Rats were given a cancer causing chemical known as N-nitrosomethylbenzylamine (NMBA).

NMBA causes cancer of the esophagus. Scientists freeze dried blackberries, strawberries and black raspberries. Different rats were supplemented with one of these berry powders before, during, and after being exposed to NMBA. At 25 weeks after exposure the rats were examined and it was found that all three of the berry powders decreased the number of esophageal tumors (papillomas – tumors on stalks in the esophagus that are precursors to squamous cell carcinoma) from 24% to 56% compared to rats not given the berries. The berry powders prevented NMBA from damaging DNA. In a second study the animals were first exposed to NMBA and then given either the strawberry or the black raspberry powder. They decreased the formation of tumors by 31% to 64% when administered after exposure to the chemical. Berries therefore inhibit three steps in the cancer process; initiation, promotion, and progression to cancer. The study appears in the current issue of the journal Nutrition and Cancer.

Studies show it is not the caffeine which helps decrease the risk of developing diabetes but probably the polyphenols.