“Light” eating

For decades, diets have been all about what we eat (we’ve scurried from the Mediterranean to the keto diet, etc.)—but the science is mounting fast that when we eat has profound metabolic and weight loss consequences. This new evidence is reflected in the rise of intermittent fasting (Google’s most-searched diet of 2019), which typically restricts eating and drinking to an eight-10-hour window a day.

A host of studies now indicate that alternating between periods of daily eating and fasting has eye-opening effects, with researchers hypothesizing that it conforms to the age-old way that humans ate: We experienced periods of food scarcity leading to “metabolic switching.” The evidence for intermittent fasting seems powerful.

A recent Johns Hopkins meta-review of studies found that it lowers blood pressure, lipid levels and heart rate. A new Salk Institute study shows the implications for the diabetes and obesity epidemic: People with metabolic syndrome who limited food/beverage consumption to a 10-hour window for three months saw big improvements in body composition and cholesterol levels. Research from the University of Texas Southwestern Medical Center found that mice that ate a normal amount of calories— but in restricted hours—lived 15% longer; if that applies to humans, that would mean increasing longevity from 80 to 92. Intermittent fasting’s association with everything from weight loss to forestalling diabetes is putting chrono-nutrition (timed food intake) front-and-center in wellness.

But is it the “intermittency” of eating or the fact that the fasting is circadian-synced that is the lynchpin? Because light and dark are the twin gods of our circadian clocks, and humans evolved to digest food in the day—what’s the metabolic (and sleep) impact of eating after dark, which jolts the brain into thinking that it’s daytime? How does matching the timing of eating with our circadian rhythms (with light and dark) impact health? More studies suggest that we should be embracing—and adopting the terminology of—a CIRCADIAN diet.

Syncing up mealtimes with circadian rhythms may lead to significantly more weight loss and other health advantages.

While intermittent fasting can have people taking their first bite (an important cue that impacts other clocks in our organs) way after the light of morning (say, 1–2 p.m.), a body of evidence shows that calories are metabolized better in the morning than evening: Researchers from Harvard University and the University of Murcia, Spain, found that early eaters lose 25 percent more weight (and faster) than late eaters. Hebrew University studies show that synchronizing mealtimes with our circadian rhythms leads to significantly more weight loss and reduced insulin resistance than if you ate the same food (of any kind) without a schedule, concluding that a larger breakfast, a medium-sized lunch and a small dinner drive optimal results.

The way that the timing of our eating communicates timing info to all the cells in our body is an extremely complex science. A 2019 study showed how insulin resets circadian clocks by increasing the synthesis of period proteins (controlled by the “clock genes”) and how the exposure to light (and its cortisol production) needs to precede the insulin/feeding timing to get the highest amplitude in clock gene rhythm—or optimal circadian rhythms. And scientists are discovering how the circadian clock directly affects the microbiome (our gut has its own circadian clock): Washington University researchers just discovered an immune cell that sets the clock for the gut, suggesting why circadian rhythm disruptions (those late nights, shift work) are linked to gastrointestinal problems and everything from obesity to colon cancer.

We’re seeing the research on intermittent fasting roll in, but we will see more studies evaluating whether all intermittent fasting is indeed created equal. We need more studies on the impact of timing meals to the light-dark cycle (circadian-synced eating and fasting), and how that impacts insulin levels and fat-burning hormones.

We predict more people will experiment with timing their eating and intermittent fasting differently: eating when it’s light, stopping when it’s dark. The potential of “clock nutrition” on weight loss and metabolic health—and research unriddling the complex interplay of light, our circadian clocks and our microbiota—is an exciting development and just revving up.

Forecasting the Future

  • If COVID-19 is an opportunity to rethink the future, and with the “bad timing” of light, biology and eating as a proven driver of obesity, diabetes, cancers, heart disease, depression, gut disorders, infections and early death, we need to rethink (as hard as it is) our love of our 24/7 calorie-intake culture: always-on supermarkets, restaurants and bars and the surge in all-day-and-night food delivery.
  • Humans are horrible at managing the things that keep our circadian rhythms in sync: when to sleep and eat and exercise and not. Each person has a different chronobiome: Some of us are hardwired genetically to be night owls (with a longer clock), teenagers have a clock two hours ahead, and the reality is most of us have different life/work schedules. Scientists are working on tests (saliva, breath, blood) that will be able to measure people’s unique circadian clock state in real-time, so we will be able to more precisely time “our lives.” Wearables and phone apps could then guide us on when to take in sun and dark and when to eat, sleep and exercise, and they could help reset us after life’s unavoidable, endless circadian disruptions. These would be breakthrough solutions—and they’re ahead.

This is an excerpt from the “Focus Shifts from Sleep to True Circadian Health” trend in the 2020 Global Wellness Trends Report.

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