Restricting the hours you can allow yourself to eat has promise as a weight loss strategy, but is it the reduction in overall food intake that causes the weight to come off or the impact of daily periods spent fasting?

According to a new study that compared time-restricted eating (TRE) with a usual eating pattern (or UEP), it's the drop in calories that makes the biggest difference. The findings can help inform future approaches to tackling a growing obesity problem worldwide.

A team of researchers led by Johns Hopkins University in the US enlisted 41 adult participants with obesity and either prediabetes or diet-controlled diabetes. The volunteers were then placed into a TRE or a UEP group, with isocaloric (calorie-matched) diets assigned to each person.

Regardless of which group they were in, significant weight loss occurred; the TRE group losing on average 2.3 kilograms (5.1 pounds) after consuming most of their calories before 1 pm, and the UEP group losing 2.6 kilograms (5.7 pounds) on average, after consuming most of their calories in the evening.

"In the setting of isocaloric eating, TRE did not decrease weight or improve glucose homeostasis relative to a UEP, suggesting that any effects of TRE on weight in prior studies may be due to reductions in caloric intake," the researchers write in their published paper.

Other markers – including glucose levels, waist circumference, blood pressure, and lipid levels – were similar across both groups. Again, that suggests that the time the eating takes place doesn't matter too much.

For the purposes of this study, the TRE group was only allowed to eat during the hours of 8 am and 6 pm – a 10-hour window (though some TRE diets shrink it to as low as four hours). By comparison, the UEP group could eat between 8 am and midnight, giving them an extra six hours to digest the same prescribed calories.

"Our results indicate that when food intake is matched across groups and calories are held constant, TRE, as operationalized in our study, does not enhance weight loss," write the researchers.

While the study sample size is a relatively small one, and participants were only monitored for 12 weeks, the findings lend support to effective methods for losing excessive weight. What's more, even though sticking to specific time windows might not directly contribute to weight loss on its own, it can help manage the most important factor here – a reduction in daily calories.

Many of us are likely to find it easier to monitor the times we eat, rather than counting calories or planning specific meals, and that's something that healthcare professionals might be able to recommend for those having issues with their weight.

In an accompanying editorial, University of Illinois Chicago nutrition scientist Krista Varady and epidemiologist Vanessa Oddo, who weren't involved in the study write that the research shows "TRE is effective for weight loss, simply because it helps people eat less."

"Although TRE is no more effective than other diet interventions for weight reduction, it offers patients a simplified approach to treating obesity by omitting the need for calorie counting."

The research has been published in the Annals of Internal Medicine.