Eat By the Sun: How Circadian Rhythm Can Help You Optimize Your Diet

By: JJ Virgin, CNS, BCHN®, EP-C

When it comes to fat loss and better health, timing is everything. Our overall health and longevity are impacted just as much by when we eat as what we eat.

That premise underlies The Circadian Code (Panda, 2020). In this groundbreaking book, author Satchin Panda, Ph.D., explains how “small changes to the way you sleep, eat, work, learn, exercise, and light up your home … will make a profound difference in every aspect of your health.”

Most of us are familiar with how circadian rhythm impacts the sleep/wake cycle, where our brain’s 24-hour internal clock regulates cycles of alertness and sleepiness by responding to light changes in our environment (Reddy et al., 2022).

We can use this same approach to optimize our diet, says Panda. By limiting the number of hours that we eat, we optimize our body clock and avoid age-related chronic diseases. This time-restricted eating pattern could also improve other areas of our lives, including getting better sleep and being more alert during the day.

What Is Time-Restricted Eating?

Time-restricted eating (TRE)—alternately called time-restricted feeding (TRF)—is a type of intermittent fasting where you consume your entire caloric intake within a window of six to 10 hours a day (Regmi et al., 2020).

In other words, you confine eating to a certain period during the day and abstain from eating during the evening.

Many modern-day habits—staring at electronic devices all day, stressful commutes, working late into the night—lead us to snack or eat meals erratically and, oftentimes, into the late evening hours. Research shows (Engin, 2017) that this pattern can disrupt our body’s circadian rhythm and increase the risk of obesity, diabetes, heart disease, and other illnesses.

This approach also mimics how our ancestors ate thousands of years ago, before our graze-all-day mentality, ubiquitous vending machines, and nighttime snacking became common. As researchers wrote in one study, TRE “is simply an appropriate eating pattern that humans have veered away from in the past several decades” (Rynders et al., 2019).

Calorie counting provides one way to improve overall health and increase longevity. However, measuring or counting can be challenging for many people. Research shows (Dorling et al., 2020) that TRE provides the benefits of restricting calories—balancing blood sugar, losing weight, boosting longevity, and more—without counting or measuring anything.

Time-Restricted Eating Can Improve Health & Longevity

TRE carries wide-ranging benefits for overall health. Preclinical studies show (Regmi et al., 2020) that eating within a certain period:

  • Reduces body weight
  • Improves glucose tolerance
  • Protects against fatty liver
  • Increases metabolic flexibility
  • Reduces problematic blood lipids
  • Lowers blood pressure
  • Improves gut function
  • Supports cardiometabolic health

Panda himself did a groundbreaking study several years ago that showed how effective TRE can be. He compared two sets of mice, one of whom had free access to food and the other who ate all their food within an eight- to 12-hour period. Panda describes the outcome in The Circadian Code:

What we found was startling: Mice that eat the same number of calories from the same foods within 12 hours or less every day are completely protected from obesity, diabetes, liver, and heart disease. More surprising, when we put sick mice on this scheduled feeding, we could reverse their disease without medication or change in diet.

Other studies have shown similar results. One study (She et al., 2021) gave obese mice either an unrestricted diet or TRE (eating within an eight-hour daily window) for four weeks.

The TRE regimen was the winner. Maintaining meal timing, researchers found, helped reduce food intake and reversed glucose intolerance, high blood glucose, and insulin resistance. They concluded that the TRE “regimen might be a potential novel nonpharmacological strategy against obesity/diabetes-induced hyperglycemia and insulin resistance.”

Human studies have also proven effective. One (Cienfuegos, 2020) compared two popular forms of TRE (four-hour and six-hour eating windows) on body weight and cardiometabolic risk factors, including insulin resistance and obesity. Researchers asked obese adults to eat only between 3 and 7 p.m. or between 1 and 7 p.m. A control group, on the other hand, had no meal-timing restrictions.

After eight weeks, both TRE groups had lost weight (about 3% on average) as well as improved insulin resistance and oxidative stress, compared with the control group. What’s more, both TRE groups naturally reduced their caloric intake by about 550 calories a day, without counting.

One reason for these improvements is that TRF can help lower inflammation. In one small study (McAllister et al., 2021), 13 firefighters consumed their meals within a 10-hour period. Eight weeks later, researchers found several inflammatory markers were also significantly lower. Their salivary cortisol response (a stress marker) was also significantly reduced.

Other research (Balasubramanian et al., 2020) shows that TRE might have a similar effect for other conditions, including longevity and brain health. Researchers here pointed out, as I noted above, that TRE provides the benefits of caloric restriction, but without the hassles of counting or monitoring calories.

Personalizing a Time-Restricted Eating Regimen

The benefits of TRE are impressive, but how can you make this approach work for you? These five strategies will help you create a plan that works for you and delivers all the benefits of TRE:

  1. Stop eating about 3 hours after dinner. It takes about five hours for your stomach to digest your last meal. Increased secretion of melatonin, which occurs at night, halts insulin production by putting the pancreas ’to sleep.” Considering that it takes about five hours for your stomach to digest your last meal, eating too late at night sends mixed hormonal signals that are bad for your sleep, weight, and blood sugar. Indeed, studies show (Gallant et al., 2014) that eating later in the day and into the night may impair weight loss and contribute to higher body weight. That’s why I want you to stop eating about three hours before bed. And no, that does not mean going to bed later!
  2. Wait 1 – 2 hours after waking to break your morning fast. This allows melatonin to lower so that your pancreas will be able to release insulin as needed (Lopez-Minguez et al., 2019).
  3. Break your fast with a loaded smoothie. Start your day with a protein-fueled smoothie, which also provides healthy fats and fiber to keep you full and focused for hours. Ingredients like unsweetened coconut milk, organic berries, unsweetened nut butters, and even leafy greens pack the nutritional wallop you need to thrive all morning.
  4. Stretch your fast. Following these strategies creates a 12-14-hour overnight fast, and you’ll be sleeping for eight or nine of those hours. Over time, you can expand that fasting window for 16 or even 18 hours, increasing autophagy (cellular level “spring cleaning”) and other benefits of maintaining a TRE regimen (Bagherniya et al., 2018).
  5. Stop snacking. Research shows (Bellisle, 2014) that snacking throughout the day can contribute to weight gain. Why? Because every time you eat, you raise your insulin levels, and this master hormone stores fat. Snacking all day (even on healthy stuff) locks your fat cells so you can’t lose weight. You’re probably not snacking on healthy stuff either. Instead, you’re bored or stressed, and there’s something sweet in the pantry or near your desk.

Let’s say you wake up at 7 a.m. You’ll have a loaded smoothie at 9 a.m., then eat by the plate with the magic trifecta of protein, healthy fats, and fiber for lunch and dinner. Close the kitchen by 7 p.m., and you’ve created a 14-hour fasting window. You can tweak this according to your schedule and needs. Maybe you have your loaded smoothie at 10 a.m. and then stop eating by 6 p.m., which creates an 18-hour fasting window.

Final Thoughts

Researchers find (Xie et al., 2022) the many benefits of TRE include weight loss, better insulin sensitivity, lower blood pressure, and reduced oxidative stress. This approach mimics how our ancestors ate, before vending machines and snacking became commonplace.

Our modern-day eat-all-day approach, on the other hand, has contributed to the rise of obesity and diabetes. The Circadian Code offers a unique approach to weight loss by encouraging us to be mindful about when we eat and restricting food intake within a certain time period. TRE could hold the key to health and longevity.


Panda, S. (2020). The Circadian Code: Lose Weight, Supercharge Your Energy, and Transform Your Health from Morning to Midnight. Rodale Books. Reddy, S., Reddy, V., & Sharma, S. (2022). Physiology, Circadian Rhythm. In StatPearls. StatPearls Publishing.

Regmi, P., & Heilbronn, L. K. (2020). Time-Restricted Eating: Benefits, Mechanisms, and Challenges in Translation. iScience, 23(6), 101161.

Engin A. (2017). Circadian Rhythms in Diet-Induced Obesity. Advances in experimental medicine and biology, 960, 19–52.

Rynders, C. A., Thomas, E. A., Zaman, A., Pan, Z., Catenacci, V. A., & Melanson, E. L. (2019). Effectiveness of Intermittent Fasting and Time-Restricted Feeding Compared to Continuous Energy Restriction for Weight Loss. Nutrients, 11(10), 2442.

Dorling, J. L., Martin, C. K., & Redman, L. M. (2020). Calorie restriction for enhanced longevity: The role of novel dietary strategies in the present obesogenic environment. Ageing research reviews, 64, 101038.

Regmi, P., & Heilbronn, L. K. (2020). Time-Restricted Eating: Benefits, Mechanisms, and Challenges in Translation. iScience, 23(6), 101161.

She, Y., Sun, J., Hou, P., Fang, P., & Zhang, Z. (2021). Time-restricted feeding attenuates gluconeogenic activity through inhibition of PGC-1α expression and activity. Physiology & behavior, 231, 113313.

Cienfuegos, S., Gabel, K., Kalam, F., Ezpeleta, M., Wiseman, E., Pavlou, V., Lin, S., Oliveira, M. L., & Varady, K. A. (2020). Effects of 4- and 6-h Time-Restricted Feeding on Weight and Cardiometabolic Health: A Randomized Controlled Trial in Adults with Obesity. Cell metabolism, 32(3), 366–378.e3. 

McAllister, M. J., Gonzalez, A. E., & Waldman, H. S. (2021). Time Restricted Feeding Reduces Inflammation and Cortisol Response to a Firegrounds Test in Professional Firefighters. Journal of occupational and environmental medicine, 63(5), 441–447.

Balasubramanian, P., DelFavero, J., Ungvari, A., Papp, M., Tarantini, A., Price, N., de Cabo, R., & Tarantini, S. (2020). Time-restricted feeding (TRF) for prevention of age-related vascular cognitive impairment and dementia. Ageing research reviews, 64, 101189.

Gallant, A., Lundgren, J., & Drapeau, V. (2014). Nutritional Aspects of Late Eating and Night Eating. Current obesity reports, 3(1), 101–107.

Bagherniya, M., Butler, A. E., Barreto, G. E., & Sahebkar, A. (2018). The effect of fasting or calorie restriction on autophagy induction: A review of the literature. Ageing research reviews, 47, 183–197.

Bellisle F. (2014). Meals and snacking, diet quality and energy balance. Physiology & behavior, 134, 38–43.

Xie, Z., He, Z., Ye, Y., & Mao, Y. (2022). Effects of time-restricted feeding with different feeding windows on metabolic health: A systematic review of human studies. Nutrition (Burbank, Los Angeles County, Calif.), 102, 111764.

Lopez-Minguez, J., Gómez-Abellán, P., & Garaulet, M. (2019). Timing of Breakfast, Lunch, and Dinner. Effects on Obesity and Metabolic Risk. Nutrients, 11(11), 2624.

About JJ Virgin:

As a triple-board certified nutrition expert and Fitness Hall of Famer, JJ is a passionate advocate of the healing power of nutrition, and is mission driven to change the way the world sees aging and longevity.

She has launched 3 multimillion-dollar businesses, including a 7-figure personal brand, and founded the Mindshare Collaborative, the most influential professional community in health, having propelled more New York Times bestsellers, PBS specials, and 7 figure brands than any other community.

JJ is a prominent TV and media personality who co-hosted TLC’s Freaky Eaters and was the nutrition expert for Dr. Phil’s Weight Loss Challenges.  She’s made numerous appearances on PBS, Dr. Oz, Rachael Ray, Access Hollywood, and The TODAY Show. She also speaks regularly, commanding audiences of 10,000 or more, and has shared the stage with other highly sought-after experts including Tony Robbins, Seth Godin, Lisa Nichols, Gary Vaynerchuk, Dr. Mark Hyman, Dan Buettner, Mary Morrissey and more.

JJ is the author of four NY Times bestsellers: The Virgin Diet, The Virgin Diet Cookbook, JJ Virgin’s Sugar Impact Diet, and JJ Virgin’s Sugar Impact Diet Cookbook. Her most recent book, Warrior Mom: 7 Secrets to Bold, Brave Resilience, shares the inspirational lessons JJ learned as she fought for her son’s life.

Evidence of JJ’s far-reaching impact can be seen in the millions of views on her YouTube channel, Instagram and Facebook, and through her popular podcast Ask the Health Expert, which has more than 14 million downloads and counting.

JJ is a 3x Inc. 5000 Founder and a top 10 finalist for the John C Maxwell award.  As an authority on transformational leadership, she has coached some of the biggest names in health and transformed the lives of millions of people around the world.

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