Healthy older adults who ate a handful of walnuts a day (approximately 1/2 cup) for two years had a slight reduction in their LDL cholesterol levels. The number of LDL particles, which is a marker of cardiovascular disease risk, was also lowered when walnuts were consumed on a daily basis. The study looked at the impact of a walnut-rich diet on overall cholesterol levels in elderly people from various countries.
Source: American Heart Association