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Human Nutrition and Metabolism

An Acute Ileal Amino Acid Digestibility Assay Is a Valid Procedure for Use in Human Ileostomates¹

Paul J. Moughan, Christine A. Butts^*, Henk van Wijk, Angela M. Rowan^** and Gordon W. Reynolds

Riddet Centre, Massey University, Palmerston North, New Zealand; ^* New Zealand Institute for Crop & Food Research Limited, Palmerston North, New Zealand; Institute of Food Nutrition and Human Health, Massey University, Palmerston North, New Zealand; and ^** Fonterra Research Centre, Palmerston North, New Zealand

²To whom correspondence should be addressed. E-mail: P.J.Moughan{at}massey.ac.nz.

An acute (24-h) feeding/digesta sampling procedure was evaluated in a preliminary study using growing pigs. The validated acute procedure was then applied using human ileostomates to determine apparent and true ileal amino acid digestibilities of 4 dietary protein sources. The acute method involved feeding ileostomized pigs a single meal containing the test protein as part of a purified diet, with no previous dietary adaptation, followed by an 8-h collection of digesta. Apparent ileal N digestibility did not differ between the acute and conventional (14-d study) procedures. Eight adult human ileostomates each received a single meal of protein-free biscuits and a drink containing sodium caseinate, whey protein concentrate, soy protein isolate, or soy protein concentrate; this meal was followed by a 9-h total digesta collection period. Acid insoluble ash was used as an indigestible marker. True ileal amino acid digestibilities (means ± SE) ranged from 90.5 ± 2.74% for cysteine in soy protein concentrate to 105.3 ± 5.66% for cysteine in sodium caseinate and were markedly higher than their apparent counterparts. True ileal digestibilities for total nitrogen were 101.9 ± 0.70, 98.3 ± 0.80, 99.5 ± 0.80, and 98.5 ± 1.20% for sodium caseinate, whey protein concentrate, soy protein isolate, and soy protein concentrate, respectively. The 4 protein sources were virtually completely digested in humans by the end of the small intestine.

KEY WORDS: • amino acids • digestibility • protein • human • methodology

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