Does Intermittent Fasting Really Work – Or Is It Just About Eating Less?

One of the major solutions to nearly every medical problem includes a “good diet.” A “good diet” generally includes foods that are less processed and lots of plants, but specifics vary. One thing that doesn’t vary is the amount. One of the hardest things to cope with in today’s society is just eating less. A big problem for many people - including the author, who is currently sitting behind a Costco amount of ice cream - is eating at night.

One increasingly popular method of controlling overconsumption is called intermittent fasting. Intermittent fasting sounds like you would periodically go a few days without eating, but it’s much simpler and easier than that. In fact, we all intermittently fast every night when we sleep. Fasting, in general, is very widespread and is practiced by most animals, usually when they sleep. While animals fast, studies have shown increased brain performance, reduced inflammation, reinforced day/night schedules, and changes in which fuels are found throughout the body. When we really boil it down, time is divided between feed time and fast time. Intermittent fasting extends rest time by narrowing the window we eat in, usually to around 8-14 hours per day.

There have been several studies on intermittent fasting, but most have few participants and are usually only a few days or weeks long. Despite these limitations, most agree that a fasting period of 12 hours is sufficient to see changes for most people, but 16 hours is so long between meals that many people will cave in for an extra meal (or two or three). Additionally, many experiments have found evidence of improvement in body weight, blood pressure, metabolic and inflammatory markers, sugar metabolism, epigenetic changes, and appetite. But how could changing your eating time affect all of these systems?

Early studies in rodents showed that mice and rats who intermittently fasted used more energy than those with normal eating times. This was unexpected but made scientists investigate if there was some mechanism to intermittent fasting that caused extra energy to be used. An intensive, clinical trial in humans was performed that tracked the precise number of calories and energy use. This found no difference in the energy use between people who intermittently fasted and those who didn’t and revealed that the difference may have been that rodents spent extra energy searching for food during the previous experiments. This difference between people and mice highlights the critical need for rigorous clinical research to translate hypotheses into evidence-based conclusions.

The next place to look for how intermittent fasting might be causing changes was in how much food is eaten. In early October, 2024, a new study was published in the Annals of Internal Medicine. This randomized, controlled trial followed over 100 people for three months to determine longer-term effects of intermittent fasting. Half of the patients restricted their eating window for four fewer hours than normal, and the results were revealing. Measures of glucose control, blood pressure, and inflammation all improved. In addition, the fasting group lost around 6 ½ pounds during the study, compared with fewer than 3 in the control group. One of the key differences between the groups, however, was caloric intake. The intermittent fasting group ate an average of 350 calories fewer than the control! That’s about the same as a normal breakfast of oatmeal or cereal with fruit! This reduction in caloric intake might be the major driver of many health benefits seen in previous studies.

Though intermittent fasting has obvious benefits, it’s not a miracle cure. Many of the studies in the literature have short time spans and few patients. The study referenced above explicitly states that one of the major limitations of the study is a short time span. Anyone who’s ever dieted knows that bodies adjust and most of the changes occur early on before plateauing - or even regressing. We still don’t know if the effects of intermittent fasting would plateau like other diets. Additionally, food is a social activity! Most of us don’t eat every meal alone (except when writing this article on a deadline) but instead eat with friends or loved ones. For this reason, intermittent fasting (and any changes to food habits) might be best done with someone else dragged along kicking and screaming.

Staff Writer / Editor Benton Lowey-Ball, BS, BFA

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References:

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. https://www.mdpi.com/2072-6643/11/6/1234

Longo, V. D., & Panda, S. (2016). Fasting, circadian rhythms, and time-restricted feeding in healthy lifespan. Cell metabolism, 23(6), 1048-1059. https://www.cell.com/cell-metabolism/fulltext/S1550-4131(16)30250-9

Manoogian, E. N., Wilkinson, M. J., O’Neal, M., Laing, K., Nguyen, J., Van, D., ... & Taub, P. R. (2024). Time-Restricted Eating in Adults With Metabolic Syndrome: A Randomized Controlled Trial. Annals of Internal Medicine. https://www.acpjournals.org/doi/abs/10.7326/M24-0859

Peeke, P. M., Greenway, F. L., Billes, S. K., Zhang, D., & Fujioka, K. (2021). Effect of time restricted eating on body weight and fasting glucose in participants with obesity: results of a randomized, controlled, virtual clinical trial. Nutrition & diabetes, 11(1), 6. https://www.nature.com/articles/s41387-021-00149-0

Regmi, P., & Heilbronn, L. K. (2020). Time-restricted eating: benefits, mechanisms, and challenges in translation. Iscience, 23(6). https://www.cell.com/iscience/fulltext/S2589-0042(20)30346-1