Determination of Glycine Requirement in Pregnancy
Condition: Pregnancy
Study type: Interventional

Summary: 
      It is important that pregnant women eat an adequate amount of protein to ensure healthy
      growth and development of the fetus. Amino acids are the building blocks of the body's
      protein. Glycine is an amino acid that can be made in the body, but under certain metabolic
      circumstances (e.g. pregnancy) the body's needs may be higher and thus glycine must be
      obtained from the diet. Currently, it is not known how much glycine may be needed from the
      diet during pregnancy. We plan to study dietary glycine requirements in healthy pregnant
      women, during early and late gestation. We will do this using a modern, safe and quick
      method.
    

Detailed description: 
      Purpose:

      To determine the dietary glycine requirement in healthy pregnant women during mid (20 - 30
      weeks) and late (31 - 40 weeks) gestation.

      Hypothesis:

      We hypothesize that there is a dietary requirement for glycine during pregnancy due to an
      increased metabolic demand. With increased glycine intake we hypothesize to observe an
      increase in protein synthesis, as measured by the indicator amino acid oxidation (IAAO)
      method.

      Justification:

      Inadequate protein intake during pregnancy may cause intrauterine growth restriction, which
      is associated with increased risk of chronic diseases later in life. Currently, the dietary
      intake recommendations for amino acids are greatly based on nitrogen balance studies of
      non-pregnant adults. There is little scientific information regarding dietary glycine needs
      during different stages of pregnancy, despite empirical evidence indicating gestational
      differences in protein metabolism.

      Objectives:

      The main objective of the current study is to determine the glycine requirement using the
      minimally invasive indicator amino acid oxidation (IAAO) method in healthy pregnant women.
      Our second objective is to compare the glycine requirement during mid (20-30 weeks gestation)
      and late (31 - 40 weeks gestation) stages of pregnancy.

      Research methods:

      We will recruit a minimum of 18 pregnant women who may take part in 2 study days in both
      gestational stages, for a total of 72 study days. Potential participants will meet us for a
      preliminary assessment where we will evaluate their eligibility to participate in the study.
      The preliminary study will take approximately 1 hr during which we will examine body
      composition (bioelectrical impedance, skin-fold measurements, height and weight), resting
      energy expenditure (indirect calorimetry), blood glucose (glucometer), and medical history
      (questionnaire). Fasted blood glucose above 6.7 mmol/L is indicative of gestational diabetes.
      Participants with fasted blood glucose concentrations above 6.7 mmol/L will be referred to
      follow-up with their primary health care provider (see letter to physician).

      We will test the participants urine using a dipstick, to assess whether proteinurea is
      present. If there is an indication of proteinurea we will refer the participant to their
      primary physician (See letter to physician - Urine results).

      We will collect a 3 day diet record to determine usual food intake and food preferences.
      Based on the 3 day food record we will prescribe a standardized diet two days prior to the
      study day to ensure protein intake of 1.5 g/kg/d and energy intake of 1.7 x resting energy.

      During each study day, eligible participants will randomly receive 1 of 36 test glycine
      intakes during both mid and late pregnancy, ranging from 10 to 100 mg/kg/d. Each subject may
      participate in 2 study days between 20-30 weeks gestation and 2 study days between 31 - 40
      weeks gestation, for a total of 4 study days. The test glycine intakes will contain a
      crystalline L-amino acid mixture based on the composition of egg protein, except for glycine.
      The test glycine intake will be administered in an experimental diet, along with enough
      non-protein energy to meet 1.7 x resting energy expenditure of each participant. The diet
      will be provided as 8 meals, each representing 1/12th of the participant's daily intake
      requirement. These meals will be provided over the course of an 8 hour study day. A stable
      isotope tracer will be added to the 5th - 8th meal. We will measure the rate of oxidation of
      this tracer in expired breath (F13CO2), and flux of this tracer by its enrichment in urine.
    

Intervention name(s): Glycine Intake
Intervention type(s): Dietary Supplement
Intervention description(s): Oral consumption of eight hourly experimental meals- Includes 4 tracer-free experimental meals containing a mixture of free amino acids, calories from a flavored liquid and protein free cookies and 4- labeled amino acid experimental meals.
Intervention MeSH terms: Glycine
Intervention model: Single Group Assignment
Masking: None (Open Label)
Primary purpose: Basic Science
Keywords: Pregnancy; Glycine requirements; Indicator Amino Acid Oxidation (IAAO) method; Stable isotopes