New Fat-Burning Pathway Found Beyond Mitochondria

A research team from the University of Washington School of Medicine has uncovered a new way brown fat generates heat, independent of the traditional mitochondrial pathway. Their study, published in Nature, offers fresh hope for developing treatments for obesity and metabolic disorders.

Brown adipose tissue, unlike white fat that mainly stores energy, is a specialized organ that burns energy to produce heat. For decades, scientists believed this process relied solely on the mitochondrial protein UCP1. However, the new study shows that even in the absence of UCP1, mice can maintain heat production through an alternative mechanism.

The researchers identified peroxisomes—small structures inside cells—as key players in this “backup heating system.” When exposed to cold, the number of peroxisomes rose sharply, especially in mice lacking UCP1. Further investigation revealed that a peroxisomal enzyme called ACOX2 metabolizes specific fatty acids to release heat. Mice without ACOX2 had reduced cold tolerance, lower insulin sensitivity, and gained weight more easily on a high-fat diet, while ACOX2 overexpression boosted heat production and improved metabolism.

Using advanced thermal imaging technologies, the team directly observed ACOX2-mediated heat generation. Intriguingly, the fatty acids involved can come from the body, diet (such as dairy and breast milk), or gut microbes, suggesting possible ways to activate this pathway through nutrition or microbiome modulation.

Although still in the animal-study stage, epidemiological data already link higher levels of these fatty acids in humans to lower body mass index. The findings open new avenues for therapies targeting obesity and metabolic diseases.