Perspective published in Advances in Nutrition says more research is needed to examine the combined effects of what we eat and when we eat

What we eat matters, but does when we eat also matter?  For decades, nutrition scientists have conducted studies that have helped us better understand the relationships between health outcomes and the consumption of different nutrients, dietary patterns, and number of calories.  Recently, however, there has been growing recognition that controlling the timing of meals is also critical for health and well-being.

One such approach, known as time-restricted eating, has recently gained much media attention and popularity.  In this approach, people limit their food intake to six- to ten-hour periods during the active phase of the day, without necessarily altering diet quality and quantity.  Scientific reviews have demonstrated the potential for time-restricted eating to reduce obesity and improve other cardiometabolic health markers.  Moreover, many of the reported health benefits of time-restricted eating appear to be independent of weight loss, but instead are thought to be linked to the timing of meals in alignment with our circadian rhythms (i.e., the body’s natural internal processes that regulate the sleep-wake cycle and repeat roughly every 24 hours).

According to “Time-Restricted Eating: Integrating the What with the When,” a Perspective published in Advances in Nutrition, “almost the entire body of dietary literature to date, along with the profession of nutrition science, has focused on what we eat: new knowledge from time-restricted eating interventions is shifting that narrative so that now it is vital we also consider that the timing of meals plays an important role in determining metabolic health outcomes.”  On the other hand, the authors note that, to date, research on time-restricted eating has largely ignored what food is consumed: “Without consideration of both what and when food is eaten, we cannot begin to understand the potential synergies between these two variables and their potential impact on reducing the burden of chronic metabolic diseases at the population level.”

The authors did present evidence from the small number of time-restricted eating studies that have considered the combined impact of both what food is eaten and when it is eaten on selected health outcomes, such as weight loss and glycemic control.  In one such study, men with prediabetes were placed on a five-week time-restricted eating diet in which three prescribed meals were eaten across a six-hour period between 8am and 2pm.  After the five-week period, the study participants showed improved measures of insulin sensitivity, blood pressure, beta-cell responsiveness and markers of oxidative stress compared to when they consumed the exact same diet over a 12-hour period from 8am to 10pm: “That study provided the first evidence to suggest that some of the health benefits of time-restricted eating may be independent of energy intake and weight loss.”

Depending on the duration and timing of the feeding-fasting cycle, research suggests that time-restricted eating can inadvertently reduce energy intake and alter nutrient intakes via “reductions in discretionary ‘time-of-day’ foods such as alcohol and confectionary, that are typically consumed in the evening (i.e., outside the eating window).”

Overall, the authors believe that time-restricted eating protocols can potentially be adapted to “tackle a variety of pre-existing metabolic conditions dependent on the goals or desired health outcomes of the individual.”  They do, however, stress that “further research expanding the use of time-restricted eating interventions in different clinical populations under free-living conditions is essential to evaluate long-term adherence and feasibility before recommending additions to national and international diet guidelines.”