Threonine is an essential amino acid and must be obtained from the diet. The body's capacity to maintain adequate mucin synthesis is directly related to the bioavailability of certain amino acids, including threonine, serine and proline (1). Moreover, the rate of mucin synthesis has been demonstrated to be directly related to the availability of dietary threonine in healthy rats (2) and piglets (3,4). Intestinal inflammation is known to increase gastrointestinal threonine uptake and mucin synthesis in enterally fed minipigs (5). Additionally, in animals, mucin function/barrier has been shown to decline with age, leaving them more susceptible to bacterial penetration. Thus, with advancing age (6), a higher dietary supply of threonine may be needed for maintaining intestinal mucosal health. Despite this, the current threonine requirement is based on studies conducted exclusively in young adults. Thus, there is a need to determine the threonine requirement directly in older adults.

To determine the threonine requirement in adults over the age of 60 years. With age, various physiological changes occur, including a decline in muscle and an increase in fat. Muscle reduction is a cause for concern as it may lead to weakness rendering regular daily activities more difficult.

The muscles in the human body are composed of proteins and those proteins are made of small building blocks termed amino acids. The human body has the ability to make some amino acids which are called the non-essential amino acids. However, there are specific amino acids that the body needs to make protein, but can only be supplied from the foods eaten. These are termed essential amino acids. Threonine is one of the essential amino acids. It is needed to synthesize mucins which are proteins that protect the gastrointestinal tract from bacterial invasion. The body's capacity to make mucins is directly related to the bioavailability of amino acids like threonine. However, evidence from animal data has shown that older mice have compromised mucus function compared to young mice leaving them more susceptible to bacterial penetration. Thus, a higher dietary supply of threonine may be needed for maintaining intestinal mucosal health as individuals age. The purpose of this study is to find out the threonine requirement in adults over 60 years using the minimally invasive Indicator Amino Acid Oxidation (IAAO) method.

Inclusion Criteria:

• Consent provided
• Aged 60 to 90 years old
• In good general health as evidenced by medical history, physical health and blood draw
• Fasting blood glucose, hemoglobin A1c (HbA1c), urea, creatinine
• Willingness to participate in the study.
• BMI <30 kg/m2.

Exclusion Criteria:

• Presence of chronic disease and/or acute illness known to affect protein/amino acid metabolism (e.g. HIV, diabetes, cancer, liver or kidney disease, acute cold or flu)
• Taking medications known to affect protein/AA metabolism (e.g. steroids)
• Inability to tolerate the diet (i.e. allergy)
• Significant weight loss during the past month or consumption of weight reducing diets.
• Significant caffeine consumption (>2 cups per day)
• Significant consumption of alcohol (>1 drink per day i.e. 1 beer or ½ glass of wine).
• Unwilling to have blood drawn from a venous access, or using a ventilated hood indirect calorimeter for the purposes of the study.