Time-restricted fasting has emerged over the past few years as a popular new diet option, but is it truly effective as a path to weight loss? Researchers from The University of Illinois at Chicago set out to answer that question by tracking and comparing the impact of two intermittent fasting regimens on a group of participants.
Some study subjects were asked to only eat within a four-hour time window each day, others could eat within a six-hour window, and a control group was asked not to change up their diet at all. By the end of the 10-week experimental period, participants in both the four-hour and six-hour fasting groups had lost about 3% body fat.
These findings have led the study’s authors to conclude that both a four-hour time-restricted diet and a six-hour time-restricted diet are indeed capable weight loss avenues.
“This is the first human clinical trial to compare the effects of two popular forms of time-restricted feeding on body weight and cardiometabolic risk factors,” says corresponding study author Krista Varady, professor of nutrition at the UIC College of Applied Health Sciences, in a university release.
Study participants who were placed in the four-hour time-restricted group were only allowed to eat between the hours of 1 p.m. and 5 p.m each day. For those in the six-hour time-restricted group, that eating period stretched from 1 p.m. to 7 p.m. Control group participants were told not to attempt any weight loss at all, or change up their usual exercise/eating routine.
Now, participants placed in either of the fasting conditions were allowed to eat whatever they wanted during their assigned “eating hours,” but after that period they weren’t supposed to consume anything containing calories.
This went on for 10-weeks across all three experimental conditions, and all the while researchers kept track of various health markers (weight, oxidative stress, cholesterol, inflammation, blood pressure, insulin resistance).
Individuals in both fasting conditions ended up cutting their daily calorie intake by 550, all just by following the fasting guidelines. Moreover, by the end of the 10-weeks, fasting subjects had lost roughly 3% of their body weight. Fasting participants also enjoyed lower oxidative stress and insulin resistance in comparison to the control group.
“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,” Professor Varady adds.
However, fasting didn’t seem to produce any benefits regarding blood pressure, LDL and HDL cholesterol levels, and triglycerides.
Beyond the study’s broader findings, it was also quite noteworthy that the four-hour and six-hour fasting regimens didn’t seem to produce any significant weight loss differences. Both approaches yielded very similar weight loss benefits.
“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,” Professor Varaday concludes.
The full study can be found here, published in Cell Metabolism.