Refeeds and Carbohydrate Cycling

Refeeds, carbohydrate cycling, diet breaks — all these strategies promise to 'restart the metabolism' during weight loss. The editorial team looked into which of this has a scientific basis and which remains marketing, and how to apply periodic increases in calorie intake sensibly.

Terms: refeed, cycling, diet break

A refeed (from English refeed) is a planned day or two with increased calorie intake, predominantly through carbohydrates, against a backdrop of an overall deficit. On such a day calorie intake is usually raised to the maintenance level or slightly higher, while protein is kept usual and fats moderate.

Carbohydrate cycling is a broader scheme in which days with high, medium and low carbohydrate content alternate over the course of a week. Often the high-carbohydrate days coincide with the hardest workouts, and the low-carbohydrate days with rest days.

A diet break is a longer pause in the deficit: usually one or two weeks of eating at maintenance level. This strategy is also called intermittent energy restriction, and it is precisely this that is best studied in controlled trials.

All three approaches are united by one idea: instead of a continuous deficit for months, to alternate periods of restriction and relative 'satiety'. They differ in duration and in which physiological effects are expected from them.

Physiology: metabolic adaptation and leptin

During a prolonged deficit, energy expenditure decreases more than can be explained by the loss of body weight. This phenomenon, which Rosenbaum and Leibel (2010) describe as adaptive thermogenesis, includes a reduction in spontaneous everyday activity, a drop in thyroid hormone levels and an increase in the efficiency of muscular work.

The key hunger signal is leptin — a hormone of fat tissue. Its level falls during a deficit faster than fat stores decrease, which intensifies appetite and contributes to metabolic adaptation. Short-term overeating of carbohydrates is able to temporarily raise leptin levels: in a study by Dirlewanger and colleagues (2000), carbohydrate, but not fat, overfeeding raised leptin and energy expenditure within a few days.

However, the effect of one or two refeed days on leptin is short-lived, and there is no convincing evidence that it substantially changes the overall dynamics of weight loss. That is precisely why the formulation 'a refeed revs up the metabolism' is an exaggeration.

A more realistic benefit of a refeed is the replenishment of muscle glycogen. After several days of low carbohydrate content, glycogen stores are reduced, and a high-carbohydrate day can improve the quality of the next hard workouts, as well as psychologically ease adherence to the diet.

What the research shows

The most famous study is MATADOR (Byrne and colleagues, 2018). Men with obesity alternated two weeks of deficit with two weeks of maintenance. Compared with a continuous diet, such a group lost more fat and better retained the result after the program ended, although the overall duration of the intervention was longer.

For trained people, the study by Campbell and colleagues (2020) is interesting: participants who, against a backdrop of a deficit, ate at maintenance level with high carbohydrate content two days a week better preserved lean mass than a group with a continuous deficit, with similar fat loss.

At the same time, the randomized ICECAP trial (Peos and colleagues, 2021) in trained people found no substantial difference between a continuous diet and a diet with breaks regarding fat loss and preservation of lean mass. Some participants in the break group reported less hunger.

So the overall picture is this: a periodic increase in calorie intake does not accelerate fat burning but can ease adherence to the diet and, possibly, help preserve muscle mass and training performance. The effects are moderate and individual.

How to organize a refeed in practice

A refeed makes sense above all for people with a low percentage of fat who have been in a deficit for a long time and feel a drop in performance. For beginners with a moderate excess of weight, it is more important to simply follow the plan consistently.

• calorie intake on the refeed day — approximately at maintenance level;
• the extra calories — predominantly from carbohydrates (grains, potatoes, fruit, bread), fats — moderate;
• protein — at the usual level;
• it is advisable to place the refeed before or on the day of the hardest workout;
• weigh yourself taking into account that the next morning your weight will rise because of glycogen and water.

The main danger is turning a refeed into uncontrolled overeating. A single 'cheat meal' of several thousand kilocalories can nullify a week's deficit. A refeed is a planned and calculated day, not a reward for suffering.

For people prone to eating disorders, rigid schemes with alternating 'correct' and 'forbidden' days can be harmful. If thoughts about food become obsessive, you should consult a specialist.

Editorial conclusions

Refeeds and carbohydrate cycling do not 'rev up' the metabolism, but they can replenish glycogen, improve training and ease the psychological burden of a diet.

The best-studied are longer diet breaks; research results are mixed, so expectations should be kept moderate.

The key to success is control: a refeed should be a planned day with a clear calorie intake, not an uncontrolled cheat meal.

We also recommend our materials on calculating macros for weight loss, on sugar in an athlete's diet and on nutrition on competition day.

References

1. Rosenbaum M, Leibel RL. Adaptive thermogenesis in humans. Int J Obes (Lond). 2010;34(Suppl 1):S47–S55.
2. Dirlewanger M, di Vetta V, Guenat E, et al. Effects of short-term carbohydrate or fat overfeeding on energy expenditure and plasma leptin concentrations in healthy female subjects. Int J Obes Relat Metab Disord. 2000;24(11):1413–1418.
3. Byrne NM, Sainsbury A, King NA, et al. Intermittent energy restriction improves weight loss efficiency in obese men: the MATADOR study. Int J Obes (Lond). 2018;42(2):129–138.
4. Campbell BI, Aguilar D, Colenso-Semple LM, et al. Intermittent energy restriction attenuates the loss of fat free mass in resistance trained individuals. A randomized controlled trial. J Funct Morphol Kinesiol. 2020;5(1):19.
5. Peos JJ, Helms ER, Fournier PA, et al. Continuous versus intermittent dieting for fat loss and fat-free mass retention in resistance-trained adults: the ICECAP trial. Med Sci Sports Exerc. 2021;53(8):1685–1698.
6. Helms ER, Aragon AA, Fitschen PJ. Evidence-based recommendations for natural bodybuilding contest preparation: nutrition and supplementation. J Int Soc Sports Nutr. 2014;11:20.