Eligible healthy adults who consent to take part in the study will be randomised to receive either a specialised milkshake for all of their normal daily diet (exculsive enteral nutrition, EEN) or the same specialised milkshake for half of their normal daily diet (partial enteral nutrition, PEN) for seven days. This randomisation is to prevent any bias. In the week before the allocated diet starts participants will be asked to give a weight and height measurement, blood sample, collect a stool and urine sample, and complete a food diary of everything they eat and drink using household measurements (e.g., a teaspoon) seven, four, and one day before the randomly allocated diet begins. Participants will also be asked to give a weight measurement, blood sample, and collect a stool and urine sample before they start the allocated diet. All participants will be asked to collect a third stool, urine, and blood sample and weight measurement at the end of the seven days dietary intervention. Blood samples collected during the study will be used to find out how the cells and proteins which instruct the immune system change during the special milkshake diet. Stool and urine samples will be used to measure the levels of different bacteria which naturally live inside the gut and how their behaviour might have changed during the diet. Those allocated to have PEN will be asked to complete a second set of food diaries for three days during your seven days of specialised milkshake.

Inclusion Criteria:

• Healthy adults (>/= 18 years)

Exclusion Criteria:

• Those sufferring from acute or chronic illness (defined as illness which requires regular visits to health services)
• Those who have experienced weight changes +/- 2kg in the past month.
• Previous gut surgery,
• Use of antibiotics or steroids in the past month
• Food allergies which prevent consumption of the enteral nutrition used (milk protein allergy)
• Current pregnancy or breastfeeding.