Understanding the role of Umami in appetite control: a protein-specific effect?

The fifth basic taste, ‘umami’, is the flavour function elicited by amino acids like monosodium glutamate (MSG) in foods. This taste is recognized for its flavour enhancing properties but little is known about its effects on appetite and intake. Thus the experiments in this thesis aimed to understand how umami influences pleasantness, appetite stimulation, satiation and satiety using MSG, with some additional focus on its associated ribonucleotide inosine 5’-monophosphate (IMP). Chapter 2 established a bland, low glutamate control soup which was used throughout all subsequent experiments to test the effects of MSG on palatability using commercially-relevant concentrations. Chapters 3 and 4 assessed the influence of increasing palatability on rated appetite and intake of this soup with either added MSG (Chapter 3) or added sucrose (Chapter 4). No increase in hunger or intake was found after the more palatable conditions. Chapter 5 explored the relationship between MSG taste and protein regulation, assessing acute and habitual protein intake with findings indicating that high protein consumers liked high MSG concentrations more after an acute protein deprivation than sweet, salty or control flavours. Chapter 6 examined the time course of rated MSG satiety alone and in combination with either protein or carbohydrate in a preload soup and found enhanced rated satiety in MSG protein conditions. This design was extended in Chapter 7 to include an intake test after a pre-specified time of consuming the preload soup. The results indicated better compensation after MSG protein conditions but no differences in intake were found across carbohydrate or control conditions. Chapter 8 assessed MSG and IMP with or without added protein using the same design as Chapter 7 and found reductions in intake in MSG/IMP conditions. This suggests that the flavour of umami plays an important role in the regulation of appetite and intake.