Exercise intensity effects on fat and glucose
Hello doctor. I think the group is closed for questions, but my niece brought a couple of exercise related questions/observations to me. I would be grateful if you can confirm/deny the veracity of these two statements: Low intensity workouts use more fat than high intensity workouts High intensity workouts also cause a high glucose spike
Thanks for the Q—both statements have a kernel of truth but need context. - “Low intensity uses more fat than high intensity”: At easier, steady efforts (zone 2), a higher fraction of energy comes from fat. As intensity rises, the body shifts toward carbohydrates. However, total calories burned per minute are higher at high intensity, so absolute fat burned over a shorter, harder session can still be substantial. The key is weekly consistency: mix zone 2 for metabolic health and some higher-intensity work for fitness and glucose control. - “High intensity causes a high glucose spike”: During hard efforts, stress hormones (adrenaline) raise glucose to fuel muscles, so a temporary rise on CGM is common. Post-exercise, insulin sensitivity improves and average glucose typically trends lower, which is beneficial overall (especially relevant to what you’re describing).