If you eat before working out, your blood sugar and insulin levels spike more during exercise than if you work out on an empty stomach.

Working out before eating breakfast burns about 3 grams more fat than working out after eating, because your body has to use stored fat for energy when you haven’t eaten.

People with obesity tend to have higher insulin levels when fasting and their blood sugar spikes more after eating carbs, but their bodies still use the sugar from those carbs just like lean people do.

Eating carbs before a workout when you haven't eaten all night might make you feel like you can lift more—but it's probably because you feel less hungry or think you're getting energy, not because your muscles actually have more fuel.

Adults with type 2 diabetes who did aerobic exercise had about 12 more mg/dL lower fasting blood sugar than those who didn't exercise, after 12 weeks.

When you work out in the evening without eating beforehand, your body burns more fat and less sugar for energy during the workout.