Food allergyis a rather fast response (minutes) by the body's immune system to a perceived invader. Signs orsymptomsare typically immediate, dramatic and visible: coughing, sneezing, vomiting, migraines, watering eyes, rashes, swelling tissue, hives – or in severe cases an anaphylactic shock which requires emergency intervention. However other symptoms like the gastro-intestinal responses nausea, vomiting and diarrhea can be delayed for hours or even days.

An Allergy triggers an allergic response in a person – often immediately - on exposure to the allergen. Generally, people suffering from an allergy have had a breakdown in their immune system: it "misreads" the allergen as an enemy invader and pulls out all stops to attack it.

Normally our immune system protects us by producing antibodies in the blood that attack bacteria and viruses invading our bodies. This lets us fight off infections without ever knowing they were there. But in a very few people the immune system produces an abnormal type of antibody in response to things like pollens, or in some cases certain foods.

Many food allergy symptoms are the same as regular allergy symptoms (those in response to pollens, chemicals and animal hair): sneezing, skin rashes, hives, watering eyes, runny nose and sore throat. For food allergies add nausea, spontaneous vomiting, weight loss and gastro-intestinal symptoms like diarrhea. In severe cases there is an anaphylactic response where the sufferer's tissues become hypersensitive and swell up to two or three times their normal size and the sufferer can go into anaphylactic shock. Immediate medical attention is required.

Food intoleranceon the other hand is rather slow onset reaction that may take hours, days or even weeks. It is an inability to process a particular food. It is also thought to be an immune system response. The gastro-intestinal tract in some people is simply unable to produce appropriate enzymes for normal chemical breakdown. The food passes through unprocessed, or lingers in the gut fermenting producing excess ‘gas'. In some cases protein fragments rupture the lining of the intestine allowing foreign particles into the bloodstream.

Symptoms of food intolerance are much more delayed. They generally manifest as nutritional deficiencies that develop over time.BUT - they can be just as life threatening as a food allergy!

Food intolerance is an inability to properly digest certain foods. In some cases food passes right through the body before digestion is complete – so is eliminated only partially processed like milk products causing diarrhea. In other cases some foods have components which actually attack the lining of the gut and damage it every time that food is eaten (like Celiacs with gluten). Fortunately most food intolerant people recover fully when the offending food is avoided.

Direct problems such as severe abdominal cramps, bloating, flatulence, diarrhea and hemorrhoids are common. However the indirect problems associated with poor absorption can be much more harmful. When food leaves the body only partially processed many vital nutrients are lost too. People with food intolerance typically catch viruses easily, may have dry skin, hair and nail problems and tire easily. Some become deficient in iron or calcium and suffer a further series of health issues like anemia. Many food intolerant people are underweight due to their inability to get full nutrient value from foods. Of course with diarrhea there is the constant risk of dehydration especially among children and elderly people.