Every incretin analogue on the market works, in the end, by making people eat less. A paper published in Science Advances on 21 August 2026 describes an orally available small molecule that reduces fat mass without reducing food intake at all, and reports that it combined more than additively with tirzepatide and semaglutide in mice.

The compound is 5-tetradecyloxy-2-furoic acid, known as TOFA. It is not a peptide, it is not in the Peptra Labs catalogue, and this is animal work. It is still the most interesting metabolic paper of the week, because of what it implies about where the ceiling of the tirzepatide class sits.

Why the authors went looking past tirzepatide

The introduction states the case against the current class more bluntly than most industry commentary would.

Incretin-based obesity treatments, the authors write, act to decrease food intake, and are associated with gastrointestinal side effects and muscle wasting. That is three complaints in one sentence: the mechanism, the tolerability, and the body composition problem. Tirzepatide is not named, but it is plainly in scope.

The third is the one the field has been circling all year. A retrospective case series published on 10 August 2026 in Obesity Pillars describes clinicians combining incretin therapy with resistance exercise and other measures specifically to protect skeletal muscle during weight loss. If a class reliably takes lean tissue along with fat, a molecule that reduces adiposity by a different route is not a competitor to tirzepatide so much as a different question.

What TOFA does that tirzepatide does not

TOFA has two mechanisms working in opposite corners of lipid handling.

It inhibits acetyl-CoA carboxylases 1 and 2, the enzymes that commit acetyl-CoA to fatty acid synthesis. Blocking them reduces lipogenesis, meaning the body makes less new fat.

It also activates peroxisome proliferator-activated receptors alpha and delta, transcription factors that switch on programmes for fatty acid oxidation and energy expenditure. That side increases the rate at which existing fat is burned.

Making less and burning more is a coherent pair, and it is why the authors describe the molecule as multi-functional rather than as an inhibitor of anything in particular.

The reported results in mice: reduced obesity, improved glucose homeostasis and improvement in fatty liver related disease, all without affecting food intake or muscle mass. Not one of those is the route tirzepatide takes.

The number that matters for tirzepatide

The combination experiment is the part with implications for the class.

TOFA acted more than additively with incretin analogues including semaglutide and tirzepatide, improving obesity, dyslipidaemia and insulin resistance beyond what either produced alone.

More than additive is a specific claim. If two treatments each reduce a measure by a fixed amount and the combination reduces it by the sum, that is additivity and it usually means two independent routes to the same endpoint. Exceeding the sum suggests the two mechanisms interact, that one makes the other work better.

The plausible reading is straightforward. Tirzepatide reduces energy coming in. TOFA increases energy going out and redirects what arrives away from storage. Those are opposite ends of the same balance sheet, and there is no obvious reason they should compete for the same ceiling.

It should be said clearly that this is a mouse result, from a paper whose author list includes an affiliation with ReRx Therapeutics, a company working in this space. Neither fact makes it wrong. Both mean the number to watch is the first human one, which does not exist.

Where it sits against the peptide catalogue

The energy expenditure route is not new to anyone tracking research compounds, and TOFA arrives into a small existing crowd. None of these compounds resembles tirzepatide chemically, and none of them works on appetite.

SLU-PP-332 is a pan-agonist of the estrogen-related receptors, described in the literature as an exercise mimetic because it activates transcriptional programmes normally switched on by endurance training. A 2026 paper in the International Journal of Biological Macromolecules reports chemical optimisation of the molecule and uses the analogues to probe how that receptor family signals. Different receptor family, same underlying idea as the PPAR arm of TOFA: push expenditure up rather than intake down.

5 Amino 1MQ sits in a third position again, targeting nicotinamide N-methyltransferase, an enzyme whose inhibition is reported to mitigate obesity-related metabolic dysfunction in preclinical models. Three compounds, three targets, one shared premise that appetite is not the only lever.

None of this is a claim about what any of them do. They are supplied as reference material and the published record for each is preclinical. What TOFA adds is a well-resourced demonstration, in a high-profile journal, that the premise survives contact with a proper multi-omic experiment.

There is also a link to something we covered last week. In a 2026 review of GLP-1 and mitochondrial biology, the authors proposed that the incretin class touches mitochondrial biogenesis and quality control, while conceding that no trial has ever included a prespecified mitochondrial endpoint. TOFA works through PPAR alpha and delta, which are among the transcription factors governing exactly those programmes. If both stories are true, the incretins may be reaching the same machinery indirectly that TOFA engages head on.

What would need to be true

Three things stand between this paper and anything clinical.

Mice metabolise differently. Rodent thermogenic capacity relative to body mass is not human thermogenic capacity, and compounds that raise energy expenditure in a mouse have a long history of not doing so in people.

ACC inhibition has a known liability. Inhibiting acetyl-CoA carboxylase can raise circulating triglycerides through a compensatory pathway, which is why earlier ACC inhibitors ran into trouble in the liver disease field. The authors report improved dyslipidaemia, and whether the PPAR arm is what neutralises that liability is the question a reader should carry into the full text.

Combination is easy to claim and hard to run. A more than additive result in mice, with tirzepatide as the partner, is a strong preclinical finding and also the point at which every metabolic programme of the last decade has said it would move to combination trials.

Retatrutide is the closest thing the peptide side has to an answer within its own chemistry, adding glucagon receptor agonism to the dual mechanism of tirzepatide and reaching for energy expenditure that way. Our triple-agonist research guide covers what the published record supports there.

Everything in the catalogue is supplied on a research use only basis.

References

The products referenced on this site are supplied for laboratory research use only. They are not medicines and are not intended for human or veterinary use. This article summarises published research for informational purposes and is not medical advice. Statements about third-party studies belong to their authors.

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About Peptra Labs Research

The Peptra Labs research desk follows peptide science: new peer-reviewed studies, EU and US regulatory decisions, and clinical trial results. Every article cites its primary sources. All compounds discussed are for laboratory research use only.

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