Our objective is to determine the requirement for the amino acid tryptophan in school age children using the indicator amino acid technique.

Seven healthy children will participate in the study. The children will participate as an outpatient basis with study days carried out in the Physiological Research Unit at the Hospital of Sick Children, Toronto, Canada. Inclusion criteria include: being healthy, not taking any medications, no recent weight changes, no history of significant illness, willing to participate in the study. Exclusion criteria were the presence of illness, significant weight change, not acceptance of the diet. Prior to enrolment, each subject will have to fill 3 days food record form to ensure his or her normal dietary behavior. The study will be explained to subjects and their parents/guardians, benefits and potential risks will be explained as well and written assent, from the children, and consent from parents will be obtained. Subjects will receive financial compensations. Each subject will receive compensation for participation. Each parent/guardian will be reimbursed for the transpiration/parking expenses and a meal each study day.

Inclusion Criteria:

• Healthy children age 6-10 inclusive

Exclusion Criteria:

• significant recent illness