Early time-restricted eating improves glucose tolerance

Key takeaways:

• An early time-restricted intermittent fasting diet was linked to greater glucose tolerance vs. caloric restriction.
• The greater benefits of fasting were observed at 6 months but lost at 18 months.

People on a time-restricted intermittent fasting diet, eating only between 8:00 a.m. and 12:00 p.m. for 3 days per week, had greater improvements in glucose tolerance at 6 months than those on a restricted caloric diet, data show.

The results of the randomized clinical trial were recently published in Nature Medicine.

“This is the largest study in the world to date and the first powered to assess how the body processes and uses glucose after eating a meal, which is a better indicator of diabetes risk than a fasting test,” Xiao Tong Teong, a PhD student at the University of Adelaide in Australia, said in a press release.

Though caloric restriction (CR) has become an established diet for weight management and type 2 diabetes prevention, the researchers wrote that prior literature has found intermittent fasting to be an equivalent strategy, with it potentially having a greater impact on insulin sensitivity and lipid metabolism than CR. Furthermore, time-restricted eating has been shown to lead to greater reductions in weight and BP than CR.

Thus, Teong and colleagues compared the two strategies as well as standard care in a three-armed randomized controlled trial that involved 209 Australian participants at risk for developing type 2 diabetes.

Among the participants (57% women; mean age, 58 years), 85 were randomly assigned to intermittent fasting plus early time-restricted eating (iTRE), 83 were randomly assigned to CR (n = 83) and 41 were randomly assigned to standard care.

Those in the iTRE group were instructed to consume 30% of calculated baseline energy requirements between 8:00 a.m. and 12:00 p.m., followed by a 20-hour fasting period for 3 nonconsecutive days a week.

Meanwhile, CR participants were instructed to restrict 30% of their calculated baseline energy requirements daily. They were also given a menu that included one meal replacement each day “to aid adherence and to ensure adequate nutrient intake,” the researchers wrote.

Teong and colleagues found that at 6 months, iTRE participants had a greater postprandial glucose area under the curve (AUC) of -10.1 (95% CI, -14.08 to -6.11) compared with CR participants (AUC = -3.57; 95% CI, -7.72 to 0.57).

However, “the increased health benefits in the active intervention groups were also lost by 18 months,” they wrote, pointing out the loss of participants by that time was partly to blame.

Both CR and iTRE showed greater reductions in systolic BP at 2 months compared with standard care, with only CR having a greater reduction at 6 months.

iTRE and CR also had greater reductions in diastolic BP, body weight and fat mass at 6 months compared with standard care. Total cholesterol and low-density lipoprotein were lower in the iTRE group compared with the standard care group at the 6-month mark.

Teong and colleagues wrote out that adverse effects were mild through the study period but reports of fatigue were higher for iTRE than CR, “which might increase difficulty in maintaining iTRE.”

They added that future studies “should investigate whether intermittent prescription of a longer daily eating window retains the benefit of iTRE versus CR, and if these interventions are more sustainable long-term.”

The study limitations included CR and standard care participants not being instructed on meal timing, which possibly reduced differences between the groups, and participants being able to change their weight maintenance plan at a 12-month follow-up, which hampered the clinical implications of that period, according to the researchers.

“The results of this study add to the growing body of evidence to indicate that meal timing and fasting advice extends the health benefits of a restricted calorie diet, independently from weight loss, and this may be influential in clinical practice,” Teong said.

References:

• Fasting diet reduces risk markers of type 2 diabetes. https://www.newswise.com/articles/fasting-diet-reduces-risk-markers-of-type-2-diabetes. Published April 6, 2023. Accessed April 6, 2023.
• Teong X, et al. Nat Med. 2023;doi:10.1038/s41591-023-02287-7.