January 15, 2014

Good News and Bad News About Chocolate

Study discusses the effects of consuming chocolate with much higher than usual polyphenol levels in patients who are overweight or obese.


Almoosawi S, Fyfe L, Ho C, Al-Dujaili E. The effect of polyphenol-rich dark chocolate on fasting capillary whole blood glucose, total cholesterol, blood pressure and glucocorticoids in healthy overweight and obese subjects. Br J Nutr. 2010;103(6):842-850.


Randomized, crossover design in which each subject acted as his or her own control.


14 overweight and obese individuals (BMI ≥ 25 kg/m2) aged 19-50, non-smokers with no history of diabetes mellitus, hypertension, or cardiovascular disease.

Study Medication and Dosage

After a 1-week run-in phase, subjects ate 20 grams of one of two forms of high-polyphenol dark chocolate daily for 2 weeks, after which they crossed over to the next intervention separated by a 1-week washout period. One of the chocolates contained 500 mg of polyphenols per serving, the other 1,000 mg.

Outcome Measures

Changes in fasting blood sugar, blood chemistry, cortisol/cortisone ratio, and blood pressure were tracked.

Key Findings

Both doses, the 500 mg and the 1,000 mg/day of polyphenols, were equally effective at reduced fasting blood glucose levels and systolic and diastolic blood pressure. This suggests a possible saturation effect with increasing doses of polyphenols. A trend towards a reduction in urinary free cortisone levels was seen, but it did not reach statistical significance. Cholesterol levels did not change.
The fact that the decrease in free cortisol did not reach statistical significance may be related to a number of factors: Sample size was small, measuring techniques could have been more complete, and all but one of the subjects had peripheral rather than abdominal obesity.

Practice Implications

The present study tells us that eating dark chocolate with 500 mg polyphenol is as effective at reducing fasting blood sugar levels in overweight or obese individuals as a dose twice as large. Obesity is associated with insulin resistance and elevated blood pressure. The authors of this study had hoped to establish a causal link to improved cortisol levels to explain some of these changes.
This study, although suggestive of a connection between chocolate and cortisol, was unable to prove a connection; though these authors did not prove it, chocolate might someday become a treatment for metabolic syndrome.
 This study, although suggestive of a connection between chocolate and cortisol, was unable to prove a connection. Though these authors did not prove it, chocolate might someday become a treatment for metabolic syndrome. This is just one in a fast growing series of papers telling us that the poyphenols in chocolate are beneficial to health. Earlier papers by Grassi et al and Taubert et al have already demonstrated decreases in fasting blood sugar and blood pressure using 500 mg/day polyphenol doses over periods of several weeks.1,2,3
The caveat in interpreting these data is that these researchers have not used “over the counter” chocolate but instead selected chocolates especially manufactured to contain much higher than usual polyphenol levels. In this particular study the chocolate was made by Barry Callebaut, a Belgium company, and manufactured using the Acticoa process, which preserves the cocoa bean flavanols that are typically lost during processing. Analysis and comparison of 20 grams of 70% cocoa solid chocolate made through the Acticoa process with a 70% cocoa solid chocolate made by conventional manufacturing processes found that the Acticoa chocolate had more than 600 mg flavanols, while the standard process had less than 30 mg.4 The chocolate used in this research is about 20 times as strong as what we might buy as ‘good’ chocolate (the brand used in this and several other recent studies is not yet sold in the United States).

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1. Grassi D, Necozione S, Lippi C, et al. Cocoa reduces blood pressure and insulin resistance and improves endothelium-dependent vasodilation in hypertensives. Hypertension. 2005;46(2):398-405.
2. Grassi D, Desideri G, Necozione S, et al. Blood pressure is reduced and insulin sensitivity increased in glucose-intolerant, hypertensive subjects after 15 days of consuming high-polyphenol dark chocolate. J Nutr. 2008;138(9):1671-1676.
3. Taubert D, Roesen R, Lehmann C, Jung N, Schömig E. Effects of low habitual cocoa intake on blood pressure and bioactive nitric oxide: a randomized controlled trial. JAMA. 2007;298(1):49-60.
4. Williams S, Tamburic S, Lally C. Eating chocolate can significantly protect the skin from UV light. J Cosmet Dermatol. 2009;8(3):169-173.
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