What if I told you there was a diet that gets better fat loss with less muscle loss, improved cardiovascular health, and better glucose control, all with less hunger, and without much risk of disordered eating or body image concerns? Well, to many people, that's exactly what so-called intermittent fasting represents. I call it so-called because in the scientific literature, you don't really see it go by that name. Instead, you have alternate day fasting, where you eat one day and fast the next day, and time-restricted feeding, where you fast for 16 to 20 hours with a 4 to 8 hour eating window.
In practice, many adherents follow the lean gains protocol, popularized by Martin Burkhand, where you fast for 16 hours with an 8 hour eating window centered around weight training. As it turns out, fasting has many benefits, but they've mainly been seen in rats, where intermittent fasting causes better weight loss, improved cardiovascular health, neuroprotective effects, decreased cancer risk, and increased lifespan, and many of these effects are independent of caloric restriction alone. It's not fully understood why fasting has these positive health effects, but one theory is that periodic food deprivation serves as a sort of preconditioning stress, one that allows for resistance to bigger stresses in the future.
It's kind of like exposing yourself to stressful germs can enhance immunity and protect against future stresses down the road. Human studies have fared pretty well too. Two studies showed weight loss, reduced blood pressure, and lowered cholesterol in obese subjects following an alternate day fasting diet for 8 to 10 weeks.
However, two similar studies on lean individuals showed weight maintenance, indicating that alternate day fasting may be a better weight loss strategy for obese folks. And as relatively short duration trials, it's difficult to say how this approach would fare over the long term. Many expressed skepticism over rampant hunger with this approach, but one study in obese patients following a 14 day fast found very impressive weight loss without an increase in hunger.
And this is a recurring theme across this body of research. Fasting can have an appetite blunting effect, and we tend to get hungry when we're used to eating. So while there may be an adjustment period when first switching to intermittent fasting, where you're more hungry than usual, maintaining a regular eating pattern will help control hunger with any diet, regardless of eating frequency.
The biggest systematic review to date, looking at 40 studies, found that while intermittent fasting was better at suppressing hunger than just continuous caloric restriction, this wasn't able to translate into significantly improved body composition or weight loss. The authors conclude that intermittent fasting represents a valid, albeit apparently not superior option to continuous energy restriction for weight loss. As a bodybuilder, one worry is that all this fasting would cause muscle to fall off.
Don't you need to eat every two hours to keep the muscle anabolic? Actually, a 2006 paper showed that even 40 hours of fasting didn't significantly alter negative regulators of muscle mass and didn't cause any significant muscle atrophy. Furthermore, even a 24-hour fast only decreases liver glycogen by less than half, meaning muscle glycogen is completely spared. And the ketone bodies that you typically see in association with alternate day fasting also spare skeletal muscle from breakdown.
Don't you need to eat like six meals a day in order to speed up your metabolism? And won't fasting slow your metabolism down? This myth is based on the correct idea that the thermic effect of food increases following a meal. However, current science indicates that this increase is proportional to the caloric content of the meal, not meal frequency per se. And changes in metabolic rate come from changes in daily caloric intake, not from changes in meal timing.
One good argument against intermittent fasting comes from a 2013 study which showed that anabolic signaling was greater when consuming four 20-gram doses of whey protein compared to two doses of 40 grams or eight doses of 10 grams, implying that from a muscle protein synthetic perspective, protein spaced more evenly throughout the day across roughly four meals may be better for optimizing anabolism. Another consideration is whether intermittent fasting is psychologically healthy. Despite the fact that research from Hadi and colleagues showed that intermittent fasting reduced depression and binge eating, the Canadian Pediatric Society classifies fasting and skipping meals as unhealthy strategies for adolescents.
So for kids and teenagers, this may not be the most suitable approach. To conclude, intermittent fasting has certainly shown itself to be an impressive and effective dieting methodology. In my opinion, it hasn't shown much merit over more standard diets that impose a caloric deficit with sufficient protein intake.
But for those who find it to fit their preferences better and lifestyle better, fasting just may be the way to go. And ultimately, I think the best diet is the one to which you can best adhere.
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