Effects of Step-Wise Increases in Dietary Carbohydrate on Circulating Saturated Fatty Acids and Palmitoleic Acid in Adults with Metabolic Syndrome

Abstract

Recent meta-analyses have found no association between heart disease and dietary saturated fat; however, higher proportions of plasma saturated fatty acids (SFA) predict greater risk for developing type-2 diabetes and heart disease. These observations suggest a disconnect between dietary saturated fat and plasma SFA, but few controlled feeding studies have specifically examined how varying saturated fat intake across a broad range affects circulating SFA levels. Sixteen adults with metabolic syndrome (age 44.9±9.9 yr, BMI 37.9±6.3 kg/m2) were fed six 3-wk diets that progressively increased carbohydrate (from 47 to 346 g/day) with concomitant decreases in total and saturated fat. Despite a distinct increase in saturated fat intake from baseline to the low-carbohydrate diet (46 to 84 g/day), and then a gradual decrease in saturated fat to 32 g/day at the highest carbohydrate phase, there were no significant changes in the proportion of total SFA in any plasma lipid fractions. Whereas plasma saturated fat remained relatively stable, the proportion of palmitoleic acid in plasma triglyceride and cholesteryl ester was significantly and uniformly reduced as carbohydrate intake decreased, and then gradually increased as dietary carbohydrate was re-introduced. The results show that dietary and plasma saturated fat are not related, and that increasing dietary carbohydrate across a range of intakes promotes incremental increases in plasma palmitoleic acid, a biomarker consistently associated with adverse health outcomes.

The Role of the Novel Lipokine Palmitoleic Acid in Health and Disease

“…It has been shown that palmitoleic acid in plasma TG and cholesteryl ester is positively related to carbohydrate intake (35). It is known that carbohydrate intake increases SCD1 expression (36) and, therefore, a direct relation between dietary carbohydrate and palmitoleate concentrations was expected.…”

“…Because cis-palmitoleate is synthesized endogenously, diet components modifying SCD1 activity as carbohydrate necessarily change serum cis-palmitoleate concentrations, which range approximately from 0.19% to 0.5% of FAs (40). An intervention with distinct groups of carbohydrate content in the diet showed that highest carbohydrate consumption increases cis-palmitoleate 1.3 times (35). In addition to carbohydrate consumption, protein intake also was associated with plasma palmitoleate (34).…”

Evidence that supports the prescription of low-carbohydrate high-fat diets: a narrative review

“…Fourth, the biological significance of these relatively small increases in LDL-C is unknown in persons eating LCHF diets and in whom there will be associated increases in LDL particle size distributions and reductions in harmful blood saturated fat concentrations,72 87 as well as other positive biological changes, including reduced ApoB concentrations,3 72 improvements in flow-mediated arteriolar dilation,71 decreased inflammatory biomarkers,49 lower systolic and diastolic blood pressures,3 improved glycaemic control with reduced HbA 1c , plasma glucose and insulin concentrations14 and preferential weight loss from the abdominal viscera indicating a greater reduction in visceral fat, including liver fat. All these changes in surrogate measures would be expected to reduce cardiovascular risk substantially 3 47…”

Fatty Acid β-Oxidation Plays a Key Role in Regulating <i>cis</i>-Palmitoleic Acid Levels in the Liver

“…7) Although some studies showed that higher blood levels of 16:1n-7 corresponded to insulin sensitivity, 61) other human subject studies described relationships between biological functions and circulating concentrations of 16:1n-7 that negatively impacted on metabolic health. 11,12,[62][63][64] Overall, the most persuasive explanation appears to be that although 16:1n-7 has biological functions, not all of these features are necessarily beneficial for human health. Since a previous study suggested the autocrine and paracrine/endocrine characteristics of 16:1n-7, 65) plasma 16:1n-7 and endogenously formed 16:1n-7 are both the most likely to contribute to its biological functions.…”