Twelve healthy individuals (age 18-40y, BMI 19-30 kg/m2) will be recruited following a health screening. An equal number of males and females will be sought to improve generalisability of data, but the study will not powered to explore sex differences in response. After a successful screening and recruitment, participants will be asked to record everything that they eat and drink in a dietary record for 4 days (3 week and 1 weekend day). This will be analysed using dietary analysis software (Nutritics, Eire) for energy, macronutrient and fibre intake to characterise the participants' habitual diets.

At 2 subsequent laboratory visits, volunteers will be asked to refrain from drinking alcohol and doing strenuous exercise on the day before. They will arrive at the laboratory by 9am after an overnight fast and a retrograde cannula will be inserted into a superficial dorsal hand vein after prior intradermal infiltration with \~0.01ml 1% lidocaine. The cannulated hand will be placed into a hot air hand warmer for the duration of the study to allow sampling of arterialised venous blood for assessment of blood glucose and insulin concentration. A 1ml fasting blood sample will be taken and participants will be asked to complete a short questionnaire containing 6 visual analogue scales. Four of these will assess subjective appetite (How full do you feel? How much food do you think that you could eat? How hungry do you feel? How strong is your desire to eat?) with 2 addressing possible gastrointestinal symptoms (How much abdominal pain are you currently feeling? How much intestinal gurgling are you experiencing?). Participants will be asked to evaluate how strong their feelings are by placing a vertical mark along a 100mm horizontal line; 0 representing not experiencing the criterion at that time, and 100 indicating experiencing the greatest degree of that feeling that they could imagine. The combined appetite score (CAS) will be calculated according to standard methods and expressed as incremental change from the score reported at the end of the meal (iCAS).

Once baseline measures have been made, participants will be given a porridge breakfast (50g Ready Brek™, 15g skimmed milk powder, 10g glucose, 200ml hot water) to which has been added 15g of D-allulose or 1 saccharin tablets (Sweetex™). Fifteen grams of D-allulose and 1 Sweetex™ will be approximately equivalent to the sweetness provided by 10g (2 tsp) of sucrose (table sugar). The base porridge will provide 1.1MJ (265 kcal), 47g carbohydrate (29.1g starch, 17.8g sugars), 10.9g protein and 3.7g fat. The saccharin tablets will add no further energy to the breakfast, but the D-allulose will add a further 25kJ (6 kcal) to the porridge. Both porridge meals have the same volume, taste and consistency. Further 1ml blood samples will be taken at 5, 10, 15, 20, 30, 40, 50, 60, 75, 90, 105, 120, 150 and 180 minutes after finishing eating breakfast, with the questionnaire completed immediately after eating and at the 20, 40, 60, 90, 120, 150 and 180 minute time points. At 180 minutes, the cannula will be removed, and participants will be offered refreshments before leaving the laboratory. Therefore, the time in the laboratory on each study visit will be \~4 hours and the amount of blood collected will be \<20ml.

The second study visit will be scheduled for at least a week after visit 1, and in the time between visits participants will resume their usual diet and lifestyle. At the second visit, the protocol described above will be repeated, but participants will receive the breakfast that they did not receive at visit 1 i.e. if they received the porridge with D-allulose at visit 1, then they will receive the porridge with saccharin at visit 2 and vice versa.

The order in which the breakfasts are given will be randomly allocated according to a predetermined randomisation plan. The randomisation sequence will be generated for males and females separately to ensure a balanced allocation within sex. Individuals will be randomised at the first laboratory visit, with their randomisation number allocated sequentially. Any participants who withdraw from the study will be replaced if time allows.