Foods such as dark chocolate, made from cacao/cocoa beans, frequently reduce insulin resistance and blood pressure in human studies.54-59
In one study on prediabetics, dark chocolate even increased insulin secretion, an effect not seen with white chocolate.57
A meta-analysis published in 2011, which pooled the results of 24 studies of cocoa on 1106 participants, found that cocoa consumption reduces insulin resistance, blood pressure and LDL cholesterol, and raises HDL cholesterol.55
How much dark chocolate is enough?
Some studies found that as little as 20 grams (0.7 ounces) of dark chocolate per day can reduce insulin resistance and blood pressure,56 demonstrating that quite small, realistic amounts can be sufficient. However, eating larger amounts like 100 grams (3½ ounces) per day may also have positive health effects.57, 59
When buying dark chocolate, it may be a good idea to aim for a cocoa content of at least 70%, otherwise it may contain a lot of sugar. There are also many other cocoa-rich products available, but I would stay away from those containing a lot of sugar.
Dark chocolate also contains pretty high amounts of magnesium, an important mineral for blood sugar control.