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Intermittent Fasting Revisited
...the authors performed an umbrella review of meta-analyses of randomized controlled trials of Intermittent Fasting vs. either Continuous Calorie Restriction or usual diet.
More evidence against intermittent fasting
Today's research is another small study, this time carried out in the UK and analyzed by an international team of researchers....
Does intermittent fasting improve weight loss?
In a study performed in Brazil, 58 women with an average age of about 31 and an average Body Mass Index of 33 (clinically obese) took part in a short-term diet designed to reduce caloric intake for just 21 days.
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We've reported on quite a few studies looking at the idea of time restricted eating (also called intermittent fasting) as a weight loss strategy. So far the evidence shows that there's no significant difference in the amount of weight lost between cutting calories overall versus intermittent fasting. Worse yet, those practicing intermittent fasting lost both muscle mass and body fat while those cutting calories lost mostly body fat.
But what if you did both?
Researchers at Southern Medical University in Guangzhou, China, teamed up with colleagues at Tulane University School of Public Health and Tropical Medicine to design a study to compare the effects of cutting calories - while also restricting when you eat - with simply cutting calories (NEJM 386;16:1495-1504).
The team in China recruited 118 men and women with clinical obesity to participate in their 12-month program. The male participants were instructed to consume 1500-1800 calories per day and the female participants were to consume 1200-1500 calories per day. All participants were to consume approximately 40-55% of calories from carbohydrates, 15-20% from protein, and 20-30% of calories from dietary fat.
To help the participants stick to their caloric goals, they were provided with a protein shake to consume on a daily basis for the first 6 months and received diet counseling throughout the study.
The participants were randomly assigned to a time-restricted-eating group (only consuming calories between 8am and 4pm local time) or the control group (no time restriction).
To make sure they were complying with the study's requirements, for the first six months of the study the participants kept a daily food diary, photographed everything they ate with a time stamp through a special app, and had individual meetings with a health coach every two weeks.
During the second six months of the study the participants kept a food diary and photographed their food three days per week and met with a health coach once a month.
At the close of the study the authors compared not only the amount of weight the participants in each group lost, but also measured body fat and lean mass, comparing the measures to readings taken at the start of the study.
There were no clinically significant differences between the two groups: the time-restricted-eating group lost an average of 8kg (about 17.6 pounds) while the control group lost an average of 6.3kg (about 13.9 pounds).
Similarly, those on the time-restricted diet lost about 5.9kg of body fat (about 13 pounds) while the control group lost 4.5kg body fat (9.9 pounds). Changes in blood pressures, fasting glucose levels, and cholesterol scores were also similar between the two groups.
The authors conclude, "our data suggest that caloric intake restriction explained most of the beneficial effects of a time-restricted eating regimen." That is, the results for both groups were likely due to cutting calories, not limiting when they ate.
May 25, 2022