Fats taken in directly from the diet or generated from sugars spark a cascade of gene activity in the liver necessary for healthy blood levels of sugar, cholesterol, and other fats, according to scientists at the Washington University School of Medicine.
They suggest that old fat stores alone failed to set those critical metabolic pathways in motion.
"The findings in mice suggest that normal metabolism requires so-called "new" fat: further evidence that a healthy diet should include an adequate source of fat," comments lead author Clay Semenkovich.
Taking the findings a step further, Semenkovich claims the results suggest that specially engineered fats might boost healthy liver metabolism, offering an alternative mechanism for fighting chronic diseases, including obesity, diabetes, and heart disease.
The researchers inactivated fatty-acid synthase, an enzyme that generates new fat from carbohydrates, in the livers of mice.
When fed a diet completely lacking fat, the mice developed low blood sugar and fatty liver. Both conditions were reversed when the researchers restored fat to the animals' diets.
Further study found that, in the absence of new fat, the mice exhibited a marked decline in the activity of genes critical for the metabolism of glucose, fatty acids, and cholesterol. These genes, say the researchers, are normally targeted by PPARa, a key energy management gene activated by fatty acids.
"In short, all fatty acids are not created equal, at least in the liver," added Semenkovich.
The findings suggest that products of fatty acid synthesis regulate glucose, lipid, and cholesterol metabolism by activating distinct pools of PPARa in the liver, say the researchers.
Further study is required, they add, to clarify the mechanism by which nutrient sensors in the body distinguish between different sources of fat.
Full findings are published in the May issue of Cell Metabolism.