Introduction: The kidneys are well-perfused organs. Adequate perfusion of the kidneys is essential
for optimal functioning. Kidneys adapt their activity according to what circulates in the blood and
what they receive, but how different foods alter kidney perfusion and function has not been studied
in detail. This project studies whether chocolate consumption induces changes in kidney physiology.
Previous studies have shown that regular consumption of cocoa (dark chocolate) may lower blood
pressure and has anti-inflammatory effects, but the effects on the kidneys have not been studied in
detail. Renal ultrasound provides a simple, non-invasive way of assessing kidney perfusion, in
particular by measuring the renal resistance index (RRI). RRI represents the resistance that blood
encounters as it passes through the kidneys. Studies have shown that a high RRI is associated with
poor renal perfusion and a high risk of decline in renal function.
The aim of the present randomized, placebo-controlled trial study is to investigate the changes that
may occur in RRI and blood pressure after eating dark chocolate as compared to white chocolate
(placebo), in healthy volunteers. The second aim is to evaluate whether the type of consumed
chocolate influences the renal response to a handgrip-test.
Methodology: Healthy volunteers were randomized to eat 1g/kg of dark chocolate (DC, 70% cocoa)
or white chocolate (WC). RRI was measured with renal Doppler ultrasound just before and two hours
after chocolate consumption. Blood pressure and heart rate was measured in parallel with a
Finapres® device. Immediately after the recordings of four RRI measurements, a 3-minute handgrip
test was be performed. During the handgrip test, at least four supplementary RRI values were
measured. One-two weeks later, the same exams were performed just before and two hours after
the consumption of the other type of chocolate.
Results: Seventeen healthy volunteers (8 women, 9 men / 47% women) with preserved kidney
function (mean estimated glomerular filtration rate (eGFR) ± SD 98 ± 10 ml/min/1.73mÇ) aged 41.5 ±
14 years were included. Dark chocolate ingestion induced a significant drop in RRI (-0.02, p=0.0393).
Dark chocolate also acutely raised systolic and diastolic blood pressure (with respectively 114/67 ±
11/9 and 122/71± 13/12 mmHg, p=0.0103 and p=0.0185), but only in non-regular DC eaters. White
chocolate did not lead to significant changes in RRI, nor in blood pressure. Handgrip (HG) exercise
systematically lowered the RRI both before and after each of the chocolates. This effect was larger in
the younger participants of 35 years old or less. In women, however, the effect of HG on lowering RRI
was greatly attenuated by the ingestion of DC.
Conclusion: This study shows that the ingestion dark chocolate leads to an acute reduction in RRI,
whereas white chocolate has no effect on RRI. Considering the potential renal benefits of lowering
RRI, these results may stimulate further studies, including in patients suffering from CKD. Handgrip
exercise led to large reductions in RRI, especially in young, male subjects. This may suggest that HG
testing is a way to assess the stiffness of renal arteries, but clearly more studies are needed to
confirm or reject this hypothesis.