Popular for weight loss, intermittent fasting may help with diabetes too

Intermittent fasting is enjoying a moment in American households — by some accounts nearing the popularity of calorie counting and plant-based diets.

The appeal?

Research suggests that simply having less time to eat can lead people to cut down on how much they ultimately consume, without the rigmarole of watching each calorie.

Now, new research bolsters the case that intermittent fasting — specifically limiting when you eat to a given window of time during the day — can be a safe and effective strategy for managing Type 2 diabetes.

The study, published on Friday in JAMA Open, finds people with Type 2 diabetes can successfully shed weight and manage their blood sugar by eating only within an 8-hour window each day.

"I think this is pretty exciting data," says Dr. Joanne Bruno, an endocrinologist at NYU Langone Health who wasn't involved in the trial.

While it's still an emerging field, a growing number of clinical trials have shown time-restricted eating can improve metabolic health and deliver weight loss. But few of these studies have focused specifically on Type 2 diabetes.

The findings add evidence that time-restricted eating has potential for helping those with high blood pressure, elevated blood sugar and other problems affecting cardiovascular and metabolic health, says Dr. Pam Taub, a cardiologist at the University of California San Diego.

"I think you get the most bang for the buck with this type of population," says Taub, who also has published studies on time-restricted eating.

An easier alternative

The study, based at the University of Illinois Chicago, ran for six months and included 75 adults with Type 2 diabetes.

The study authors say it's the first randomized controlled trial directly comparing time-restricted eating to counting calories in patients with Type 2 diabetes, looking at effects on body weight and A1C, a test that shows blood sugar levels over the past three months.

Overall, the study found that time-restricted eating led to about the same improvements as calorie-counting in A1C levels. Both groups had a drop of over 0.7% from baseline over the course of six months.

Given that most medications used for diabetes will reduce that number by about 1%, Bruno says this represents a "significant change and can have meaningful clinical benefits."

The difference in weight loss was the most remarkable result.

Those who only ate between 12 p.m. and 8 p.m. ended up losing nearly double the amount of weight as those who counted their calories.

"I was surprised," says Krista Varady, a professor of nutrition at the University of Illinois and the study's lead author. She notes her previous studies have shown the same amount of weight loss as calorie counting, not more.

"They didn't need to count calories or carbs or anything like that," she says, "They ended up reducing their calorie intake just by eating in that 8-hour window."

The study included three arms: the controls who made no changes to their diet, those who were instructed to count calories and reduce their intake by about 25%, and the time-restricted eating group.

On average, those who kept their eating to an 8-hour window shed about 10 pounds and lost more fat than the calorie counting group, which dropped a total of about 6 pounds.

Varady says they picked the noon to 8 p.m. window because observational studies show that's when most people who do intermittent fasting prefer to eat.

"They really found time-restricted eating to be a nice, refreshing alternative," she says.

Many study participants said in interviews they had spent years being advised to count calories and were disillusioned with the approach, says Varady.

Benefits go beyond weight-loss

Despite being the largest clinical trial to date on Type 2 diabetes, it's still considered "fairly small," but it was well-performed, says Benjamin Horne, an epidemiologist at the Intermountain Heart Institute in Salt Lake City and an adjunct professor at Stanford University.

"I would say it's the best study in that population to date, so I think we can be confident that there are potential benefits," he says.

Indeed, Varady and her co-authors acknowledge it needs to be followed up with larger trials and caution that the findings on weight loss shouldn't be interpreted as proving that time-restricted eating is better.

"It's not a one diet fits all approach," she says. "We're just showing that time-restricted eating is another option."

Horne points out some of the study's strengths. It included a diverse patient pool: A majority of the participants were Black and about a third were Hispanic. And those who did the time restricted eating had good adherence, sticking to the 8-hour window on average about six out of seven days a week.

Finally while the weight-loss groups did meet with dietitians regularly, the study offered a practice that people can replicate even if they're not in a clinical trial.

"It's very easy to do a fasting regimen," he says, "You don't need a prescription to do it. It doesn't cost anything."

In an era of blockbuster weight-loss and diabetes drugs, Taub says the study adds to the evidence that this lifestyle intervention can also help.

"It's not one or the other," says Taub, "One of the things that I strive for with my patients with Type 2 diabetes is how do I minimize the pharmacotherapy and maximize the lifestyle?"

In fact, Taub's work has shown that for people with metabolic syndrome, a 10-hour eating window not only improves their ability to manage blood sugar, but also reduces other metrics like blood pressure and cholesterol.

A study on shift workers has found that intermittent fasting, even if it's done late in the evening, can still confer benefits. "It's about giving your body that fasting period, that metabolic rest," she says.

What research suggests, she says, is that time-restricted eating can offer metabolic benefits above and beyond what'd you'd expect simply from losing a given amount of weight.

For those with Type 2 diabetes though, Taub and Bruno say patients should not take up intermittent fasting without medical supervision.

For example, in the JAMA Open study, some participants needed to have their medications adjusted depending on their blood sugar test.

Bruno says concerns about hypoglycemia from fasting appears to be one reason there haven't been more studies on people with Type 2 diabetes till now.

While there are still lingering safety questions that need to be studied, especially for those taking insulin, she says overall it does seem to be safe and effective.

And increasingly it's a tool that she offers her patients.

"Many do feel liberated in some ways by this dietary strategy," she says. "I'm hopeful that time-restricted feeding will get its due."

Carmel Wroth edited this story. [Copyright 2023 NPR]