Investigating a progression of carb and saturated fat intakes

Saturated fat reduction has long been a major target of dietary guidelines, although recent meta-analyses have failed to show an association with heart disease. Current recommendations in the U.S. include limiting saturated fat intake to less than 10% of total energy intake. However, a reduction in fat intake typically leads to an increase in carbohydrate intake. A consequence of overconsumption of carbohydrates is increased de novo lipogenesis. DNL is a process which involves the synthesis of fatty acids from non-lipid sources, such as carbohydrates or amino acids.

Interestingly, even energy-balanced diets, and single-meal consumption of carbohydrates above the normal oxidative capacity of the body have been shown to increase DNL. The percentage of ingested carbohydrate contributing to DNL is however quite minor^[1] in those who aren’t insulin resistant and overfeeding on refined carbohydrate.

The major end-product of DNL is the saturated fat palmitic acid (denoted 16:0, referring to 16 carbons and zero double bonds), which can be desaturated within the body to form the monounsaturated fat palmitoleic acid (16:1). Higher blood levels of palmitoleic acid have been associated with an increased risk of metabolic syndrome and greater amount of inflammatory markers. Palmitoleic has mixed evidence however, also being associated with some positive biomarkers such as higher HDL^[2] and greater insulin sensitivity. Divergent impacts could be due to the effects of different lifestyle factors and different physiological conditions (such as how much of DNL is from adipose tissue versus from the liver).

This study sought to assess how incremental changes in dietary carbohydrate intake and decreases in saturated fat intake affect plasma saturated fatty acid and palmitoleic acid levels. The study was conducted in adults with metabolic syndrome under hypocaloric conditions.

Saturated fat is commonly targeted for reduction by dietary guidelines. This typically leads to an increase in carbohydrate intake, which at high levels may cause the body to create fats through de novo lipogenesis. This study investigated several levels of saturated fat and carb intake to see how they affected plasma saturated fats and palmitoleic acid.