Potential Role of Nut Consumption for Improving Insulin Sensitivity : Results from a Systematic Review and Meta-analysis of Randomized Controlled Trials

By Heather Nelson Cortes, PhD and Kevin C Maki, PhD

 

Worldwide incidence and prevalence of type 2 diabetes mellitus (T2D) diabetes are increasing at alarming rates, largely following increases in incidence of overweight and obesity.  The World Health Organization reports that ~1.9 billion adults are overweight in 2019, including 600 million that are obese and thus at heightened risk for T2D1.  Overweight and obesity are associated with impaired whole-body insulin sensitivity (i.e., increased insulin resistance), which is believed to be the key pathophysiologic link to increased risk for T2D 2.

 

Many epidemiological studies have examined the association of nut consumption with risks for T2D and mortality.  Systematic reviews and meta-analyses of prospective cohort studies have suggested a reduction in T2D risk with regular nut consumption 3-5

 

Tindall and colleagues recently published a review of 40 randomized, controlled trials with a median duration of 3 months (N = 2,832 subjects), that examined the effects of consuming tree nuts and peanuts on glycemic markers, including homeostasis model assessment of insulin resistance (HOMA-IR), fasting insulin and glucose, and glycated hemoglobin (HbA1C) 6.  The median intake of nuts was 52 g/d (range: 20-113 g/d).

 

In pooled analyses, consumption of tree nuts or peanuts reduced both HOMA-IR (weighted mean difference [WMD] −0.23; 95% confidence interval [CI] −0.40, −0.06; I2 = 51.7%) and fasting insulin (WMD −0.40 μU/mL; 95% CI −0.73, −0.07 μU/mL; I2 = 49.4%) compared to the control conditions 6.  However, there were no effects of nut consumption on fasting blood glucose (WMD −0.52 mg/dL; 95% CI −1.43, 0.38 mg/dL; I2 = 53.4%) or HbA1C (WMD 0.02%; 95% CI −0.01%, 0.04%; I2 = 51.0%).
 Further analyses showed no associations between the dose of nuts/peanuts consumed and the mean difference between nut and control treatments for any of the measured outcomes.  Analysis by nut type showed no deviations from the main results.

 

Comment. While there were no effects of nut consumption on HbA1C or fasting glucose, there were statistically significant reductions in HOMA-IR and fasting insulin, suggesting improved insulin sensitivity.  Future studies are needed to help determine the mechanisms through which nut/peanut consumption affects insulin sensitivity. 

 

References

  1. World Health Organization. Global report on diabetes. Geneva, Switzerland: World Health Organization; 2016. 

  2. Kahn SE, Hull RL, Utzschneider KM. Mechanisms linking obesity to insulin resistance and type 2 diabetes. Nature. 2006;444:840–6.
  3. Afshin A, Micha R, Khatibzadeh S, Mozaffarian D. Consumption of nuts and legumes and risk of incident ischemic heart disease, stroke, and diabetes: a systematic review and meta-analysis. Am J Clin Nutr 2014;100(1):278–88. 

  4. Aune D, Keum N, Giovannucci E, et al. Nut consumption and risk of cardiovascular disease, total cancer, all-cause and cause-specific mortality: a systematic review and dose-response meta-analysis of prospective studies. BMC Medicine 2016;14(1):207.
  5. Luo C, Zhang Y, Ding Y, et al. Nut consumption and risk of type 2 diabetes, cardiovascular disease, and all-cause mortality: a systematic review and meta-analysis. Am J Clin Nutr 2014;100(1):256–69. 

  6. Tindall AM, Johnston EA, Kris-Etherton PM, Petersen KS. The effect of nuts on markers of glycemic control: a systematic review and meta-analysis of randomized controlled trials. Am J Clin Nutr. 2019;109:297–314.


 

Photo by Vitchakorn Koonyosying

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