As I write this sentence, I’m coming up on the 14-hour mark of my daily fast. I’m somewhat hungry, but not uncomfortably so. And my mind is fully alert. As alert as it’s going to get, anyway.
That’s a good thing, because I’m about to explain the whys and hows of fasting in a way that, fingers crossed, actually makes sense.
I’ll start with the benefits, and there are plenty of them. Then, once you’re feeling good about fasting, I’ll get into the science behind how it works. Autophagy and AMP-activated protein kinase are not only cool processes activated by fasting, but they’re also fun terms to drop in mixed company.
Finally I’ll explain how ridiculously easy it is to incorporate fasting into your life. Then you can go forth and reap the benefits.
Sound good? Cool.
Why Should You Fast?
The human body is an intricate machine honed over millions of years of hominid evolution. But unlike most machines in this age of technology, our beautiful bag of skin can actually repair itself. That is, if we know what levers to pull.
One of those levers is fasting. Fasting activates a number of processes that make us stronger, faster, harder to kill, perhaps even better looking. I’ll get to these processes in a moment, but as promised, here’s a list of scientifically-validated benefits from fasting:
- Fat loss: Fasting for 16 hours a day causes significant fat loss without a loss of lean muscle mass in athletes. Fasting also reduces visceral fat around the organs.
- DNA protection: fasting protects DNA (in mice) from massive doses of chemotherapy
- Insulin sensitivity: Fasting improves insulin sensitivity (meaning: better regulation of blood sugar – important for reducing inflammation) in both mice and men
- Better brain function: Fasting improves alertness in humans, and prevents cognitive decline in rats
- Lower inflammation: Fasting reduces inflammatory markers in people with asthma (If you’ve read my stuff before, you know how important inflammation is for healthy aging)
- Longevity (via cellular cleanup): Fasting activates autophagy (cellular cleanup), which plays an important role in longevity and healthy aging
- Hormonal improvements: A 24 hour fast boosted growth hormone by 1300% in women and 2000% in men (yeah, you read those numbers correctly)
- Improved metabolism: Fasting, even for 16 hours, turns white fat into brown fat in our bodies (brown fat burns more calories)
There are more benefits, but to prevent this article from becoming a giant list of bullet points, I’m going to stop there. I have my dignity.
Circadian Rhythm and Nutrient Sensing Pathways
When you read the literature on fasting, one thing comes up again and again: circadian rhythm enhancement. By not eating overnight, you are literally calibrating your sleep / wake cycle for optimal performance. And since this cycle regulates a large chunk of the human genome – genes that control everything from metabolism to cellular defense to immunity – you’ll want to get it calibrated like a Swiss watch.
By now you’ve probably heard that light regulates the circadian rhythm. Bright light, from the sun or a light box, actives a little dandy called the suprachiasmatic nucleus (SCM) in your brain. This supra-clock is just what it sounds like: it’s the super clock, the master clock, the boss of the circadian rhythm.
But there are also secondary clocks in your muscle and organ tissue, and these clocks are regulated by food. So what happens when you eat (or don’t eat) something? Basically, food sends a signal to these secondary clocks to activate “nutrient sensing pathways.” And these pathways control a lot of those benefits I listed earlier.
mTOR, AMPK and Cellular Repair
Take, for instance, the mammalian target of rapamycin (mTOR) pathway. mTOR is activated when you eat, and it helps you build muscle. But if mTOR is active all the time (because you’re always snacking, say), you will constantly remain in an anabolic state. Always building, never stopping to fix things.
Here’s where fasting comes in. When you fast, mTOR is suppressed and an enzyme called AMP-activated protein kinase (AMPK) becomes active. Ah, AMPK. It gets you burning fat, repairing cells.
One such repair process mediated by AMPK is called autophagy. Autophagy is when your cells digest themselves, when your cells take out the trash, when AMPK causes activation and dephosphorylation of the ULK kinases and blah blah blah – whatever that means. The takeaway is that autophagy is associated with greater longevity.
And it’s not just autophagy enhanced by an overnight, circadian-friendly, fast. Metabolism, insulin sensitivity, blood glucose, inflammation, weight regulation, the list goes on. Bottom line: fasting overnight appears to be a no-brainer for optimizing health.
How to Incorporate Fasting
The way I see it, there are a few main options on the fasting menu:
1) The Circadian Special: Fast overnight for 12 hours to get the circadian (and some of the repair) benefits. This is also called “Time Restricted Eating,” and there is strong science on this intervention for both practicality and improving various biomarkers. Good for beginners.
2) Standard Intermittent Fast: Fast for 16 hours, including the overnight fast. This intervention has fairly strong evidence for metabolic improvements, fat loss, etc. Plus the longer you fast, the more AMPK and autophagy you activate.
3) The Day Long: Occasionally go 24 hours without food. More autophagy, etc here still. But you run the risk, in my view, of circadian rhythm disruption because many internal clocks are regulated by food. And you’ll get dang hungry.
4) The Full Reset: A longer, 3-5 day fast. I haven’t tried this myself (I’m scared), but there’s evidence it can reset the immune system and cause a huge increase in stem cell production. If you go for the full reset, get supervision.
As for me, my fasting protocol falls somewhere between options 1 and 2. Some days I fast for 13 hours, others for 17. I find this strikes a nice balance between circadian rhythm entrainment, cellular repair activation, and the joy of eating.
Speaking of, it’s now been 16 hours and I’ve worked up a mean appetite writing this article. So if you’ll excuse me, I’m going to open my fridge and grab the first thing that looks edible.
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