Does intermittent fasting burn more fat?

No more than any other way of eating less. In a year-long trial, people on a calorie budget who ate only between 8 am and 4 pm lost about 18 pounds, and people on the same budget with no clock lost about 14. The gap was small enough to be chance. Fasting works when it helps you eat less.

Why it sounds like more

The idea is that long hours without food switch the body into burning fat. Over weeks, though, what decides the total is how much you ate against how much you burned, and that’s what the trials below measured.

An eating window is like a store’s opening hours. Shorter hours only cut spending if people don’t buy more while the store is open.

What the trials found

• With a calorie budget. In a 2022 trial in China, 139 adults with obesity cut calories for 12 months, and half also ate only between 8 am and 4 pm. They lost about 18 pounds against 14 (8.0 kg and 6.3 kg). The difference wasn’t statistically clear.
• Without a calorie budget. In TREAT (2020), 116 adults ate only between noon and 8 pm for 12 weeks. They lost about 2 pounds (0.94 kg), and the group eating normally lost about 1.5 (0.68 kg). In the 50 people measured in the clinic, the fasting group lost more lean mass from their arms and legs.

Who it suits

It suits people who would rather skip a meal than eat three small ones, and people whose extra calories come late at night. It doesn’t suit people who then overeat at the first meal, or anyone with a history of disordered eating.

What to do

• Try it for a month if it sounds easy for you, and judge it by your weekly average weight.
• Keep your protein up. Fewer meals means more protein in each to reach your total.
• Keep lifting, since the TREAT group lost more lean mass than the comparison group.