The present invention is a method for increasing the digestibility of a food protein by subjecting the food protein to a single-cycle of ultra high pressure. Food proteins of the instant invention find application in nutraceutical, nutritional food, nutritional product or dietary supplement compositions for providing a protein source to a subject with a protein deficiency. In particular embodiments, the food protein is a whey protein useful in preventing or treating diseases or conditions associated with glutathione deficiency.