Why food intolerance tests fail to deliver on their promises

Around 40% of the planet’s inhabitants have some type of gastrointestinal problem. This was the conclusion of a recent analysis by an international team of scientists who collected data from 73,000 people in 33 countries on six continents. Obviously, the severity of those problems varies greatly, but it suggests that a large part of the population feels that, at some point, their guts could certainly be working better than they are. Some people find relief in medicine, but many fail to pinpoint the reason for their discomfort. And whenever someone has an unresolved problem, there are those who will sell them a solution, even if they do not have it.

The prevalence of digestive discomfort is behind the success of solutions with little scientific support, such as food intolerance tests. These have been pushed on social media lately and some kits can be used at home, promising to detect the foods that are causing those annoying symptoms. These tests, which are sold for prices that range between €100 and €200, supposedly identify foods to which our body is especially sensitive and may be causing us gut problems. Some simply require taking a hair or blood sample at home, by pricking a finger, and then sending it to a laboratory for analysis.

Montserrat Fernández Rivas, head of the Allergy service at the San Carlos Clinical Hospital in Madrid, warns that “there is no scientific evidence” to back up these food intolerance tests. “Food sensitivity is not a diagnosis, it is an invention; a concept that gained traction among the general population, especially among those with chronic digestive discomfort due to functional disorders of the intestine. And some opportunists are doing business with it,” she explains. According to this expert, the results of these tests “have no relation to food tolerance.”

Miguel Ángel Martínez Olmos, a member of the Nutrition Area of the Spanish Society of Endocrinology and Nutrition (SEEN), does not believe in the usefulness of these tests, either: “They appeared a few years ago and supposedly detect food intolerances, even promising to be useful in finding the cause of chronic disorders such as migraine, irritable bowel or obesity,” he notes. “All the scientific societies of allergology, immunology and nutrition reject the use of these so-called food intolerance tests,” he adds. The results they offer, in the opinion of Martínez Olmos, “influence people into submitting to strict diets that can put their health at risk.”

Gut problems, however, are real and some of them can be solved, although distinctions must be made. On the one hand, there are allergic reactions to certain foods; these are uncontrolled reactions of the immune system to some substances that can cause serious damage and even death with very small amounts of the allergen. For this type of reaction to food, “there are very good and precise tests,” says Alfredo Martínez, director of the Precision Nutrition and Cardiometabolic Health Program at the IMDEA Food Institute in Madrid.

“Food sensitivity is not a diagnosis, it is an invention”

Montserrat Fernández Rivas, head of the Allergy service at the San Carlos Clinical Hospital in Madrid

Food intolerances, such as those suffered by people with celiac disease due to an autoimmune reaction caused by gluten, or those who are intolerant to lactose due to a lack of the gene that produces the enzyme that allows milk to be properly digested, are something different. Intolerances can produce progressive damage, depending on the amount of food consumed. In a bid to identify an immune response to some foods, some intolerance tests measure IgG, a kind of antibody that gained notoriety during the Covid pandemic. But studies have not proven whether the data these tests offer really identify food intolerances or are simply the result of a normal reaction of the immune system. In the case of intolerances, Martínez explains, “there are tests that are well defined and others that are not so well defined, and there are people who get the concepts of allergies and intolerances mixed up.” To know the difference, the scientist recommends asking a specialist. “There is information on precision nutrition that is based on allergy tests, and there are genetic tests that can detect some intolerances but must be complemented with body composition, biochemical and phenotypic data,” he explains. In any case, these tests must be “comprehensive” before prescribing the withdrawal of specific foods.

Together with some breath tests, such as those that can identify lactose intolerance, or some tests for gluten intolerance, in general terms, “the only reliable method for diagnosing food intolerances is the detailed collection of information by the patient, including what foods are eaten and the symptoms that appear,” indicates Martínez Olmos. “Once the suspected food is identified, you can try to confirm the intolerance with a specific test, if any, such as hydrogen breath after taking lactose.” But the best approach, he concludes, “is to exclude the food from the diet and see if the symptoms go away.”