There’s an assumption that running or cycling on an empty stomach will help you burn more body fat. The strategy is better known as fasted cardio, but a study published in the Journal of the International Society of Sports Nutrition suggests drinking a protein shake before cardio can help increase resting energy expenditure and fat oxidation to a greater extent than consuming nothing.
Eleven college aged men ran on a treadmill at 55% to 60% of reserve heart rate for half an hour. They hadn’t consumed any food for 8 to 10 hours before training, but on separate occasions consumed a calorie-matched supplement containing either 25 grams of whey protein isolate, 25 grams of casein protein, 25 grams of maltodextrin or a non-caloric control drink.
Consuming whey or casein before running significantly increased energy expenditure after exercise compared to maltodextrin and also helped burn more calories than the control drink. Post-workout fat oxidation also increased more with protein consumption, and casein increased fat oxidation to a greater degree than whey. Even maltodextrin consumption helped oxidize more fat than the non-caloric control drink.