With a global diet industry worth US$168.95 billion, it’s clear the world is obsessed with weight loss. But what’s the best diet for losing weight and improving health? One of the most promising diets to have gained attention recently is intermittent fasting, which the media has crowned a miracle weight loss solution. But according to a recent study, when it comes to losing weight, intermittent fasting isn’t any more effective than conventional dieting.
Intermittent fasting is an eating pattern that condenses daily food intake into one time-restricted period, then fasting for the rest of the day. One of the most popular versions of intermittent fasting is the “5:2 diet”. This allows five days of unrestricted eating and two days (usually non-consecutive) eating a very low-calorie diet, typically about 500 kcal. The diet’s biggest appeal is the flexibility to tailor it to your lifestyle.
Enthusiasm for intermittent fasting was fuelled by data from animal studies that suggested fasting could help reduce the risk of diabetes, cardiovascular disease and certain types of cancer. However, few studies have actually examined the effects of intermittent fasting on humans for longer than six months. Carrying out long-term studies that control diet is difficult because it’s hard to get people to stick to them, and results can be affected by outside factors.
A diet that’s definitely not a good idea to try? The 101 Day Detox diet. Just ask Brigid Delaney.
This recent study was conducted over a 50-week period, making it one of the longest intermittent fasting studies to date. Researchers split 150 participants into three groups. One group followed the 5:2 intermittent fasting diet (with two non-consecutive “fast” days per week eating about 500 kcal), while the second group reduced daily calorie intake by approximately 20%. A third control group weren’t instructed to change their diet.
During the first 12 weeks, a trained dietitian worked closely with participants to ensure they stuck to the allocated diet. After 12 weeks, participants continued following their diet without the dietitian. The effects of the diets were then evaluated using a number of health assessments after 12, 24 and 50 weeks.
Researchers measured body weight, body fat, insulin sensitivity (risk of diabetes indicated by ability to control blood glucose) and cholesterol. They also analysed 82 genes linked to obesity and metabolic disease.
The study’s key finding was that intermittent fasting and daily calorie restriction both led to significant weight and fat loss compared to the control group. But intermittent fasting was no more effective than conventional dieting for losing weight. Intermittent fasting also didn’t improve any marker of health more than daily calorie restriction.
Drop-out rates were low but similar for both diet groups, suggesting participants found these similarly easy to stick to. Other long-term intermittent fasting studies in humans have shown similar results.
This study essentially confirms a well-understood weight loss principle: whatever method you use, in order to lose weight you must reduce your total calorie intake. The 5:2 diet is designed specifically to reduce your total weekly calorie intake by a similar amount as a daily calorie restriction diet. So perhaps its not too surprising that end results are similar.