A 1970s Molecule Might Solve GLP-1's Muscle Loss Problem

Key takeaways

• A decades-old molecule called TOFA increased energy use in mice by as much as 18%, without any increase in movement or body heat.
• Treated mice lost body fat while largely holding onto lean muscle, and also saw improvements in blood sugar handling, triglycerides, and liver fat.
• When paired with GLP-1 medications like semaglutide and tirzepatide, the combination outperformed either approach alone, hinting at a complementary rather than competing strategy for long-term weight management.

Two levers, one we rarely use

Body weight comes down to two dials: how much energy goes in, and how much goes out. Most of today's weight-management tools, including the popular GLP-1 class of medications, work almost entirely on the first dial by curbing appetite. Researchers at UC Berkeley decided to go after the second dial instead, revisiting a compound first identified back in the 1970s called 5-tetradecyloxy-2-furoic acid, or TOFA for short.

In mice, TOFA pushed energy expenditure up by as much as 18%, and it did this without the animals moving more or running a higher body temperature. That's a notable distinction, since many strategies for raising metabolic rate work by nudging animals (or people) to be more active or to generate more heat. Here, the extra energy use appears to come from something happening at the cellular level instead.

What the molecule actually does

TOFA belongs to a class of compounds called ACC inhibitors, which interfere with the body's production of lipids like cholesterol and triglycerides. That part isn't new; several ACC inhibitors have made it into mid-stage trials over the years. The catch has always been that blocking lipid production this way tends to raise triglyceride levels, which isn't a great trade for long-term cardiovascular health.

TOFA seems to sidestep that problem because it does something extra: it also switches on two cellular receptors, PPARα and PPARδ, that turn on genes involved in pulling fat into cells and burning it for fuel. Researchers describe this as a coordinated response rather than a single lever being pulled. The molecule isn't just dialing down fat production; it's simultaneously dialing up the machinery that clears fat and glucose out of circulation. That dual action may explain why the usual triglyceride downside didn't show up in this study.

Why muscle preservation is the interesting part

For anyone thinking about long-term healthspan, the muscle-sparing result is arguably more compelling than the fat loss itself. Weight-loss strategies that shrink both fat and muscle can leave people lighter but functionally weaker, which matters a great deal as we age and lean mass becomes harder to rebuild. In this study, mice treated with TOFA lost body fat with no significant drop in lean muscle mass, alongside better insulin sensitivity, glucose control, and liver fat.

That combination — fat down while muscle holds steady — is the profile both researchers and patients care about most. It's a reminder that the goal isn't just a lower number on the scale; it's shifting body composition in a direction that supports strength and metabolic resilience over decades.

A complementary tool, not a replacement

The researchers also tested TOFA alongside semaglutide and tirzepatide, the active ingredients behind Ozempic, Wegovy, Mounjaro, and Zepbound. GLP-1 medications work primarily by reducing appetite, and while effective for weight loss, they've also been associated with muscle loss and nutritional gaps when calorie intake drops sharply. Pairing TOFA's energy-expenditure effect with a GLP-1's appetite-suppressing effect produced larger improvements in body weight, glucose control, insulin levels, and triglycerides than either approach used alone.

The senior researcher framed it plainly: the two strategies worked additively, sometimes even synergistically, which is why the team views TOFA as something to stack alongside existing tools rather than a competitor to them. It's an early signal that future weight-management approaches may end up combining an appetite lever with a metabolism lever, rather than relying on just one.

The takeaway

This is still mouse data, and TOFA hasn't been tested in people yet, so there's real distance between this finding and anything applicable today. But the concept is worth tracking: a molecule that increases how much energy your body burns at rest, while protecting the muscle you already have, targets a piece of the weight and metabolic-health puzzle that appetite-focused approaches don't touch. If that effect holds up in human trials, it could reshape how we think about pairing tools for healthy body composition across a lifespan, rather than leaning on a single mechanism.

References:

Justin Y. Lee, Chi Zhu, Melissa A. Boldridge, Rachelle L. Stark, Gracia Bonilla, Kosuke Watari, Christina Papa, Lei Xu, Federico Gonzalez, Xin Tang, Kaitlyn T. Dang, Kook Son, Kashish Chetal, Prabha Ibrahim, Ruslan I. Sadreyev, Bilal N. Sheikh, Michael Karin, Anders M. Näär. A multi-functional oral small molecule targeting energy and lipid metabolism... Science Advances, 2026; 12 (34). DOI: 10.1126/sciadv.aed3119