Carbohydrates are our main source of energy, whether we are athletes or not. When manipulated correctly, their intake can affect our hormones and consequently, weight and health. One approach to optimize carbohydrate intake is to alternate or “cycle” their consumption on a daily, weekly, or monthly basis. When you cycle your carb intake, you vary how many carbs you eat throughout the week, with some days being low-carb and others high-carb while protein and fat remain the same. The aim is to time carbohydrate intake to when it provides maximum benefit and exclude carbs when they are not needed. This can simply be carb loading before a long-distance race or reducing their intake to lose weight. But does this popular diet really work?
Main Sources of Carbohydrates
Carbohydrates can be found in plant foods and dairy products, such as fruit, vegetables, legumes, cereals, grains, milk, and yogurt. When carbohydrate-containing foods are digested, they are broken down into glucose, our main source of energy.
Carb Cycling for Weight Loss
Unfortunately, we don’t have a lot of evidence in this field for the moment, but what we do have is promising. Recent studies show that carb-cycling leads to greater weight and fat loss than slightly reducing calories every day. The carb cycling works because the dieter eats less in one week than they normally would. Any time we create a caloric deficit, we lose weight. The key however, is to not overeat carbs (and calories) on the high carb days.
Have we found the miracle diet? Not quite. Not only do we have very few studies, we also don’t have evidence for long-term success. Losing the weight can be easy if a diet is followed regularly, it’s maintaining the weight loss long term that is more difficult, and we still don’t have evidence for the success of this diet. If you are someone who loves carbs or has a difficult time following a structured plan, this may not be for you. We also do have evidence that other, easier to follow diets do have long-lasting weight loss results!
Another caveat to these carb-cycling studies is that the way you carb-cycle can differ. It can consist of restricting carbs for 24 hours or 2 days a week, which would have a different impact on hormones and weight loss results.
Finally, carb cycling should not be approached by women who are pregnant, people with diabetes, anyone with a health condition or who takes medication on a regular basis. Restricting carbs too much can also make people dizzy, lightheaded, tired, and moody.
Moreover, it is important to note that even if you decide to restrict carbohydrate intake, opt for good-quality ones on higher-carb days, like whole wheat grains and products, and high fiber starchy vegetables.
Carb Cycling & Sports Performance
Again, there are many applications to carb cycling, whether it being eating more carbs before an endurance event or reducing intake to lose body fat.
As we have seen above, carb cycling while reducing calories may have a positive impact on losing body fat while minimizing muscle loss. This can be helpful for those who are in a weight-sensitive sport or who want to shed a few pounds to improve performance. But, if you are carb cycling to lose body fat, remember not to cut calories too drastically as rapid weight loss will lead to loss of water and muscle mass, both of which have a negative impact on performance.
On the other hand, increasing carbohydrate intake on days where performance is needed, such as in a sports competition or endurance event like a marathon or triathlon, can top up energy, delay fatigue and prevents the decline in skill performance and mental concentration. This method called carb loading, maximises our muscle reserves of glucose before our event and can improve performance over a set distance by 2-3%. Although this may seem minimal, seconds are crucial for elite athletes!
There are many ways and degree to which you can cycle carbohydrates. Carb cycling, if done properly, can have beneficial effects on body composition and performance, but there may be easier methods of obtaining these desired effects. Again, because we do not know the long-term effects, carb cycling should not be done for more than a few months.
Note: The information included is based on the best available evidence at the time and may not be applicable for all athletes. Please consult your local dietitian to get personalized advice.
Position of the American Dietetic Association, Dietitians of Canada, and the American College of Sports Medicine: Nutrition and Athletic Performance. (2016).
Rosenbloom, C. (2012). Sports nutrition a practice manual for professionals. (5th ed.). Chicago, Ill.: Academy of Nutrition and Dietetics.
Westerterp-Plantenga, M. S., Lemmens, S. G., & Westerterp, K. R. (2012). Dietary protein – its role in satiety, energetics, weight loss and health. British Journal of Nutrition Br J Nutr, 108(S2). doi:10.1017/s0007114512002589
Zeina is a registered dietitian-nutritionist and is part of l’Ordre professionnel des diététistes du Québec and Dietitians of Canada. She currently works at Le Fitness Loft Kinesiology Clinic in Dorval where she consults an active clientele that desires to change their lifestyle habits, whether it is to lose weight, increase muscle mass, improve performance or simply live healthier. Zeina has a passion for teaching and conveying her knowledge about overall healthy eating habits and makes sure every client receives personalized recommendations based on their lifestyle and preferences.
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