Prolonged fasting and a fasting-mimicking diet are both comparable to exercise in that they involve cycles of cellular damage and repair. During a fasting-mimicking diet, the body consumes both visceral fat and lean body mass for energy. However, upon refeeding only lean muscle mass is regenerated. The overall result, a loss of visceral fat without depleting lean muscle mass, is a desirable feature of a prolonged fast, particularly for athletic performance. In this clip, Dr. Valter Longo describes how a fasting-mimicking diet can be used for fat loss while preserving lean muscle mass.

Rhonda: Something else I that comes to my mind as well as wanting the IGF-1 to go where it's supposed instead of sitting around in your serum, and the bloodstream, but going to the muscle, going to the brain. And I know that it's been shown in humans that IGF, yeah, it's been shown in humans that acute exercise, I think it was aerobic, lowers serum IGF-1. And I think it's because it's going to the muscle, also to the brain, because in mice, it's been shown that exercise causes IGF-1 to cross the blood-brain barrier and get into the brain. So, that's another good reason to exercise is because, now, the IGF-1 that you have, you know, is going to the places where it should.

Valter: Right. Yes. So exercise out, obviously there's no doubt that it's very beneficial. And some of it may be related to the fasting, meaning that exercise is known to do damage to the muscle, right? And so, that damage, and then it's known that after the damage, you get repaired. And that's also known that the repair is what builds the muscle, right? So, this may be not as potent as the fasting, but if you do it all the time, it could be that you have all these small regenerative processes occurring every couple of days, if you access every couple of days. And then, you know, eventually, those cumulatively, it could be actually very powerful, and, yeah, so...

Rhonda: Really in combination with the fasting too, I mean, if you're going to eat your protein and activate IGF-1, then it's good to exercise to make sure it's going to the right place, right? And so, it's...

Valter: Yeah. Yeah, yeah. And, yeah, absolutely. And in the book that I wrote, I really talked about exercise and the need to exercise to make sure that some of these restrictions don't end up in loss of lean body mass. Because the exercise, especially the weight training, is very important in sending the signals to the muscle to rebuild it. And this is really another very interesting thing about fasting, which is it takes the energy from the visceral fat, but it also takes energy from the muscle. But then, unlike other diets, it rebuilds the muscle. And so, now, in clinically, we see a specific loss of fat only significant in the visceral area, and then, no loss, or very minimal loss of lean body mass, right? Because there is a temporary loss, but then rebuild it. So, it's really interesting, and is what athletes are starting to become very interested in this fasting-mimicking diets because...

Rhonda: Right. Yeah.

Valter: Because, you know, most of the diets will get rid of water, muscle, and fat, right?

Rhonda: Right. And you wanna increase lean muscle mass, and decrease fat mass, I mean, that's...

Valter: Yeah. Or at least leave alone the lean body mass, and decreasing fat. Where you have, you know, you're switching to a state that is much more beneficial to your pro-athletic performance, yeah.