According to the Centers for Disease Control and Prevention (CDC), the adult obesity rate in the U.S. is over 40%.1 Poor nutrition is an additional, related issue experienced by many. Dietary science and nutrition have grown more prominent in preventive medicine, for weight control as well as many other aspects of health. The efficacy of different dietary approaches, including calorie restriction (eating less than a specific number of calories each day) and time-restricted eating (eating at specific times of day), are particularly important. Indeed, both time-restricted eating and calorie restriction, in addition to the combination of the two, have shown health benefits.
Studies in a variety of animals, ranging from worms and flies to mice, rats, and primates, have shown that restricting calories can lead to a longer, healthier life. Such experiments report weight loss, improved metabolism, lower blood pressure, improved immunity,2 and reduced inflammation.3 Fascinatingly, a key gene has even been found to mediate the effect between calorie restriction and longer life: sustained calorie restriction leads to it being down-regulated, which is a crucial factor to lowering inflammatory mechanisms and contributing to longevity.4
In parallel, certain studies have shown that time-restricted eating helps not only to reduce calorie intake but also to improve cognition and yield a number of anti-inflammatory effects.5
A randomized clinical trial from 2022 that studied nearly 140 patients across 12 months suggested that time-restricted eating was associated with a 1.9 kg difference in weight loss compared to calorie restriction on average, although the magnitude of the effect was not statistically significant. The results seemed to clearly point to a strategy of time-restricted eating combined with caloric intake restriction, as prescribed according to current dietary guidelines, as a viable and sustainable approach for obesity management. Furthermore, the study laid forth an important benchmark for a dietary lifestyle intervention combining quality, quantity, and timing of nutrition.6
A study from 2021 focused on mice showed that fasting drives the molecular, metabolic, and life-lengthening effects of a calorie-restricted diet. Using a series of feeding regimens, the researchers specifically dissected the effects of calories and fasting – clearly demonstrating that fasting alone results in many of the physiological and molecular effects of calorie restriction.
A more recent study from 2022 that followed hundreds of mice over their lifespans found that calorie restriction combined with time-restricted eating boosted longevity. Indeed, the study’s results showed that eating only during the most active time of day substantially extended the lifespan of mice on a reduced-calorie diet.7 A reduced-calorie diet alone extended the animals’ lives by 10% . However, feeding mice when they were most active, i.e. only at night, extended their lives by about 35%. The particular combination of a reduced-calorie diet and a nighttime eating schedule added on nine months to the animals’ typical two-year median lifespan. (The analogous strategy in humans would be to limit eating to daytime hours.)
Although they ultimately represent different strategies for supporting metabolic health and weight loss maintenance, both time-restricted eating and calorie restriction have benefits. Individuals should select a strategy that best suits their lifestyle, while keeping in mind that the quality of food, alongside its quantity and intake program, remains one of the important facets of healthy nutritional habits.
References
1. Products – Data Briefs – Number 360 – February 2020. Available at: https://www.cdc.gov/nchs/products/databriefs/db360.htm. (Accessed: 29th August 2022)
2. Spadaro, O. et al. Caloric restriction in humans reveals immunometabolic regulators of health span. Science (80-. ). 375, 671–677 (2022). doi: 10.1126/science.abg7292.
3. Calorie restriction, immune function, and health span | National Institutes of Health (NIH). Available at: https://www.nih.gov/news-events/nih-research-matters/calorie-restriction-immune-function-health-span. (Accessed: 29th August 2022)
4. Candels, L. S., Becker, S. & Trautwein, C. PLA2G7: a new player in shaping energy metabolism and lifespan. Signal Transduct. Target. Ther. 2022 71 7, 1–2 (2022). doi: 10.1038/s41392-022-01052-5.
5. Stockman, M. C., Thomas, D., Burke, J. & Apovian, C. M. Intermittent Fasting: Is the Wait Worth the Weight? Current obesity reports (2018). doi:10.1007/s13679-018-0308-9
6. Liu, D. et al. Calorie Restriction with or without Time-Restricted Eating in Weight Loss. N. Engl. J. Med. 386, 1495–1504 (2022). doi: 10.1056/NEJMc2207023.
7. Acosta-Rodríguez, V. et al. Circadian alignment of early onset caloric restriction promotes longevity in male C57BL/6J mice. Science (80-. ). 376, 1192–1202 (2022). doi: 10.1126/science.abk0297.