While some substances in grapes have shown promise in early trials, there is very little reliable evidence that a diet high in grapes, or grape compounds, can prevent or treat cancer. More research is needed to understand the possible long-term health benefits of grapes. Several studies have shown that proanthocyanidins, the chemicals found in grape seed extract, have antioxidant properties. A small randomised clinical trial of grape seed extract demonstrated that these antioxidants have the potential to inhibit the development of some types of cancer. Other studies in laboratory animals have suggested that grape seed extract may act against prostate, colon and breast cancer. Proanthocyanidins may also reduce the body’s production of oestrogen, which may have an effect on hormone-sensitive tumours, such as some types of breast cancer. While there is no proof that grape seed extract can help prevent cancer, grapes are a healthy addition to the diet. A balanced diet that includes two serves of fruit and five serves of vegetables each day, along with foods from a variety of other plant sources such as nuts, seeds, wholegrain cereals and beans, has been shown to reduce the risk of some cancers.