Humans are diurnal animals, meaning we work during the day, and sleep and restore (both physically and mentally) at night. But things like technology, long work days, and even light bulbs have drastically expanded what we consider ‘waking hours’ compared to those of our evolutionary ancestors. For most of history, when the sun went down, our bodies knew it was time for bed. But now, most of us couldn't possibly imagine sacrificing those extra few hours between sunset and bedtime!
So if we're not relying on light as a cue for day and night, what do we use? Well, the overwhelming answer is food! The first bite or sip of anything other than water in the morning kicks your metabolism into gear for the day ahead. But recent research shows that hacking this system by limiting how often we eat can improve multiple different facets of health. Here's how to biohack your body clock.
Enter: Intermittent Fasting
Because we're naturally fasting when we sleep, our bodies have evolved to associate the fasted state with biological repair. Intermittent Fasting (IF) is the concept of limiting how and when we eat, thereby keeping us in a restorative mode longer.
IF comes in many forms. Most common is probably the time-restricted feeding (TRF) variation, in which all of someone’s calories are consumed in a relatively short window, typically 8 hours. This might not seem restricting at first, but considering 50% of people eat their meals in a 15 hour time window on any given day, an 8 hour limit will almost definitely require your eating habits to change.1
Another approach (not for the faint of heart) is prolonged fasting (PF), in which a fasting period lasts 2 or more days with at least a week’s time of normal eating before the next round of fasting.2
Lastly, alternate-day fasting (ADF) lands somewhere between TRF and PF, as it's characterized by a two-day cycle of one fasting day (consuming around 500 calories or less for an entire day) and one normal 'feeding day.'
While the concept of any level of fasting may seem difficult and, well, unnatural, research has shown IF has a positive impact on many different corners of the health and wellness universe.
The benefits of IF
You might think that, if you were to limit the hours during which you can eat, you might get hangry and overcompensate for ‘lost time’ come mealtime. But you’d be wrong! Evidence suggests that, if anything, IF results in lower calorie intake overall. And even if you were to throw calorie restriction entirely out the window during “feeding” times, you may still see significant weight loss; evidence shows TRF can help you lose weight, irrespective of calories.
Metabolic disease risk factors
As a general rule of thumb, chronic body clock dysregulation can increase your risk of metabolic disease (like diabetes, heart disease, and high blood pressure). Luckily, many studies show that IF has a positive impact on multiple risk factors for these diseases, including insulin sensitivity, blood pressure, appetite, markers of stress, and belly fat measurements.3,4 It’s through these mechanisms that intermittent fasting can have significant beneficial effects on your glucose and lipid biomarker levels.
Inflammation and immune response
If your white blood cell count is chronically high, TRF may help you return it to optimal.5 On the other hand, if your white blood cell levels are low, a fasting routine can still help! PF has shown to kick stem cell growth into gear, thereby replenishing the immune system with fresh, new cells.6
Giving your body an extra long rest from metabolizing food also gives your digestive system a chance to relax and reset, which may help to lower levels of low-grade inflammation (like hsCRP levels) in your gut.
Feel like your endurance has hit a plateau? Incorporating IF into your routine may help to improve your performance and energy efficiency.7 However, as noted above, IF may inherently come with reduced caloric intake, so make sure you’re still hitting your training fueling needs and getting sufficient levels of endurance-related nutrients like sodium and potassium.
In addition to accelerating the development of metabolic diseases, an off-kilter body clock can also accelerate the aging process (ever noticed someone appear to age quickly after a few especially stressful and sleepless years?).2 Luckily, it seems that fasting helps to reset your body clock and protect against these harmful effects. In fact, IF may directly protect DNA against oxidative damage – a major contributor to the aging process.2
PF may also help to keep bones stronger for longer, as it can help to slow bone mineral (like calcium) loss.8 So far, the evidence is only in mice, but this could be a good indicator that similar results will be found in humans.
Experts agree that mammals have evolved habits to be active when hungry (here’s lookin’ at you, hangry jitters) and sedentary when fed (we don’t have to remind you what a food coma is). It makes sense, then, that studies have found a fasted state to be associated with enhanced overall brain function and memory.9,10
There's also a particular impact on verbal memory, so if you’re someone who frequents podiums or the front of the board room, IF might help boost your stage presence. Your energy levels and mental clarity may also improve as your brain becomes less dependent on a constant steady source of fuel.
As a general rule of thumb, cancer cells don’t act like normal cells – they fuel, grow, and divide in abnormal ways. It’s through these differences that IF can have a positive impact on cancer treatment; multiple studies have shown that fasting can have a protective effect on normal cells but not on cancer cells, priming the body for an optimized response to chemotherapy.11,12,13,14 Do note: if you’re undergoing treatment for any illness or syndrome, consult your physician before making any changes to your treatment.
IF rules to live by
If you're interested in trying IF out for yourself, there are a few tips that might help.
First, there are no rigid fasting hours for TRF! If you're an early bird and like to enjoy breakfast with the sunrise, do it! Just eat your last meal of the day equally early. The opposite is also true – if you're a notorious breakfast-skipper, ride that wave and start your feeding window later in the day.
Second, while they don't have calories, even things like black coffee and tea contain compounds (like caffeine) which must be broken down by enzymes in your body. The jury is still out, but this process might wake your metabolism up to some extent. Many people drink black coffee during fasting hours and still report good results, but if you're trying to be by the book 100%, try to stick to plain water during those hours.
If you need help keeping to your fast, apps like Zero can be especially helpful in tracking your fasted hours and learning more about the process.
Not So Fast
If you decide to follow a fasting regimen, be sure to listen to your body; if you start feeling weak, losing more weight than you intended, or experiencing any other negative side-effects, return to your normal eating habits and recalibrate. Nothing is one-size-fits-all, especially your health.
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 Gill, S., & Panda, S. (2015). A smartphone app reveals erratic diurnal eating patterns in humans that can be modulated for health benefits. Cell metabolism, 22(5), 789-798.
 Longo, V. D., & Panda, S. (2016). Fasting, circadian rhythms, and time-restricted feeding in healthy lifespan. Cell metabolism, 23(6), 1048-1059.
 Sutton, Elizabeth F., et al. "Early time-restricted feeding improves insulin sensitivity, blood pressure, and oxidative stress even without weight loss in men with prediabetes." Cell metabolism 27.6 (2018): 1212-1221.
 Harvie, M. N., Pegington, M., Mattson, M. P., Frystyk, J., Dillon, B., Evans, G., ... & Son, T. G. (2011). The effects of intermittent or continuous energy restriction on weight loss and metabolic disease risk markers: a randomized trial in young overweight women. International journal of obesity, 35(5), 714.
 Gasmi, M., Sellami, M., Denham, J., Padulo, J., Kuvacic, G., Selmi, W., & Khalifa, R. (2018). Time-restricted feeding influences immune responses without compromising muscle performance in older men. Nutrition, 51, 29-37.
 Cheng, C. W., Adams, G. B., Perin, L., Wei, M., Zhou, X., Lam, B. S., ... & Kopchick, J. J. (2014). Prolonged fasting reduces IGF-1/PKA to promote hematopoietic-stem-cell-based regeneration and reverse immunosuppression. Cell stem cell, 14(6), 810-823.
 Pons, V., Riera, J., Capó, X., Martorell, M., Sureda, A., Tur, J. A., ... & Pons, A. (2018). Calorie restriction regime enhances physical performance of trained athletes. Journal of the International Society of Sports Nutrition, 15(1), 12.
 Brandhorst, S., Choi, I. Y., Wei, M., Cheng, C. W., Sedrakyan, S., Navarrete, G., ... & Di Biase, S. (2015). A periodic diet that mimics fasting promotes multi-system regeneration, enhanced cognitive performance, and healthspan. Cell metabolism, 22(1), 86-99.
 Kretsch, M. J., Green, M. W., Fong, A. K. H., Elliman, N. A., & Johnson, H. L. (1997). Cognitive effects of a long-term weight reducing diet. International Journal of Obesity, 21(1), 14.
 Witte, A. V., Fobker, M., Gellner, R., Knecht, S., & Flöel, A. (2009). Caloric restriction improves memory in elderly humans. Proceedings of the National Academy of Sciences, 106(4), 1255-1260
 Tinkum, K. L., Stemler, K. M., White, L. S., Loza, A. J., Jeter-Jones, S., Michalski, B. M., ... & Piwnica-Worms, H. (2015). Fasting protects mice from lethal DNA damage by promoting small intestinal epithelial stem cell survival. Proceedings of the National Academy of Sciences, 112(51), E7148-E7154.
 Raffaghello, L., Lee, C., Safdie, F. M., Wei, M., Madia, F., Bianchi, G., & Longo, V. D. (2008). Starvation-dependent differential stress resistance protects normal but not cancer cells against high-dose chemotherapy. Proceedings of the National Academy of Sciences, 105(24), 8215-8220.
 Safdie, F., Brandhorst, S., Wei, M., Wang, W., Lee, C., Hwang, S., ... & Longo, V. D. (2012). Fasting enhances the response of glioma to chemo-and radiotherapy. PloS one, 7(9), e44603.
 Lee, C., & Longo, V. D. (2011). Fasting vs dietary restriction in cellular protection and cancer treatment: from model organisms to patients. Oncogene, 30(30), 3305.
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