetitions of bench press, and 30-second all-out Wingate cycling after either seven days on their normal diet or seven days on a very low-carb (less than 6 percent) diet. Now before I give you the results, this level of carbs was less than 30 grams per day (their calories were just under 2,200), so this would have probably put all the subjects into ketosis, a state in which the body can’t make enough glucose to fuel the brain, so it has to use the alternate fuel, ketones. So we are talking about a proper “low-carb” diet!

Anyhow, for these short-term power, strength, and aerobic tests,
these subjects didn’t experience any decrease in performance. So if you’re worried about getting weaker from a low-carb diet, this study shows that you should have no fear. However, these tests were all quick, all-out efforts. I have no doubt that if they’d done several sets of 8 to 20 reps or one or two more Wingate cycling tests, performance would have begun to decline. So this result does not apply to people who will be exercising intensely for even short workouts and certainly not for proper bodybuilding or HIIT sessions. Finally, I’m sure most of you will be wondering what happened to their body weight and muscle over the seven days on very low carbs.

The authors of the study reported that the body mass loss from the low-carb diet was probably mostly due to water, although the women also lost a significant amount of fat. Unfortunately, this study measured body composition using a bioelectrical impedance scale, and as I’ve stated on more than one occasion, these are notoriously inaccurate, so I would take the fat-loss/water-loss results with a huge pinch of salt. Now before the skeptics speak up, keep in mind that this isn’t a “one off” study result because another study several months ago also showed that power athletes can maintain their performance on a
very low-carb diet.

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Photo of Christopher Wong courtesy of Simon Lau