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Rainie Cheng

The Skinny on Carb Cycling

If you have been browsing the internet for nutrition information on weight loss, you have likely come across many diets recommending eliminating or significantly reducing your carb intake. Enter the "carb cycling" paradigm of dieting. But, what exactly is carb cycling, and will it help you lose weight?


What is carb cycling?

Simply put, carb cycling refers to alternating between "high-carb" days and "low-carb" days in a scheduled way. The alternation can occur daily, weekly, or monthly, varying from person to person and can become very complex. The purpose is that your carbohydrate intake will coincide with the days that you are more or less active.


This cycling approach was initially used by athletes and bodybuilders to improve endurance performance, lose fat, and achieve maximum carbohydrate intake efficiency. Muscle glycogen is our primary fuel during exercise, and its synthesis relies on our consumption of carbohydrates. Furthermore, glycogen stores at the start of training are directly related to the onset of fatigue [5], and post-exercise carbohydrate intake helps to replenish the muscle glycogen lost during exercise [1]. Therefore, one popular carb cycling approach is pairing high-carb intake on high training days to help fuel workout and facilitate muscle recovery. Conversely, on rest days or low activity days, one would consume fewer carbohydrates.





Does carb cycling make you skinnier?

A research study examining carb cycling in athletes indicates that adopting a carb cycling plan paired with specific training strategies can increase fat loss without muscle loss compared to other diets [9]. However, in non-athletes, the implication of carb cycling on weight and fat loss is relatively new. Therefore research in this area is minimal. Nevertheless, theoretically, it has some indirect impact on weight loss by regulating appetite hormones and overcoming the weight loss plateau.


When we restrict our caloric intake and lose weight, our body recognizes this as a starvation signal. Therefore, it activates a compensatory mechanism to this prescribed deficit by:


  • Dropping our basal metabolic rate so that physiologically, we are expending less energy [2].

  • Increasing our hunger hormone ghrelin and decreasing our satiety hormone leptin, so that psychologically, we want to eat more [2].


It becomes hard to further lose weight once we have reached a plateau. The only way out is to induce a more significant caloric deficit by exercising more or eating less.


Now here's how carb cycling kicks in:


Theoretically, recurring high-carb days are used as a "jumpstart" to prevent your body from metabolically adapting. Note that this is a hypothesized biochemical standpoint as there is currently no solid evidence for support. There is, however, no current evidence to contradict either.


Some studies show that short-term carbohydrate over-feeding (i.e., high-carb days) may temporarily increase leptin level and function, as well as energy expenditure [3, 8]. Another study has shown that ghrelin levels may temporarily decrease when short-term over-feeding is paired with increased physical activity[4]. This will tell your brain to reduce your appetite so that you eat less. Note, however, that in these studies, overfeeding occurred consecutively for more than one day.


Again, there is little research examining the carb cycling strategy for weight loss in non-athletes and whether carb cycling can help lose fat without losing muscle.


BUT‼ There is one thing we can be sure about: remember the concept of energy balance?


Energy in < energy out (over time) = weight loss


This holds true for every weight loss approach. First, make sure that your carb cycling routine meets a sustainable caloric deficit. And yes, you will lose fat and weight over time.







The Pros:

  • Better endurance performance and carb utilization for athletes [1, 5, 9].

  • Help overcome the weight loss plateau by regulating some appetite hormones [3, 4, 8] and, theoretically, by preventing the body from metabolically adapting.

  • Carb cycling may make it easier to stick to following a lower-carb diet.

  • A low-carb diet has shown some benefits for people living with diabetes and metabolic syndrome [7]. Because carb cycling is not as restrictive as the ketogenic diet, for instance, allowing for high-carb days may help some individuals maintain a low-carb eating style. Remember, a diet style works best when it fits your eating preferences and lifestyle.

  • Other theoretical hypotheses include improved insulin sensitivity and an increased ability to burn fat. However, there is currently minimal supporting scientific evidence. Moreover, due to our biological complexity and difference in carb cycling routine, what works for one may not work for others.


The Cons:

You may actually gain weight

  • If you use high-carb days as "cheat days" and indulge in low quality and calorie-dense carbs on high-carb days.


Carb cycling is a hyper-specific eating regimen:

  • It requires adherence to exact macronutrient ratios, macronutrient counting, and a great deal of nutrition planning. Thus it could be challenging for most people. Therefore, it is not recommended as a first step to better eating habits nor to weight loss.


Things can get complicated for people with chronic health conditions:

  • For example, for individuals living with diabetes who exercise regularly, uncontrolled low-carb days may lead to hypoglycemia [6, 11]. On the other hand, uncontrolled high-carb days may also cause higher blood sugar levels in type 2 diabetes. Therefore, carb cycling should be implemented under the supervision of a registered dietitian.


To Recap:

  • There is currently no strong evidence on the effectiveness of carb cycling over other diets on weight loss in non-athletes.

  • Give it a try if carb cycling aligns with your lifestyle. Use it as an add-on experiment to your settled good eating habits rather than the first step into weight loss.

  • For weight loss purposes, be sure to incorporate a caloric deficit on carb cycling and prioritize high-quality carbs (i.e., low glycemic index carbohydrates and high fibre).


Incorporate exercise to avoid excess muscle loss as you lose fat.

  • Schedule exercise on high-carb days so the carbs can be used to fuel your workouts and facilitate post-exercise muscle recovery.

  • The carb cycling routine and the amount of carbs consumed on high- and low-carb days should be tailored to the individual's needs, and goals. But, again, working with a dietitian is the best way to get the most accurate information!


Remember that our body biochemistry is very complex, and what works for one may not work for others. Therefore, do not be discouraged if carb cycling is not the best dietary strategy for you. Instead, always prioritize general healthy eating habits, and consult a dietitian to further help achieve specific goals.


Best,


Rainie




Sources:

  1. Alghannam, A., Gonzalez, J., & Betts, J. (2018). Restoration of Muscle Glycogen and Functional Capacity: Role of Post-Exercise Carbohydrate and Protein Co-Ingestion. Nutrients, 10(2), 253. https://doi.org/10.3390/nu10020253

  2. Casanova, N., Beaulieu, K., Finlayson, G., & Hopkins, M. (2019). Metabolic adaptations during negative energy balance and their potential impact on appetite and food intake. Proceedings of the Nutrition Society, 78(3), 279–289. https://doi.org/10.1017/s0029665118002811

  3. Dirlewanger, M., Vetta, V. di, Guenat, E., Battilana, P., Seematter, G., Schneiter, P., & Tappy, L. (2000). Effects of short-term carbohydrate or fat overfeeding on energy expenditure and plasma leptin concentrations in healthy female subjects. International Journal of Obesity, 24(11), 1413–1418. https://doi.org/10.1038/sj.ijo.0801395

  4. Hägele, F. A., Büsing, F., Nas, A., Hasler, M., Müller, M. J., Blundell, J. E., & Bosy-Westphal, A. (2019). Appetite Control Is Improved by Acute Increases in Energy Turnover at Different Levels of Energy Balance. The Journal of Clinical Endocrinology & Metabolism, 104(10), 4481–4491. https://doi.org/10.1210/jc.2019-01164

  5. Jensen, R., Ørtenblad, N., Stausholm, M. L. H., Skjærbæk, M. C., Larsen, D. N., Hansen, M., & Nielsen, J. (2020). Heterogeneity in subcellular muscle glycogen utilisation during exercise impacts endurance capacity in men. The Journal of Physiology, 598(19), 4271–4292. https://doi.org/10.1113/jp280247

  6. Johnson‐Rabbett, B., & Seaquist, E. R. (2019). Hypoglycemia in diabetes: The dark side of diabetes treatment. A patient‐centered review. Journal of Diabetes, 11(9), 711–718. https://doi.org/10.1111/1753-0407.12933

  7. Kirkpatrick, C. F., Bolick, J. P., Kris-Etherton, P. M., Sikand, G., Aspry, K. E., Soffer, D. E., Willard, K.-E., &amp; Maki, K. C. (2019). Review of current evidence and clinical recommendations on the effects of low-carbohydrate and very-low-carbohydrate (including ketogenic) diets for the management of body weight and other cardiometabolic risk factors: A scientific statement from the National Lipid Association Nutrition and Lifestyle Task Force. Journal of Clinical Lipidology, 13(5). https://doi.org/10.1016/j.jacl.2019.08.003

  8. Kolaczynski, J. W. (1996). Response of leptin to short-term and prolonged overfeeding in humans. Journal of Clinical Endocrinology & Metabolism, 81(11), 4162–4165. https://doi.org/10.1210/jc.81.11.4162

  9. Marquet, LA., Brisswalter, J., Louis, J., Tiollier, E., Burke, L. M., Hawley, J. A., & Hausswirth, C. (2016). Enhanced Endurance Performance by Periodization of Carbohydrate Intake. Medicine & Science in Sports & Exercise, 48(4), 663–672. https://doi.org/10.1249/mss.0000000000000823

  10. Mawer, R. (2017, June). What is Carb Cycling and How Does it Work? Healthline. https://www.healthline.com/nutrition/carb-cycling-101.

  11. Schrader, M., Treff, B., Sandholtet, T., Maassen, N., Shushakov, V., Kaesebieter, J., & Maassen, M. (2016). Carbohydrate supplementation stabilises plasma sodium during training with high intensity. European Journal of Applied Physiology, 116(9), 1841–1853. https://doi.org/10.1007/s00421-016-3429-4


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