How Your Circadian Rhythm Impacts Your Diet

by JJ Virgin on May 9, 2023

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

That premise underlies The Circadian Code.1 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 folks are familiar with how the circadian rhythm impacts your sleep/wake cycle, where your brain’s 24-hour internal clock regulates cycles of alertness and sleepiness by responding to light changes in your environment.2 

You can use this same approach to optimize your diet, says Panda. By limiting the number of hours you eat, you optimize your body clock and avoid age-related chronic diseases. This time-restricted eating pattern could also improve other areas of your life, 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 specific window of time during the day.3  

Many modern-day habits (staring at electronic devices all day, stressful commutes, working on your laptop late into the night) lead us to snack or eat meals erratically and, oftentimes, into the late evening hours. Research shows that this pattern can disrupt your body’s circadian rhythm and increase the risk of obesity, diabetes, heart disease, and other illnesses.4 

This approach also mimics how our ancestors ate thousands of years ago, before the graze-all-day mentality, convenience foods, 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.”5 

Calorie counting provides one way to improve overall health and increase longevity. However, measuring or counting can be challenging for many people. Research shows TRE provides the benefits of restricting calories—balancing blood sugar, losing weight, boosting longevity, and more—without counting or measuring anything.6 

Time-Restricted Eating Can Improve Health & Longevity 

TRE carries wide-ranging benefits for overall health. Preclinical studies show that eating within a certain time frame: 

  • 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 health7 

Panda himself did a groundbreaking study several years ago that showed how effective TRE can be. He compared two sets of mice; one set of mice had free access to food and the other mice 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 research has shown similar results. One study 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.”8 

Human studies have also proven effective. A 2020 study published in Cardiometabolic Health 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 3-7pm or between 1-7pm 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) and improved insulin resistance and oxidative stress, compared with the control group. What’s more, both TRE groups naturally reduced their calorie intake by about 550 calories a day, without counting.9

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

Other research shows that TRE might have a similar effect on 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.11 

Personalizing a Time-Restricted Eating Regimen  

The benefits of TRE are impressive, but how can you make this approach work for you? I suggest starting with an overnight fast. Have a healthy dinner with a balance of protein, healthy fats, and fiber, and then close the kitchen for the evening.  

Panda recommends stopping eating about two or three hours before you go to sleep, and I agree. Studies show that eating later in the day and into the night may impair weight loss and contribute to higher body weight.12 

Break your morning fast by 9 or 10am with a loaded smoothie, which contains protein, fat, and fiber to keep you full and focused for hours. You naturally create a 12-14-hour 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.13 

One last thing: Panda tells readers to stop snacking, which can help them burn fat. Again, I agree. Research shows snacking throughout the day can contribute to weight gain.14 

Why? Because every time you eat, you raise your insulin levels, and this master hormone stores fat. Snacking all day (even on healthy food) locks your fat cells so you can’t lose weight. 

The Key to Health and Longevity 

Researchers find the many benefits of TRE include weight loss, better insulin sensitivity, lower blood pressure, and reduced oxidative stress.15 This approach mimics how our ancestors ate.  

Our modern 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. 

Starting your day with a loaded smoothie using my All-In-One Shakes is the best way to break a fast, delivering 20+ grams of protein to help you stay energized and feel fuller longer. Available in four rave-worthy flavors, with both paleo-inspired and plant-based options.  


  1. Panda, S. (2020). The Circadian Code: Lose Weight, Supercharge Your Energy, and Transform Your Health from Morning to Midnight. Rodale Books.  
  2. Reddy, S., Reddy, V., & Sharma, S. (2022). Physiology, Circadian Rhythm. In StatPearls. StatPearls Publishing.  
  3. Regmi, P., & Heilbronn, L. K. (2020). Time-Restricted Eating: Benefits, Mechanisms, and Challenges in Translation. iScience, 23(6), 101161.  
  4. Engin A. (2017). Circadian Rhythms in Diet-Induced Obesity. Advances in experimental medicine and biology, 960, 19–52. 
  5. 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. 
  6. 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.  
  7. Regmi, P., & Heilbronn, L. K. (2020). Time-Restricted Eating: Benefits, Mechanisms, and Challenges in Translation. iScience, 23(6), 101161.  
  8. 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. 
  9. 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.  
  10. 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.  
  11. 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.  
  12. Gallant, A., Lundgren, J., & Drapeau, V. (2014). Nutritional Aspects of Late Eating and Night Eating. Current obesity reports, 3(1), 101–107.  
  13. 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.  
  14. Bellisle F. (2014). Meals and snacking, diet quality and energy balance. Physiology & behavior, 134, 38–43.  
  15. 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.