Nutrient sensing on the tongue: Effect of calories and sweeteness.

Rationale:

Humans easily prefer and select carbohydrate rich foods because of their inborn preference for sweet taste. However, recently done studies indicate that a nongustatory factor, caloric content, might also play a role in the formation of preferences for these foods. Nutritive and non-nutritive sweeteners have been shown to differentially affect brain activation during oral exposure. Furthermore, oral exposure to a carbohydrate solution during exercise improved performance, but oral exposure to an artificial sweetener solution did not. Above findings suggest the existence of an oral carbohydrate receptor that responds to carbohydrates rather than to sweetness. However, whether this receptor responds to all carbohydrates or only to specific ones, and whether energy (carbohydrate) sensing takes place in the absence of sweetness is not yet known.



Objective:

The primary objective of this study is to assess whether oral exposure to caloric and non-caloric stimuli elicits discriminable responses in the brain independent of sweetness.



Study design:

The study has a randomized crossover design in which participants taste a fixed amount of six test stimuli, once in fasted and once in a fed state, while their brain responses are measured using functional MRI. Stimuli are subdivided in (i) three sweet caloric food-stimuli (solutions of glucose, fructose and maltodextrin + sucralose), (ii) one non-sweet caloric food-stimulus (solution of maltodextrin), (iii) one sweet non-caloric food-stimulus (solution of sucralose) and (iv) one non-sweet non-caloric food-stimulus that is perceived as neutral (control stimulus: water). The order in which participants are exposed to these stimuli is randomized and counterbalanced.



Study population:

The study population consists of 30 apparently healthy, right-handed, normal weight (BMI 18.5-25 kg/m2), unrestrained women between the age of 18 and 35 y.



Main study parameter/endpoint:

The main study parameter/endpoint is taste activation in response to exposure to different caloric and non-caloric food stimuli.

We hypothesize that discriminable responses between oral exposure to caloric and non-caloric stimuli are observed in the following areas: the anterior cingulate cortex, the striatum, the amygdala and areas related to brain reward circuitry (e.g. VTA, substantia nigra and the medial prefrontal cortex). This effect is thought to be seen independent of sweetness (i.e. to exist in the presents and absence of sweet taste).

1. Taste activation measurements are obtained during two fMRI scans, one during hunger and one during satiety. The scans are minimal 5 days apart;

2. Questionnaires and tasks are filled out before the fMRI scans are made.

There are two interventions:

1. Hunger and sated: Participants will undergo one fMRI scan while sated (a meal will be offered to the participant by the researchers) and one fMRI scan while hungry;

2. Exposure to divers types of sugars and sweeteners: During the two scans (hunger and sated) different types of sugars and sweeteners will be offered in a randomized order. The stimuli offered are subdivided in (i) three sweet caloric food-stimuli (solutions of glucose, fructose and maltodextrin + sucralose), (ii) one non-sweet caloric food-stimulus (solution of maltodextrin), (iii) one sweet non-caloric food-stimulus (solution of sucralose) and (iv) one non-sweet non-caloric food-stimulus that is perceived as neutral (control stimulus: water). During one fMRI scan, each of these six stimuli will be offered to the participant 12 times in 2 ml sips by a gustometer.