Carbohydrates serve as the primary energy source for athletes training at high intensities, and levels of muscle glycogen are a major determinant of exercise capacity, here Adam M. Gonzalez, Ph.D shares his insights into carb back-loading.
One popular strategy, called carb back-loading, advocates eating little to no carbs in the morning hours and beginning carb intake in the evening starting with your post-workout meal. The rationale for carb back-loading is based upon the action of insulin, an anabolic hormone that facilitates the movement of glucose into cells following a meal.
Insulin sensitivity is heightened following a hard training session via mechanisms that include an increase in glucose uptake transporters known as GLUT4, and an increase in the activity of glycogen synthase, the enzyme promoting glycogen storage. While it’s great to appreciate the intricacies of metabolism, it’s unclear if this makes a meaningful difference at the end of the day. We need to analyse a diet over a 24-hour period, a week and a month, rather than isolate physiological characteristics at certain time points.
The case for carb back-loading comes from a study published in the Journal of Obesity, in which overweight people adhered to a calorically restricted diet for six months. These individuals were split into two groups that consumed the same amount of calories, protein, carbohydrates and fat. The only difference was that one group ate carbs throughout the day, whereas the other group consumed the majority of their carbs (approximately 80 per cent of total intake) at night.
The group consuming their carbs at night lost significantly more weight and body fat than those who were free to eat carbohydrates throughout the day. Additionally, restricting carbohydrates to nighttime led to better satiety and less feelings of hunger. Overall, the study showed that limiting carb dosing to a single bolus rather than spreading them throughout the day may help limit insulin secretions and improve feelings of fullness. However, the results of this study have yet to be replicated in trained individuals.
All in all, the research on carbohydrate timing is not overly convincing to make general recommendations that we should be eating a majority of our carbs at nighttime, and carb back-loading does not appear to be the often-proclaimed magical remedy. On the other hand, constraining carbohydrate intake to a certain time frame can help limit overall carbohydrate intake during periods of restriction and provide a structured system for dietary habits. Restricting carbohydrate intake for fat loss is challenging; therefore, compartmentalising carbohydrate intake to certain times of the day may make the psychological challenges of dieting feel easier.
Bottom line, carb back-loading does provide a viable option for limiting carbohydrates during periods of restriction, but it’s not a magic solution for muscle growth and fat loss. Muscles do not have some magical ability to absorb an unlimited amount of carbs after a workout.
Ultimately, the quality and quantity of carbohydrate intake appears to be more important than the timing of carbohydrate intake, so don’t use this approach as a reason to regularly stuff your face with cake and ice cream just because you saved your carbs for nighttime. Whether you decide to eat your carbs at night or throughout the day, stick to your healthier carb choices such as grains, vegetables and fruits, which include additional benefits such as fibre, vitamins and minerals. Also, keep in mind that in order for weight loss to occur, a calorie deficit is needed.
Maintaining a calorie deficit and assuring adequate protein in the diet is a more appropriate approach to fat loss and muscle gain rather than indiscriminate eating within a selected time frame.