Based on the all the information, it appears as though drinking four or more cups of coffee a day is the closest we can get to a research-based recommendation. This amount is most likely to lower the risk of type 2-diabetes and promote healthy insulin function.
What appears to be more important is, the time of the day you drink your coffee. For example, the consumption of coffee after a meal is shown to significantly slow carbohydrate release into the bloodstream. This has a favorable effect on plasma glucose and insulin responses, as well as gastrointestinal hormone profiles, all of which promote more efficient metabolism of fat.
Therefore, a cup of coffee after a meal appears to be a great strategy that promotes a lower, steadier blood sugar response. This promotes lower insulin secretion which is conducive to better utilization of fat as a fuel source. The bottom line is, a cup of coffee after some of your meals may help promote a hormonal response that makes fat loss easier.