The main goal of this study is to determine the difference in amino acid digestibility of milk, sorghum and black beans between older (65-80 years) and younger (20-35 years) adults using the dual tracer method.

Older adults should meet their amino acid requirements to prevent development of sarcopenia. Dietary protein quality is of importance, as determined by amino acid composition and digestibility of the consumed protein. There is a need to investigate the impact of ageing on amino acid digestibility and thus quality in vivo. The dual tracer method is an indirect, minimal-invasive method to determine amino acid digestibility in humans. It is expected that amino acid digestibility decreases with age and that the effect between age groups is greater for poorly digestible protein sources. In this randomized, cross-over study, the researchers will determine the difference in amino acid digestibility of milk, sorghum and black beans between older (65-80 years) and younger (20-35 years) adults using the dual tracer method. Secondary objectives concern the difference in amino acid kinetics between older and younger adults and the association between gut health plasma markers and amino acid digestibility.

Inclusion Criteria:

• Age: 20-35 years or 65-80 years
• Body Mass Index (BMI): 20.0 - 30.0 kg/m2
• Veins suitable for blood sampling
• Healthy as assessed with a questionnaire
• Regular and normal Dutch eating habits as assessed with a questionnaire
• Having given written informed consent
• Willing to comply with study procedures
• Accept use of all encoded data, including publication, and the confidential use and storage of all data for 15 years.

Exclusion Criteria:

• Chronic disease, for example:

  • Diabetes mellitus, being treated for high blood glucose or increased fasting blood glucose (> 6.7 mmol/l in finger prick blood)
  • Active cardiovascular disease
  • Hepatic disease (e.g. hepatitis)
  • Renal disease
  • Cancer
  • Bowel disease (e.g. inflammatory bowel disease, ulcers, bleeding)
  • Pancreatitis

• History of medical or surgical events that may affect GI function and the study outcomes, for example:

  • Bariatric surgery
  • Gastrointestinal tract surgery
  • Digestive tract disorder
  • Chewing problems

• Medicine use that interferes with GI function and the study outcomes, for example:

  • Glucose lowering drugs
  • Proton pump inhibitors
  • Laxatives

• Habits that interfere with the study outcomes:

  • Probiotics and/or protein supplement use
  • Smoking
  • Drug abuse
  • Alcohol consumption for men >21 units/week and >4/day and for women >14 units/week and >3/day
  • Following a weight-loss diet, medically prescribed diet or other diet with a low calorie intake or an unbalanced nutrient intake like a vegan or very low carbohydrate diet
  • Moderate to high intense physical activity for more than 5 hours a week
  • Difficulties with eating breakfast in the morning

• Other:

  • Self-reported allergy or intolerance to the tested products (milk, sorghum, black beans)
  • Weight loss of more than 3 kg in the month prior to study screening
  • Being pregnant
  • For men: Hb <8,5 mmol/l and for women: Hb <7,5 mmol/l
  • Recent blood donation (<2 months prior to start of the study)
  • Current participation in other research and <2 months previous participation in other research
  • Not having a general practitioner
  • Not willing to accept information-transfer concerning participation in the study, or information regarding his or her health, like laboratory results and eventual adverse events to and from his general practitioner
  • Working at the department of Human Nutrition and Health at Wageningen University & Research