Intermittent fasting (IF) is an emerging nutritional strategy being utilised by many for the purposes of reducing body fat and improving overall body composition. IF is usually divided into the subtypes:
- Alternate day fasting (ADF) – This involves a 24 hour fasting period alternated with a 24 hour feeding period.
- Whole day fasting (WDF) – This involves one or two 24 hour fasting periods during the course of a week.
- Time restricted feeding (TRF) – This involves a fasting and a feeding window included within each 24 hour period e.g. 16 hours fasting, 8 hours feeding.
A key reason why IF has been shown to be an effective nutritional strategy for fat loss and body composition improvement is because the fasting periods of any IF protocol help to ensure that an energy deficit is being enforced. Without an energy deficit fat loss will not occur. An individual following an IF diet will not completely compensate during feeding periods for the calories not eaten during fasting periods, hence weight loss and fat loss occurs as the individual is consuming a calorie intake below that required to meet their daily energy expenditure (referred to as maintenance calorie requirement).
ADF, WDF and TRF have a reasonably strong evidence base for being equally successful for fat loss and improving body composition; even sometimes outperforming standard daily caloric restriction. A study by Moro et al., (2016) reported a significantly greater loss of fat mass in a TRF group compared to a normal diet control group (1.6kg vs 0.3kg) after 8 weeks, where participants exercised three times per week. Although, it must be noted that not all research into ADF and WDF use zero calorie intake during fasting periods and have ad libitum feeding cycles; therefore, do not involve precise tracking of food intake. There is emerging evidence for TRF combined with resistance training for effective fat loss whilst maintaining muscle mass and strength.
An extensive systematic review of the existing research investigating IF was carried out by Seimon et al., (2015). The review included 40 studies that have previously looked into IF. The authors of the review concluded that IF can prove to be an effective dieting strategy for reducing body weight, fat mass, improving glucose regulation and enhancing satiety (i.e. reducing hunger). However, IF does not prove to be superior to standard daily calorie restriction.
Following any IF protocol should be approached with caution. Careful planning and consideration should take place for IF, especially for those who require their nutritional strategy to facilitate optimal athletic performance.
Supplementation can be utilised during the fasting periods of IF protocols to help offset the loss of lean tissue, as IF has been reported to result in losses in muscle mass as well as fat mass. Essential amino acids (EAA’s), especially leucine, HMB (a metabolite of leucine) and fish oil (Omega 3) could be taken during fasting periods, as all have been shown to reduce muscle protein breakdown (MPB); thus, protecting lean tissue. Similarly, a whey protein supplement could also be utilised during extensive fasting periods (i.e. 24 hours) to protect muscle mass, as the existing literature indicates that the benefits of IF can still be achieved even if fasting periods are not completely zero calorie. A quality whey protein supplement with high protein content and low carbohydrate/fat content (therefore, low calorie) could help promote the retention of muscle during long fasting periods; still yielding the benefits of the IF strategy.