Weight management: playing fast and loose with strength?

In most sports, the loss of excess body fat almost always produces enhanced performance. When excess fat is shed, not only is power-to-weight ratio (the amount of power available to each kilo of bodyweight, which is a fundamental determinant of performance – see this article) improved, there are other benefits too. These include increased agility, and a reduced injury risk through reduced impact loading, especially in weight-bearing sports such as running.

Routes to leanness

The age-old question for athletes of course is how best to shed excess pounds and keep them off without resorting to extreme diets or training schedules that might lead to muscle mass loss, reduced strength and power, increased risk of injury, and even illness. The go-to method recommended by most dieticians is the use of mild calorie restriction, over an extended time period^(1,2). But while this can be an effective route in the general population, it can be more difficult for athletes in training, who generally need significantly more calories than their sedentary counterparts in order to fuel training.

In recent years, other methods of weight management have found favour among athletes, one of which is intermittent fasting, which has been shown to be equally as effective for weight loss as conventional calorie controlled diets⁽³⁾. Indeed, some evidence suggests that intermittent fasting may be even more effective than continuous calorie control⁽⁴⁾. A variation on this is ‘alternate day fasting’, which has also been demonstrated to be an effective route to weight loss and improved body composition⁽⁵⁾, while yet another method for which robust evidence exists is the use of meal-replacement drinks to replace the main meal of the day⁽⁶⁾.

Leanness without calorie restriction

There’s another alternative to fasting for weight loss, which has become increasingly popular in recent years – time restricted feeding or TRF for short. The idea of TRF is that instead of eating freely throughout the day, meals and calories are consumed within a relatively narrow time interval each day of around eight hours (see figure 1). The theory behind TRF is that by having 16 or so hours in each 24 hours as ‘food intake free’, fat burning gene activity is upregulated, helping to shed excess body fat. In this respect, TRF can be considered as a short term fast; rather than lasting a day or two, it lasts no more than 16 hours.

A key point however is that TRF can be continued for many days by athletes as it does not involve a restriction in the number of calories or amount of protein and carbohydrate consumed. It only affects the time window in which the normal calorie intake is consumed. A number of studies (but not all – see this article) have shown that restricting food intake to a 4-12 hour slot in the day, without reducing calorie intake, is associated with improved body weight maintenance, and that TRF can therefore be considered as a useful weight reduction strategy^(7-9).

Figure 1: Time–restricted feeding (24-hour clock)