Fasting diet study reveals ideal duration for fat loss

Fasting, particularly intermittent fasting, has become a popular dieting protocol for those looking to lose weight. Many different fasting schedules and methods exist, but questions remain over which are ideal for burning fat. Researchers with the University of Illinois at Chicago sought an answer to this, reporting in a new study that two fasting diets in particular can be used effectively to lose weight.

Fasting, of course, is the practice of abstaining from food for a period of time ranging from hours to days — or, in the most extreme cases, for weeks. This practice has largely been undertaken for religious reasons, but in modern years it has become popular among health and fitness enthusiasts. A number of past studies have linked intermittent fasting with various potential health benefits.

This latest study details the first human clinical trial to investigate two different popular varieties of fasting protocols and their impact on body fat, among other things. One fasting diet involved only eating during a four-hour window of time, while the second involved a six-hour eating window.

In the case of this study, the first group only ate between 1PM and 5PM, whereas the second group could eat only between 1PM and 7PM. The study participants were allowed to eat whatever they wanted during this time, but when fasting, they were limited to just calorie-free liquids and water.

As far as the control group is concerned, the researchers told them to stick to their usual diet and activity levels in order to maintain their weight. By following these fasting requirements, the participants cut their daily calorie intake by around 550 calories and managed to lose 3-percent of their body weight. Multiple benefits were seen in the study groups compared to the control group, including decreases in oxidative stress and insulin resistance.

Ultimately, the study's corresponding author Krista Varady said:

The findings of this study are promising and reinforce what we've seen in other studies — fasting diets are a viable option for people who want to lose weight, especially for people who do not want to count calories or find other diets to be fatiguing. It's also telling that there was no added weight loss benefit for people who sustained a longer fast — until we have further studies that directly compare the two diets or seek to study the optimal time for fasting, these results suggest that the 6-hour fast might make sense for most people who want to pursue a daily fasting diet.