The allergenicity of food is how likely a given food will elicit an allergic-type immune response. And gym-rats like us should care because we're likelier to experience allergic-food-responses and they thwart fitness improvement. The reason we're likelier to suffer from food allergies/sensitivities is because we're prone to eating the same stuff all the time; which dietary-redundancy increases the likelihood of your food alarming immunity! And, overactive immunity impairs fitness in ways like impaired nutrient absorption and cortisol-induced fat-gain/muscle-loss!
Good news is that you can overcome the threat of food allergenicity with a number of strategies. First is to either get blood tests and/or pay attention to how your body reacts after ingesting certain food. Secondly is to eat the most immune-friendly foods possible. And, thirdly, if/when you're integrating potentially irritating food, interval said foods to reduce the likelihood of over-exposure causing sensitivity.
Bodily reactions and/or blood-tests indicate what food irritates the immune system through observation of the results displayed. On the bodily reaction front, digestive stress, skin irritation, inflammation, and water retention can appear shortly after ingesting allergenic food. Blood tests, on the other hand, reveal the actual immune response to suspect food. In both cases, it's wise to avoid offending foods.
To minimize the threat of food allergen exposure all together, eat the "friendliest" foods possible and avoid the "offenders". In both categories, it's usually the more protein rich foods that warrant the most attention as all food-allergens are proteins. The "friendliest meats/proteins" (see the allergenicity scale posted below as foods are listed from most to least allergenic from top to bottom) include farm-mammals/birds and game. The "most offensive" meats/proteins include eggs, shellfish, finfish, and processed meats.
If, the idea of food avoidance repulses you, however, rotating foods at a sufficient interval might minimize allergenicity. Rotating food is believed to minimize the redundancy that causes certain food to become allergenic. As such, interval recommendations of 4-10 days are suggested between ingestion of allergenic food.
So keep in mind that food allergenicity is a valid concern for us gym-rats. Our propensity to keep lean-eating simple by eating redundantly make us likelier candidates for food allergies. Furthermore, we're especially concerned about anything thwarting our fitness efforts. So determine if you're suffering from food allergies and, accordingly implement the mentioned strategies to to overcome them.