Effect of Dietary Protein Intake Distribution on Protein Metabolism and Skeletal Muscle

The demonstrated benefits of increased protein intake on sarcopenia and many physiological functions is becoming increasingly evident. For this reason, there is growing importance to ensuring that Americans consume the recommended amount of protein, calculated to be 17-21% of caloric intake. As it relates to the prevention of sarcopenia, adequate protein consumption inherently assumes that sufficient protein is ingested to stimulate protein anabolism. Specifically, adequate essential amino acid precursors, and anabolic triggers such as leucine, must be present for protein anabolism to occur. Population data from the NHANES study suggests that American protein intake pattern is skewed towards the evening meal. The NHANES data also suggests that the average protein consumption of both men and women over the age of 50 yrs is approximately 1.1 g/kg/d. Thus, the prevalent consumption pattern ensures that many individuals consume adequate protein, or amino acid precursors sufficient to stimulate protein synthesis, only with the larger, or dinner meal. The investigators have demonstrated that frequent stimulation of protein synthesis with amino acids preserves strength and function. Others have demonstrated that adequate protein intake stimulates muscle protein synthesis and increases lean mass. Given these data, The investigators studied the effects of two different protein intake patterns on metabolic and functional outcomes in older individuals after 8 wks of dietary control. The mean protein intake for this group of 1.1 g/kg/d was consumed in two distinct meal patterns. Participants consumed high quality protein in the ratio of 15/20/65% of total protein intake for breakfast/lunch/dinner, respectively (Uneven protein intake pattern), or protein consumption was distributed equally among each meal (33% of total protein)(Even protein intake pattern). The investigators determined the longitudinal effects of this consumption pattern on the metabolic outcomes of whole-body net protein synthesis and muscle protein synthesis in older participants.

Inclusion criteria

• Men and women, ages 50-70 years
• BMI between 24 and 30 kg/m2

Exclusion criteria

• Current diagnosis of diabetes
• History of malignancy in the 6 months prior to enrollment
• History of lactose intolerance or dairy allergy
• History of egg allergy or intolerance
• History of gastrointestinal bypass surgery.
• History of a chronic inflammatory condition or other chronic disease (Lupus, HIV/AIDS, etc)
• Subjects who do not or will not eat animal proteins
• Subjects who cannot refrain from consuming protein or amino acid supplements during their participation in this study
• Subjects who report regular resistance exercise (more than twice per week)
• Hemoglobin less than 9.5 mg/dL at the screening visit
• Platelets less than 150,000 at the screening visit
• Concomitant use of corticosteroids (ingestion, injection or transdermal)
• Any other disease or condition that would place the subject at increased risk of harm if they were to participate, at the discretion of the study physician