A long endurance session or tough weight-training workout requires post-workout fueling to help replenish your energy stores and repair your muscles. That snack or meal won't cause you to gain weight, unless it pushes you above the number of calories you need to maintain your weight. If you use exercise as an excuse to eat, especially high-calorie foods and treats, it could cause weight gain.
Why Eat After a Workout?
Eating after a long run, cycle ride or lifting session should be approached as functional, not as a reason to take in hundreds of calories because you just "burned" them off. You need carbohydrates after a workout that your body turns into glucose and stores as glycogen -- energy stores in your muscles and liver.
Protein eaten after a workout provides amino acids that your body uses to help repair and build muscle fibers. A 2012 study published in the British Journal of Nutrition found that about 20 grams of post-workout protein maximally stimulated muscle protein synthesis, the process by which muscles grow. How much of each nutrient you eat depends on your goals. Classic advice recommends a ratio of carbs to protein of 4 to 1. But athletes trying to lose body fat should aim for a 1-to-1 ratio instead.
Fueling Isn't Necessary After a Moderate Workout
A post-workout snack is really only required if you've worked longer than an hour or are training for a competition, whether that's a marathon or a bodybuilding show. The average person who is just trying to stay fit and meet the Centers for Disease Control and Prevention guidelines of 150 minutes of moderate-intensity cardiovascular exercise and two mild strength-training sessions per week doesn't need a specific post-workout nutrition plan. A brisk walk for 30 minutes doesn't call for a specific after-workout meal -- you can wait until the next time you eat.
Eating a snack after a moderate workout won't add weight, however, unless it makes you exceed your daily calorie needs. Eating a surplus of calories causes weight gain.
Indulging in Too Many Calories
You may feel like you worked hard and earned a burger, fries and an ice cream sundae, but chances are you didn't work off all those calories. Burning off a fast-food kid's meal with chocolate milk, for example, takes an average of four hours of Frisbee playing; one slice of cheese pizza takes about 22 minutes of biking at 12 to 14 miles per hour; and burning off a cinnamon roll would require 40 minutes of running. It's not eating after exercise that can cause the weight gain -- it's the choices you make if you believe you can eat anything you want after exercising.
A post-workout snack should consist of healthy options just like other meals you eat during the day. Lean proteins, low-fat dairy, whole grains, vegetables and fruits make nutrient-rich choices.
Figuring Your Post-Exercise Needs
To determine how many calories you should eat after a workout, use an online calculator to estimate your daily calorie needs for weight maintenance. Account for your age, size, gender and activity level. Divide these calories up over three meals and two smaller snacks. For example, if you need 2,000 calories per day, you could plan on three 500-calorie meals and two 250-calorie snacks. One of those 250-calorie snacks could fall after your workout.
Examples of good post-exercise food are a smoothie made with milk, nonfat dry milk, strawberries and a banana; a deli turkey sandwich on whole-grain bread with lettuce and tomato; roasted salmon with a sweet potato and spinach; or two hard-boiled eggs with woven wheat crackers and an apple.