Today’s blockbuster weight-loss medications largely pull the same powerful lever: They help people eat less. Scientists at UC Berkeley just experimented with the other side of the equation.
Instead of suppressing appetite, an experimental compound made obese mice burn more energy—and they lost fat without significant muscle loss.
Before anyone gets too excited, there’s a very large mouse-shaped caveat: It hasn’t been tested in humans.
The compound made mice burn more energy
Researchers studied a decades-old compound called 5-tetradecyloxy-2-furoic acid, mercifully shortened to TOFA.
According to UC Berkeley, the compound works differently from today’s GLP-1 medications.
Rather than primarily reducing calorie intake, TOFA increased energy expenditure in obese mice by as much as 18% without making them eat less or exercise more. The animals lost weight primarily from fat while showing no significant reduction in lean muscle mass.
Researchers also reported improvements in insulin sensitivity, blood-sugar control, triglycerides and signs of fatty liver disease. The findings were published in Science Advances.
Why preserving muscle matters
Losing weight and losing fat aren’t necessarily the same thing. When body weight falls significantly, some of that loss can come from lean tissue, including muscle.
That’s particularly concerning for older adults, who are already vulnerable to age-related muscle loss.
Muscle supports far more than appearance—it helps maintain strength, mobility, balance, metabolic health and independence.
That’s why the next generation of obesity treatments may increasingly be judged not simply by how many pounds people lose but by what those pounds consist of.
A treatment that preferentially reduces fat while preserving muscle would be extremely attractive. Whether TOFA can do that in humans remains completely unknown.
It works very differently from GLP-1 drugs
Semaglutide and other GLP-1-based medications help people lose weight largely by reducing appetite and calorie intake. TOFA appears to attack the equation from another direction.
Researchers found that it blocked enzymes involved in producing fats while simultaneously activating cellular pathways involved in burning fat and using energy.
Instead of turning down energy coming in, the experimental compound appeared to turn up energy going out. That’s an appealing idea because appetite suppression can create challenges.
Some GLP-1 users struggle to consume enough protein and nutrients, and nausea and other gastrointestinal effects can make eating difficult.
A drug that doesn’t depend on suppressing food intake could theoretically avoid some of those problems. The word “theoretically” is doing a lot of work here.
Researchers also combined it with semaglutide and tirzepatide
The scientists didn’t only test TOFA by itself. They also combined it with GLP-1-based medications.
In mice, TOFA used alongside semaglutide or tirzepatide produced greater improvements in several metabolic measures than either approach alone.
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That raises an intriguing possibility. Instead of replacing GLP-1 medications, a future drug targeting energy expenditure might complement them—reducing calorie intake from one direction while increasing energy use from the other.
But again, these experiments were performed in mice. No one knows whether the same combination would be effective—or safe—in people.
TOFA isn’t a new weight-loss drug you can ask your doctor for
This is where headlines about early drug research can become misleading.
TOFA has existed as a research compound since the 1970s, but it has not been approved as a treatment for obesity, diabetes or anything else. It hasn’t even reached the stage where researchers know whether this approach is safe and effective in humans.
Other drugs targeting similar enzymes have encountered problems, including increases in triglycerides.
Interestingly, the Berkeley researchers didn’t observe that effect with TOFA in their mouse experiments. That makes the compound scientifically interesting. It doesn’t make it a medicine.
Most promising mouse drugs never become human medicines
This is worth remembering whenever a dramatic preclinical study makes headlines. Mice are invaluable to medical research, but human metabolism is considerably more complicated.
A drug that produces spectacular results in mice can fail because it doesn’t work in people, causes unacceptable side effects or behaves differently at doses humans can tolerate.
The journey from “this worked in mice” to “your doctor can prescribe this” is long, expensive and filled with failures. The Berkeley researchers acknowledge that human safety and effectiveness haven’t yet been established.
Researchers involved in the work have also founded a company to develop the technology, an important potential conflict of interest disclosed by UC Berkeley.
Still, the idea behind the research matters
Even if TOFA itself never becomes a medication, the study points toward a larger change in obesity science.
The first generation of blockbuster obesity drugs proved that powerful biological treatments can produce substantial weight loss. Now researchers are asking a more sophisticated question.
Can we improve the quality of that weight loss? That could mean preserving muscle, protecting bone, reducing visceral fat or finding treatments that don’t depend entirely on appetite suppression.
The number on the scale may eventually become only one measure of whether an obesity treatment works.
Final word
Nobody should be looking for TOFA online or wondering when they can switch from Ozempic. This is early-stage animal research—not a new treatment.
But the science behind it is fascinating because it challenges the assumption that effective obesity drugs must work primarily by making people less hungry.
Our weight is influenced by both the energy we consume and the energy our bodies expend. Today’s most successful medications have dramatically changed one side of that equation.
The next generation of weight-loss drugs may go after both.
And if researchers can eventually help people lose fat while protecting the muscle underneath it, that could be a much more meaningful victory than simply making the number on the scale smaller.
