Intermittent Fasting Helps People with Type 2 Diabetes Lose Weight, Control Blood Sugar

A woman checks her blood sugar at a table.
A study found that eating during an 8-hour window may help people with type 2 diabetes. Caíque de Abreu/Getty Images
  • People with type 2 diabetes who limited their eating to an eight-hour window each day lost more weight than those who intentionally reduced their calorie intake
  • This approach, known as time-restricted eating or intermittent fasting, still led to a decrease in how many calories people ate, even without calorie counting.
  • Experts suggest that people interested in time-restricted eating talk to their doctor first and find dietary and accountability support.

Eating only during an 8-hour window each day can help people with type 2 diabetes lose weight and control their blood sugar levels, according to a new study.

This approach, known as time-restricted eating or intermittent fasting, was easier for patients to stick with than intentionally reducing their calorie intake, another common recommendation for people with type 2 diabetes.

People in the study who did time-restricted eating also ate fewer calories each day, without having to count calories and while being able to eat whatever they wanted.

“This study shows that [time-restricted eating] can be as good as or better than the traditional advice we give people, which is to count every calorie you eat,” said Dr. Adam Gilden, an associate professor at the University of Colorado Anschutz Medical Campus, who was not involved in the new study.

Greater weight loss with fasting

The study, published Oct. 27 in JAMA Network Open, included 75 participants, who were randomly assigned to do one of three interventions for six months.

People in the time-restricted eating group could eat whatever they wanted between noon and 8 pm each day. The rest of the time, they were allowed to drink water or any other zero-calorie beverage.

Study author Krista Varady, PhD, a professor of nutrition at the University of Illinois Chicago, said this particular eating window helps people stick with the fasting regimen, which supports weight loss.

“We chose 12 pm to 8 pm so people could continue to eat dinner with their family or attend social events in the evening,” she told Healthline. “It’s difficult to socialize if the eating window is placed too early in the day.”

People in the time-restricted eating group lost more weight over six months than participants who were asked to reduce their daily calorie intake by one-quarter.

On average, people in the time-restricted eating group lost 4.3% of their weight, which was slightly greater than the amount lost by participants in earlier trials who restricted their eating to an 8- or 10-hour window. Those earlier trials, though, were less than 6 months long.

This amount is also similar to the 5.2% weight loss in one study of people who did a year of the Diabetes Prevention Program, a lifestyle change program that involves healthy eating, physical activity and learning to deal with stress. This program is covered by Medicare.

In contrast, people in the new study who cut their daily calorie intake by one-quarter lost about 1.75% of their weight over six months.

Calorie restriction is a common recommendation for people with type 2 diabetes to help them lose weight. But it can be challenging because it requires people to track their calories.

Participants in the new study who did calorie restriction met with a dietitian at the start of the study to develop a weight loss plan. They also used an app to track the foods they ate each day.

Those in the study’s third group, known as the control group, were instructed to maintain their weight and usual eating habits.

All participants were asked to keep their usual physical activity habits during the study. 

Small blood sugar improvement

Researchers also found that people who did time-restricted eating or calorie restriction had similar reductions in their long-term blood sugar levels, as measured by the hemoglobin A1C (HbA1c) test

In both groups, the HbA1c level decreased on average by about 0.7 percentage points from the start of the study.

“This [decrease] is pretty major,” said Varady, pointing out that both groups started with an average HbA1c of around 8. 

“So if they continued the [time-restricted eating] diet for up to a year, they might actually achieve diabetes remission,” she said.

Diabetes remission is when HbA1c levels are below 6.5% for at least 3 months after someone stops their diabetes medication.

People in the time-restricted eating group also had an easier time following the regimen. Over the 6 months, those in this group stuck with the 8-hour eating window on 87% of the days.

In contrast, the calorie restriction group met their daily calorie target 68% of the time.

Participants did not report any serious adverse events during the study. Also, occurrences of low blood sugar (hypoglycemia) and high blood sugar (hyperglycemia) were similar among all three groups.

Just over half the participants in the study were Black and another 40% were Hispanic. In the United States, rates of diabetes are highest among these groups, according to the Centers for Disease Control and Prevention.

Support can help people succeed

The study was small and will need to be followed by larger, and possibly longer-term, ones. But it shows that time-restricted eating may be an effective and easily accessible approach for people with type 2 diabetes to lose weight and help control their blood sugar level.

Varady recommends that anyone trying this approach talk with their doctor first to see if they need to make adjustments to their diabetes medications.

While more research on time-restricted eating is needed, “it’s something that patients can start doing now, if they have some support,” Gilden told Healthline.

In the study, this support included weekly meetings with a dietitian for the first three months, and biweekly meetings afterwards.

“I’m not saying patients shouldn’t try it on their own,” said Gilden. “But I think the best chance of success is if you have somebody working with you.”

Dietary counseling — such as from a dietitian or nutritionist — can help people improve their diet quality. 

“It’s not just, ‘I’m going to eat during an eight-hour window each day,’” said Gilden. “It’s also a matter of what you eat during those eight hours. And that’s where the dietitian comes in.”

Another benefit of the regular meetings with a dietitian was keeping people on track.

“With any diet, I think it’s best to either find a healthcare professional to keep you accountable, or to join a weight loss support group,” said Varady.

Takeaway

A new study found that people who did time-restricted eating, also known as intermittent fasting, lost more weight than those who reduced their daily calories by one-quarter.

Both groups saw similar improvements in their long-term blood sugar levels, as measured by the HbA1c test. Experts say this small improvement is still significant and may lead to better blood sugar control over time.

People in the study had frequent visits with a dietitian, which can be helpful, but time-restricted eating can be done without that extra support. However, experts recommend that people with type 2 diabetes talk to their doctor before trying this approach.

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