One topic I seem to be asked about all the time is intermittent fasting (IF)—and it’s pretty obvious why this happens. If your life is busy, it’s easy to just not eat all day, then blast through a few thousand calories before going to bed. I’m pretty busy, so when this notion appealed to me a few years ago—and I wanted to save time and preserve my body composition—I gave it a shot. The verdict? Good idea, poor execution. IF does cause weight loss—at least this particular protocol does—but the problem comes when you think about what kind of tissue the lost weight actually comes from.
Are you really burning fat? Are you really building muscle? I found out the hard way.
When I tried
Why, I wondered, didn’t IF preserve my lean muscle mass as promised, despite the supposed massive increase in GH we’re always hearing about from IF proponents?
Well, being muscular and defined is a war between breakdown and synthesis. Being jacked depends on shifting all your forces toward growth and defending against destruction. As it turns out, IF does the exact opposite of what we need by shutting down synthesis and letting catabolic processes run wild.
Simply put, your body is not kind to your muscle mass while you’re fasting. Fasting rapidly adjusts several regulators of growth—many of which act to shut down the all-important mTOR pathway, one of the most critical pathways for protein synthesis and protection against protein breakdown. This cascade of suppression signals starts quickly, typically within 12 hours of fasting. Inhibiting the mTOR pathway prevents resistance training from triggering muscle growth when mTOR is deactivated. Not only can you not build muscle, but the same changes that prevent the activation of mTOR also prevent insulin from stopping the breakdown of muscle.
Although GH concentrations increase with IF, free IGF-1 levels decrease. This means that although GH goes up, only its fat-burning properties persist. Its muscle-building properties disappear. This decrease in free IGF-1 suppresses the mTOR pathway even further. It’s confusing, but by practicing IF, you’ll get greater GH release, but ablated anabolic response. mTOR activation protects against the destructive effects of cortisol. Shutting down mTOR allows glucocorticoids— catabolic steroids—to chew up muscle tissue.
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