The Health Benefits of Intermittent Fasting

benefits of intermittent fastingAt this point, intermittent fasting isn’t a new concept, nor is it a difficult one. You take in all of your calories for the day within a limited window of time, and the rest of the day, you stick with water, maybe a cup of coffee, or tea in the morning if you feel so inclined. The idea is that giving your body a period of time “off” from digesting food allows your cells to heal and renew in other ways.

A Practice Born Because Calorie Restriction is Unpleasant

Intermittent fasting became popular because calorie restriction was found to contribute to healthy aging. A few mouse and worm studies seem to show that drastic reductions in food intake over a long period of time could prolong your life.

The research is compelling, but I’m not convinced actively restricting your calorie intake through sheer will is the true path to enjoyable longevity. I don’t want to be thin, frail, distractible, or preoccupied with food. I’d rather be vibrant and full of zest. I want to eat big strapping meals of steak and veggies smothered in butter without worrying about calories. I want to maintain muscle mass and have enough energy to go on long hikes and have the legs to still leap for high passes (over the young guys) at the end of Ultimate games. And as I appreciate the neuroprotective and autophagy-promoting qualities of calorie restriction, I’d rather not expend the mental energy and fortitude required to maintain such a regimen day-in and day-out.

Intermittent fasting is the workaround. Pushing off breakfast for a few hours gives me all of the benefits of calorie restriction, without all the misery.

Fasting is the way to have your cake and eat it too. Beyond the already proven benefits of a Primal Blueprint low-carb lifestyle, fasting once in a while seems to offer many of the same benefits of calorie restriction – you know, stuff like increased longevity, neuroprotection, increased insulin sensitivity, stronger resistance to stress, some cool effects on endogenous hormone production, increased mental clarity, plus more – but without the active, agonizing restriction.

You just eat Primally, focusing on meat and vegetables with plenty of animal fat, and skip meals on occasion. A sixteen-hour fast is on the low-but-still-effective end, or you could opt for longer, more intermittent fasts – say, a full twenty-four hours once or twice a week. Women may need to time fasts a little differently than men. More on that here.

When you’re done with the fast, eat as much as you want (which usually isn’t an issue, once you’re keto-adapted). It essentially turns into “eat when you’re hungry,” because let’s face it: eating the types of foods we evolved eating induces powerful satiety and makes eating the right amount of food a subconscious act. Fasting becomes a whole lot easier (and intuitive) when you’ve got your food quality dialed in. And I’ll come back to that little caveat at the end here.

“Fasting” was the top search term for MDA last week, and I hadn’t done a big post on it in a while, so I thought I’d do a comprehensive rundown of all the benefits (some conclusive, others prospective) you can expect to obtain from IF.


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Intermittent Fasting and Longevity

Everyone wants to live longer, but I find longevity pointless if you’re not enjoying yourself. Otherwise, life becomes dreary.

The popular c. elegans worm enjoys increased longevity with both twenty-four and forty-eight hour IFs via signaling through a gene that we all have.

One study (full PDF) from the 1940s found that varying amounts of twenty-four hour IFs (every other day, every fourth day, every eighth day, etc) prolonged the lifespan of rats without retarding or stunting the growth (as occurred with calorie restricting them). Female rats responded best to every eight day fasts, while males responded best to every other day fasts.

Reductions in brain insulin signaling have been shown to increase lifespan in animals, either by calorie restricting or actively knocking out brain insulin receptors. Fasting also reduces brain insulin signaling, at least in rats.

Blood Lipids

Going in and pharmaceutically manhandling your cholesterol synthesizing equipment is one thing; eating real food and exercising, resulting in possible alterations to your lipid profile, is another. We don’t set out to force your blood lipids into submission, but lifestyle changes that happen to change them for “the better” are usually a good thing. Fasting brings potent changes to blood lipids in an “organic” way – you’re just letting your machinery do its thing on its own – and this is probably a very good thing.

Intermittent fasting is as effective or even more effective than calorie restriction in improving metabolic syndrome markers in overweight women, and it’s a whole lot easier to stick with.

Alternate day fasting improved cardiovascular risk markers, including lowered triglycerides and LDL-C numbers (although it’s unclear whether the improvements were related to the weight loss alone or something unique to fasting).

I discussed this last week, but it can’t hurt to mention that short-term alternate day fasting wrought improvements in LDL particle size and distribution in obese adults.

Sticking with Intermittent Fasting

A dietary regimen is useless without compliance. In fact, that’s what we’ve always said about the low-fat, low-calorie diet advice we’re inundated with: sure, they might work, but they’re impossible for most people to maintain. Eating Primally solves this problem, because it’s simple, easy, delicious, and satiating (you just have to enjoy cooking, or learn to), and intermittent fasting is another compliance-breeding regimen that blends quite nicely with the Primal Blueprint. A lot of Primal eaters find that fasting just kinda happens without them setting out to do it, so it’s not even a conscious struggle.

Obese individuals were able to quickly adapt to alternate day modified fasting, which meant on fasting days they’d get 26% of their normal caloric intake. They were also able to maintain physical activity despite the fasting.

Heck, intermittent fasting even helped cocaine addicts stick to their treatment and rehab program. Not bad.

Intermittent Fasting and Cancer

The notion of IF reducing cancer incidence and improving survival is compelling, but little evidence in humans exists. Ketogenic diets may also offer exciting potential for cancer patients, and both intermittent fasting diets and ketogenic diets share something: fat (either dietary or from your own adipose tissue) as primary fuel sources.

While you might not want to be in a constant state of ketosis, intermittent fasting is sustainable, simple, and can be integrated into your current diet. As of now, most of the evidence for IF’s protective effects against cancer exist in animal trials, mostly using mice. Still, fasting seems to confer so many other benefits that working it into your life for its anti-cancer potential is probably worth it. Some of the evidence:

Calorie restriction has been shown to fight cancer cell proliferation in mice, but researchers found that intermittent fasting was just as effective. In fact, here’s a review of most of the animal anti-cancer evidence. It’s quite compelling.

Some researchers are speculating, based on substantial evidence, that fasting before and during cancer treatment should result in reduced morbidity, better tolerance of chemotherapies, and higher cure rates. This is refreshing news. A preliminary study in human cancer patients found that fasting during chemotherapy reduced the negative side effects of the treatment. The authors are quick to point out that the results are in no way a prescription for fasting in chemotherapy patients and that controlled trials are needed to change official recommendations, but that doesn’t mean you – the individual – can’t experiment.

Growth Hormone

Aging humans “normally” experience reductions in growth hormone. While it’s true that unchecked growth hormone can lead to unwanted cell proliferation (like, ya know, cancer), growth hormone therapy can really help stave off the doldrums of old age. A study found that resistance training actually blunted hunger for an hour. I’ve found this to be the case for me. If the body “needs” food right after a workout, why would hunger be blunted? This is why I tend to hold off on the eating post-workout. Every little bit helps, especially as you age.

Neurological Health

Fasting doesn’t cause your brain tissue to waste away, contrary to what some people will tell you. It’s actually good for brain health. Any dietary restriction tends to increase neuronal plasticity and promote neurogenesis, but it was IF that had the greatest effect (with the fewest downsides). Another study of mice found that meal frequency impacts neuronal health. That is, mice who ate larger meals more infrequently saw greater increases in brain and overall bodily health. Still another study found that IF was beneficial for peripheral nerve function in mice by promoting the maintenance of the neuronal pathways responsible for locomotor performance. It’s almost like this stuff just puts your brain in repair, or maintenance mode.

Fasting and Autophagy

Fasting turns on autophagy (most studies nowadays treat this as common knowledge), which is the process by which cells recycle waste material, eliminate or downregulate wasteful processes, and repair themselves. Why is autophagy so important? It’s required to maintain muscle mass, and inhibiting it induces atrophy of adult skeletal muscle.  It reduces the negative effects of aging and reduces the incidence and progression of aging-related diseases. In fact, researchers have determined that autophagy is the essential aspect of the anti-aging mechanism of fasting.

Without the autophagy that fasting provides, you would get very few of the benefits. Fasting even increases neuronal autophagy, which aids in maintaining mental health and function. Short term fasting, too. No marathon thirty-six hour fast required.

Fasting and Fitness

You’ll hear that you should never exercise on an empty stomach. You’ll hear that fasted training will burn your  muscles and cause you to waste away. You’ll hear that performance will surely suffer. None of these things are necessarily true – and they are even less so if you are well-adapted adapted to a low-carb eating strategy. Fasted training can actually result in better metabolic adaptations (which mean better performance down the line), improved muscle protein synthesis, and a higher anabolic response to post-workout feeding (you’ll earn your meal and make more muscle out of it if you train on an empty stomach). Studies on Muslim athletes during Ramadan show no effect on performance while fasting, as well as a more favorable lipid profile in those who exercise and fast rather than just fast. When you train in a fasted state, glycogen breakdown is blunted and more fat is burned, leaving you more glycolytic energy in the tank for when you really need it and less body fat. Those are just a sampling of the benefits to fasted training; there are dozens more.

Mental Well-being and Clarity

A lot of health influencers will tell you that failure to eat something every few hours will cause mental fog and sluggishness, so keep a banana or a granola bar on your person at all times. Of course, this is all based on an assumption that we need to supply exogenous carbs on a regular basis to properly fuel the brain. This notion that fasting is only the province of anorexics or “caveman” has kept many people from experiencing the vast array of benefits.

I maintain that one’s comfort in handling intermittent fasting effortlessly does increase dramatically when you’ve reprogrammed those cells (and genes) to predispose your body to derive most of your day-to-day energy from fat, as opposed to constantly dipping into glycogen stores (as happens when we rely so much on refeeding carbs every few hours).

Overall, fasting just seems right. It’s like a reset button for your entire body, presumably across a large spectrum of maladies and dysfunctions. It puts your body into repair mode – at the cellular level – and it can restore normal hormonal function in the obese or overweight. Now, you don’t have to fast, but it’s definitely something to consider.

Have you tried intermittent fasting yet? Let me know how intermittent fasting has worked – or hasn’t – with your lifestyle in the comment section!

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About the Author

Mark Sisson is the founder of Mark’s Daily Apple, godfather to the Primal food and lifestyle movement, and the New York Times bestselling author of The Keto Reset Diet. His latest book is Keto for Life, where he discusses how he combines the keto diet with a Primal lifestyle for optimal health and longevity. Mark is the author of numerous other books as well, including The Primal Blueprint, which was credited with turbocharging the growth of the primal/paleo movement back in 2009. After spending three decades researching and educating folks on why food is the key component to achieving and maintaining optimal wellness, Mark launched Primal Kitchen, a real-food company that creates Primal/paleo, keto, and Whole30-friendly kitchen staples.

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