I found many many articles on the internet that make claims that consuming coffee makes it harder to lose weight because of various factors. Here is an excerpt:
Caffeine intake often perpetuates many of the factors contributing to weight gain and continued obesity. Coffee and caffeine intake aggravates stress, including physical, mental, and emotional stress, leading to increased levels of the glucocorticoids including cortisol. A well documented relationship exists between chronically elevated levels of these stress hormones and deposition of excess fat in the abdomen leading to obesity as well as increased caloric intake, particularly increased ingestion of fats and sugars.4