Examine publishes rigorous, unbiased analysis of the latest and most important nutrition and supplementation studies each month, available to all Examine Members. Click here to learn more or log in.

In this article

Counting hours, not calories: a potential prediabetes solution

Restricting eating to a few hours a day could have health benefits for people with prediabetes. But does the timing of the eating window matter?

Study under review: Early Time-Restricted Feeding Improves Insulin Sensitivity, Blood Pressure, and Oxidative Stress Even without Weight Loss in Men with Prediabetes.


Although specifics vary, everyone alternates between a feeding period and a fasting period. The ability for humans to sustain activity and metabolism using stored fuels during the fasting period was essential through our evolution, especially during times of famine when food was scarce. A re-emerging theory[1] from the 1960s suggests that mimicking the feed-fast cycling of our ancestors may actually be protective and beneficial in the midst of rising obesity, diabetes, and cardiovascular disease rates.

Over the past decade, both the research and the nutrition communities have taken an interest in a way of eating called intermittent fasting, which refers to a variety of regimens that aim to prolong the fasting period of a typical feed-fast cycle. Studies performed in a variety[2] of species have demonstrated reductions in chronic diseases and extended lifespan through intermittent fasting. Likewise, human studies have shown promise related to health: extended feed-fast cycles improve bodyweight[3], body composition, inflammation[4], and glucose control[5].

Time-restricted feeding[6] (TRF) falls under the umbrella of intermittent fasting and involves eating within a shortened period of time. For example, people tend to eat during 15 hours[7] of the day, and most of our discretionary calories are consumed later in the day, after 6:00 p.m.. On the other hand, TRF restricts the feeding window to a duration of three to 12 hours, depending on the regimen.

TRF studies in rodents[6] have reported improved glucose regulation factors, even if bodyweight remains unchanged. Interestingly, one study[8] fed high-fat, high-sugar diets to rats under a TRF regimen of eight hours for five out of seven days a week and found TRF to be protective against metabolic dysfunction in obese rats. It stands to reason that TRF may help to counter the consequences of our modern obesogenic food scene. Despite the promotion of TRF through mainstream media, only a handful of TRF studies have been performed in humans. These studies point to potential health benefits[3], but there have been no attempts to isolate the effect of TRF from that of weight loss. Furthermore, an intermittent fasting study showed that participants with the highest degree[9] of insulin resistance may benefit the most from extended fasting compared to those with the lowest degree of insulin resistance. However, no TRF studies have been performed in a prediabetic population.

Additionally, none have addressed the optimal timing of the TRF window. This is important to consider, since, as you can see in Figure 1, many aspects of our metabolism are influenced by our circadian rhythm. Some research has shown that meal timing and content can throw circadian rhythms out of sync[10], which may contribute to weight gain and the development of metabolic syndrome.

The present study sought to assess early TRF (eTRF, which restricts the feeding window to the earliest part of the waking day) to a more typical 12-hour diet under controlled feeding conditions for five weeks in men with prediabetes.

Time restricted feeding (TRF) is a form of intermittent fasting with the potential to improve health by restricting access to food to a shortened window of time. Initial work in this area is promising, but studies addressing the timing of food intake and in at-risk populations are necessary to optimize recommendations.

Who and what was studied?

Become an Examine Member to read the full article.

Becoming an Examine Member will keep you on the cutting edge of health research with access to in-depth analyses such as this article.

You also unlock a big picture view of 400+ supplements and 600+ health topics, as well as actionable study summaries delivered to you every month across 25 health categories.

Stop wasting time and energy — we make it easy for you to stay on top of nutrition research.

Try free for two weeks

Already a member? Please login to read this article.

What were the findings?

Become an Examine Member to unlock this article.

Already a member? Please login to read this article.

What does the study really tell us?

Become an Examine Member to unlock this article.

Already a member? Please login to read this article.

The big picture

Become an Examine Member to unlock this article.

Already a member? Please login to read this article.

Frequently asked questions

Become an Examine Member to unlock this article.

Already a member? Please login to read this article.

What should I know?

Become an Examine Member to unlock this article.

Free 2-week trial »

Already a member? Please login to read this article.

Other Articles in Issue #44 (June 2018)