Experimental Compound TOFA Promotes Fat Loss While Preserving Muscle in Mice

For anyone who has ever tried to lose weight, the biological math is frustratingly stubborn: shedding fat almost always means sacrificing hard-earned muscle. The body, when deprived of calories, does not discriminate perfectly between the energy stored in adipose tissue and the functional tissue of skeletal muscle.[4]

The current generation of GLP-1 medications has amplified this dilemma. While highly effective at reducing appetite and driving significant weight loss, they often lead to a proportional loss of lean mass. For aging populations, this side effect raises serious concerns about long-term frailty and metabolic resilience.[2]

Now, researchers at the University of California, Berkeley, have identified a decades-old compound that appears to flip this metabolic script. Rather than suppressing the urge to eat, the molecule signals the body to actively burn fat for fuel, preserving muscle in the process.[2]

The compound, known as 5-tetradecyloxy-2-furoic acid or TOFA, was originally discovered in the 1970s. It belongs to a class of molecules called ACC inhibitors, which were designed to block the body's internal production of lipids.[2]

In a study published in the journal Science Advances, the UC Berkeley team demonstrated that TOFA operates through a dual mechanism that sets it apart from both appetite suppressants and previous ACC inhibitors.[1]

First, TOFA inhibits acetyl-CoA carboxylases 1 and 2, the enzymes responsible for synthesizing new fats. Second, and crucially, it activates PPARα and PPARδ—cellular receptors that switch on the genetic programs required to take up existing fat and burn it for energy.[1][3]

When administered to obese mice, this coordinated metabolic response increased the animals' cellular energy expenditure by up to 18 percent. Remarkably, this increase in calorie burning occurred without any changes to the mice's physical activity levels or body temperature.[2]

The physical results of this heightened energy expenditure were striking. The mice lost significant amounts of weight, and that loss was driven almost entirely by a reduction in fat tissue. Their lean muscle mass remained virtually intact.[1][2]

Beyond body composition, the compound improved a suite of metabolic markers. The treated mice showed better insulin sensitivity, improved glucose control, and a reduction in the signs of fatty liver disease.[2]

Historically, pharmaceutical companies abandoned ACC inhibitors because they paradoxically caused blood triglyceride levels to spike, increasing cardiovascular risk. TOFA's ability to simultaneously activate fat-burning pathways appears to bypass this critical flaw, safely clearing excess lipids from the bloodstream.[2]

Recognizing the dominance of GLP-1 medications in modern obesity treatment, the researchers also tested TOFA in combination with semaglutide and tirzepatide. The goal was to see if the two distinct metabolic levers—taking in fewer calories and expending more energy—could work together.[1]

The combination proved highly effective. In the mouse models, pairing TOFA with GLP-1 drugs produced additive and synergistic effects, leading to greater improvements in body weight, glucose control, and insulin levels than either treatment achieved on its own.[1][2]

Anders Näär, a professor of metabolic biology and nutrition at UC Berkeley and senior author of the study, noted that the two approaches are entirely complementary. While GLP-1s focus on the intake side of the energy equation, TOFA addresses the expenditure side.[2]

Despite the promising data, the research remains entirely preclinical. Animal models, particularly mice, have metabolic pathways that can diverge significantly from human biology, and many compounds that succeed in rodents ultimately fail in human trials.[4]

The safety and efficacy of TOFA in humans are completely unknown. The compound is not approved for human use, and it will require years of rigorous clinical testing to determine if the muscle-preserving fat loss seen in mice can be safely replicated in patients.[4]

To advance this research toward potential clinical application, the UC Berkeley team has founded a new company, ReRx Therapeutics, with support from the university's life sciences entrepreneurship ecosystem.

For the general public, the immediate takeaway is not a new pill, but a validation of a core physiological principle. Preserving muscle during weight loss requires more than just a caloric deficit; it requires signaling the body to prioritize fat oxidation.[4]

While TOFA remains years away from any pharmacy shelf, its discovery marks a pivotal shift in the science of obesity. By moving beyond the simple suppression of appetite, researchers are opening the door to therapies that actively optimize metabolic health and protect the physical strength we need as we age.[4]