An allergy occurs when the body reacts to a substance (called an allergen) in the same way it would an invading microorganism that could cause an infection. Any food can provoke an allergic reaction in susceptible people. The top eight food allergens are eggs, milk, peanuts, tree nuts, fish, shellfish, wheat, and soy. Food allergies can be diagnosed with a blood test.
Food allergy symptoms usually start very soon after eating the allergen; they may start within minutes. Gastrointestinal symptoms can include nausea, vomiting, and diarrhea. Respiratory symptoms include shortness of breath, wheezing, and a repetitive cough. Swelling can occur around the eyes, lips, and in the tongue, throat, and airways. Allergies can also cause hives. Anaphylaxis is a severe allergic reaction that can be life-threatening; the patient may be unable to breathe, develop circulatory collapse and become unconscious.
The human intestinal system contains millions of bacteria (called the gut microbiome) that affect many functions in the body. Some of those bacteria protect against allergic reactions. When the mix of bacteria is changed because of antibiotic use, eating habits or other factors, weight gain can result. If the bacterial imbalance is corrected with prebiotics (food ingredients that promote growth of beneficial bacteria in the gut) and probiotics (beneficial bacteria in supplements or fermented foods), many patients are able to lose weight. Leaky gut syndrome occurs when the intestinal wall is damaged and allows large molecules of food to get into the bloodstream.
Some people use the terms food allergy and food intolerance interchangeably, but they are not exactly the same; the immune system over-reaction doesn't occur with a food intolerance. Food intolerance usually results in gastrointestinal symptoms like cramping, bloating, nausea, diarrhea or constipation. Gluten intolerance causes celiac disease, while lactose intolerance causes symptoms when people eat or drink dairy products. "Wheat belly" is a term coined by cardiologist William Davis, MD, to describe abdominal fat that results from eating wheat and other high-carbohydrate grains. According to Dr. Davis, most people are intolerant to modern wheat and other grains.