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Intermittent fasting lowers HbA1c levels and reduces weight in diabetes

An easier alternative to calorie-restricted diets.

Pippa Wysong

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Intermittent fasting lowers hemoglobin A1c (HbA1c) in people with type 2 diabetes (T2D) and helps with weight loss. 

Many patients don’t stick to a calorie restricted diet because calorie intake must be constantly monitored. Yet with the increasing rates of diabetes, “innovative lifestyle strategies to treat T2D are critically needed,” said researchers in JAMA Network Open.

Time-restricted eating (TRE) is increasingly popular. This entails limiting daily food intake to 6 to 10 hours and then fasting for the rest of the day. Studies show the approach reduces energy intake by 200 to 500 kcal per day. Plus, people can eat freely during a large part of the day leading to greater adherence. Few studies have looked at diabetics.



A six-month, parallel-group, randomized trial was conducted between January 2022, and April 2023. It included 75 participants, 71% female. They had a mean age of 55 years and ranged in age from aged 18 to 80 years. Inclusion criteria included a diagnosis of T2D, HbA1c levels between 6.5% and 11.0%, and body mass index (BMI) between 30 and 50.

Participants were randomized to one of three groups: TRE, a calorie-restricted diet, or control group. 

The TRE group could eat between 12:00 p.m. and 8:00 p.m. daily, and fasted from 8:00 p.m. to 12pm. There were no food restrictions. 

People in the CR group were instructed to reduce their energy intake by 25% of their baseline energy needs each day. They were also helped with developing personalized weight loss meal plans, and logged their daily food intake into an app.

All three groups met with a study dietitian at regular intervals, and wore a continuous glucose monitor for 10 days at baseline, and again at months three and six.

By month six, mean body weight and fat mass both significantly decreased in the TRE group, but not the CR group, relative to controls. 

“Both TRE and CR led to reductions in waist circumference by month 6, but not lean mass or visceral fat mass, compared with controls. Relative to controls, BMI decreased in the TRE group by month 6, but not the CR group.

Mean HbA1c levels were reduced about the same amount in both the TRE and CR group, relative to controls. 

“Our findings also show that TRE is safe in patients who are using either diet alone or medications to control their T2D. However, for people using sulfonylureas and/or insulin, adopting a TRE regimen will require medication changes and regular monitoring, particularly in the initial stages of the diet,” the study said.




PV Mayer

Dr. Perry Mayer is the Medical Director of The Mayer Institute (TMI), a center of excellence in the treatment of the diabetic foot. He received his undergraduate degree from Queen’s University, Kingston and medical degree from the Royal College of Surgeons in Ireland.