Research does indeed show that the coffee cup runneth over with health benefits: It's linked with a reduced risk of type-2 diabetes and some cancers, and improved cardiovascular function. But there may be a point at which coffee drinking backfires bitterly: around five cups. A polyphenol in coffee called chlorogenic acid (CGA) is the cause, suggests a study on rodents at the University of Western Australia. The good news is that CGA in moderation is beneficial and thought to aid weight loss. The bad news is that in excess it may actually worsen the effects of a bad diet. Lab mice that consumed the equivalent amount of CGA in five or six cups of coffee gained more weight despite the compound's reputation as a diet aid. They also developed worse pre-diabetes disorders (increased glucose intolerance and insulin resistance), compared with CGA-free mice that ate the same high-fat food.
The lesson: Research on the interaction between food and the compounds in coffee is ongoing. But, to be safe, especially on days you're eating high-fat foods, consider limiting your intake to three to four cups. The cutoff also applies to decaffeinated coffee and tea, which, sorry to report, also contain CGA.