This article originally posted 22 March, 2005 and appeared in Issue 252
Dark Chocolate Improves Insulin Sensitivity/Resistance and Blood Pressure
It is probably the flavanols and procyanidins contained in the dark chocolate and not white chocolate that is associated with the observed health effects.
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"Numerous studies indicate that flavanols may exert significant vascular
protection because of their antioxidant properties and increased nitric oxide
bioavailability," write Davide Grassi, from the University of L'Aquila in
Italy, and colleagues. "In turn, nitric oxide bioavailability deeply influences
insulin-stimulated glucose uptake and vascular tone. Thus, flavanols may also
exert positive metabolic and pressor effects."
After a seven-day cocoa-free run-in phase, 15 healthy participants were randomized
to receive either dark chocolate bars or white chocolate bars for 15 days, followed
by another seven-day cocoa-free washout phase and then crossover to the other
chocolate. The dark chocolate bars weighed 100 g and contained approximately 500
mg polyphenols; the white chocolate bars weighed 90 g and presumably contained
no polyphenols. At the end of each period, oral glucose tolerance tests were performed
to calculate the homeostasis model assessment of insulin resistance (HOMA-IR)
and the quantitative insulin sensitivity check index (QUICKI).
Mean HOMA-IR was 0.94 ± 0.42 after dark chocolate ingestion and 1.72 ±
0.62 after white chocolate ingestion (P < .001). Mean QUICKI was 0.398 ±
0.039 vs 0.356 ± 0.023, respectively (P = .001). Systolic blood pressure
was lower after dark than after white chocolate ingestion (107.5 ± 8.6
vs 113.9 ± 8.4 mm Hg; P < .05).
"Dark, but not white, chocolate decreases blood pressure and improves insulin
sensitivity in healthy persons," the authors write. "These findings
indicate that dark chocolate may exert a protective action on the vascular endothelium
also by improving insulin sensitivity. Obviously, large scale trials are needed
to confirm these protective actions of dark chocolate or other flavanol-containing
foods in populations affected by insulin-resistant conditions such as essential
hypertension and obesity."
Am J Clin Nutr. 2005;81:541-542, 611-614
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