Tea is a drink that is rich in antioxidants. In particular, tea contains high amounts of the flavan-3-ol group of flavonoids, also known as catechins. Tea is associated with protection from digestive system cancers and the suggestion is that the presence of the tea in the gut, inhibits the formation or propagation of free radicals. This process in turn protects the genetic material of the gut cells, preventing the initiation of cancer. Coffee is also a rich source of antioxidants and contains a number of polyphenolic compounds that confer significant antioxidant effects. In particular kahweol and cafestol are two diterpenes that are present in coffee and these have been shown to be effective antioxidants. These two antioxidants are present in the fat soluble component of coffee beans and are known to be present in filter coffee in reasonably high concentrations. Both tea and coffee therefore are rich sources of antioxidants, but it is less clear if coffee is beneficial at protecting from gut cancer.
However, as with tea, coffee comes in many different forms, and so it is often difficult to determine which component of coffee is associated with gut cancer. Some studies have addressed this issue by measuring individual coffee metabolites in blood. For example, in one study1 researchers measured the metabolites detected in blood following consumption of coffee in order to be able to try to identify possible factors that influence the association. In this regard they detected a number of metabolites in blood that can differentiate coffee drinkers from non-coffee drinkers in future studies. Coffee drinkers can therefore be identified biochemically, and this can allow specific biochemical associations to be made with gut cancers. However the association between coffee consumption and gut cancer is highly complex and influenced by a number of factors. For example, coffee is drunk along with other foods that also influence cancer and in this regard separating these factors is highly difficult.
Another problem with the association between coffee and colorectal cancer is that not all coffee is the same. Coffee can be filter coffee or instant, and no food connoisseur would claim that these are the same product. They may both be derived originally from coffee beans, but clearly freeze dried instant coffee is more highly processed that filter coffee. Analysis between filter coffee and instant coffee shows that they are not the same compositionally, with filter coffee maintaining far higher concentrations of antioxidant nutrients compared to instant coffee. As the consumption of these type of coffee varies between countries, regions and even within families, it becomes very difficult to interpret data referring to coffee as a whole. Bean type, roast length and other processing and storage factors may also play a role in altering the composition of coffee. As with tea then, coffee is a heterogeneous group of drinks nad unless this is considered, associations between coffee and disease become difficult to understand mechanistically.
RdB
