• Posted October 30, 2023

Fasting Diets Beat Low-Cal Regimens for Folks With Diabetes

Time-restricted dieting may be a better way for people with type 2 diabetes to lose weight than counting calories, a new study suggests.

Researchers found that people who only ate between noon and 8 p.m. each day lost more weight than those who reduced their calories by 25%. Both groups, however, had similar reductions in long-term blood sugar levels based on a test of hemoglobin A1C. The test shows blood sugar levels over the past three months.

"It's important to give people with type 2 diabetes more than one strategy to lose weight and decrease their HbA1C," said lead researcher Krista Varady, a professor of nutrition at the University of Illinois, Chicago.

"Some people find it difficult to count calories. Others don't have weekly or monthly support and they need a dietary pattern that is simple to follow, such as watching the clock," Varady added.

In the United States, about 1 in 10 U.S. residents has diabetes, and that number is rising, the researchers said. It's crucial to find more ways to control weight and blood sugar levels for these patients.

While the study represents a "proof of concept" showing that time-restricted eating is safe for those with type 2 diabetes, Varady said people with diabetes should consult their doctor before starting this sort of diet.

Also, "some medications for type 2 diabetes will lower blood sugar and need to be taken with food," she said.

But the positive effect of weight loss on lowering blood sugar should enable people to reduce their diabetes medications, Varady said.

"Individuals with type 2 diabetes usually have to increase their medication throughout their lifetime, often taking three oral medications at one time since most medications decrease HbA1C only a little," she noted. "Being able to improve their glucose through just lifestyle is very important for reducing medication burden."

For the study, Varady and her colleagues divided 75 people into three groups: One group followed a time-restricted diet, another was told to cut calories by a quarter and the others followed neither diet plan. Average BMI (body mass index) was 39, which is considered obese. Average HbA1C was 8.1% (the normal range is 4% to 5.6%, according to the National Institutes of Health).

After six months, the researchers found those on the time-restricted diet lost about 4% of their body weight, while those who restricted calories lost about 2% of their body weight. Both groups lowered their blood sugar by about 1%.

Whether following a time-restricted diet will result in continued weight loss over a longer time isn't yet known, Varady said, noting larger studies are needed.

"This is the first study comparing an eight-hour time-restricted diet to calorie counting in those with type 2 diabetes," she said. "Our findings will hopefully give doctors and dietitians confidence to implement time-restricted eating in individuals with diabetes who need an alternative diet to help with weight loss and blood sugar management."

Imran Syed, a New York expert not part of the study, thinks time-restricted dieting may be easier to follow than calorie counting.

"I've dealt with patients where mostly it's always been caloric restricted," said Syed, a dietitian at North Shore University Hospital in Manhasset. "Caloric restriction has also been short-lasting, because it's a behavioral control over eating whereas time restriction is something more approachable, where time can be easier to control," he said.

A diet style that is easier to follow means that patients are more likely to adhere to it, he said.

"The time restriction seems to be a better approach. It is something I would advise while taking medication management into consideration so blood sugar doesn't drop too low," Syed said.

The report was published online Oct. 27 in the journal JAMA Network Open.

More information

For more on type 2 diabetes, see the U.S. Centers for Disease Control and Prevention.

SOURCES: Krista Varady, PhD, professor, nutrition, University of Illinois, Chicago; Imran Syed, RD, North Shore University Hospital, Manhasset, N.Y.; JAMA Network Open, Oct. 27, 2023, online