This study aims to compare the effect of meals high in protein, fat and carbohydrate but equal in energy and volume on energy intake, perceived appetite and gastric emptying in younger (<40 years) and older (> 65 years) people living in the United Kingdom (UK).

To assess if increasing protein intake in older adults will have a compensatory decrease in energy intake due to protein's satiating effects.

To compare the effect of meals high in protein, fat and carbohydrate but equal in energy and volume on energy intake and perceived appetite in younger (<40 years) and older adults (>65 years).

To compare the effect of meals high in protein, fat and carbohydrate but equal in energy and volume on gastric emptying in younger (<40 years) and older adults (>65 years).

Inclusion Criteria:

• either aged >65 years or <40 years
• healthy

Exclusion Criteria:

• having a disease and/or using a medication that can impact on appetite in the past three months;
• having an allergy to any of the test foods;
• disliking or cannot eat any of the test foods;
• being pregnant or breastfeeding;
• being obese (BMI > 30 kg/m2);
• being on a weight loss diet;
• smoking more than 10 cigarettes a day.

No personal identification data will be shared. The study is not under an obligation to share data, however, it is possible that some of the individual (unliked / non-identifiable) data will be useful in a meta-analysis and, hence sharing individual participant data (IPD) will be considered.