Food allergy vs food intolerance continue to be terms that are misused and misunderstood by the general public. A frequent misconception is that all reactions to food are allergy-based. When an allergic food reaction occurs, proteins from the food, called allergens, must be absorbed from the gastrointestinal tract, interact with the immune system , and produce a response. This reaction occurs consistently after consumption of a particular food and causes functional changes in target organs. NOT ALL REACTIONS ARE ALLERGY BASED. Until the actual food allergy is properly diagnosed, the term adverse food reaction, which is an umbrella term used for any undesired food reaction, should be used.
A food intolerance is an adverse reaction to a food caused by toxic, pharmacologic, metabolic are idiosyncratic reactions to food or chemical substances in food. There are two types of adverse food reactions, intolerances and hypersensitivities. Food hypersensitivity occurs when the immune system reacts to a substance (food) that is usually harmless because the immune system erroneously assumes it is harmful.
Symptoms of true food allergies may occur within seconds or up to 2 hours after consuming the food. Most commonly (Type I allergies), they may include nausea, vomiting, severe abdominal pain, bloating, diarrhea, eczema, itching, hoarseness, wheezing cough, chest tightness, hypotension, and shock. Of course, we are all familiar with anaphylaxis (this is the most dangerous allergic reaction). There is a wide range of symptoms (actually they are classified into 4 types).
Symptoms of food intolerances include some of the same things that food-allergy sufferers experience, including gastrointestinal, cutaneous, and respiratory disorders. However, allergy skin testing is not used in diagnosing food intolerances.
As for weight implications, there is no evidence that I’m aware of that links overweight issues to food allergies. In fact, in children, there may be decreased weight for height due to malabsorption and food allergy. Clinical signs of malnutrition would have to be assessed, including the evaluation of fat and muscles stores.
Bloating is a common side effect of food intolerances, but should not be confused with actual weight gain, and in and of itself is not a basis for diagnosing anything.