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Maintaining lower blood glucose levels is an important preventive step against prediabetes. Maskot/Getty Images
  • Early time-restricted feeding is when a person limits their daily eating to the first 6 to 8 hours of the day.
  • Researchers say this eating pattern can help stabilize fluctuations in blood glucose levels and lower the risk of developing prediabetes.
  • Experts say one reason early time-restricted feeding is effective is that it allows for people to be physically active after they’ve finished eating for the day.

Early time-restricted eating (TRE) can improve fluctuations in blood glucose levels.

That’s according to a study presented today at the Endocrine Society’s annual meeting.

In their findings, which haven’t been published yet in a peer-review journal, researchers report that this form of intermittent fasting can also reduce the amount of time blood glucose levels are above normal levels.

“Our research shows that just one week of following this diet strategy reduces fluctuations in blood sugar levels and reduces the time that the blood sugar is elevated above normal levels,” Dr. Joanne Bruno, a study author and an endocrinology fellow at NYU Langone Health in New York, said in a press statement.

“This suggests early time-restricted feeding may be a helpful strategy for those with prediabetes or obesity to keep their blood sugars in a normal range and prevent them from progressing to type 2 diabetes,” she added.

Early time-restricted feeding is a form of eating that restricts eating to only the first 6 to 8 hours in the day.

To examine the impact of this method of dieting on blood glucose levels, the researchers developed a study in which they compared early time restricted eating with a usual diet pattern.

Ten participants who had prediabetes or obesity were allocated to either the early time restricted feeding group where they ate 80% of their calories before 1 p.m. or the usual feeding pattern group, where they ate 50% of their calories after 4 p.m.

They maintained this diet for 7 days before switching to the other method for the next week.

Study participants wore a continuous glucose monitor for the duration of the study. Additionally, they had their glucose tolerance tested before the study began and also at day 7 and day 14.

The researchers reported that the weight of the participants was stable for the full two weeks of the study. The early time restricted feeding way of eating led to a decreased time spent above the normal blood glucose range when compared with the usual eating pattern.

“Eating the majority of one’s calories earlier in the day reduces the time that the blood sugar is elevated, thereby improving metabolic health,” Dr. Bruno said.

The researchers said more studies are needed to determine if early time-restricted feeding could be used as an effective intervention strategy for improving blood glucose levels.

Dr. Pouya Shafipour, a family and obesity medicine physician at Providence Saint John’s Health Center in California, said the findings of the study aren’t surprising and support his own recommendations to patients.

“I’ve been recommending time restricted eating… since 2015. I also started practicing it myself. Studies show prolonged fasting and time restricted eating does help with insulin sensitivity and stabilizing blood sugar levels. So it puts the body in or extends the level of ketosis that we get into late at night. So the ketosis, in a sense, stabilizes blood sugar control more, and it prevents highs and lows, the peaks and valleys of blood sugar.”

— Dr. Pouya Shafipour, family and obesity medicine physician

Early time restricted feeding is just one form of intermittent fasting.

Other examples include the 5:2 diet, which involves eating normally for five days of the week and eating only 500 to 600 calories on two days of the week.

Another method is the 16:8 diet, which involves fasting for 16 hours and eating only within an 8 hour window.

Dr. Marilyn Tan, an endocrinologist at Stanford University in California, says a possible benefit to eating the majority of calories in the earlier part of the day is having the opportunity to be active after eating.

“In America at least, we eat the majority of our calories in the evening with dinner. Very frequently that’s our biggest meal of the day and then afterwards we’re sedentary, we sit down in front of the TV or the computer, and then we go to sleep, and don’t move for eight hours. So we don’t really have an opportunity to exercise and improve the insulin sensitivity after that,” she told Medical News Today.

“We don’t fully understand the mechanisms of the improved metabolic benefit of shifting that time-restricted eating to earlier in the day. But one possibility is just that we are more active during the day. And so if people are walking around more, doing more physical activity shortly after they eat that may improve the glucose response,” she added.

“This study suggests that it’s not just a time restriction, but it’s the timing of that time restriction that is causing a significant benefit. There hasn’t been a large randomized trial, but there have been other studies looking at this and there have been other studies that suggested that earlier time window… has metabolic benefits beyond just doing it later in the day.”

— Dr. Marilyn Tan, endocrinologist

Dr. Anne Peters, an endocrinologist at Keck Medicine of USC in California, says time-restricted eating can be beneficial for cardio-metabolic health, but it should be done under the direction of a physician.

“The human body is not meant to always be in the ‘fed state.’ We are meant to have periods of fasting and being a little bit ketotic (which happens with fasting) is good for the heart,” she told MNT.

“Time-restricted eating is medically safe under the direction of a physician. However, it is important not to get dehydrated so drinking non-sugary fluids is good,” Peters noted.

“These time-restricted eating approaches seem to work best if people are consistent, so they should choose the best time for themselves.”