Time-restricted eating improves blood sugar control in adults at risk of type 2 diabetes regardless of time of day

Restricting the eating window to 8 hours a day significantly improves blood glucose control in adults at risk of type 2 diabetes irrespective of whether it is earlier or later in the day, according to a randomised crossover trial to be presented at this year’s Annual Meeting of The European Association for the Study of Diabetes (EASD), Madrid (9-13 Sept).

“Our study found that restricting eating to a window of 8 hours per day significantly improved the daily time spent in the normal blood glucose range and reduced fluctuations in blood glucose levels. However, altering the 8-hour restricted eating period to earlier or later in the day did not appear to offer additional benefits,” said lead author Dr Kelly Bowden Davies from Manchester Metropolitan University, UK.

She added: “Our findings, which can be attributed to the 16-hour fasting window rather than the time of eating or changes in energy intake, also highlight that the benefit of time-restricted eating can be seen within just three days. Although time-restricted eating is becoming increasingly popular, no other studies have examined tightly controlled diet and altered the clock time of an eight-hour eating window on glycaemic control in people at risk of type 2 diabetes.”

Previous studies indicate that TRE (which limits when, but not what, individuals eat) can improve insulin sensitivity (the body’s ability to respond to insulin) and glycated haemoglobin (HbA_1c; average blood sugar levels over a period of weeks and months) in people at risk of type 2 diabetes.

However, the effect on glycaemic variability (fluctuations in blood glucose levels) is not clear and previous studies have attributed the positive effects of TRE to reduced energy intake. This study sought to understand alterations in meal timing when participants were in energy balance (energy intake was matched with energy expenditure).

To find out more, researchers investigated the impact of TRE in a eucaloric manner—with diets provided to match energy requirements (taking into account sex, age, weight, height, activity level—comparing an early (E_TRE; between 8:00 and 16:00 hours) versus a late (L_TRE; between 12:00 and 20:00 hours) eating window on glycaemic control in overweight sedentary adults.

Fifteen sedentary individuals (9 female/6 male; average age 52 years; BMI 28 m/kg²; HbA_1c 37.9 mmol/mol) who habitually spread their eating period over more than 14 hours per day were assigned to two different eating patterns for 3 days at a time.

Researchers compared the E_TRE regimen (eating only between 8:00 am and 4:00 pm) and L_TRE regimen (eating only between midday and 8:00 pm) periods, and the habitual eating regimen (more than 14 hours/day). A eucaloric standardised diet [50% carbohydrates, 30% fat and 20% protein] was provided during the TRE periods but participants consumed their own diets during habitual (free) living conditions.

Continuous glucose monitoring was used to assess daily time spent in euglycaemia (with a normal concentration of blood glucose of 3.9-7.8 mmol/l) and markers of glycaemic variability, including mean absolute glucose (MAG), coefficient of variation (CV), and mean amplitude of glucose excursions (MAGE).

The analyses found that in comparison to habitual eating (more than 14 h/day), TRE (8 h/day) significantly increased time spent within the normal blood glucose range by on average 3.3%, and also reduced markers of glycaemic variability—MAG by 0.6 mmol/l, CV by 2.6%, and MAGE by 0.4 mmol/l.

However, no significant differences in glycaemic control were found between the E_TRE and L_TRE regimens.

“Many people find counting calories hard to stick to in the long term, but our study suggests that watching the clock may offer a simple way to improve blood sugar control in people at risk of type 2 diabetes, irrespective of when they have their 8-hour eating window, which warrants investigation in larger studies and over the longer term,” said Dr Bowden Davies.