Nick NorwitzMD PhD, Oxford-Harvard | Metabolic Health Educator | “Stay Curious”

⁠Gain Muscle, Lose Fat? The New Biology Behind It

4 Jun 2026 · 2 min

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1:32

In this video, the presenter announces a breakthrough in manipulating muscle growth and fat loss by targeting hormonal brakes—specifically myostatin and activin A. He frames the discussion with an evolutionary perspective, explaining that humans have historically been programmed to store fat as energy insurance and limit excess muscle because it is energetically costly. Recent research using combined myostatin/activin A blockers showed dramatic body‑composition changes in monkeys (≈30% fat loss, ≈10% lean‑mass gain over five months) and, in a first‑in‑human trial, a single eight‑week treatment produced roughly +7 lb lean mass and –9 lb fat mass. Acknowledging initial skepticism, the speaker encourages curiosity, directs viewers to a link for more details, and asks them to subscribe for further metabolic‑health content.

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We just made a breakthrough in the science of muscle growth and fat loss— don't do that— and fat loss. This is based on a series of new studies conducted in monkeys and early human clinical trials that, if true, is a big deal for the future of human health and body composition. But let's back up. It all started hundreds of thousands of years ago with evolution. Evolutionarily, body fat is energy insurance, and excess muscle, more than you need, is energetically expensive. So evolution evolution has primed us to put on fat and not to hold on to too much muscle. And it did this in part by putting certain hormonal brakes on muscle growth. But we've just identified some of these hormonal brakes and we're starting to figure out how to target them, how to block them, how to break the brake on muscle growth. In a new series of studies, researchers tested a combination of what are called myostatin and activin A blockers, and they found first in monkeys, that they could decrease fat mass by 30% while increasing lean mass by 10% in 5 months. And in a first-of-its-type human trial, with just one treatment over 8 weeks, people gained about 7 pounds of lean mass while losing 9 pounds of fat mass. Just one treatment over 8 weeks. Now, I know you might be skeptical. I was too. But you should also be curious because everything seems impossible in science and physiology until we do it. For more details, check out the link below and subscribe for more cutting-edge metabolic health content.