High-fat diets don't increase risk of type 2 diabetes, finds review

Current dietary guidelines on the prevention of T2D recommend a diet low in total fat and animal fat and high in vegetable fat. Additionally, higher intakes of monounsaturated fatty acids, polyunsaturated fatty acids, and omega-3 fatty acids, as well as lower intakes of saturated fatty acids and trans-fatty acids are recommended. However, the role of dietary fat and fatty acid intake in type 2 diabetes prevention is under debate. Therefore, researchers of the University Düsseldorf, Germany, conducted a study to investigate the associations between the intake of dietary fat and fatty acids and T2D and to evaluate the certainty of evidence.

It was a systemic review and meta-analysis in which researchers systematically searched PubMed and Web of Science through 28 October 2019 for prospective observational studies in adults on the associations between intake of dietary fat and fatty acids and T2D incidence. They identified 180studies and included 23studies. They also conducted linear and nonlinear random-effects dose-response meta-analyses to calculate the summary relative risks (SRRs) with their corresponding 95% confidence intervals (95% CIs) and assessed the certainty of evidence.

Key findings of the study were:

Upon evaluation, they observed no or weak linear associations between dietary fats and fatty acids and T2D incidence.

• In nonlinear dose-response meta-analyses, they noted that the protective association for vegetable fat and T2D was steeper at lower levels up to 13 g/d (SRR [95% CI]: 0.81) than at higher levels in 5 studies.

• They also noted that the saturated fatty acids showed an apparent protective association above intakes around 17 g/d with T2D (SRR [95% CI]: 0.95) in 11 studies.

• They found a nonsignificant association of a decrease in T2D incidence for polyunsaturated fatty acid intakes up to 5 g/d (SRR [95% CI]: 0.96]) in 8 studies and for alpha-linolenic acid consumption up to 560 mg/d (SRR [95% CI]: 0.95, n = 11), after which the curve rose slightly, remaining close to no association.

• They noted that the association for long-chain omega-3 fatty acids and T2D was approximately linear for intakes up to 270 mg/d (SRR [95% CI]: 1.10, n = 16), with a flattening curve. However, the certainty of the evidence was very low to moderate.

The authors concluded, "There was no association between total fat intake and the incidence of T2D. However, for specific fats and fatty acids, dose-response curves provided insights for significant associations with T2D. In particular, a high intake of vegetable fat was inversely associated with T2D incidence. Thus, a diet including vegetable fat rather than animal fat might be beneficial regarding T2D prevention."

For further information:

https://journals.plos.org/plosmedicine/article?id=10.1371/journal.pmed.1003347