Risk factors of cancer include unhealthy dietary habits, physical inactivity, smoking, various genetic and environmental factors. Cancer is the second cause of death after cardiovascular diseases with increased incidence; moreover, 80% of gastrointestinal, breast and prostate cancers are attributed to unhealthy eating habits. Many surveys have investigated the role of diet in cancer prevention. Here we summarized current knowledge about dietary factors associated with cancer incidence. There is a strong correlation of the protective effect of fruits and vegetables with colon cancer and the negative effect of red meat and the protective effect of milk on colorectal cancer. High alcohol consumption is related to higher incidence of mouth and esophageal cancers, with hot drinks playing a role in mouth or even gastrointestinal cancers. High fat consumption seems to play a negative role in colorectal cancer, where sugar and salt might be negatively related to stomach cancer. Beyond nutrition, physical inactivity and body fat seems to play an important role in cancer, where there are strong evidence that the first protects against colorectal cancer and the second increases the incidence of breast cancer after menopause. Data for the role of micronutrients, vitamins and minerals lead to the suggestion that dietary supplements should be avoided and all nutritional needs should be covered through a well balanced diet.