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Eating more unsaturated fats and less carbohydrate reduces blood glucose, study finds

BMJ 2016; 354 doi: (Published 21 July 2016) Cite this as: BMJ 2016;354:i4053
  1. Susan Mayor
  1. London

Eating more unsaturated fats, especially polyunsaturated fatty acids, and eating less carbohydrate and saturated fat reduces blood glucose levels and improves insulin resistance and secretion, a large meta-analysis of randomised controlled trials has shown.

Researchers systematically searched for randomised controlled trials investigating the effects that macronutrients in the diet have on blood glucose, insulin, HbA1c, insulin sensitivity, and insulin secretion in adults aged over 18. They found 102 trials including 4220 adults that met their criteria.

Using the trial findings, the research group then estimated the effect of replacing 5% of total dietary energy from particular macronutrients with saturated fats, monounsaturated fats, or polyunsaturated fats.

Results showed that replacing carbohydrate with polyunsaturated fats significantly reduced HbA1c (–0.11% (95% confidence interval –0.17 to –0.05)) and fasting insulin (–1.6 pmol/L (–2.8 to –0.4)). Replacing saturated fat with polyunsaturated fatty acids significantly lowered glucose, HbA1c, C-peptide, and insulin resistance (homeostasis model assessment for insulin resistance; HOMA-IR).

In contrast, replacing 5% of energy from carbohydrate with saturated fat had no significant effect on fasting glucose (+0.02 mmol/L (–0.01 to +0.04)), but it lowered fasting insulin (–1.1 pmol/L (–1.7 to –0.5)).

Overall, dietary polyunsaturated fats had consistently favourable effects on glucose-insulin homeostasis when compared with carbohydrate, saturated fats, or monounsaturated fats.

“Until now, our understanding of how dietary fats and carbohydrate influence glucose, insulin, and related risk factors has been based on individual studies with inconsistent findings,” said the lead author, Fumiaki Imamura, of the University of Cambridge, UK. “By combining results from more than 100 trials, we provide the strongest evidence to date on how major nutrients alter these risks.”


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