Limited-time food (also known as limited-time feeding) is a new nutritional concept that shortens the time between the first and last daily calorie intake. There is strong evidence of the health benefits of TRE in animals. Recent small studies by our research group and other scientists suggest that humans, too, benefit from it.
Many new researches on animals and humans have shown clear connections between our circadian (daily) rhythms, metabolism, and diet. Circadian clocks exist throughout our bodies, including tissues that have a major impact on our metabolic health.
Roughly speaking, these watches enable our bodies to actively deal with food intake during sleep and to release energy from the stores while they sleep. As a result, we process the food consumed during the day more efficiently than an identical meal in the evening or at night.
There is indeed increasing evidence that our metabolic health is regulated not only by what we eat, but also by our food. This interaction between circadian rhythms and nutrition is today often referred to as "Chrononutrition".
One of the ways that Chrononutrition is applied to the health of the diet is the TRE. Animal studies on species as diverse as mice and fruit flies have shown that TRE can reduce obesity caused by a high-fat diet and reduce the risk of heart and metabolic diseases. However, metabolic and nutritional studies in animals do not always affect humans, so it is important to test TREs in humans before health claims can be made.
TRE in humans
An early indication of the effects of TRE in humans are available in the form of Ramadan studies. Islamic religious fasting limits food and drink to the night between sunrise and sunset. Recent meta-analyzes of these Ramadan observational studies show improvements in some risk markers for diabetes and heart disease.
However, these studies are difficult to interpret as Ramadan involves a change from day to night meals as well as a change in meal duration. Changes are short-lived and limited to the one-month Lent.
In human intervention studies, TRE has been achieved in a number of ways, including avoidance of nocturnal eating and restriction of intake to four, six or eight (19659002). The latter is one approach we recently used in the Journal of Nutritional Science have used a published pilot study. We divide the participants into two groups. One group – the TRE group – delayed their breakfast by 90 minutes and had their dinner 90 minutes earlier. The other group (the control group) ate meals as they usually did.
Participants had to submit blood samples and complete diet diaries before and during the 10-week intervention, and to complete a feedback questionnaire immediately after the study.
We found a statistically significant reduction in caloric intake and body fat in the TRE group compared to controls. Our data also indicated that TRE could benefit from blood markers of metabolic diseases such as fasting blood glucose (glucose). Questionnaire data suggested that some, but not all, of the TRE participants felt eating was a continuation.
It should be noted that pilot studies should provide preliminary data and help shape future large-scale research. The number of participants in pilot studies is low, so that no conclusive conclusions can be drawn from the results.
In general, TRE studies have yielded mixed results, given the diversity of protocols. Various forms of TRE have been shown to either improve or have little influence on the risk factors for heart disease and diabetes. Some studies have shown improvements in body composition, such as reduced body fat, both in overweight and obese people, and in men who exercise regularly, although this is not found in all studies.
A common result is that people tend to reduce food intake during TRE, even if they are not asked. This is itself a finding that could have great health benefits. But even where there is no energy restriction or too low, there is strong evidence that TRE can still affect metabolism, which means that the benefits of TRE can go beyond regulating energy intake.
Important issues that need to be addressed include fasting times that work better than others, how TRE could benefit your health, even if calorie intake is the same, and whether TRE benefits patients with metabolic disorders such as type 2 diabetes.
In this fast paced area, we and others are now looking to expand on the first results described here. Even if we live in our modern 24-hour society, eating a pattern that matches our internal circadian rhythms can be of great health benefit.