How much carbohydrate intake can exercise offset on a ketogenic diet?

Question

The ketogenic diet advises keeping carb intake under 50 grams per day, and ideally under 20 grams.

Assuming that a person performs intense cardio exercise (e.g. crossfit), burning, say, 400 calories per session (day), does that offset an increase in carb intake?

In order words, if I'm sedentary and stay under 20 grams of carbs per day, I remain in ketosis. Carbs provide 4 calories per gram, so if I burn 400 calories via exercise, how many extra grams of carbs can I eat and still remain in ketosis? (100?)

Answer 1

Would you consider an experimental approach to answering your own question?

Get some ketone test strips, and confirm you're in ketosis at your target carb intake. With that baseline established, vary your carb intake and exercise burn while keeping accurate records. Confirm whether or not you're in ketosis daily with the ketone test strips.

My hypothesis would be that you can eat somewhat less than your total exercise burn in carbs before you begin to burn the carbs directly (kicked out) for at least part of the day. I further hypothesize that the timing of when you eat versus exercise, composition of the carbs, and individual metabolism will make it highly variable.

Answer 2

I have read research by Dr. Peter Attia that suggests that intake of carbohydrates immediately after exercise (within 1 hour) will mostly be used to restore glycogen stores and will not trigger the usual insulin response. Since everyone's metabolism is slightly different, you would have to test yourself using a ketone monitor and test strips to verify this.

The bigger question is why would you do this? My own response to exercise while in ketosis shows no adverse affects, no matter how strenuous my workouts. I often go several hours after exercise without eating. Clearly, being in ketosis doesn't adversely affect recovery from exercise.