Low-fat diet fails to improve insulin sensitivity in metabolic syndrome
MedWire News: Reducing dietary intake of saturated fatty acids (SFA) does not appear to influence insulin sensitivity in obese people with the metabolic syndrome, a randomized trial has shown.
By contrast, in the LIPGENE study, increasing intake of long-chain n-3 polyunsaturated fatty acids (LC n-3 PUFAs) in combination with a low-fat diet improved selected indices of cardiometabolic risk.
LIPGENE was a pan-European randomized dietary intervention study designed to determine the relative efficacy of altering the quality and quantity of dietary fat on insulin sensitivity and metabolic risk factors.
In all, 417 people with the metabolic syndrome from eight countries were randomly assigned to one of four isoenergetic diets: high SFA - control diet; high monounsaturated fatty acids (HMUFA); low-fat, high-complex carbohydrate (LFHCC) plus long-chain n-3 polyunsaturated fatty acids (LC n-3 PUFAs) 1.2 g/day; or LFHCC plus placebo.
The study lasted for 12 weeks and the primary endpoint was insulin sensitivity estimated from an intravenous glucose tolerance test.
Reporting their findings in the International Journal of Obesity, Helen Roche (University College Dublin, Ireland) and co-authors reveal that reducing SFA intake did not alter insulin sensitivity, low-density lipoprotein cholesterol, blood pressure, or markers of systemic inflammation.
Indeed, the only significant changes were improvements in plasma levels of triglycerides and non-esterified fatty acid levels among people assigned to the LFHCC plus n-3 PUFA diet. These changes were most pronounced in men.
Disappointingly, insulin sensitivity did not improve with any of the four dietary interventions. However, subgroup analysis revealed a potential benefit in the subgroup of women with a habitual low intake of total fat (36% of total energy). In this subgroup, those assigned to the HMUFA diet showed a significant reduction in insulin resistance.
"Perhaps the impact of replacing SFA with MUFA on insulin resistance is dependent on pre-intervention fat intake," the authors write, although they admit this is merely a hypothesis to be tested in future studies.
Roche and colleagues conclude: "More extensive dietary fat modification may be required to significantly improve insulin sensitivity and other risk factors associated with the metabolic syndrome, perhaps in combination with weight loss.
"Although our study was designed with the weight-stable phenotype, potential interactions per synergism between dietary fat modification and weight loss need to be clarified."
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By Joanna Lyford