The effect of diet on cancer is tough to determine for many reasons, including the fact that most studies rely on data self-reported by participants, researchers say in a new study. The Imperial College London scientists looked at 860 meta-analyses of published studies involving 11 anatomical sites and found that only a few provided strong evidence of a cancer link—including several involving alcohol. The researchers do say, however, that there's evidence alcohol consumption is connected to more cancers than previously believed, including bowel cancer and several cancers of the head and neck, including throat cancer, Guardian reports. They say there's also evidence of the previously known risk of liver cancer and postmenopausal breast cancer.
In a study published in the journal Nature, the researchers say evidence was also weak for most associations between food and drinks and a reduced risk of cancer, but there was strong evidence suggesting at least one cup of coffee a day—either caffeinated or decaffeinated—reduces the risk of skin cancer and liver cancer. There was also strong evidence for a link between consumption of dairy products and whole grains and a reduced risk of colorectal cancer. "Further research needs to better understand the mechanisms involved in the links between coffee and cancer, as well as between alcohol and different cancer subtypes," Giota Mitrou of the World Cancer Research Fund tells the Guardian. (Read more alcohol stories.)