Many studies have been carried out to investigate the possible effects of dark chocolate on our body.

Especially dark chocolate (DC) has been studied because it contains large quantities of cocoa and flavonoids. Regular cocoa consumption (dark chocolate) has antihypertensive and anti-inflammatory effects. A previous study demonstrated that dark chocolate may also have cardiovascular benefits. Their study showed that the consumption of DC (70% cocoa) induces vasodilation of the coronary arteries. In a cross-over study performed in 2013 by the PI of this study, dark chocolate (containing 70% cocoa) improved kidney oxygenation as assessed with renal MRI in healthy people two hours after its ingestion, whereas white chocolate did not induce any changes. The reasons for this increase remained hypothetical, as other aspects of renal physiology such as renal perfusion were not measured in this study. Chocolate intake also has potential side effects. As it is rich in calories and carbohydrates, long term, regular intake may lead to weight gain and its associated problems. Besides, the hemodynamic effects on DC intake in patients suffering from chronic kidney diseases (CKD) are also largely unknown. Hence, more insight in the renal physiological effects of DC intake is needed before any recommendation can be made on the potential usefulness of randomized controlled trials to test short-and long-term renal effects of DC intake.

Renal physiology, especially perfusion, can be monitored using renal ultrasound thanks to its Doppler mode. In particular, the renal resistive index (RRI) of intra-renal segmentary arteries is an interesting parameter in this context. RRI is defined as the difference between maximum systolic and minimum diastolic velocity divided by the maximum systolic velocity. RRI stands for the resistance that blood faces when passing through the kidneys. From a physiological viewpoint, vasoconstriction of intra-renal segmentary and interlobar arteries will increase RRI, whereas vasodilation of the main renal arteries will decrease the RRI. As chocolate induce vasodilatation of arteries, RRI is expected to decrease after DC intake.

Renal perfusion is also affected by the sympathetic nervous system, as its activation generates vasoconstriction of peripherical arteries, and possibly of the renal arteries. The handgrip test is a way to activate the sympathetic nervous system. With this test, volunteer applies an isometric strength with his hand to a handgrip device, which activates the sympathetic nervous system. . Therefore, the handgrip test can there be seen as a renal vascular stress test, but its effects on the RRI have not been studied. Besides, whether the RRI is influenced by the hand grip test, and whether this change is altered by DC intake, is also unknown. The handgrip test will therefore be used in the present study.

The aim of the present randomized controlled trial study is to investigate changes that may occur in kidneys after eating white and dark chocolate, as well as to see how renal perfusion works in this context and to evaluate responses to renal vascular stress (handgrip test). The innovation of the present study stands in the fact that the effect of chocolate intake on renal physiology has, to the best of our knowledge, not been investigated using renal ultrasound. It is also unknown whether the intake of chocolate may balance the renal physiology changes in response to stress (i.e. handgrip test).