Does unsaturated fat substitution improve glucose homeostasis?

Replacing saturated with unsaturated fat seems to have no significant impact on insulin sensitivity or pancreatic β-cell function, according to a study.

A team of investigators conducted this systematic review and meta-analysis to examine the effects of replacing dietary saturated fatty acids (SFA) with mono- (MUFA) or poly-unsaturated fatty acids (PUFA) on insulin sensitivity, pancreatic β-cell function, and glucose tolerance, as surrogate endpoints for type 2 diabetes (T2D).

The databases of Medline, Scopus, and the Cochrane Library were searched up to 9 January 2023 for randomized controlled trials that replaced ≥5 percent of total energy intake provided by SFA with MUFA or PUFA and reported indexes of insulin sensitivity, β-cell function, and/or glucose tolerance. Isocaloric interventions were eligible for inclusion. A random-effects model was used to synthesize the data.

A total of 6,355 records were identified, of which 10 parallel and 20 crossover trials with 1,586 participants (47 percent male) met the eligibility criteria. The mean age of participants was 42 years. Their mean body mass index (BMI) was 26.8 kg/m², median baseline fasting glucose was 5.13 mmol/L, and median duration of interventions was 5 weeks.

Substitution of SFA with MUFA or PUFA provided no substantial effects on insulin sensitivity (standardized mean difference [SMD] SFA vs MUFA, 0.01, 95 percent confidence interval [CI], ‒0.06 to 0.09; I², 0 percent; SMD SFA vs PUFA, 0, 95 percent CI, ‒0.15 to 0.14; I², 0 percent).

Likewise, replacing SFA with MUFA showed no significant effect on β-cell function, as assessed by the disposition index (mean difference, ‒12, 95 percent CI, ‒158 to 133; I², 0 percent).

“Evidence on glucose tolerance (SFA compared with MUFA or PUFA) and on β-cell function when SFA were replaced with PUFA was scant,” the investigators said.

“Future studies are needed to elucidate longer term effects of dietary fat saturation on glucose homeostasis,” they added.