Carbohydrates are the most important fuels during exercise at intensities above 65 percent of maximum effort. Unfortunately, consuming high-carbohydrate diets might trigger weight gain and obesity. Cycling carb intake (carb-cycling) is a nutritional technique that promotes fat loss without decreasing performance. Carb-cycling refers to training when you are glycogen depleted to improve fatty acid oxidation (burning fat calories for energy) and increasing mitochondria. Glycogen is carbohydrate stored mainly in the liver and muscles. Mitochondria are the tiny furnaces inside cells that provide energy. Increasing mitochondria improves endurance and enhances the capacity to lose fat.
Carb-cycling works in trained and untrained people. Studies have found increased fat burning and glycogen replenishment in elite athletes, recreational exercisers and unconditioned people.
Carb-cycling might give endurance athletes a nutritional shot in the arm because it:
Does not decrease endurance
• Promotes fat burning and helps preserve glycogen— essential stored carbohydrate for high intensity exercise.
• Promotes fat loss
• Increases fitness with less training
The Science Behind Carb-Cycling
The technique works by depleting muscle and liver glycogen with an aerobic training session, followed by an intense interval training workout several hours later. Interval training is a series of high-intensity exercises followed by short rest periods. A typical interval workout is six, 30-second repetitions on a stationary bike at 100 percent of maximum effort with two minutes rest between reps.
Interval training when you are glycogen depleted is difficult and painful, but it is great for fat loss. While it works well for endurance athletes, it might be inappropriate for power athletes because it reduces training intensity and does not increase lean body mass. However, this method is appropriate for people interested in fat loss or cross training for personal fitness. Carb-cycling increases critical enzymes involved in carbohydrate and fat metabolism and upregulates genes that trigger fat burning.
Exercising during sugar deprivation causes cell adaptations that promote alternative fuel use. Fatty acids, certain ketones and even alcohol can serve as fuel for metabolism. Sugar (glucose) is the preferred source of energy during short, intense activity. The cells become more dependent on fatty acids when less sugar is available. Processing fatty acids is slower than carbohydrates, particularly during exercise. Mitochondria cannot speed up the process, so cells meet the increased energy demands by creating more mitochondria. This allows muscles to meet the energy demands of exercise by metabolizing more fatty acids and breaking down more fat.
Carb-Cycling as Part of Your Training
The technique involves performing high-intensity interval training when you are glycogen depleted. In response, the cells will increase mitochondria and burn more fat.
Do aerobic exercise, such as running or cycling, at 70 percent of maximum effort for 60-90 minutes. You can promote glycogen depletion by reducing carbohydrate intake for one to two days before the workout.
- Rest two hours. Don’t eat any carbs during this rest period.
- Do an interval training workout, such as running 8 x 200-meter sprints at 90 percent effort with two minutes rest between intervals.
This technique is inappropriate for strength and power athletes because it decreases training intensity by 10 percent or more. This is also a poor training method for people who want to increase muscle mass. However, this is a terrific way lose fat rapidly. Carb-cycling is not a magic bullet for preventing obesity, but it is an effective training method for jump-starting your weight-loss program.
Burke LM. Fueling strategies to optimize performance: training high or training low? Scand J Med Sci Sports, Oct;20 Suppl 2:48-58.
Hansen AK, Fischer CP, et al. Skeletal muscle adaptation: training twice every second day vs. training once daily. J Appl Physiol, Jan;98(1):93-9.
Hawley JA, Burke LM. Carbohydrate availability and training adaptation: effects on cell metabolism. Exerc Sport Sci Rev, Oct;38(4):152-60.
van Loon LJ, Goodpaster BH. Increased intramuscular lipid storage in the insulin-resistant and endurance-trained state. Pflugers Arch, Feb;451(5):606-16.