Lysine Requirement of Elderly Men and Women Over 60 Years of Age
Condition: Healthy
Study type: Interventional

Summary: 
      This study aims to determine the requirement for lysine in men and women over the age of 60
      years.

      Seven different levels of lysine intake will be tested in each subject in random order. Each
      level of lysine intake will involve a 3-day maintenance diet, with measures (breath, urine,
      and blood samples) being collected on the third.
    

Detailed description: 
      Lysine is an amino acid that is essential in the diet. In our body, lysine makes up protein.
      It is known that as people get older, over the age of 60, our body goes through many changes
      such as increase in fat mass and decrease in lean mass such as muscle. This is why we are
      studying how much of the essential amino acid, lysine, the body needs at this particular age.

      The indicator amino acid oxidation (IAAO) method is a minimally invasive method for
      determining essential amino acid requirements.

      As essential amino acids cannot be stored in the body, they are either partitioned into
      protein synthesis or oxidized if in excess. The premise of the IAAO is that when any
      essential amino acid is limiting in the body then all other amino acids lose their ability to
      contribute to protein synthesis and are instead oxidized. The method therefore involves
      providing graded intakes (from deficient to excess) of the test amino acid, lysine, and then
      measuring the oxidation of another amino acid, which is called the indicator amino acid. This
      is done by isotopically labelling the indicator amino acid (13C- phenylalanine) and then
      measuring the appearance of labelled carbon dioxide (13CO2) in breath with the different
      intakes of the test amino acid, lysine. The requirement for lysine will be determined by the
      "breakpoint" - the point at which oxidation of 13C- phenylalanine will plateau.

      For the study, participants will first participate in a pre-study assessment in which height,
      weight, body composition (fat mass and muscle mass) and resting energy expenditure and
      medical history will be assessed. Also, 5 ml of blood will be collected to test for diabetes
      and kidney function. The purpose of the pre-assessment is to calculate the participant's
      dietary requirements for the study, and to assess health status, activity level and dietary
      patterns.

      Participants will then participate in up to 7 different 3-day studies that will be separated
      by a minimum of 1 week between each 3-day study. The first 2 days are adaptation days and
      participants will consumed the maintenance diet at home as 4 equal meals. The 3rd day is
      called a study day and participants will consumed 8 hourly formulas; the first 3 are consumed
      at home and the remaining 5 are consumed at the Clinical Research Centre at the Hospital for
      Sick Children. Immediately after the 4th meal, 4 baseline breath and 3 baseline urine samples
      are collected over the period of an hour. After the 5th meal, rate of carbon dioxide
      production (VCO2) is measured by indirect calorimetry for a period of 20 minutes. The 5th,
      6th, 7th, and 8th meal will contain a small amount of isotope labelled phenylalanine (13C
      phenylalanine). Two and a half hours after the isotope (13C phenylalanine) is given (between
      meal 7 and 8) 4 plateau breath and 3 plateau urine samples are collected for a period of an
      hour. Between the 7th and 8th meal, a 15 ml blood sample will be taken - 10 ml will be used
      to check for glucose and insulin levels and the remaining 5 ml for amino acid analysis.

      Breath samples are used to measure the enrichment of isotopic labelled CO2 (13CO2). Urine
      samples are used to measure the enrichment of isotopic labelled phenylalanine (13C
      phenylalanine). Through a series of calculations and applying a two-phase regression
      analysis, we will be able to determine the requirement for lysine.
    

Intervention name(s): Lysine intake provided as a milkshake
Intervention type(s): Dietary Supplement
Intervention description(s): There are 7 different lysine test levels ranging from 10 to 80 mg of lysine per kilogram body weight per day (10 - 80 mg/kg/d)
Intervention model: Single Group Assignment
Masking: None (Open Label)
Primary purpose: Health Services Research
Keywords: lysine, elderly, amino acid requirement, diet