Fatty liver disease now affects roughly one in four adults globally, yet dietary strategies beyond general caloric restriction remain poorly defined. Emerging evidence suggests the liver-protective properties of tomato consumption may not rest solely on lycopene — the pigment that has dominated carotenoid research for decades — but on a colorless upstream precursor that has largely escaped scientific scrutiny.
The study examined 15-cis-phytoene, a colorless carotenoid precursor abundant in tomatoes, in a 24-week mouse model of metabolic dysfunction-associated steatotic liver disease (MASLD) induced by a high-refined carbohydrate diet. Phytoene supplementation measurably elevated the compound's concentrations in intestinal tissue, liver, and serum, while significantly attenuating diet-induced hepatic fat accumulation in wild-type animals. The hepatoprotective effect was mechanistically linked to upregulation of SIRT1, PGC1α, and PPARα — key regulators of mitochondrial biogenesis and lipid homeostasis — along with enhanced phosphorylation of AMPK and ACC and increased fatty acid oxidation gene expression. Critically, gut microbiota composition was not implicated. When the same protocol was applied to mice lacking both carotenoid-cleaving enzymes BCO1 and BCO2, protection was entirely absent despite even greater phytoene accumulation in the liver, pointing to cleavage metabolites rather than intact phytoene as the biologically active agents.
This finding reframes how researchers should interpret tomato bioactivity studies and challenges the assumption that lycopene is the principal functional molecule. The SIRT1–PGC1α–PPARα axis is a well-validated target in metabolic liver disease, lending biological plausibility to the result. However, the exclusive use of mouse models, a single dietary challenge, and the absence of dose-response data in humans are significant constraints. The BCO1/BCO2 enzyme system shows meaningful inter-individual genetic variation in humans, which would complicate extrapolation. At this stage, the work is mechanistically compelling but requires human cohort confirmation before its implications for dietary guidance can be assessed.