What Time-Restricted Eating Does and Doesn’t Affect
In Cell Reports Medicine, researchers have published a study demonstrating that, while it has no impact on many aspects of intestinal function, time-restricted eating (TRE) reduces markers of blood glucose.
A matter of when rather than what
People who conduct TRE, choosing to consume food only at certain times of the day, often report improvements to health due to the ensuing weight loss; they consume less food per day in general [1]. However, human clinical trials that have controlled the amount of food consumed, so that everyone involved is eating the same amount, have found that it improves glucose use and reduces biomarkers of aging [2]. More studies have found that it improves muscle performance in healthy men [3].
Other research has found that the gastrointestinal system changes throughout the day, following the circadian rhythms of other bodily systems [4]. However, the researchers suggest that this is more due to TRE being associated with overeating; someone who only eats during certain times of the day often eats a large meal, and doing this can slow down the gastric system [5].
Better glucose metabolism confirmed
To test their hypothesis, the researchers conducted a six-day test in which 16 healthy adults followed personalized eating and drinking recommendations between either 8:00 AM to 2:00 PM (TRE) or 8:00 AM to 8:00 PM (control). The diets provided were balanced, with moderate amounts of eggs, fowl, and dairy products; no red meat was present. The TRE group and control group had similar eating schedules, with the TRE group’s being compressed into half the time.
All participants were studied on a large number of gastrointestinal and metabolic metrics, including stool examinations, subjective hunger, resting energy expenditure, gene expression, and metrics related to glucose and insulin use.
The results were largely in accordance with previous studies, showing that glucose metabolism was, indeed, positively affected by TRE. Total glucose was diminished, and glycemic variability, the fluctuations in glucose over a day, was also significantly reduced by TRE. However, this study’s key findings are largely of the things that didn’t happen.
No effects on nutrients, but effects on hunger
Analyzing the stool of the participants, the researchers found that energy use was not affected by TRE. Digestibility of fats, carbohydrates, and proteins was unaffected, as was fiber and consistency of stool. Urine was similarly unaffected by TRE, both in amount and in nitrogen content. Resting energy expenditure was also unaffected, as were the metabolites in blood plasma and the bacterial contents of stool.
The researchers also used indigestible dye capsules to determine how long it takes for stool to pass through the digestive system. This metric was similar between both the study and the control groups. Hydrogen production due to fermentation in the gut was also not affected. This, the researchers note, affects the circadian rhythm by increasing satiety during daylight hours.
However, the TRE group was considerably less hungry during the day than the control group. Participants were asked about their hunger, their capacity to eat, and their desire to eat, all of which were not affected before breakfast but significantly reduced in the TRE group at noon and at 5:00 PM. On the other hand, they became significantly (and expectedly) more hungry at 9:00 PM.
While many of these results show that nothing significant has happened in many respects, this makes them of interest to nutritionists and anyone considering a meal plan that involves TRE. This approach seems to have beneficial effects on glucose metabolism but does not affect how the gut absorbs nutrients. This was a small study, but it appears to be the case that a nutritionist creating a defined meal plan could compress it into an early-morning meal plan without adverse effects.
Literature
[1] Pellegrini, M., Cioffi, I., Evangelista, A., Ponzo, V., Goitre, I., Ciccone, G., … & Bo, S. (2020). Effects of time-restricted feeding on body weight and metabolism. A systematic review and meta-analysis. Reviews in endocrine and metabolic disorders, 21, 17-33.
[2] Jamshed, H., Beyl, R. A., Della Manna, D. L., Yang, E. S., Ravussin, E., & Peterson, C. M. (2019). Early time-restricted feeding improves 24-hour glucose levels and affects markers of the circadian clock, aging, and autophagy in humans. Nutrients, 11(6), 1234.
[3] Jones, R., Pabla, P., Mallinson, J., Nixon, A., Taylor, T., Bennett, A., & Tsintzas, K. (2020). Two weeks of early time-restricted feeding (eTRF) improves skeletal muscle insulin and anabolic sensitivity in healthy men. The American journal of clinical nutrition, 112(4), 1015-1028.
[4] Segers, A., & Depoortere, I. (2021). Circadian clocks in the digestive system. Nature Reviews Gastroenterology & Hepatology, 18(4), 239-251.
[5] Basolo, A., Hohenadel, M., Ang, Q. Y., Piaggi, P., Heinitz, S., Walter, M., … & Krakoff, J. (2020). Effects of underfeeding and oral vancomycin on gut microbiome and nutrient absorption in humans. Nature Medicine, 26(4), 589-598.
