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Circadian Rhythm

What Mice Tell Us About Our Eating Habits

Metabolism, a guardrail against out-of-control weight gain, is all about timing.

Key points

  • Metabolism works best when eating times are restricted to fixed daylight hours.
  • Late-night eating may upset the rhythm of fat storage for energy, creating an energy buildup and weight gain.
  • Light exposure has a direct influence on metablic functions such as digestion and energy storage.
Rudmer Zwerver/Shutterstock
Source: Rudmer Zwerver/Shutterstock

Here we go with mice again. I am a cautionary skeptic when I read about scientific experiments that deal with social hypotheses. As someone who has worked in risk analysis, I squint at imaginative proposals suggesting that some peculiar physiological conditions are related to abnormal biomedical conditions.

I’ve seen doozies, such as suggestions that people with naturally black hair live longer than people of any other color. I consider that nonsense, blaming hidden variables and mishandled statistics.

But when mice are trying to tell us something about our bodies, I listen in vigilant belief. Here we go with mice, again.

Mice are ready to tell us a great deal about our own bodies. Following my post last August, “Out-of-Sync Circadian Rhythms Link With Weight Gain in Mice,” some serious issues need clarification. First, we are not mice. Certainly not, but our human genome and that of mice are almost identical. Almost. By that, I mean within 1 percent of a difference. Chimpanzees would be better models, since they are more closely related to us in many ways besides the molecular similarities.

Mice, though, are the perfect specimens for studying weight gain because of their small size. It doesn’t take much food to cause a mouse to double its size.

What Do Mice Tell Us?

When we eat at inappropriate times, we tend to burn fewer fat cells. Those cells are responsible for storing fat and connective tissue work. In mice, any wild deviations from circadian rhythms create metabolic changes leading to obesity. The latest studies suggest that irregular eating habits are likely to throw off metabolism control and impair thermogenesis, the process of burning fat cells.

Slowed burning contributed to increased weight gain in mice that were fed during docile times. Of course! That is what we should expect from mice and humans because the metabolic functions of mice and humans slow down at their individual nocturnal phases of activity. The latest mice studies corroborate what we always knew.

Life in this fast world, with food consumed at all hours of day and night, tends to build habits unfavorable to dietary health. I have written a great deal about why eating habits that are out-of-step with circadian rhythms jolt metabolic processes at the cell level. Those misalignments of night and day food consumption can increase the risk of serious weight gain.

Human Metabolic Systems Work Best When They're In-Sync with Circadian Rhythms

It’s all about thermogenesis, the metabolic production of heat. Being nocturnal, a mouse's feeding cycle is antipodal to a typical human’s active phase of a daily eating cycle. When mice were fed at times of high activity to fuel their expenditure of energy according to the circadian clock, their weights were stable. Feeding rhythms misaligned with body clocks disrupt thermogenesis enough to possibly cause obesity along with the complimentary metabolic syndrome of high blood pressure and high blood sugar.

A high-fat feeding during relatively inactive times decreases the protein metabolism process in mice. Mice studies also show that cells specializing in fat storage prefer rhythmic patterns aligning with the daily light-dark cycle. They suggest that time-restricted eating is the most efficient way to process nutrients while keeping fat cells stable.

It’s only a study of mice. But it is also likely by the common sense notion that, during human docile times, the body—though still mildly active—does not need to expend energy and therefore would burn fat cells at a relatively slow rate. It makes sense because we are all animals on this planet and almost all biological, physiological, and behavioral processes at the molecular level follow the planet’s 24-hour clock. That goes for heart rate, body temperature, and hormones.

And what about that pea-sized clock in the brain sitting next to the pineal gland? That gland synchronizes almost all body rhythms. It works by cues from the optic nerves to signal to cells throughout the body, letting them know the arrival of daylight or nighttime.

That makes sense. After all, many organisms perform best at certain hours of the day. Bees forage for nectar at the exact timing of nectar secretions for individual species of flowers. Like most plants and insects, they start and end their routines by the clock.

The human mind and body behave according to a built-in circadian rhythm, a coordinated assembly motivated to perform certain tasks that we might call the microbiological clock. At the molecular level, there is a circadian oscillator, specific cell groups that work together, like the mechanism of a clock, to cause a larger system of mind and body to function in a daily rhythm.

Why Now?

Weight gain and weight loss studies have been performed by scientists for centuries, with mice as the preferred subjects of biological experimentation. The coincidence of increasing numbers of obesity cases in humans, with a novel understanding of how the master body clock instructs cell protein buildup in tissues and organs, gives compelling confidence in the theory that circadian rhythms play a significant role in biophysical functions.

It is not surprising that the sleep-wake cycle shapes the body’s metabolism. So, we find that rhythmic thermogenesis connects to protein metabolism supplying energy to living tissue and to cells that specialize in fat storage is clock-set to circadian rhythms.

When we move from mice to humans, we have corroborating information to follow. For instance, randomized, controlled, clinical trials involving patients with obesity tell us that humans with obesity who follow time-restricted eating measures do tend to lose weight and improve their heart health. And besides weight control, time-restricted eating may improve blood pressure and stress and give some protection against type 2 diabetes.

We owe so much to those little creatures we call mice.


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