Experts debate whether early or late time-restricted eating confers more benefits
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Key takeaways:
- Early time-restricted eating may offer more cardiometabolic benefits than late time-restricted eating.
- Adherence to late time-restricted eating may be better due to cultural norms.
SAN DIEGO — Early time-restricted eating may confer more cardiometabolic benefits for adults than late time-restricted eating, but a later eating window may result in better adherence, according to two speakers.
During a debate at the American Diabetes Association Scientific Sessions, Courtney M. Peterson, PhD, MS, MSc, MASt, associate professor in the department of nutrition sciences at the University of Alabama at Birmingham, said mechanistic and clinical research have shown eating earlier in the day may be more beneficial than eating later. She cited studies that revealed adults have better glucose tolerance, lower insulin resistance and lower fasting glucose when eating earlier in the day.
“The circadian system produces daily rhythms in our metabolism ... including insulin sensitivity, insulin secretion, the thermic effect of food, repetitive hormones, appetite [and] adipose tissue gene expression,” Peterson said during the debate.
Kelsey Gabel, PhD, RD, assistant professor of nutrition at the University of Illinois Chicago, said she agreed with Peterson that early time-restricted eating may offer better cardiometabolic benefits than late time-restricted eating. However, she said some studies have shown the timing of time-restricted eating is not associated with differences in cardiometabolic metrics. Additionally, she said a later eating window may lead to better time-restricted eating adherence, which is a big challenge for adults trying to achieve weight loss.
“Individuals should place the eating window where it best fits [for them] so that they achieve calorie restriction,” Gabel said.
Early time-restricted eating linked to better cardiometabolic benefits
Research showing the benefits of eating early dates back decades, according to Peterson. A study conducted shortly after the development of the oral glucose tolerance test showed glucose tolerance was better in the morning than at later times in the day.
Peterson said findings were similar in a study conducted at her lab and published in the Journal of Diabetes and Its Complications in 2014. The study analyzed 3-hour OGTTs that were conducted at either 7 a.m. or 7 p.m. for adults with prediabetes.
“What we found is that glucose tolerance was worse in the evening than it is in the morning,” Peterson said. “We also looked at insulin levels, and we found delayed release or secretion of insulin levels when we eat in the evening. And we were able to trace this back to insulin sensitivity and beta-cell function. Insulin sensitivity tends to be lower in the evening as well as beta-cell responsiveness.”
Peterson reviewed clinical research on studies that changed calorie distribution to earlier in the day as well as ones that changed meal times to earlier in the day. In a randomized controlled trial published in Obesity in 2013, 93 women with overweight were randomly assigned to eat a large breakfast and small dinner or a small breakfast and large dinner. In the study, the large breakfast group lost more weight and reported less hunger than the small breakfast group.
A study published in JAMA Internal Medicine in 2022 examined the effects of early time-restricted eating among adults with obesity. The intervention group had an eating window between 7 a.m. and 3 p.m. compared with a control group with normal eating window of 12 hours or more. The early time-restricted eating group lost more weight than the control group.
An analysis of seven studies showed that early time-restricted eating may produce more cardiometabolic benefits than midday or late time-restricted eating. Peterson said there are a few mechanisms that may explain those findings. In a study published in Cell Metabolism in 2022, researchers found eating later is associated with higher subjective hunger and ghrelin-to-leptin ratio compared with eating earlier. Eating later in the day was also associated with decreased energy expenditure and increased fat storage gene expression.
Despite some evidence revealing the benefits of early time-restricted eating, more studies need to analyze whether eating early could result in more weight loss, according to Peterson. She said larger and longer-term studies are also needed on early time-restricted eating.
“Early time-restricted eating appears to improve both glycemic control and blood pressure more than practicing time-restricted eating by eating in the middle of the day, again suggesting that eating early in the day has benefits,” Peterson said. “I will acknowledge the data are a little bit mixed right now on whether it’s superior for weight loss.”
Adherence may be better with late time-restricted eating
Gabel said some studies have shown benefits for time-restricted eating, but others point to no difference in cardiometabolic outcomes between early and late time-restricted eating.
Gabel questioned whether eating breakfast makes a difference in weight-loss outcomes. In a study published in the American Journal of Clinical Nutrition in 2014, adults who wanted to lose weight were randomly assigned to skip breakfast, to eat breakfast or to a control group with no requirement to eat or skip breakfast.
“This data suggests that weight loss is the same, regardless of the timing of the first meal intake,” Gabel said. “And the individuals do not eat more just by skipping that breakfast meal.”
Similar findings were observed in studies examining late time-restricted eating. Focusing on studies that permitted ad libitum eating in free-living conditions, Gabel said an analysis of nine studies showed that late time-restricted eating or time-restricted eating with a self-selected window results in a 1% to 5% weight loss for participants. Additionally, Gabel said time-restricted eating is associated with reductions in BP and improvement in glucoregulatory factors, regardless of timing, though she cautioned there are limitations with many of the studies and that larger and longer-term studies are needed.
Four studies comparing early time-restricted eating and late-time restricted eating were examined. Across the trials, there were no differences in weight loss and cardiometabolic risk factors. One of the studies, published in Current Developments in Nutrition in 2020, found adherence was higher among adults performing late time-restricted eating vs. early time-restricted eating.
Beyond cardiometabolic benefits, Gabel said, late-time restricted eating aligns better with the cultural norm of families and friends joining together for evening dinners. She cited four studies that revealed the biggest barriers to time-restricted eating are social commitments, work schedules, family lifestyle and occasions of holidays, vacations and cultural significance.
“In order to make the greatest impact, we really need to meet people where they are at,” Gabel said during the debate. “Based on the current data, late time-restricted eating results in similar benefits in its truest form. It supports social norms in the U.S., and it still results in cardiometabolic benefits. We have decades of evidence that calorie restriction works, but the hard part for weight loss and weight maintenance is consistency and adherence. You need both and late time-restricted eating offers that.”
References:
- Dhurandhar EJ, et al. Am J Clin Nutr. 2014;doi:10.3945/ajcn.114.089573.
- Jakubowicz D, et al. Obesity. 2013;doi:10.1002/oby.20460.
- Jamshed H, et al. JAMA Intern Med. 2022;doi:10.1001/jamainternmed.2022.3050.
- Sonnier T, et al. J Diabetes Complications. 2014;doi:10.1016/j.jdiacomp.2014.04.001.
- Vujovic N, et al. Cell Metab. 2022;doi:10.1016/j.cmet.2022.09.007.
- Wijayatuna N, et al. Curr Dev Nutr. 2020;doi:10.1093/cdn/nzaa063_099.
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Peterson CM, et al. Only time will tell — early eating or just eating. Presented at: American Diabetes Association Scientific Sessions; June 23-26, 2023; San Diego (hybrid meeting).
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