According to one lab that tests for "toxic food syndrome," eating green peppers may cause bloating or lethargy. Lemons might trigger headaches. Other common foods like corn, soy, egg whites, whey and chicken "may act like a poison in your body," the website warns.
This company and others promise to detect such hidden problems with blood tests that can range in cost from hundreds to thousands of dollars, depending on how many foods are tested for.
Other health practitioners may say they can diagnose food sensitivities by assessing muscle strength, by analyzing hair, gastric juice or body tissue, or by reading the body's "energy pathways." Consumers are told that dietary triggers can cause gastrointestinal complaints such as heartburn or irritable bowel syndrome as well as fatigue, attention deficit problems, autoimmune diseases and arthritis.
But allergists and gastroenterologists say that although food intolerance does occur -- most of it involving specific food sugars like lactose or fructose -- the tests being marketed to consumers have no scientific basis. Blood tests for food sensitivities are prone to false positives that can lead people to eliminate harmless foods from their diets, they say.
The best way to test for the problem is to eliminate various foods from the diet until the symptoms clear, then reintroduce them one at a time, experts say. None of the other tests is recommended by U.S. or European allergy or immunology societies or the National Institutes of Health.
"Blood testing is confusing to patients," said Elana Lavine, a pediatric immunologist in Toronto who now spends part of her time counseling anxious parents whose children have undergone food sensitivity testing. Armed with their itemized results, which list dozens of forbidden foods, they ask her what to feed their children.
Part of the confusion lies in the difference between food intolerances and allergies, terms that are often used interchangeably by testing companies, health practitioners and even in peer-reviewed medical journals.
In an allergic reaction, the immune system overreacts to a food by producing an antibody called Immunoglobulin E that causes hives, vomiting, diarrhea and respiratory problems, among other symptoms. To diagnose an allergy, allergists use a blood test that checks for IgE, skin prick testing and other methods. The gold standard is an oral food challenge, which involves eating small doses of the suspect food under medical supervision.
Food intolerances are unpleasant reactions that do not involve the immune system, according to the National Institute of Allergy and Infectious Diseases. They can be caused by enzyme deficiencies, sensitivities to food additives such as sulfites and monosodium glutamate, or reactions to naturally occurring chemicals.
For example, people who lack an enzyme needed to digest sugar in milk have lactose intolerance. Sulfites used to preserve dried fruit, canned goods and wine trigger asthma attacks in sensitive people.
Adverse reactions to wheat or the protein gluten come in several forms. Celiac disease is an immune system reaction to gluten that causes inflammation in the small intestine. A wheat allergy is an allergic reaction to wheat, almost always caused by the gluten. And gluten sensitivity means a person has symptoms after ingesting gluten but doesn't have either of the other conditions, said Stefano Guandalini, founder and medical director of the University of Chicago's Celiac Disease Center.
Lavine and other critics say the food sensitivity tests being marketed are muddying the waters for people with legitimate allergies, which are on the rise. There's a big difference between a child who has a true milk allergy and another who has been labeled with a milk "sensitivity," said Lavine.
Blood tests are a common way to test for sensitivity or intolerance; many of these also involve an antibody, this one called Immunoglobulin G, or IgG.
The tests often purport to check for sensitivities to hundreds of common foods, many of which rarely trigger food allergies, such as sugar or yeast. Blood is exposed to a panel of food proteins, and the labs measure the degree of IgG antibody that binds to each food.
But while IgE can indicate the presence of an allergen, IgG hasn't been shown to be a similar marker for intolerance. Instead, IgG is believed to indicate exposure to food and possibly even tolerance, Lavine wrote in the Canadian Medical Association Journal.
"There is no IgG testing of value," said Robert Wood, a professor of pediatrics and chief of pediatric allergy and immunology at Johns Hopkins University in Maryland. "All of us make IgG to the foods we eat, and they are not related to disease, including food intolerance."
Meanwhile, nearly everyone who takes these tests is told he or she has some kind of intolerance. One Florida lab boasts that "95 percent of the people we've tested show that one or more foods they regularly eat cause a toxic reaction in their body."
Proponents of the testing, primarily integrative physicians or alternative health practitioners, argue that the tests can be useful even if they are imperfect. IgG-based testing "showed promise, with clinically meaningful results," according to a 2010 review published in the journal Nutrition in Clinical Practice.
Some suggest that the test results could be used to guide which foods are chosen for testing through elimination from the diet, a trial-and-error process that can be time-consuming and difficult.
Peter Whorwell, a professor of medicine and gastroenterology at the University Hospital of South Manchester in Britain, found in 2004 that using IgG antibodies to guide food elimination diets may be effective in reducing the symptoms of irritable bowel syndrome.
The tests have particular appeal to people who have been coping with chronic symptoms but repeatedly hear: "We can't find anything wrong." When Jeffrey Sesol, of Homer Glen, started feeling strangely fatigued and achy, he went to his internist, a gastroenterologist, a neurologist and a rheumatologist, but no one had an answer.
"Grasping for straws," he went to see chiropractor Nicholas LeRoy at the Illinois Center for Progressive Health in Chicago.
LeRoy took Sesol off the acid reflux medicine he'd been taking for years -- something no other doctor suggested -- and ordered food allergy testing. Out of 150 foods tested, 33 registered positive, including yeast, wheat, eggs, milk, beans, cheese, garlic, ginger, nuts, lemon, mushrooms, rice, sesame, sugar and squash.
"The list was overwhelming, but I took out as many foods as I could," Sesol said. Within weeks his energy returned, he said, and after 45 days his acid reflux and aches disappeared.
"It was life-changing for me," said Sesol, 51, who now tries to avoid wheat, eggs, milk, brewer's yeast and baker's yeast but has added other foods back in his diet, including cheese. The test also helped his daughter, 24-year-old Amy, who was having similar symptoms, Sesol said.
LeRoy said testing has been extremely effective for his patients. "Ninety-five percent of the time I run a test, for whatever reason, it ameliorates a condition," he said. "There can be a relationship between foods and things that wouldn't seem likely related -- asthma, chronic sinusitis and other systemic issues."
Some observers say personalized test results may not be as important as overhauling a lousy diet. Eliminating processed foods makes almost everyone feel better, said nutrition specialist Kelly Dorfman, author of "What's Eating Your Child? The Hidden Connections Between Food and Childhood Ailments."
Many insurance companies will not cover tests for intolerance. For example, although Blue Cross and Blue Shield of Illinois pays for allergy testing and therapy when medically necessary, it no longer covers IgG blood tests and at least 13 other testing methods that it considers experimental and unproven.
Sesol's insurance company paid for the acid reflux medication but didn't cover his $1,540 bill for food intolerance testing.
Dr. Gerard Mullin, a gastroenterologist, nutritionist and director of Integrative GI Nutrition Services at Johns Hopkins Hospital, said he used to be "vigilant" about ordering the tests. Now, although he thinks the IgG test can be useful for people who have trouble sticking to a strict elimination diet, he says partnering with a dietitian is a better use of money.
One of his patients, Nadine Oswald, 53, has taken several food sensitivity tests over the years to see if dietary changes could help with chronic fatigue, sinus congestion and gastrointestinal problems. She said the last test she took, which Mullin ordered, looked at whether she was allergic to or intolerant of 157 foods. The company billed her more than $5,000 for the tests, and her insurance company has refused to approve the benefit.
Still, her symptoms haven't resolved.
"You get desperate," said Oswald, a physician's assistant in Baltimore. "You get to the point where you want to feel better and do whatever the doctor suggests to get there. But clearly, spending $5,000 for a test that really didn't fix anything is frustrating.