Tag Archives: meal timing

You Are When You Eat | The Paleo DietRenowned evolutionary biologist Theodosius Dobzhansky said “nothing in biology makes sense except in the light of evolution.”[1] Throughout our evolution, we have lived in daily cycles of light and dark. These cycles have led to the development of natural circadian rhythms that impact many aspects of our health and vitality.

Circadian rhythms are triggered by the bright light stimulus in the morning and darkness in the evening. The hypothalamus area of the brain – specifically the suprachiasmatic nucleus (SCN) – is the master regulator, synchronising the body’s circadian clock based on information it receives from photoreceptors in the eyes in response to light [2]. The impacts of circadian rhythm are wide-reaching;

Disruption of the circadian clock can have a big impact on the body’s ability to function optimally. Jet lag – that feeling of fatigue, disorientation and mental sluggishness after travelling through multiple time zones – is a classic example [3-6]

Unfortunately, the negative effects can be more serious than just a little sluggishness. The incidence of workplace injuries and traffic accidents increases when the clocks move forward in the spring [7, 8].

Experts are just starting to uncover the many potential ripple effects of circadian dysfunction on our health: from heart disease [9, 10] and cognitive decline [11, 12], to blood sugar dysfunction and increased diabetes risk [13]; to changes in body-fat storage and breakdown [14-16], reduced liver, pancreatic, and cardiac and skeletal muscle function [17-25].


Late-Night Eating & Circadian Rhythm

Today, there are many ancestral circadian mismatches with modern life. Late-night eating may be one of the most glaring incongruous elements. We’re in the midst of a weight gain and obesity epidemic with 70% of adults over the age of 20 in America are overweight or obese and 50% of the population now classified as pre-diabetic or diabetic.[26-27] A body of research is appearing showing that late-night eating may be a significant contributor [27-29].

A 2014 study of overweight and obese diabetics investigated the impacts of a late-night snack on their requirement for supplemental insulin. Subjects were divided into carbohydrate, whey protein, casein, or placebo groups. All groups required significantly more insulin after all late-night snacks, though the protein snack did compare more favourably to the carbohydrate snack [30]. These results confirmed a 2003 study on late-night eating and diabetics. This earlier study showed consistently higher blood sugar levels when snacking late at night, regardless of the macronutrient composition of the meal [31].

Why is late-night eating potentially so bad for us? One possible explanation is our circadian rhythms may prevent us from effectively managing food eaten later at night. There is evidence showing the thermic effect of food is reduced in the evening, due to the circadian regulation of insulin sensitivity, meaning your blood sugar and insulin response to carbs at night is more exaggerated than during the day [32].


Solutions for A Modern Circadian Mismatch

Our Paleolithic ancestors would’ve rarely (if ever) eaten after dark. Yet in today’s modern world, the light emitted from iPads, laptops, TVs and mobile devices make it far easier to stay up later at night. This presents a circadian mismatch to our evolutionary biological clocks which translates into more opportunity (and likelihood) to eat. If you’re struggling with weight gain, chronically high blood sugar, pre-diabetes or diabetes then shifting your focus to “meal-timing” can be a simple and highly effective part of the solution to improving your health.

To support a healthy circadian clock, implement the following “meal-timing” strategy:

  • Avoid eating late at night – consider abstaining from all food after 6:00 or 7:00 pm or ditch your late-night snacking while on the couch and try sipping on a herbal tea instead
  • Go for an evening walk, do some light stretching, or take a relaxing bath.


In my experience as a clinician, I see major progress in clients who decide to abstain from food in the evening. Once they get through the first few nights, the cravings plummet and it becomes much easier to ingrain the new habit.

Supporting your circadian clock with meal-timing strategies can be an “easy win” to restoring health and vitality [33]. It’s simple and highly effective. 


1. Gerhart-Hines, Z. and M.A. Lazar, Circadian metabolism in the light of evolution. Endocr Rev, 2015. 36(3): p. 289-304.
2. Guler, A.D., et al., Melanopsin cells are the principal conduits for rod-cone input to non-image-forming vision. Nature, 2008. 453(7191): p. 102-5.
3. Tapp, W.N. and B.H. Natelson, Circadian rhythms and patterns of performance before and after simulated jet lag. Am J Physiol, 1989. 257(4 Pt 2): p. R796-803.
4. Leloup, J.C. and A. Goldbeter, Critical phase shifts slow down circadian clock recovery: implications for jet lag. J Theor Biol, 2013. 333: p. 47-57.
5. Comperatore, C.A. and G.P. Krueger, Circadian rhythm desynchronosis, jet lag, shift lag, and coping strategies. Occup Med, 1990. 5(2): p. 323-41.
6. Vosko, A.M., C.S. Colwell, and A.Y. Avidan, Jet lag syndrome: circadian organization, pathophysiology, and management strategies. Nat Sci Sleep, 2010. 2: p. 187-98.
7. Coren, S., Daylight savings time and traffic accidents. N Engl J Med, 1996. 334(14): p. 924.
8. Varughese, J. and R.P. Allen, Fatal accidents following changes in daylight savings time: the American experience. Sleep Medicine, 2001. 2(1): p. 31-36.
9. Maemura, K., [Circadian rhythm and ischemic heart disease]. Nihon Rinsho, 2013. 71(12): p. 2124-9.
10. Marchant, B., Circadian rhythms and ischaemic heart disease. Br J Hosp Med, 1996. 55(3): p. 139-43.
11. Gehrman, P., et al., The relationship between dementia severity and rest/activity circadian rhythms. Neuropsychiatr Dis Treat, 2005. 1(2): p. 155-63.
12. Ancoli-Israel, S., et al., Variations in circadian rhythms of activity, sleep, and light exposure related to dementia in nursing-home patients. Sleep, 1997. 20(1): p. 18-23.
13. Afsar, B., Disruption of circadian blood pressure, heart rate and the impact on glycemic control in type 1 diabetes. Diabetes Metab Syndr, 2015. 9(4): p. 359-63.
14. Cincotta, A.H., et al., Circadian neuroendocrine role in age-related changes in body fat stores and insulin sensitivity of the male Sprague-Dawley rat. Chronobiol Int, 1993. 10(4): p. 244-58.
15. Wang, L. and S. Liangpunsakul, Circadian clock control of hepatic lipid metabolism: role of small heterodimer partner (Shp). J Investig Med, 2016. 64(7): p. 1158-61.
16. Gnocchi, D., et al., Lipids around the Clock: Focus on Circadian Rhythms and Lipid Metabolism. Biology (Basel), 2015. 4(1): p. 104-32.
17. Gerhart Hines, Z., et al., The nuclear receptor Rev-erbα controls circadian thermogenic plasticity. Nature, 2013. 503(7476): p. 410-413.
18. Bookout, A.L., et al., FGF21 regulates metabolism and circadian behavior by acting on the nervous system. Nat Med, 2013. 19(9): p. 1147-52.
19. Shostak, A., J. Meyer-Kovac, and H. Oster, Circadian regulation of lipid mobilization in white adipose tissues. Diabetes, 2013. 62(7): p. 2195-203.
20. Boden, G., et al., Evidence for a circadian rhythm of insulin secretion. Am J Physiol, 1996. 271(2 Pt 1): p. E246-52.
21. Degaute, J.P., et al., Quantitative analysis of the 24-hour blood pressure and heart rate patterns in young men. Hypertension, 1991. 18(2): p. 199-210.
22. Zambon, A.C., et al., Time- and exercise-dependent gene regulation in human skeletal muscle. Genome Biol, 2003. 4(10): p. R61.
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24. Kettner, N.M., et al., Circadian Homeostasis of Liver Metabolism Suppresses Hepatocarcinogenesis. Cancer Cell, 2016. 30(6): p. 909-924.
25. Zhou, D., et al., Evolving roles of circadian rhythms in liver homeostasis and pathology. Oncotarget, 2016. 7(8): p. 8625-39.
26. CDC: Center for Disease Control & Prevention. Retrieved from – https://www.cdc.gov/nchs/fastats/obesity-overweight.htm
27. Menke, A., et al., Prevalence of and Trends in Diabetes Among Adults in the United States, 1988-2012. JAMA, 2015. 314(10): p. 1021-9.
28. Cleator, J., et al., Night eating syndrome: implications for severe obesity. Nutr Diabetes, 2012. 2: p. e44.
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31. Kinsey, A.W., et al., Influence of night-time protein and carbohydrate intake on appetite and cardiometabolic risk in sedentary overweight and obese women. Br J Nutr, 2014. 112(3): p. 320-7.
32. Kalergis, M., et al., Impact of bedtime snack composition on prevention of nocturnal hypoglycemia in adults with type 1 diabetes undergoing intensive insulin management using lispro insulin before meals: a randomized, placebo-controlled, crossover trial. Diabetes Care, 2003. 26(1): p. 9-15.
33. Bo, S., et al., Is the timing of caloric intake associated with variation in diet-induced thermogenesis and in the metabolic pattern? A randomized cross-over study. Int J Obes (Lond), 2015. 39(12): p. 1689-95.
34. Mattson, M.P., et al., Meal frequency and timing in health and disease. Proc Natl Acad Sci U S A, 2014. 111(47): p. 16647-53.




You Are When You Eat | The Paleo Diet

You don’t have to be on the Paleo Diet for long to start noticing extravagantly packaged, brightly colored foods that weren’t part of our Paleolithic past. But with all the time we spend explaining that hunter-gatherers didn’t eat Big Macs and jelly beans, we sometimes forget that these foods aren’t the only unnatural consequence of our modern lifestyle. Just fly across five or six time zones to see how ill equipped your body is to handle time change. As fit as our Paleolithic ancestors were, they were never able to run quite fast enough to experience jet lag.

Our bodies are, in fact, directed by circadian rhythms that dictate when we are active, when we sleep, and even when we eat. Modern conveniences such as artificial lighting and always-within-reach snacks may disturb these rhythms placing additional evolutionary stress on our bodies that ultimately affects our diet and our health. At least this is the theory presented in a recent review published in the Proceedings of the National Academy of Science by Dr. Mark Mattson et al. These researchers proposed that our health isn’t just about what we eat, but when we eat.1

Natural 24-hour rhythms permeate the entire animal and even the vegetable kingdoms.2,3 In humans, circadian oscillations have been found in over 10% of our expressed genes affecting almost all of our bodies’ metabolic, neurological and endocrine pathways.4The suprachiasmatic nucleus (SCN) in the hypothalamus acts as our “master clock,” responding to daily light-dark cycles through photoreceptive ganglion cells in our retinas.5

Mattson et al. questioned whether the invention of artificial light and shift work perturbed this circadian clock, promoting longer daily cycles of consumption (especially nighttime meals.)

In turn, our erratic eating behaviors affect our biological clocks. Two of the main pathways in our bodies that respond to fasting and feeding – cAMP response element binding protein (CREB) for fasting and the insulin-dependent mammalian target of rapamycin (MTOR) for feeding – can directly influence circadian oscillations. In one mouse study, researchers were able to use feeding to rapidly shift liver oscillations 10 hours out of sync with the light-sensitive SCN.6

This cycle of altered eating behavior and perturbed rhythms building on one another may be a major cause of obesity and metabolic disturbances.

Which raises the question, if our natural eating pattern has been altered, is the daily western habit of three square meals truly a healthy lifestyle or a consequence of disturbed rhythms? Does it actually contribute to unnecessary metabolic stress?7-10

Recent reports of hunter-gatherer eating behavior and Dr. Cordain’s own ethnographic research paint the picture of a very different eating cycle. One of hunter-gatherers consuming a single large meal in the late afternoon or evening after spending the day hunting and gathering on little to no food.11, 12 Nor did hunter-gatherers eat consistently day-to-day. While anthropological research has debunked the notion of intermittent starvation in Paleolithic times,13 without the modern joys of a stocked fridge and preservative-packed foods, hunter-gatherers likely had frequent days of severely reduced energy intake.

So if three daily large meals puts us at evolutionary odds, how should we eat?

The health benefits of a calorie restricted (CR) diet, including a positive effect on longevity, have already been established.14-17 In their review, Mattson et al. go a step further proposing two timing-dependent variations on a CR diet that are more consistent with Paleolithic behavior and may actually enhance the health benefits.18

The first is a time-restricted feeding (TRF) diet where consumption is limited to a short period during the day – a four to eight hour window – to better match life before artificial lighting. The second was intermittent energy restriction (IER) consisting of periodic days where calories are greatly reduced (i.e. just 500 calories) such as twice per week – an eating pattern that would be more consistent with a Paleolithic lifestyle. Examples of both diets are shown in the figure below:

Circadian Rhythms | The Paleo Diet

Mattson, M.P., et al., Meal frequency and timing in health and disease. Proc Natl Acad Sci U S A, 2014. 111(47): p. 16647-53.

More and more studies are touting the health benefits of IER, but studies of TRF are less promising, often finding no benefits over a standard calorie restricted diet.19,20 Mattson et al. found four potential explanations for why an IER diet prevents and even reverses a variety of chronic diseases including cancer, CVD, diabetes and neurodegenerative diseases.21

Better “Stress” Management

IER creates a mild stress in our bodies. But instead of being damaging, it may spark an adaptive response that ultimately enhances our defense mechanisms against more serious stress. A variety of animal studies have supported this claim showing that alternate day fasting can prevent age-related decline in the antioxidant enzymes superoxide dismutase I and catalase and can protect and even strengthen neurons against oxidative, metabolic, and proteotoxic damage.22

Improved Bioenergetic Profile

A three meal-per-day paradigm has a consequence of maintaining elevated blood sugar and insulin levels both of which have been shown to have multiple health consequences including obesity, diabetes and a variety of metabolic disorders.25-28Due to extended periods of fasting, both IER and TRF diets improve metabolic profiles including lower blood concentrations of sugar, insulin and leptin, increased insulin sensitivity, better mobilization of fatty acids, and elevated ketones which can promote neuron health and protect against cancer.18, 29,30 The figure below shows improved insulin sensitivity and blood triglyceride concentrations on an IER diet over even a daily CR diet.

Circadian Rhythms | The Paleo Diet

Harvie, M.N., et al., The effects of intermittent or continuous energy restriction on weight loss and metabolic disease risk markers: a randomized trial in young overweight women. Int J Obes (Lond), 2011. 35(5): p. 714-27.

Reduced Inflammation

More and more research is revealing that almost all chronic diseases are linked to inflammation both locally and throughout the body. An IER diet reduces key inflammatory markers such as TNF-α and IL-6.31 However, Mattson et al. were uncertain whether the diet had a direct effect on inflammation or if it was a side effect of the weight loss typically associated with the diet.

Improved Repair and Maintenance

Damaged organelles and misfolded proteins are a natural consequence of daily living. Fortunately our cells have mechanism, such as autophagy to take up and remove damaged cellular material. Inhibition of autophagy may accelerate aging.32Eating puts the body in a protein building mode which suppresses autophagy.33Extended periods of fasting allow our cells to switch gears and cleanse themselves.

Meal timing is a promising area of research that can bring us one step closer to eating like our Paleolithic ancestors. However, even the authors of the review pointed out that long term controlled studies are still limited and there is no consensus yet on how to best implement an IER diet. A healthy Paleo Diet should still focus primarily on what you eat. But even if you don’t want to try a timing-dependent variation, it might be worth questioning whether 9:00 pm is the best time to eat baked salmon or if you really need that big a bowl of fruit and almonds every morning.

Thanks for reading!

Trevor Connor | The Paleo DietTrevor Connor is Dr. Cordain’s last mentored graduate student and will complete his M.S. in HES and Nutrition from the Colorado State University this year and later enter the Ph.D. program. Connor was the Principle Investigator in a large case study, approximately 100 subjects, in which he and Dr. Cordain examined autoimmune patients following The Paleo Diet or Paleo-like diets.


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