The two studies investigate the relationship between dietary factors (meat intake and fruit/vegetable intake, respectively) and cancer risk.

"Eating a plant-based diet, increasing physical activity, maintaining a healthy weight and not smoking remain the most important things individuals can do to stop cancer before it starts," Butrum said.

"The new JAMA study on meat intake and colorectal cancer found diets high in red meat, and processed meat in particular, to be associated with increased risk. These results are in close accordance with earlier evidence from large-scale epidemiological investigations, as well as laboratory studies.

"The second JAMA study found no significant association between consumption of vegetables and fruits and reduced risk for breast cancer. This finding is harder to place in context; while previous ... studies and laboratory investigations generally support the contention that diets high in vegetables and fruits protect against breast cancer, evidence from cohort studies like this one tends to be less consistent.

"Evidence linking such diets to lower risk for colon, stomach, lung and many other cancers, however, is significantly stronger."