INTRODUCTION: Obesity is a global epidemic, with over 2.5 billion adults being classified as overweight and 890 million of these classified as obese. Overweight and obesity are the 5th cause of mortality globally, with an estimated 2.8 million related deaths among adults. The rising prevalence of obesity in adults is leading to a rise in the prevalence of type 2 diabetes, with an estimated 462 million individuals affected globally. At present, the most effective non-surgical obesity treatments offered by the National Health Service (NHS) are the subcutaneously administered GLP-1 receptor agonists. However, they may present potentially serious side effects following short-term use, and there are still uncertainties around long-term use side effects. Therefore, a dietary approach to weight loss or maintenance seems preferable.

Increasing protein intake is a commonly applied nutritional approach to appetite regulation. The increase in protein intake is often achieved by supplementation, using proteins isolated from dairy, such as whey and casein. However, with more individuals following plant-based diets over recent years, the interest in plant-based protein supplements has increased. While dairy-based proteins are well-characterised, the appetite regulatory characteristics of plant-based proteins have not yet been fully elucidated.

The main aim of this study is to investigate the effects of protein-enriched food items on appetite regulation compared to a standard carbohydrate-rich meal. Furthermore, this study will investigate whether there are any differences in appetite-related hormonal responses to a plant protein-containing meal replacement shake (containing rice and pea protein) or a potato protein-enriched standard carbohydrate-based meal compared to a whey protein-enriched standard carbohydrate-based meal.

Intervention study with four treatment groups in a randomised, single-blind, quadruple crossover design.

Healthy male participants (between the ages of 18 to 50 years) will receive four different isocaloric intervention meals with the same mass, on separate visit days, following a minimum of 8 hours overnight fast. The four meals will contain oat porridge prepared with coconut milk as a control, oat porridge prepared with coconut milk with added whey or potato protein isolates, and a complete meal replacement shake containing plant-based pea and rice proteins. The intervention meals will be followed by a standardised pasta-based ready meal after the 3-hour observation period. All participants will observe at least a two-day washout period between the differing treatments.

Biological samples (blood) will be collected at various times during the visit. Blood samples will be collected at baseline 0 min prior (T0), then at 30 min (T30), 60 min (T60), 120 min (T120) and 180 min (T180) after the intervention meal consumption.

In addition, pertinent questionnaires, Visual Analogue Scale [VAS] for assessing satiety and VAS for assessing intervention meals' perception and palatability will be collected. VAS for the assessment of satiety will be collected at T0, T30, T60, T120 and T180 and VAS assessing the perception and palatability of the intervention meals will be collected immediately following meal consumption.

Inclusion Criteria:

• Males (18-50 years of age)
• Lean and Overweight subjects (BMI 18.5 - 30 kg/m2)
• Sedentary and physically active subjects
• Healthy subjects

Exclusion Criteria:

• Female
• <18, >50 years
• Dieting
• Consumption of >14 units of alcohol/week
• Allergies to test foods/drinks
• Illnesses or on medication (with a possible effect on taste and/or appetite)
• Devices such as pacemakers
• Smokers
• Gastrointestinal disorders
• Eating disorders

Single