Can you lose weight by changing when you eat? It sound too easy to be true, but it’s the approach some new diets are taking based on circadian rhythm research.

By Carolyn Williams, PhD, RD
Updated March 01, 2019
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Two trending diet books, What to Eat When by Drs. Michael Roizen and Dr. Michael Crupain and The Circadian Code by Dr. Satchin Panda, are getting attention by suggesting that when you eat is just as important as what you eat. The premise of both books is that today’s environment often encourages one to go against the body’s biological clock (particularly when it comes to eating and sleeping), and when continued, creates disrupted circadian rhythms.

Chronically disrupted circadian rhythms not only affect sleep, but also prevent the body systems from working efficiently, which leads to insulin resistance, fat storage, and increased disease risk. According to Drs. Roizen, Crupain, and Panda, the way to improve health, lose weight, and lower disease risk is to align the times that one eats and sleeps to work with, rather than against, the body’s circadian rhythms.

 

What Are Circadian Rhythms?

To understand why disrupted circadian rhythms might matter, here’s a quick overview of how the body’s clocks and rhythms work:

  • Every person’s brain has a “master clock” that oversees all bodily functions that must occur within a 24-hour period.
  • Since the body can’t do all required functions at the same time, the master clock manages the scheduling of each through biological clocks—internal clocks in every organ and body system—so they occur at the most efficient time of day. Each biological clock then keeps functions related to its area running on time by producing circadian rhythms.
  • Circadian rhythms remind the body to perform scheduled task, as well as give the task a little push of encouragement. This may mean secreting a hormone to make you more alert or sleepy, raising body temperature, or lowering heart rate. If you're a morning person and tend to naturally wake up early most days, it's probably because of circadian rhythms attempting to keep you in sync with your body’s clock. The reverse is true for most night owls.

The Problem With Disrupted Rhythms

Circadian rhythms become disrupted when we ignore and override them, something that is easy to do in our society due to busy lifestyles, unusual work hours, modern technology, and continuous food availability. When tasks don’t occur as scheduled, the body is forced to perform those tasks at a later time when it’s not necessarily primed or able to carry it out efficiently or effectively.

For example, if you ignore sleepiness and put off going to bed for several hours, then when you do sleep, the rest is likely not as deep or restorative. The reason is that functions and tasks that enable good quality sleep were scheduled for five hours ago. The same is true for eating; there are windows where food can be digested and used for energy more effectively. Research suggest going against these promotes insulin resistance and fat storage, and both books cite disrupted circadian rhythms as being at the root of most weight and health issues.

How to Follow a Circadian Rhythm Diet

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Both books propose that a key way to start aligning meal times with circadian rhythms is eating within a shorter window of time each day. Dr. Panda advocates TRE (time-restricted eating) or consuming daily calories within an 8 to 11 hour block, while Drs. Roizen and Crupain advocate eating only when the sun is up. Though described differently, the two approaches encourage the same thing—having a 12+ hour break between your last meal of one day and the first meal of the next day.

What to Eat When by Drs. Roizen and Crupain provides a general framework to align eating and sleep times with one’s circadian rhythms. The approach is easy to follow, the two main techniques being to eat when the sun is up and to eat larger meals earlier in the day since most body clocks are designed to digest and metabolize food in the first half of the day.

The Circadian Code by Dr. Panda goes more in-depth to try and determine rhythm needs based on a quiz that factors in current food and sleep habits, health, and lifestyle. He lists specific foods to avoid (primarily processed, high-glycemic foods) and also aligns exercise to circadian rhythms to address specific health issues.

Is There Any Science to Support This?

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In the past, circadian rhythms were considered ideal to follow, but not essential to health. However, findings over the past decade suggest these rhythms shouldn’t be ignored or consistently disrupted. The reason is that research now associates continually disrupted circadian rhythms with a greater risk of obesity, insulin resistance, metabolic syndrome, type 2 diabetes, hypertension, heart disease, inflammation, immune system deficiencies, certain cancers, and aging.

And while the research suggests a definite relationship between circadian rhythms, food, hormones and metabolism, there’s not enough known to fully understand the details of this relationship. Currently, researchers know that effects of disrupted rhythms in regards to meal times appear to be largely metabolic and related to insulin and glucose—factors that discourage using body fat for fuel and reduce glucose sensitivity.

The bottom line: There is a large and growing body of research to support the importance of aligning meal and sleep times with circadian rhythms for improved health. This likely leads to greater efficiency when it comes to digestion, metabolism and use of fat stores but there’s little research to-date on this. New research that looks further into the effects of restricting food intake to an 8- to 12-hour window each day is a key area to watch as more is discovered about circadian rhythms and meal times. These books aren’t going to provide regimented diet or a quick weight loss solution, but could possibly lead to improved overall health, as well as a healthier body weight.