Whey Protein Study - Identification of Sustainable Satiety

This study will have the primary aim to investigate within-day changes in appetite after consumption of high-protein (HP, 30% of calories) and normal, or low, protein (LP, 15% of calories) whey protein meal, in solid and liquid form, on appetite and ad libitum food intake. Secondary objective will be to assess the statistical relationship between plasma concentrations of gut hormones and visual analogue scales (subjective hunger and fullness) and transit time.

In order to investigate the interaction of food structure and protein content on appetite, this requires, in practice, either a differing amount (g) or calorie (kJ) load as a function of energy density (defined as kJ/100g). Delivering the test meal as a solid and liquid form gives an easy solution to achieve this manipulation without compromising the nutritional profile. Following on from this decision, it is easier to produce different preloads using whey protein (rather than meat protein), since it is easily incorporated into test meals.

A randomized crossover design in 10 overweight/obese (BMI 26-40) men and 10 lean men (BMI 18.5-25). The control will be water. Each subject will attend the HNU on six separate occasions. The five test meal challenges will involve subjects attending the Human Nutrition Unit (HNU) in the morning, after an overnight fast. The total time of test meal visits will be approximately 4½hours. They will be provided with a standardised meal, after which blood samples will be collected for the first 2hrs. The following five treatments will be tested:

Treatment 1 Control - Water + Egg Yolk Mixture + 13C Octanoic Acid Treatment 2 HPL (High Protein Liquid): 30% protein; 30% fat and 40% carbohydrate (CHO) Treatment 3 LPL (Low Protein Liquid): 15% protein; 30% fat and 55% CHO Treatment 4 HPS (High Protein Solid): 30% protein; 30% fat and 40% CHO Treatment 5 LPS (Low Protein Solid): 15% protein; 30% fat and 55% CHO Test meals will be of fixed nutritional composition for all participants. The liquid meal will be a milk/fruit smoothie mixture and the 'solid' will be in a milk jelly (set) form.

Ad libitum pasta meal: 15% protein; 30% fat and 55% CHO as a homogenous mix and energy density of around 400kJ/100g - served in excess as a individual 600g portion to 'help-yourself'.

Subjective average appetite will be measured (every 30 min by visual analogue scales) over 4hr and ad libitum food intake will measured 4hr after treatment consumption. Ad libitum lunch will be a homogenous pasta meal with tomato sauce and a bottle of water. Blood samples will be collected every 10 min for the first half hour, every 15 min for the second half hour and every 30mins subsequently. The breath gastric emptying measurement will be assessed using the 13Carbon (13C) Octanoic Acid stable isotopic technique19. This involves mixing the tracer into food and taking breath samples and measured by isotope ratio mass spectrometry. 13C Octanoic acid is a medium chain fatty acid which is rapidly absorbed in the duodenum and metabolised in the liver. Following oxidation, the resulting Carbon Dioxide (CO2) is excreted into breath (12 samples will be collected during the 4hr test day).

Eligibility Criteria:
Inclusion Criteria:

* BMI = 18.5-40kg/m2

Exclusion Criteria:

* Diabetes
* Severe gastrointestinal disorders
* Kidney disease
* Thromboembolic or coagulation disease
* Hepatic disease
* Alcohol or any other substance abuse
* Gout
* Eating disorders
* Food allergy
* Unregulated thyroid disease
* Psychiatric disorders (including severe depression, lithium treatment, schizophrenia, severe behavioural disorders)
* Vegetarians \& Vegans

Medication Exclusion Criteria:

* Orlistat (Xenical)
* Oral antidiabetics, insulin
* Rimonabant (Acomplia)
* Digoxin, anti-arrhythmics
* Sibutramine (Reductil)
* Tricyclic antidepressants, neuroleptics