Time-Restricted Eating vs. Simple Calorie Restriction
If you’ve been a follower of our newsletter for some time, you’ll know Dr. Mayer touts the benefits of time-restricted eating (TRE). There has been plenty of preclinical and clinical data showing the benefits of restricting the time of daily food intake to 8 hours, giving the gut a rest period of 16 hours every day. These intriguing findings led our family to experiment with TRE at the beginning of the pandemic, and we all noticed a significant, sustainable weight loss after 2 weeks on the new eating pattern, as well as increased energy and a sense of well-being among other things.
To our surprise, a new study led by Dr. Deying Liu, M.D., and published in the prestigious New England Journal of Medicine on April 21st, 2022, found that there was no statistically significant difference in weight loss in individuals on a diet restricted in calories, if they had unrestricted access to food compared to being on a time-restricted eating schedule. In order to test their hypothesis that TRE is more effective in losing weight, the researchers randomly assigned 139 patients with obesity to either an 8-hour feeding window (8:00am – 4:00pm) with a calorie restriction or just simply the calorie restriction for 12 months. The restriction was 1,500 – 1,800 kcal per day for men, and 1,200 – 1,500 kcal for women.
“…analyses of weight circumferences, BMI, body fat, body lean mass, blood pressure, and metabolic risk factors were also not found to be significantly different.”
Out of the 139 participants, 118 completed the 12-month follow-up visit. The results showed that the average weight loss from baseline was -9.0 kg (~20lbs) in the TRE group, and -6.3 kg (~14lbs) in the control group with unrestricted access to the same number of calories. However, the observed 30% greater weight reduction in the TRE group did not reach statistical significance at the 12-month assessment. Results of analyses of weight circumferences, BMI, body fat, body lean mass, blood pressure, and metabolic risk factors were also not found to be significantly different.
Although previous studies both in animals and humans had shown that there were significant benefits of TRE vs. calorie restriction in both weight loss as well as reduction in blood pressure and overall improved longevity, those studies were shorter in duration whereas this spanned a full 12-month period. The findings of the Liu et. al 2022 study will certainly not be the last words on this topic. As mentioned by the authors, subgroups of individuals may be more sensitive to the intervention, and normal or overweight subjects may get more benefit than obese individuals.
So now you may be thinking, what’s the big deal about TRE if there’s no difference in losing weight by just putting yourself in a caloric deficit and eating whenever you want? Other than the fact that TRE may help some people follow through with their calorie restriction, the benefits of TRE extend further than simply losing weight.
“The period of having an empty stomach is very important, and has been shown to benefit our gut microbiome in several ways…”
Depending on the time window you decide on when doing TRE, you generally have a minimum of 16 hours where your stomach is empty. This period of being empty is very important and has been shown to benefit our gut microbiome in several ways. During this empty period or “fasting state”, the upper gastrointestinal tract (stomach & small intestine) exhibits a specific periodic migrating contraction pattern, known as the migrating motor complex (MMC). The MMC is a cyclic, powerful wave of contraction recurring motility pattern which starts in the stomach slowly moving down the small intestine during fasting which is promptly interrupted by eating. The MMC can be divided into four distinct phases, with phase 3 being the most active. From the time of its original demonstration in both humans and animals, it has been referred to as the intestinal housekeeper, emptying the stomach from undigestible food components, and cleansing the intestine from debris. Recently, more intriguing functions of this unique motility pattern have been identified.
These powerful contractions (Dr. Mayer tells me it is strong enough to crack a walnut in its shell), are likely to play a role of reducing the number of gut microbes in the small intestine, sweeping them down into the colon, their primary habitat. Because of this cleansing function, the MMC has been implicated in preventing the persistent colonization of the small intestine with microbial organisms that normally don’t live there, causing small intestinal bacterial overgrowth (SIBO). It has been found that the persistent interruption of this contraction pattern by diseases affecting the ability of the small bowel to contract (such as scleroderma) and generate the MMC can be associated with SIBO. This intrinsic cleansing mechanism of our gut has existed for thousands of years until it was compromised by our modern eating habits, leaving less and less time for the gut to cleanse itself. The time of not having food in our digestive system, has not only important effects on this small intestinal cleansing mechanism, but also on the interaction of the gut microbes with our gut, including the gut-based immune system.
“The changes in food systems within Western societies has not only affected what we eat and in which quantities, but also when we eat throughout the day.”
Our food system in Western societies has drastically changed over the last 75-100 years. This change has not only affected what we eat and in which quantities, but also when we eat throughout the day. As Dr. Mayer has explained in detail in The Gut Immune Connection, both aspects of our diet and the resulting consequences on our gut microbes and the gut based immune system are playing a crucial role in our epidemic of chronic non-transmissible diseases affecting every organ in our bodies, including the gut, the heart, the brain, and our liver. Obviously I am biased as my main interest is in nutrition and the gut microbiome, but I’d be willing to bet changes in our diet with downstream effects on the gut microbiome and immune system over the last 100 years play a significant role in the current states of disease we live in.
So, should you start or continue time-restricted eating? If you find it practical in your schedule not to have dinner after 7PM and wait until midday to eat, we think the answer is a definite yes. Although weight loss is generally the primary reason people follow a diet, TRE gives you the added benefit of cleansing your gut, maximizing gut health, and restoring a flourishing gut microbiome, while also helping you lose weight and get your metabolic parameters in the healthy range.
E. Dylan Mayer is a graduate from the University of Colorado at Boulder with both a major in Neuroscience and minor in Business. He is fascinated by the interactions of brain, gut and microbiome, and the role of nutrition in influencing the health of our microbiome, as well as our own well-being.