Intermittent fasting may not be the best way to lose weight, new study suggests
TORONTO -- Those looking to lose weight and reduce fat may have less success with intermittent fasting than with simply reducing their calorie intake, a small new study suggests.
Intermittent fasting, in which dieters go a period of time without eating, has gained popularity in recent years despite some experts cautioning that it may not be the weight-loss solution many of its adherents are hoping for.
Researchers at the University of Bath in the United Kingdom attempted to quantify the benefits of intermittent fasting by studying the weight-related outcomes of 36 willing test subjects over three weeks.
As they detail in their report, which was published Wednesday in the journal Science Translational Medicine, the subjects were divided into three groups.
One group alternated between days of fasting and days in which they consumed twice their usual amount of calories. Another group alternated between days of fasting and days of eating 1.5 times their usual intake. The third group ate every day, but always 25 per cent fewer calories than normal.
In other words, one group practised fasting without reducing overall calorie intake, one group practised fasting with a reduced calorie intake, and one group did not fast but did reduce its calorie count by the same amount as the second group.
After the three weeks were up, the researchers report, the group that did not fast lost 1.9 kilograms on average, versus 1.6 kilograms for those who did fast and reduce their intake.
That difference was bigger than it sounds, because the non-fasting group lost nearly all of their body weight from fat, while the fasting group's weight loss was almost evenly split between fat and muscle.
The other group, members of which did fast but did not reduce their calorie intake, did not experience any significant weight loss.
The researchers say that this is because their overall calorie consumption remained the same, meaning they did not need to draw on their body's fat reserves even when they were fasting.
“Intermittent fasting is no magic bullet and the findings of our experiment suggest that there is nothing special about fasting when compared with more traditional, standard diets people might follow," lead researchers James Betts, director of Bath's Centre for Nutrition, Exercise and Metabolism, said in a press release.
“Most significantly, if you are following a fasting diet it is worth thinking about whether prolonged fasting periods is actually making it harder to maintain muscle mass and physical activity levels, which are known to be very important factors for long-term health.”
All participants in the study were considered lean, with body mass index levels between 20 and 25, and normally consume a typical diet of 2,000 to 2,500 calories per day.