Those of use that take Protein Powders after a workout expose ourselves to large quantities of individual proteins. If the powders are tolerated then personal goals are more easily achieved due to the a high bioavailability of the protein molecules. However, if you are intolerant to the protein powder you are using, this can present as a food intolerance.
Manifesting as bloating, Irritable Bowel Syndrome (IBS), weight gain, fatigue, skin problems, migraines or joint pain, even a mild food intolerance to protein powders may have a major impact upon exercise and appearance, as well as a person’s day to day activities. The possibility of a sensitivity to protein types should therefore be high priority for those that take their exercise seriously.
Smartblood Story - Matt's Intolerance to Whey Protein