Coffee Components and By-Products for Brain–Gut Axis Health ^†

Brain–gut axis disorders, such as functional dyspepsia and irritable bowel syndrome (traditionally known as functional gastrointestinal disorders), have a prevalence of more than 10% in most countries and affect females more than males. In these disorders, visceral pain and motor alterations affecting the gastrointestinal tract are the key symptoms, together with psychoaffective alterations (depression and anxiety). Two main etiologies are generally recognized for their development: they may be caused by a local inflammatory or infectious problem in the gastrointestinal tract that sensitizes the visceral afferents and lead to central hypersensitization; alternatively, they may be associated with some kind of prolonged psychological stress in vulnerable people or vulnerable periods of life (i.e., due to early life stress). In recent years, studies have focused on the effects of coffee, its components (melanoidins) and its by-products (e.g., coffee spent grounds and coffee silver skin derivatives) on the functions of the brain–gut axis, showing that these products may cause subtle alterations in gastrointestinal motility, visceral sensitivity and behavioral parameters, in a sex-dependent manner. For example, using male rats, we showed that melanoidins and coffee spent grounds slightly accelerate gastrointestinal transit in vivo. In contrast, the regular consumption of instant cascara (IC) did not alter GI transit or behavior in either male or female rats in vivo, but increased both the responses to mechanical intracolonic stimulation and the non-muscarinic responses to electrical field stimulation of the colonic muscle in vitro, specifically in females. These effects need to be taken into account when new functional foods based on coffee and its by-products are to be developed for the general population. Considering the high prevalence of the brain–gut axis disorders and its higher impact on women, with significant symptoms affecting visceral sensitivity and bowel habits, the effects of coffee components and by-products need to be more deeply evaluated in both relevant animal models of brain–gut axis disorders and in clinical trials.