You can only lose weight on low carb diets, say low carb diet fans. And go on to tell us that athletic performance from running marathons to lifting weights is just as good when you say no to carbohydrates.
But already in 1939 two Danish scientists put people on a low, moderate or high carbohydrate diet and after a week assessed their endurance to exhaustion on a stationary bike. The people on the low carb diet lasted 81 minutes. Those on a high carb diet were able to ride for 206 minutes (Christensen EH, Hansen O, Zur Methodik der respiratorischen Quotient-Bestimmungen in Ruhe und bei Arbeit. Skand Arch Physiol 1939, 81:137-71).
And in the last 71 years the pile of scientific evidence for this effect has accumulated; the latest study I am aware of that looked into it is from 2006, where scientists from New Zealand put cyclists on either a high carb or high protein diet with no difference in calories consumed. They as well came to the conclusion that a high protein diet has a detrimental effect on exercise performance.
Yet we get tons of what pretty much amounts to "now explain that away!" defenses for fitness on low carb, where someone knows someone who or even himself went low carb and experienced astonishing athletic success.
What we don't know is if that account is truthful or how the person would have performed with an adequate amount of carbohydrates. Which is why scientific research is always conducted in an environment where all factors that can come into play are accounted for.
Even when low carb fans do look at the mountain of scientific research that clearly indicates a low carb nutrition is hindering exercise performance, a remarkable capability of selective cognitivity comes into play, that effectively blinds out everything that simply cannot and shouldn't allowed to be.
An Australian study had cyclists on a low carb diet with a high carb day right before a race. They found no significant impact on fat adaption, meaning that stamina didn't improve by the body previously having used more fat for fuel and then doing a carb-loading.
But one blog author titles his piece "Low-carb diet gives endurance athletes more stamina" and tells us:
The authors [of the study] therefore conclude that a low-carb diet is not of interest to endurance athletes. "A high-fat, low-carb diet, followed by 1 day of carb restoration, increased fat oxidation during prolonged exercise, yet, this study failed to detect a statistically significant benefit to performance", they write. We on the other hand, not hindered by a knowledge overload, draw the opposite conclusion.
A 2004 paper (PDF) tries to make a point for moderate low carb diets, but it too has to conclude that "performance is limited by the low muscle glycogen levels induced by a ketogenic diet, and this would strongly discourage its use under most conditions of competitive athletics". On a popular low carb forum however, we find mention of this paper in a completely different light:
I have no doubt, that you can run marathons on a low carb diet. I've been on a low carb diet for 1 1/2 year and I don't think, that my endurance has decreased.
There's also a very good scientific paper about ketogenic diets and physical performance:
The problem is, most people won't believe in the superiority of low carb diets, as long as all professional athlets follow a high carb diet.
It's really strange, that nobody can tell just a single name of a professional athlet following a low carb diet. As far as I know, Lance Armstrong was not on a low carb diet, he was probably just better doped than the others 🙂
The discussion then continues and puts the blame on "carb-indoctrinated" trainers that just can't acknowledge that a low carb diet is at least as good for professional athletes.
Draw your own conclusions, maybe experiment a bit and see what allows you to perform better. But the dogmatic disregard and abuse of scientific research displayed by the people above is akin to denying that gravity exists, because one day an apple might come along that just might fall upwards.
Picture courtesy of Richard Masoner.