Walnuts are not true botanical nuts, but the edible seed of a drupe – fruit containing a large pit in the center. They contain a fair amount of polyunsaturated fat that gives walnuts a rich, buttery texture. The bitterness of walnuts comes from the high tannins (antioxidant) content in their skin. Research published in the AHA journal Circulation found that those who ate about half a cup of walnuts every day for two years had moderately lower levels of low-density lipoprotein (“bad”) cholesterol and a reduction in total cholesterol. As a good source of the plant form of omega-3 fat (alpha-linolenic acid), eating walnuts may also help reduce heart disease risk.
Polyphenols are a category of compounds naturally found in walnuts. These have antioxidant properties that may provide protection against conditions like breast, prostate and colorectal cancers. Polyphenols are also thought to reduce inflammation, a root cause of many chronic illnesses.
One small study found that walnuts increased activation in a region of the brain that helped participants resist tempting food cues such as cake. This provides some initial insight as to how walnuts may help control appetite and weight, potentially correlating to a lower risk of type 2 diabetes.
Despite the plentiful health benefits, walnuts are one of the most common tree nut allergies worldwide. Some individuals may also experience adverse reactions like diarrhea and weight gain from excessive consumption. As with everything else, moderation is key.