Early vs Late Fast Window: Is One More Effective?

MADRID — A daily 8-hour eating window controls blood glucose whether followed early or late in the day by people at risk for type 2 diabetes, showed a time-restricted eating (TRE) study presented at the European Association for the Study of Diabetes (EASD) 2024 Annual Meeting.

The study, examining shifting the time of day for the 8-hour eating window along with a tightly controlled diet, found that 8 hours of TRE — whether early or late in the day — led to a significant improvement in the time spent within a normal daily blood glucose range and in glycemic variability.

“We didn’t show a benefit in terms of early versus late TRE, but we did show a benefit of time-restricted eating within a window of eight hours per day,” said study lead Kelly Bowden Davies, MSc, PhD, from Manchester Metropolitan University, Manchester, England, when presenting the work. “It doesn’t matter when you restrict eating, but if you restrict it to eight hours then, according to our study, it benefits glycemic control in people at risk of type 2 diabetes.”

The researcher added that the effect was seen after only 3 days, and “demonstrates its therapeutic role in adults at risk of type 2 diabetes, which warrants investigation in the longer term.”

The current study examined the effect of shifting the time of day for the TRE window from early (8 am-4 pm) to late (12:00 pm-8 pm) in people at risk of developing type 2 diabetes due to a lifestyle characterized as sedentary and poor diet.

Previous studies indicate that TRE, which limits when, but not what, individuals eat, can improve insulin sensitivity and A1c in people at risk for type 2 diabetes.

But Bowden Davies pointed out that the effect of TRE on glycemic variability remained unclear. While prior work had attributed the positive effects of TRE to reduced energy intake, this study provided a diet where energy consumption matched energy expenditure — taking into account sex, age, weight, height, and activity level, termed a “eucaloric” diet.

“Some research groups recognize that if we manipulate the time at which we eat, then we can better align with circadian metabolic rhythms to improve whole body insulin sensitivity and glycemic variability,” explained Bowden Davies. “It may be that eating in the morning may be better aligned [with circadian rhythms] and cause greater improvement in glucose control.”

Three-day TRE plan led to blood glucose control

In a cross-over study design, all 15 participants were randomized to follow the early and late TRE regimens with a 7-day washout period in the middle. Participants had a mean body mass index (BMI) of 27.7 kg/m², a mean waist circumference of 73 cm, were sedentary, and followed a poor diet.

“Participants were normoglycemic so had good glucose control, but due to having overweight and obesity, they are considered as having risk factors for the development of type 2 diabetes,” noted Bowden Davies.

Before the TRE period, participants provided researchers with a dietary record. If they started on the early TRE, they crossed over to the late TRE after the washout period, and vice versa, she explained.

Continuous glucose monitoring (FreeStyle Libre 2, Abbott Laboratories) was carried out across the study to assess the daily time spent in euglycemia (3.9-7.8 mmol/l) and provide markers of glycemic variability, including mean absolute glucose, coefficient of variation, and mean amplitude of glucose excursions. Blood draws both pre- and post-TRE period provided biochemical measurements, and anthropometric readings were also taken.

There were nine female participants, with a mean age of 52 years, a BMI of 28 m/kg², and an A1c level of 37.9 mmol/mol (5.6%). They tended to snack across an eating period of 14 hours per day or more (habitual eating). They were assigned to two different investigational eating patterns for 3-day durations: Early or late, and these findings were compared with those from participants who continued their habitual eating.

Participants were provided with a eucaloric, standardized diet [50% carbohydrates, 30% fat, and 20% protein] to be eaten during the TRE period, whereas they ate as usual (ie, as and what they wanted) when not on the TRE regimen.

No changes were seen in the biochemistry markers assessed. “Given they only followed the TRE for three days, this is unsurprising,” remarked Bowden Davies. “We did see weight loss after only three days of TRE of around 1.1 kg across the two interventions,” she reported.

Referring to the early vs late TRE regimen, she added that “we didn’t see a benefit (no significant differences in glycemic control) of early compared with late TRE, but we did see a benefit of restricting the eating window to eight hours per day, so both conditions (early and late TRE regimens) had a benefit on glucose control.”

Variables of blood glucose control were also reduced while on the TRE regimen compared with habitual eating (more than 14 h/day), with significantly increased time spent within the normal blood glucose range on average by 3.3%, and also reduced mean absolute glucose by 0.6 mmol/l, coefficient of variation by 2.6%, and mean amplitude of glucose excursions by 0.4 mmol/l.

“Within three days, this is quite striking,” Bowden Davies pointed out.

She added that these data were interim analyses, but “these are positive in terms of participants seeing a benefit in glucose control and glycemic variability, which is a risk factor for developing type 2 diabetes but also for microvascular complications. We also saw improved time in range in terms of tight glucose control.”

“Even in three days, there were small, subtle differences which are subclinical — but this is not a clinical cohort. The results are statistically significant and a promising piece of data to suggest a feasible intervention that could be translated across different populations,” she said, adding that over a longer time period, changes between TRE timing might show changes in people at risk for type 2 diabetes who don’t have compromised circadian rhythms.

Moderating the session was Lutgarda Bozzetto, MD, from the University of Naples Federico II, Naples, Italy. She told Medscape Medical News, “It’s a hot topic right now, and the finding that there’s no difference in the time of day when the restricted eating is done suggests that in people at risk of diabetes, the hormonal flux and cycle involved in blood glucose control is not so strong or sensitive.”

Using a continuous glucose monitor, they can look at their blood glucose levels after eating, and this might “be powerful in guiding behavioral change,” said Bozzetto.

Abbott Laboratories funded the continuous glucose monitoring. Neither Bowden Davies nor Bozzetto had any other relevant financial disclosures.