Differential effect of polyphenol-rich dark chocolate on biomarkers of glucose metabolism and cardiovascular risk factors in healthy, overweight and obese subjects: a randomized clinical trial

Food Funct. 2012 Oct;3(10):1035-43. doi: 10.1039/c2fo30060e. Epub 2012 Jul 16.


The association between excess cortisol and various parameters of metabolic syndrome including hypertension, insulin resistance and dyslipidaemia is increasingly recognised. The present single-blind randomised placebo-controlled cross-over study compared the effect of polyphenol-rich dark chocolate (DC) on biomarkers of glucose metabolism, lipid profile, and blood pressure (BP) in females with BMI ≥ 25 kg m(-2) (n = 21) and females with BMI < 25 kg m(-2) (n = 21). Volunteers consumed 20 g of DC containing 500 mg polyphenols or a placebo DC with negligible polyphenol-content daily for 4 weeks, separated by a 2-week washout period. Systolic BP and diastolic BP decreased after 4 weeks of polyphenol-rich DC. Placebo raised fasting insulin, homeostasis model assessment of insulin resistance (HOMA-IR) and salivary cortisol, an effect that was significantly different from polyphenol-rich DC which had a negligible effect on fasting insulin, HOMA-IR and salivary cortisol. Females with BMI ≥ 25 kg m(-2) responded less favourably to placebo than lean females and consequently had higher fasting insulin and HOMA-IR, in addition to a lower quantitative sensitivity check index (QUICKI) after ingestion of placebo compared to polyphenol-rich DC. No significant changes in lipid profile were observed. This study provides evidence for the metabolic benefits of consuming polyphenol-rich dark chocolate while demonstrating the possibility of adverse effects occurring with polyphenol-poor chocolate placebo.

Publication types

  • Randomized Controlled Trial

MeSH terms

  • Antioxidants / administration & dosage
  • Antioxidants / analysis
  • Biomarkers / blood*
  • Blood Glucose / analysis
  • Blood Glucose / metabolism*
  • Blood Pressure
  • Body Mass Index
  • Cacao / chemistry*
  • Candy
  • Cardiovascular System / metabolism*
  • Cross-Over Studies
  • Fasting
  • Female
  • Glucocorticoids / blood
  • Humans
  • Insulin / blood
  • Insulin Resistance
  • Obesity / physiopathology
  • Overweight / physiopathology
  • Polyphenols / administration & dosage*
  • Risk Factors
  • Single-Blind Method


  • Antioxidants
  • Biomarkers
  • Blood Glucose
  • Glucocorticoids
  • Insulin
  • Polyphenols