Intermittent fasting for athletes: The pros and cons
Intermittent fasting has become a popular approach to weight loss and health improvement in recent years. The practice involves restricting food intake for a certain period, followed by a period of eating. While it may seem counterintuitive for active individuals to limit food intake, several studies have suggested that intermittent fasting may be beneficial for some.
What is Intermittent Fasting?
Intermittent fasting (IF) is an eating pattern that involves alternating periods of fasting and feeding. There are several methods of IF, including the 16/8 method, the 5:2 method, and the eat-stop-eat method.
The 16/8 method involves restricting food intake to an eight-hour window each day, while the 5:2 method involves consuming a limited number of calories (around 20-70% less calorie intake) for two days of the week and eating normally for the other five days. The eat-stop-eat method involves fasting for 24 hours once or twice per week.
Possible benefits to Intermittent Fasting
While most of the research on intermittent fasting has focused on weight loss and metabolic health, some studies have looked at its potential benefits. Here are some of the key findings:
Improved body composition: Several studies have shown that intermittent fasting can help reduce body fat and improve muscle mass. A study published in the Journal of Translational Medicine found that IF combined with resistance training led to greater fat loss and muscle mass gain than resistance training alone.
Reduced cellular ageing: Fasting and restriction in energy intake increases activities like cell clean up of dysfunctional cellular material and recycle them. Along with these, IF also triggers self-digestion of any dysfunctional cells, both of these programmed cell activities can show up as decreased inflammation or improved longevity.
Reduced risk of cancer: Some research shows evidence that fasting decreases growth factors such as IGF-1, increases cellular repair and clean up, reduces the expression of some cancer genes, and in some cases increases the response of some cancer treatment drugs.
There is a caveat however, fasting alone did not prevent cancer, only when combined with other approaches was it able to fight off diseases. In addition to this there is ample evidence that weight cycling (on-off or yo-yo dieting) increases risk of cancer. Therefore its important that any “diet” should be approached in moderation as to not drastically change the body weight too quickly.
Improved heart health: IF seems to lower heart rate and HRV (heart rate variability) which is a marker of stress. It has also been shown in some cases to lower blood pressure by releasing brain chemicals that run on the “rest and digest” branch of our nervous system.
Reduced risk of type 2 diabetes: One small study of 3 participants who have had diabetes for 10-25 years practiced IF for 4 weeks and were able to stop using insulin completely. However some large scale studies showed mixed results.
Increased mental clarity: Intermittent fasting has been shown to slow cognitive decline by reducing inflammation, helping to control glucose and insulin, slow down brain cell ageing and stimulating the brain’s ability to form new synaptic connections.
However, some people have reported increased brain fog during IF, so more research is needed to clarify this point.
Potential Downsides of Intermittent Fasting for Athletes
While intermittent fasting may offer several potential benefits for athletes, there are some downsides to consider. Here are a few:
Reduced glycogen stores: Glycogen is the primary fuel source for high-intensity exercise, and restricting food intake can reduce glycogen stores in the muscles. This may impair performance during intense exercise.
Increased risk of injury: Fasting can reduce muscle mass and strength, which may increase the risk of injury during training or competition.
Nutrient deficiencies: Restricting food intake may lead to nutrient deficiencies if athletes are not careful to consume adequate nutrients during feeding periods.
Increased incidences of disordered eating behaviours: There is an overwhelming amount of evidence that suggests IF can increase food cravings and bingeing when food is reintroduced resulting in increased preoccupation with food and food guilt.
Exercise and intermittent fasting
According to research, the following types of movements don’t pair too well with IF:
Activities that involve intense effort such as 200-400 metre runs
High intensity work in short bursts
Explosive movements like jumping
Strength work
So if you’re an athlete that engages in these types of movements, expect your performance to suffer during periods of fasting.
Female athletes and intermittent fasting
There is a lot of evidence that women suffer more severely from extreme diets. This could be down to the differences in male and female hormones. For example, Kisspeptin, which is a hormone found in both sexes, although much higher in females, is very sensitive to insulin, leptin and ghrelin (hormones that affect appetite and energy balance), making it much more sensitive to calorie restrictions.
For more information on IF for female athletes check out this blog Exercising and dieting during menopause: what athletes should know.
Ramadan and exercise
During the month of Ramadan, many athletes that practice fasting may need to adjust their training intensity and schedule to fit their meal times.
To aid in recovery during that time, here are few strategies some athletes may find helpful:
#1 Decrease training intensity: Because high intensity movements rely heavily on glycogen, this may result in a drop in energy and performance. Each athlete will be different but scaling back on overall training volume may help with better recovery.
#2 Time your training session nearer to meal times: Making sure that you have “something in the tank” around training will increase your chances of keeping your energy high during training.
#3 Pair low intensity exercises during that month: If your goal is to maintain or lose weight, you may wish to increase low intensity exercises as a means to increase overall energy expenditure by utilising slow and steady cardio.
Conclusion
Intermittent fasting has become a popular approach to weight loss and health improvement, and some athletes have reported improved performance while practicing IF. While there are potential benefits to intermittent fasting, there are also some downsides to consider, especially for athletes.
IF can lead to weight loss as it often results in a calorie deficit over the course of a week, not due to any inherent superiority, but simply because it naturally restricts caloric intake.
When it comes to weight loss, the relationship between total daily energy expenditure and the total daily intake is what will determine whether you lose or gain weight.
Because intermittent fasting gives you a smaller window of opportunity to eat, it usually results in weight loss. However, in many cases, this can backfire leading to binge eating.
Athletes should consult with a healthcare professional or qualified coach before implementing an IF plan to ensure that it is appropriate for their individual needs and goals.
References
Furmli S, Elmasry R, Ramos M, Fung J. Therapeutic use of intermittent fasting for people with type 2 dHeadland M, Clifton PM, Carter S, Keogh JB. Weight-loss outcomes: a systematic review and meta-analysis of intermittent energy restriction trials lasting a minimum of 6 months. Nutrients. 2016;8.
Harvie M, Howell A. Potential benefits and harms of intermittent energy restriction and intermittent fasting amongst obese, overweight and normal weight subjects—a narrative review of human and animal evidence. Behav Sci. 2017;7: 4.
Colombarolli, M.S., de Oliveira, J. & Cordás, T.A. Craving for carbs: food craving and disordered eating in low-carb dieters and its association with intermittent fasting. Eat Weight Disord 27, 3109–3117 (2022). https://doi.org/10.1007/s40519-022-01437-z
