Walnuts can help protect against the harmful effects of lead by reducing oxidative stress in the body. A study on mice found that those given lead showed increased levels of a harmful substance called malondialdehyde (MDA) and decreased activity of an important antioxidant enzyme called superoxide dismutase (SOD). However, when the mice were also given walnut supplementation, the MDA levels decreased and SOD activity increased, showing that walnuts can help prevent damage caused by lead exposure.