Do you count calories religiously and work out like a gladiator but still struggle to lose weight? What could be the possible cause? According to some experts, the culprit may not be what is contained in the foods themselves, but your own body's reaction to these foods causing water retention. This reaction is known as food intolerance.

Food allergies are typically easy to detect as the body often reacts with extreme and even deadly symptoms when the allergen is eaten. Food intolerance, by contrast, is much more subtle and may take long periods of repeatedly eating a given food to manifest itself.

Food intolerance can have several causes such as lack of a particular digestive enzyme or sensitivity to additives in processed foods. Experts estimate that as many as one in every 10 people suffer from some type of food intolerance, and a study in the UK found the figure to be as high as 45%.

According to Muriel Simmons, Chief Executive of Allergy UK, food intolerance occurs when an immune reaction is brought on by IgG antibodies that are released when certain trigger foods are ingested. A food allergy, by contrast is caused by an IgE immune response, which is much more powerful.

When the IgG immune response is activated, it increases the permeability of the body's smallest blood vessels called the capillaries, which allows more fluids to pass through into the cells causing water retention, thus weight gain.

How do you know when you have a food intolerance? Symptoms might include irritable bowel syndrome (IBS), fatigue, indigestion, difficulty breathing, eczema, migraine, hives, or bloating. An internist or gastroenterologist can run tests to diagnose food intolerance, but it is also possible to identify the trigger at home by eliminating the foods most commonly associated with food intolerance such as wheat and dairy products. If the symptoms persist, also try eliminating eggs, soy, corn and nuts, as well as processed foods which contain preservatives.

After a few weeks, slowly reintroduce each of the eliminated foods back into your diet one at a time until you identify which one is the culprit. If you suffer from a severe intolerance to this food, it may be best to remove it from your diet completely. In cases of mild food intolerance, it might be possible to treat the symptoms by taking a probiotic supplement daily that replenishes your body's "good bacteria," which aid in digestion and prevent bloating and water retention.

Food intolerance is one of many possibilities for why someone engaging in proper diet and exercise might still struggle to lose weight. The most important thing to remember if you are one of the millions of people fighting the scales every day is not to give up. The solution is out there even if it is not so easy to find.