The efficacy of Roux-en-Y gastric-bypass (RYGB) and other bariatric surgeries in the management of obesity and type 2 diabetes mellitus and novel developments in gastrointestinal (GI) endocrinology have renewed interest in the roles of GI hormones in the control of eating, meal-related glycemia, and obesity. Here we review the nutrient-sensing mechanisms that control the secretion of four of these hormones, ghrelin, cholecystokinin (CCK), glucagon-like peptide-1 (GLP-1), and peptide tyrosine tyrosine [PYY(3-36)], and their contributions to the controls of GI motor function, food intake, and meal-related increases in glycemia in healthy-weight and obese persons, as well as in RYGB patients. Their physiological roles as classical endocrine and as locally acting signals are discussed. Gastric emptying, the detection of specific digestive products by small intestinal enteroendocrine cells, and synergistic interactions among different GI loci all contribute to the secretion of ghrelin, CCK, GLP-1, and PYY(3-36). While CCK has been fully established as an endogenous endocrine control of eating in healthy-weight persons, the roles of all four hormones in eating in obese persons and following RYGB are uncertain. Similarly, only GLP-1 clearly contributes to the endocrine control of meal-related glycemia. It is likely that local signaling is involved in these hormones' actions, but methods to determine the physiological status of local signaling effects are lacking. Further research and fresh approaches are required to better understand ghrelin, CCK, GLP-1, and PYY(3-36) physiology; their roles in obesity and bariatric surgery; and their therapeutic potentials.

Fatty acids are the chemical moieties that are thought to stimulate oral nutrient sensors, which detect the fat content of foods. In animals, oral hypersensitivity to fatty acids is associated with decreased fat intake and body weight. The aims of the present study were to investigate oral fatty acid sensitivity, food selection and BMI in human subjects. The study included two parts; study 1 established in thirty-one subjects (29 (SEM 1·4) years, 22·8 (SEM 0·5) kg/m 2 ) taste thresholds using 3-AFC (3-Alternate Forced Choice Methodology) for oleic, linoleic and lauric acids, and quantified oral lipase activity. During study 2, fifty-four subjects (20 (SEM 0·3) years, 21·5 (SEM 0·4) kg/m 2 ) were screened for oral fatty acid sensitivity using oleic acid (1·4 mM), and they were defined as hypo-or hypersensitive via triplicate triangle tests. Habitual energy and macronutrient intakes were quantified from 2 d diet records, and BMI was calculated from height and weight. Subjects also completed a fat ranking task using custard containing varying amounts (0, 2, 6 and 10 %) of fat. Study 1 reported median lipase activity as 2 mmol fatty acids/ min per l, and detection thresholds for oleic, linoleic and lauric acids were 2·2 (SEM 0·1), 1·5 (SEM 0·1) and 2·6 (SEM 0·3) mM. Study 2 identified twelve hypersensitive subjects, and hypersensitivity was associated with lower energy and fat intakes, lower BMI (P,0·05) and an increased ability to rank custards based on fat content (P,0·05). Sensitivity to oleic acid was correlated to performance in the fat ranking task (r 0·4, P,0·05). These data suggest that oral fatty acid hypersensitivity is associated with lower energy and fat intakes and BMI, and it may serve as a factor that influences fat consumption in human subjects.

| Functional dyspepsia is one of the most prevalent functional gastrointestinal disorders. Functional dyspepsia comprises three subtypes with presumed different pathophysiology and aetiology: postprandial distress syndrome (PDS), epigastric pain syndrome (EPS) and a subtype with overlapping PDS and EPS features. Functional dyspepsia symptoms can be caused by disturbed gastric motility (for example, inadequate fundic accommodation or delayed gastric emptying), gastric sensation (for example, sensations associated with hypersensitivity to gas and bloating) or gastric and duodenal inflammation. A genetic predisposition is probable but less evident than in other functional gastrointestinal disorders, such as irritable bowel syndrome (IBS). Psychiatric comorbidity and psychopathological state and trait characteristics could also play a part, although they are not specific to functional dyspepsia and are less pronounced than in IBS. Possible differential diagnoses include Helicobacter pylori infection and peptic ulceration. Pharmacological therapy is mostly based on the subtype of functional dyspepsia, such as prokinetic and fundus-relaxing drugs for PDS and acid-suppressive drugs for EPS, whereas centrally active neuromodulators and herbal drugs play a minor part. Psychotherapy is effective only in a small subset of patients, whereas quality of life can be severely affected in nearly all patients. Future therapies might include novel compounds that attempt to treat the underlying gastric and duodenal inflammation. NATURE REVIEWS | DISEASE PRIMERS VOLUME 3 | ARTICLE NUMBER 17081 | 1 PRIMER © 2 0 1 7 M a c m i l l a n P u b l i s h e r s L i m i t e d , p a r t o f S p r i n g e r N a t u r e . A l l r i g h t s r e s e r v e d .standard therapy for gastro -oesophageal reflux disease. Paediatric dyspeptic symptoms are being addressed in a separate classification effort 10 . This Primer covers functional dyspepsia in adults only, although we sporadically refer to paediatric functional dyspepsia when similarities exist. EpidemiologyThe population prevalence of functional dyspepsia is quite variable across the globe, with overall high numbers (10-40%) in Western countries and low numbers (5-30%) in Asia, independent of the respective functional dyspepsia definitions 11 . A large-scale health and nutrition survey from France 12 (which involved >35,000 people) identified that 15% of individuals had suspected functional dyspepsia, 28% had irritable bowel syndrome (IBS) and 6% had both. The population of patients who are affected by both IBS and functional dyspepsia has been reported to range between 10% and 27% in previous studies 13 and to approach 30% in popu lation samples; it could be even higher in specific populations 14,15 . This observation has given rise to the term 'overlap syndrome' (REF. 13), which calls into question the sensitivity and specificity of the Rome criteria, at least for IBS and functional dyspepsia. This argument is also supported by the observation that patients with functional dyspepsia m...