When you’re trying to lose weight, proper nutrition is essential as you learn how to count calories, strike the perfect balance of macronutrients and schedule meals and snacks to support your metabolism without overeating. Add exercise, pre-workout fuel and post-workout recovery to the mix, and there’s even more to consider.
“Nutrient timing and exercise is a hotly debated topic in the nutrition world as there are clear physiological benefits to eating both before and after a workout,” says Terence Boateng, RD, a sports dietitian and certified exercise physiologist based in Toronto. Your body primarily relies on stored energy in carbohydrates (glycogen) and body fat to fuel workouts. You also need adequate carbs and protein to rebuild after tough workouts to avoid metabolism-zapping muscle breakdown.
If you have to choose, research on which is better — eating before or after a workout — remains limited, and recommendations vary depending on your fitness level and the type of training, according to a meta-analysis published in the Journal of Functional Morphology and Kinesthesiology. While some small studies show fasting before a workout may increase fat burn, others suggest there’s no significant impact on fat loss either way — even when it comes to a 6-week HIIT workout routine.
Here, registered dietitians weigh in on whether to prioritize pre-workout nutrition or post-workout refueling:
EATING BEFORE A WORKOUT
While both pre- and post-workout nutrition is important, eating before a workout may come with greater benefits for weight loss. In particular, a pre-workout snack or meal with easy-to-burn carbohydrates has been shown to improve performance and, in turn, how many calories you burn. More research is needed, but eating before a workout may also help increase the amount of fat you burn compared to how much you’d burn if you fasted, according to a small study of young men who ran with or without breakfast.
Though some studies show there may be advantages to fasted exercise for fat burning, for the average person trying to lose weight, not eating before a workout can lead to diminished performance, difficulty concentrating, reduced motivation and early fatigue — which means fewer calories burned. Research shows a pre-workout snack tops off your body’s store of ready-to-burn energy, which allows you to exercise with more intensity for a longer time. While it might seem counterintuitive to eat to lose weight, in this case, the proper nutrition allows you to burn more calories.
Optimizing performance during a workout could, in theory, increase calories burned, but the impact of pre- and post-workout fuel depends on the type and duration of exercise, ratio of macronutrients and timing. One literature review finds eating carbs and protein before a workout improves performance for exercise when you have a long recovery period (more than eight hours between workouts); it doesn’t have a significant impact for a shorter recovery period (less than eight hours).
EATING AFTER A WORKOUT
While it’s true post-workout fuel stimulates muscle growth, the extra calories could hinder weight loss, especially if it’s an added meal or snack you wouldn’t have eaten otherwise. What’s more, a pre-exercise meal may have a similar muscle-building effect to eating immediately after a workout anyway, finds a study of weightlifters who drank a protein shake before or after their workout.
When you’re trying to slim down, it’s crucial to incorporate a meal high in protein and carbohydrates after a workout to ensure you’re burning fat but minimizing muscle loss. Studies suggest the best way to maximize your results after weightlifting, for example, is to refuel with carbs and protein in a short window (15–30 minutes) after your workout to improve protein absorption and stimulate muscle rebuilding and growth. Over time, more lean muscle mass improves your metabolism for more efficient calorie burn throughout the day.
THE BOTTOM LINE
Until more research is done, it’s difficult to say whether eating before or after a workout is better for weight loss. Ultimately, experts agree that for shedding pounds, a well-balanced diet is essential regardless of timing.
That said, tracking what you eat with an app like MyFitnessPal can be particularly helpful since you still need to be in a calorie deficit. “There’s a common misconception that because you’re burning calories through exercise, you can eat more — but we typically burn fewer calories than we think,” says Boateng. Thus, lighter workouts such as walking and yoga for less than 60 minutes generally don’t require pre-workout snacks or post-workout recovery fuel, whereas heavy weightlifting workouts or endurance activities longer than 60 minutes would.
“To avoid adding extra calories and hurting your weight-loss efforts, aim to schedule your workouts between meals that are already part of your eating plan,” suggests Boateng. Think: a small breakfast of easy-to-digest carbs like toast with peanut butter or oatmeal before your workout, followed by a recovery snack with protein and carbs such as a protein shake or turkey sandwich after your workout. Don’t forget to drink up, too — “hydration is key to keep your energy up before, during and after your sweat session,” adds Wilson.
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