What if I told you that an essential part of healthy eating includes short periods of not eating? That line of thinking runs counter to everything we do today. You probably have a snack, if not a full meal, before running out the door. You might have another snack once you get to work and make your coffee, maybe a banana, a handful of nuts, or — if you dare — a donut. Before lunch, you might have a granola bar just to tide you over. After lunch, you may need a small pick-me-up if your energy starts lagging in the afternoon. Are you keeping track? That’s five times you’ve eaten before dinner. And then there’s an after dinner snack, and the midnight snack. Have humans always eaten like this?
Intermittent Fasting - In-depth Interview with Dr. Goldhamer & Dr. Group
Length: 93 minutes
Fasting in Human Evolution and Culture
Humans didn’t always have access to food whenever they felt a craving for a snack, so the human body, your body, evolved to expect long periods of time in which food was nil or scarce. Of course, your ancestors still needed to find food if they had any hope of reproducing and passing their genes on, so certain side effects of hunger developed to increase their success at getting food. A day or two without food left your progenitors with a singular focus to find a source of calories. If they weren’t able to function during times of scarcity, chances are they wouldn’t have had the opportunity to bear children and pass their genes down to you through the generations.
As society developed, regular periods of not eating became less of a consequence of food scarcity and more of an integral part of cultural norms and identities. Meals were eaten at certain times of the day. But as technologies like electricity progressed and spread to the general populace, society’s habits and meal times changed to fit the highly variable daily schedules of modern people.
There are a lot of changes in human history that have collectively altered the health, and indeed the girth, of the world’s population, but the effect of technology and modern life may have especially far-reaching implications on hunger, weight, and energy levels. This is where intermittent fasting comes in.
What Is Intermittent Fasting?
Put simply, intermittent fasting is alternating periods of fasting with periods of eating. This can occur during the same day or you can fast for 2 days per week and eat the other 5 (the so-called 5:2 Diet). Many people who practice intermittent fasting adjust their eating schedule to align with the natural rhythms of hormonal and sleep-wake cycles of the body. This cycle can be one of your own devising, or it can be a more established pattern like 12 hours of fasting followed by a 12-hour window in which you can eat normally, or 16 hours of fasting and 8 hours of eating.
The protocol you choose hinges on your health goals, energy needs, and willpower. Intermittent fasting to improve physical fitness is different from intermittent fasting for weight loss. The schedule and foods you choose are the primary differences.
Why Try Intermittent Fasting?
One argument for intermittent fasting is that it’s easier to stick to compared with dieting or eating small amounts of food throughout the day for weeks or months. Eating things in moderation or miserly portions isn’t for everyone. In fact, most people find dieting difficult for this very reason. If you take an “all or nothing” approach to dietary changes, intermittent fasting might help you get the results you want. Indeed, alternating periods of fasting with short periods of eating appears to increase weight loss compared to traditional calorie restriction.
An even better argument for intermittent fasting is that regimented intermittent fasting periods combined with earlier mealtimes work with, rather than against, your hormonal rhythms to promote a healthier metabolism. Your appetite, energy expenditure, satiety (feeling full), and fat storage all respond to hormonal and environmental cues like your sleep-wake cycle. Eating on a regimented schedule, like intermittent fasting, can help you optimize your eating habits for weight maintenance, weight gain, and weight loss.[5, 6] Intermittent fasting also brings many health benefits.
Eating on a Schedule With Intermittent Fasting
When you eat at times when your body isn’t prepared for food enzymatically or hormonally, you start throwing all the various clocks in your body out of sync. That midnight snack triggers your digestive system to start secreting all the digestive juices it needs to break down that cup (ok, bowl) of ice cream during a time when your brain is calling for sleep. A few hours later, when you’re sleeping, your blood floods with sugar from the meal and your pancreas deploys insulin to herd that sugar into cells. Your cells don’t need a rush of sugar at 2 a.m., and this throws your organ systems and hunger-regulating hormones off-kilter. Eating out of sync with what your body needs can affect how your body responds to hormones like insulin, ghrelin, and leptin. Disrupting these hormones can significantly affect your appetite, and how you use and store energy in your body.
Ideally, your hormonal cycle should sync up with your sleep-wake cycle to fuel and support your daily activities. But your stress, eating habits, and hectic daily schedule can easily prevent these two systems from running on the same schedule. To stick to an intermittent fasting schedule, you’ll have to be diligent about eating on time and avoiding snacks and meals if they fall out of the designated eating window.
The Many Benefits of Intermittent Fasting
Research hints at the far-reaching implications of intermittent fasting for diverse populations. The brain, weight loss, and fitness benefits make intermittent fasting an appealing option for anyone looking to improve their health, especially for anyone trying to maintain weight loss after obesity or people with type 2 diabetes.
Slowed Aging and Improved Longevity
Caloric restriction has received a lot of press the last few years for its role in extending lifespan in animal studies, but it’s near impossible to ethically study long-term food restriction on humans. Intermittent fasting triggers the same effects of caloric restriction, so you get the improved aging and a longer, healthier lifespan.
Boosts Brain Growth, Repair, and Function
Intermittent fasting offers several benefits for the brain. Tightly regulating your eating schedule seems to improve memory, generate new neurons, enhance brain recovery after trauma, elevate mood, and lower your risk of the cognitive decline associated with aging.[8, 9]
Regulates Hormone Levels
Insulin, ghrelin, and leptin levels and response in the body improve with intermittent fasting. This means your body is able to better respond to the rise and fall in blood sugar, and regulate feelings of hunger and fullness. Human growth hormone, the hormone that triggers growth in children and helps regulate sugar and fat metabolism, also increases during cyclical fasts.[10, 11]
Improves Blood Composition
Your body is better able to regulate the ebb and flow of energy resources when you adopt a regular eating schedule. Fasting both lowers and somewhat paradoxically helps sustain healthy blood sugar levels, blood pressure, insulin levels, and cholesterol. Improved blood composition decreases oxidative stress in the body.
Decreases Oxidative Stress
Eating, in general, results in oxidative stress, depleting your antioxidant defenses against free radicals in your tissues. Intermittent fasting, by its nature, significantly decreases your exposure to the inflammatory effects of converting food to energy because you eat less often.[1, 13]
Enhances Fat Burning
Low insulin levels occur during the fasting state because you’re not absorbing a steady supply of glucose from the digestive tract. Low insulin levels prompt fat burning to keep energy levels stable. Intermittent fasting gives you better access to your fat stores.[1, 14]
Mimics the Beneficial Effects of Exercise
Athletic training provides many beneficial effects on the brain, heart, vascular system, stress response, and body composition. Intermittent fasting mimics many of the same benefits, such as lower your resting heart rate, improved immune function, increased DNA repair, better motor function, ketone production, improved resistance to stress, faster recovery from stress, and enhanced recycling of old or malfunctioning cells.
Intermittent Fasting Patterns
Generally, the longer the fasting period, the better the results. Some people find they experience some emotional effects with fasting. You may find that you feel irritable and short tempered while adjusting to an intermittent fasting schedule.
Typical Intermittent Fasting Schedules
|Schedule||Eating Period||Fasting Period|
|12:12||12 hours||12 hours|
|10:14||10 hours||14 hours|
|8:16||8 hours||16 hours|
|6:18||6 hours||18 hours|
|4:20||4 hours||20 hours|
|2:22||2 hours||22 hours|
|Alternate day||Duration of one meal||24 hours after end of meal|
Getting Started With Intermittent Fasting
If you can stretch your fast out for longer periods of time, you’ll quickly see lower insulin levels and spend more time in ketosis, the fat-burning state. To start intermittent fasting, I recommend starting with 12:12 schedule: a 12-hour window in which you can eat followed by 12 hours of fasting. If you find this schedule easy, try an 8:16 schedule next. Fasting for longer periods with comparatively short windows to eat (6:18 or 4:20) are a key component of the warrior diet regimen, a diet inspired by our ancestors' eating habits. Extend your fast beyond even that benchmark and you reach alternate day fasting.
You’ll have to evaluate what works with your daily schedule and workout goals to find a stable, sustainable intermittent fasting pattern. Some fasters find that a 10:14 or 6:18 fasting plan is a better fit for them. Fasting, in general, will yield an array of health benefits, so don’t be afraid to shift your schedule around to suit your needs. Just make an effort to eat earlier in the day rather than late at night to decrease fat storage. However, if you typically skip breakfast, feel free to begin your eating period around lunchtime.
The physical effects of fasting on an individual depends on an incalculable number of variables. Some people respond to fasting significantly better than others. If you are particularly stressed out or you’re going through some difficult life events, I would advise you to put fasting on hold until you get your stress under control due to the hormonal imbalance that usually accompanies (and feeds) the stress response.
What to Eat During an Intermittent Fast
Although you don’t have to adopt a different diet to try intermittent fasting, it’s never too late to eat healthier. I recommend a whole food, plant-based diet with lots of raw vegetables, fruits, nuts, and seeds to improve nutrition and maintain health.
If you’re looking to your diet to kickstart fat loss, try my ketogenic fast. Unlike most ketogenic diets or fasts, which rely on a substantial amount of animal fat and protein to shift your body into ketosis, I designed mine to cleanse the body with whole plant foods like avocado and walnuts that promote a healthy blood composition and lower oxidative stress in addition to torching your fat reserves.
- Van Praag, H., et al. "Exercise, Energy Intake, Glucose Homeostasis, And The Brain." Journal of Neuroscience 34.46 (2014): 15139-15149. Web. 18 Apr. 2017.
- Longer, Valter, and Satchidananda Panda. "Fasting, Circadian Rhythms, And Time-Restricted Feeding In Healthy Lifespan." Cell 23.6 (2017): 1048-1059. Web. 18 Apr. 2017.
- 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." International Journal of Obesity 35.5 (2010): 714-727. Web. 18 Apr. 2017.
- Williams, K. V., et al. "The Effect Of Short Periods Of Caloric Restriction On Weight Loss And Glycemic Control In Type 2 Diabetes." Diabetes Care 21.1 (1998): 2-8. Web. 18 Apr. 2017.
- Garaulet, M., et al. "Timing Of Food Intake Predicts Weight Loss Effectiveness." International Journal of Obesity 37.4 (2013): 604-611. Web. 18 Apr. 2017.
- Lewis, Gary F., et al. "Disordered Fat Storage And Mobilization In The Pathogenesis Of Insulin Resistance And Type 2 Diabetes." Endocrine Reviews 23.2 (2002): 201-229. Web. 18 Apr. 2017.
- Perkins, Robert. "Diet That Mimics Fasting Appears To Slow Aging." News.usc.edu. N.p., 2017. Web. 18 Apr. 2017.
- Bair, Stephanie. "Intermittent Fasting: Try This At Home For Brain Health." Stanford Law School. N.p., 2017. Web. 18 Apr. 2017.
- Martin, Bronwen, Mark Mattson, and Stuart Maudsley. "Caloric Restriction And Intermittent Fasting: Two Potential Diets For Successful Brain Aging." Aging Research Reviews 5.3 (2017): 332–353. Web. 18 Apr. 2017.
- Alzoghaibi, Mohammed A., et al. "Diurnal Intermittent Fasting During Ramadan: The Effects On Leptin And Ghrelin Levels." PLoS ONE 9.3 (2014): e92214. Web. 18 Apr. 2017.
- Ho, K.Y., et al. "Fasting Enhances Growth Hormone Secretion And Amplifies The Complex Rhythms Of Growth Hormone Secretion In Man." Journal of Clinical Investigation 81.4 (1988): 968-975. Web. 18 Apr. 2017.
- Azevedo, Fernanda Reis de, Dimas Ikeoka, and Bruno Caramelli. "Effects Of Intermittent Fasting On Metabolism In Men." N.p., 2013.
- Faris, Mo'ez Al-Islam Ezzat, et al. "Impact Of Ramadan Intermittent Fasting On Oxidative Stress Measured By Urinary 15--Isoprostane." Journal of Nutrition and Metabolism (2012): n. pag. Web. 18 Apr. 2017.
- Fung, Jason, and Jimmy Moore. "The Complete Guide To Fasting." 1st ed. Victory Belt Publishing. Print.
- Torres, Susan, and Caryl Nowson. "Relationship Between Stress, Eating Behavior, And Obesity." Nutrition 23.11-12 (2017): 887-894. Web. 18 Apr. 2017.
†Results may vary. Information and statements made are for education purposes and are not intended to replace the advice of your doctor. If you have a severe medical condition or health concern, see your physician.