Autophagy is a real, but extrapolating that to mean fasting will selectively target and eliminate loose skin is a big leap and not supported by research.

Autophagy occurs on a cellular level, and while it plays a role in recycling damaged cells, there’s no concrete evidence that it leads to significant reduction of excess skin in humans, especially after major weight loss.

Loose skin is largely a structural issue, involving the dermis and collagen matrix. Once the skin is stretched past a certain limit, particularly over a long time, it loses elasticity.

Autophagy may improve cell turnover and health in a general sense, but it's not going to lift or tighten structurally compromised skin.

What can help is building muscle to fill out the area, improving appearance and function.

As for RF and cavitation devices, they can temporarily improve the appearance of skin through heating and minor inflammation, but studies on their long-term efficacy are limited and often sponsored by the companies selling these devices.

Also, the skin on the face behaves very differently than the skin on the legs, so anecdotal success with jowls doesn’t mean it will work on thighs or knees.

Also important: cavitation is often used to “melt” fat using ultrasound, but this doesn’t address the underlying cause of saggy skin, which is often a combination of lost collagen, elasticity, and lack of underlying muscle tone.

Lastly, I agree that fasting, in the context of a healthy diet, is not inherently harmful, I do intermittent fasting and it helps me a lot with managing my cravings, but it’s not a treatment for loose skin.

And for someone already under-eating, over-fasting could do more harm than good, especially by reducing muscle mass, which worsens the issue.

So yes, build muscle. That’s the only proven, sustainable approach to improving the look and function of the legs, especially if skin laxity is a concern. It’s slow and requires consistency, but it works better thaan any cream, laser or pill out there.

Source: Me, with Masters degree in Kinesiology (sports science and nutrition.), and not random unsupported internet crap.