Keto diets and exercise


A small study, but interesting nonetheless:


It’s funny that they are actually looking at that. Keto isn’t gonna get you on the podium in any intense athletic event. Athletes already know this.

Sure you could win gold in archery or something on a keto diet. But not in any intense activity or event that relies on endurance.

For aerobic activity, fat metabolism produces ATP about 2.5 times slower than muscle glycogen. And for anaerobic activity, fat metabolism is about 5.8 times slower in ATP production than muscle glycogen!

Yes, you can go much further with fat metabolism. But not nearly as fast.

Fuel systems speed - fastest to slowest:

  • Substrate level phosphorylation - PCr + ADP + H -> ATP + Cr
  • Stored carbs - Anaerobic glycolysis - Glucose -> Pyruvate -> Lactate
  • Stored carbs - Aerobic carb metabolism - Glucose -> Pyruvate -> CO2 + H2O
  • Stored fat - Aerobic lipid metabolism - Fatty acid -> Acetate -> CO2 + H2O


The thing is, there are all sorts of fads circling around in the athletic community. I have heard of some ultra-marathoners who swear by this, and there’s a researcher (Louise something?) in Australia who did a very comprehensive study of this with elite runners because it was genuinely something people were discussing and trying. I have also heard some exercise experts advocate something along the lines of keto for weightlifting.


A lot of them are snake-oil salesmen. Just trying to sell their books. Phinney and Volek are two of the worst. They have done so many ridiculous experiments that are totally biased, just trying to prove their point.

It’s easy to see the truth, just by looking at what the elites are doing. Like in Nike’s “Breaking 2” project. They did everything they could to break 2 hours in the marathon. All the top people involved in that project. Measuring muscle glycogen in the athlete’s legs before and after runs, coming up with new shoe designs to maximize energy return, having moving water hand-offs so the runners wouldn’t have to slow own to pick up the water bottles, doing wind tunnel testing. Every little thing they could. The idea of low-carb was clearly not in their plans.

Ask @daisymae what thing I have been emphasizing for her over and over, before swimming, after swimming, for dinner. I always tell her the same thing. Carbs!

Yes, some runners will train with glycogen depletion on some days. I do that too. Just like people who will sometimes train at elevation, or train when tired. Because they know they will be depleted at some point in the race. But they don’t start the race in a depleted state!

Like If I run 10 miles, and then the next day I run 20 - yes, that is good training. But I sure wouldn’t want to run 10 miles the day before a marathon. There is a difference in what you do for training versus competition.