What is Carb Cycling?

Carb Cycling Explained

We have explored the importance of carbohydrate availability for exercise performance.  Carbohydrate improves long, low intensity workouts and short, high intensity workouts. (1) In recent years there has been further research on the impact of different forms of carbohydrate consumption (such as diet manipulation and carbohydrate consumption before or during training).  One form of diet manipulation utilised in sport is “carb cycling”.  Let’s explore what carb cycling is, the relationship between carb cycling and sports performance and weight loss, the pros and cons and what the science is saying.

In its simplest form, carb cycling is “a planned change in carbohydrate intake in order to prevent a fat loss plateau and maintain metabolism along with workout performance”. (2)  Carb cycling alternates carb intake on a daily, weekly or monthly basis.  Ultimately, carb cycling aims to time carbohydrate intake to when it provides maximum benefit and exclude carbs when they’re not needed. (2, 3).

You can set your carb cycling based on many objectives.  The two most relevant objectives for our purposes are body composition goals and training and rest days.  Leading up to a sporting event is another potential objective to use carb cycling.

So what does carb cycling look like?  A typical carb cycling week might include one to two high-carb days, two to three moderate-carb days and three low carb days.  Protein intake will be similar across the week, while fat proportion will vary based on carb intake (ie on a high carb day, lower fat intake and on a low carb day, higher fat intake).

Scientific Research on Carb Cycling

Now, let’s look at the pros and cons of carb cycling, backed by science.

As we explored in the Intermittent Fasting post, some evidence suggests that brief and relatively infrequent periods of fasting and/or carbohydrate restriction may actually be advantageous for both health and body composition.

The high-carb days are in place to refuel muscle glycogen, which may improve exercise performance and reduce muscle breakdown (5, 6)  Strategic high-carb periods may improve the function of hormones leptin and ghrelin – the hormones that regulate weight and appetite. (7, 8)  The high carb days may also increase thyroid output which can help control hunger. (13)

The low-carb days are reported to switch the body over to a predominantly fat-based energy system.  This could improve metabolic flexibility and the body’s ability to burn fat as fuel in the long-term (9, 10).  A useful adaptation for exercise performance and body composition goals.  The low-carb days and the targeting of carbs around your workouts may also improve insulin sensitivity, which as we have explored, is vital for achieving and maintaining a healthy weight. (11)  The carbohydrate manipulation in carb cycling also allows the body to take advantage of anabolic effects of insulin, supporting body composition goals. (13)

It is important to raise here that there have not been enough controlled studies directly focused carb cycling.  Therefore these benefits should be interpreted with caution. (9, 12)

Downsides to Carb Cycling

One of the downsides to carb cycling is that it can be challenging to follow, especially as a beginner.  Another word of caution would be that our bodies handle deprivation relatively well in the short term, but in the longer term calorie or carb restriction can be hard on the body.

Overall, the mechanisms behind carb cycling, point to the possibility that it could be beneficial for weight loss if it is implemented in line with a calorie deficit.

References:

  1. https://www.ncbi.nlm.nih.gov/pubmed/23657935
  2. https://www.precisionnutrition.com/all-about-carb-cycling
  3. https://www.ncbi.nlm.nih.gov/pubmed/1895362
  4. https://www.ncbi.nlm.nih.gov/pubmed/8897388
  5. https://www.ncbi.nlm.nih.gov/pubmed/9694422
  6. https://www.ncbi.nlm.nih.gov/pubmed/14594866
  7. https://www.ncbi.nlm.nih.gov/pubmed/11126336
  8. https://www.ncbi.nlm.nih.gov/pubmed/3510362
  9. https://www.ncbi.nlm.nih.gov/pubmed/25275931
  10. https://www.fasebj.org/doi/abs/10.1096/fasebj.28.1_supplement.lb444
  11. https://www.ncbi.nlm.nih.gov/pubmed/25527677
  12. https://www.ncbi.nlm.nih.gov/pubmed/15767618
  13. https://www.ncbi.nlm.nih.gov/pubmed/12055988

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