Metabolic Availability of Lysine from Oats and Whole Milk Assessed in School-Aged Children

Abstract

Objectives

The objective of this study was to assess protein quality by determining the metabolic availability (MA) of lysine from commonly consumed plant and animal-based food sources in school-aged children, using the indicator amino acid oxidation (IAAO) method.

Methods

Using a repeated-measures design, six healthy school-aged children randomly received 10 lysine intakes from either crystalline L-lysine (3, 6, 9, 12 mg/kg/day), moist cooked oats (9, 12 mg/kg/day), oven-baked granola (12 mg/kg/day), or whole milk (6, 9, 12 mg/kg/day). All diets provided protein at 1.5 g/kg/day and calories at 1.7x the participant´s measured resting energy requirement. All test diets were isocaloric and isonitrogenous. Every study day, breath samples were collected at baseline and during isotopic steady state and the ,¹³C enrichment was measured using an isotope ratio mass spectrometer. MA of lysine from food sources was determined using slope ratio analysis of ,¹³C-phenylalanine oxidation response to feeding lysine from whole foods compared to L-lysine from a reference crystalline amino acid diet.

Results

Lysine from whole milk was highly available, (∼100%, similar to our crystalline-lysine reference). The MA of lysine from cooked oats was 92.7%. When the same oats were oven-baked the availability of lysine was reduced by ∼50%. This reduction may be due to lysine loss through the Maillard reaction.

Conclusions

Lysine is highly metabolically available from milk and from moist cooked oats. However, dry cooking of oats reduces lysine MA considerably. The protein quality of cereal- based diets is dependent in the lysine content and bioavailability of the individual foods. Therefore, it is imperative to study how the human body utilizes this nutrient, especially in growing children. These are the first studies that assess protein quality in commonly consumed foods directly in children. This data will help build a knowledge base that can be further used to develop accurate dietary combinations that fully meet amino acid needs.

Funding Sources

Supported by: Dairy Farmers of Canada and National Dairy Council.