It’s a diet trend endorsed by everyone from Hollywood A-listers to Rishi Sunak, yet intermittent fasting doesn’t work for everyone.
Now scientists say they’ve found a way to boost its effects — focusing on what you eat, rather than when you eat.
Specifically, a group of US researchers discovered the diet is only effective for weight loss and stabilising blood sugar when people doing it eat fewer calories than they need.
In other words, the amount of calories you consume matters more than the timing.
Obese people who stuck to a 10-hour eating window from 8am to 6pm, eating most of their calories in the morning, lost 2.3kg (5.1lbs) on average over 12 weeks.
For comparison, volunteers who ate between 8am and midnight, consuming the majority of calories in the evening, lost 2.6kg (5.7lbs).
Both sets of volunteers stuck to an expert-recommended diet that featured a balance of fruit and vegetables, whole grains and no junk foods, with little saturated fat.
Nisa Maruthur, study co-author and an associate professor of medicine at Johns Hopkins University, said: ‘It makes us think that people who benefit from time-restricted eating — meaning they lose weight — it’s probably from them eating fewer calories because their time window’s shorter and not something else.’
Jennifer Anniston, Chris Pratt and Kourtney Kardashian are among the Hollywood A-listers to have jumped on the fasting trend since it shot to prominence in the early 2010s.
But, despite swathes of studies suggesting it works, experts remain divided over its effectiveness and the potential long term health impacts.
Some argue that fasters usually end up consuming a relatively large amount of food in one go, meaning they don’t cut back on their calories — a known way of beating the bulge.
They even warn that it may raise the risk of strokes, heart attacks or early death.
The researchers analysed data from 41 participants, aged 59 and with a BMI of 36 on average.
At the beginning of the study, the researchers assessed participants’ history and activity level to estimate baseline caloric needs.
The participants received prepared meals with identical macronutrient and micronutrient compositions.
They ate the same number of calories daily throughout the study.
During the eating windows, the trial didn’t limit beverages if they were calorie- and caffeine-free.
Participants were also each allowed one cup of coffee, diet soda and alcoholic beverage per day. Outside the designated time periods, only water was allowed.
After 12 weeks, the scientists also discovered there were no real differences in fasting glucose, waist circumference, blood pressure, or lipid levels.
Writing in the journal Annals of Internal Medicine, the researchers said: ‘Time restricted eating did not decrease weight or improve glucose homeostasis relative to a usual eating pattern.
‘This suggests that any effects of time restricted eating on weight in prior studies may be due to reductions in caloric intake.
