About one-third of all cancers are more likely to happen when there is poor diet and a lack of physical exercise. In fact, about one-third of cancer deaths are related to poor nutrition, lack of physical activity and excess weight. Obesity can cause complications such as heart and blood vessel disease, diabetes, and osteoporosis. Weight loss for obese people, and exercise, are safe and recommended during cancer treatment. For people who are not obese keeping weight stable during treatment is also important.