Whether you eat carbs, protein, or nothing before a hard cycling workout with short bursts of maximum effort, your power output stays the same — your body can still push hard regardless of what you...

If a male cyclist eats a super high-fat diet for 6 days and then loads up on carbs for 1 day, it won’t slow them down in a 100-km race compared to eating lots of carbs all along.

If elite male cyclists eat a super high-fat diet for 6 days before carb-loading for a day, they’ll feel just as fast over a long 100-km ride — but they’ll have less power for short, intense sprints compared to when they eat a high-carb diet first.

For young guys with obesity, doing short bursts of intense running burns 300 calories faster than jogging steadily — about 8 minutes less effort for the same result.

If elite male cyclists eat a super high-fat diet for six days and then carb-load for one day, they’ll perform worse in sprints—even though they don’t feel more tired, their heart rate doesn’t change, and their muscles fire the same way.

If you're not an athlete and start doing short bursts of intense exercise like sprinting or HIIT, your body gets better at burning fat while you work out—after about a month, you’ll start seeing this effect, and it keeps improving a little bit each week after that.