Jan 29, 2015
Food for Thought

Intolerances and sensitivities to food are tough to diagnose in anyone, but especially in athletes. Once found, simple adjustments to their diet usually solve the problem.

By Sally Hara

Sally Hara, MS, RD, CSSD, CDE, is the Owner of ProActive Nutrition, a professional nutrition clinic in Kirkland, Wash. Among her specialties are sports nutrition and food sensitivities. She can be reached through the company Web site at: www.ProActiveNutrition.net.

Two weeks into the NCAA track and field season, the team’s athletic trainer was confronted with two athletes complaining of diarrhea that was hindering their training. The first runner, a sprinter, admitted to not eating within two hours of the start of practice in order to minimize his symptoms during training. The second athlete specialized in distance events, and was having trouble finishing long-distance training runs that took her far away from a bathroom. In addition, she complained of extreme fatigue and chronic muscle aches.

After ruling out a food borne illness, the athletic trainer suspected that food intolerances or sensitivities were to blame for the athletes’ intestinal distress. Indeed, it turned out that this was the case, and both athletes’ symptoms were resolved by modifying their eating habits.

Food intolerances and sensitivities appear to be somewhat more prevalent in athletes than non-athletes, or at least more frequently detected. An athlete may also be slightly more susceptible to symptoms of food sensitivities because of the stress a training regimen can place on the body.

For example, if training results in temporary inflammation of muscles or joints, any inflammation caused by a food sensitivity may further exacerbuate this and result in painful movement that interferes with training. Or if the reaction to a food includes gastrointestinal problems like the track athletes experienced, the result can sideline an athlete if not corrected.

Unfortunately, athletes often tend to ignore the symptoms of intolerances and sensitivities, chalking it up to their training. But by paying closer attention to diet, any reactions can be avoided altogether.


Food allergy, food sensitivity, and food intolerance are all terms used to describe negative reactions to food. While people sometimes use these terms interchangeably, technically they describe three different types of reactions to food.

Food allergies are immune system responses to consuming a food or food additive. In such cases, the offending food is perceived by the immune system to be a foreign antigen. This results in the production of antibodies, which attack the foreign substance. There are several subtypes of these antibodies, but the one involved in most acute reactions is immunoglobulin E (IgE).

A true food allergy, also known as a type-I hypersensitivity, usually causes a reaction immediately after the food is consumed and is severe, triggering a systemic response such as hives or anaphylaxis. Scientists believe that only three to four percent of adults are affected by true food allergies. Examples of common allergens are peanuts, milk, eggs, fish, wheat, nuts, and soy.

Food sensitivities also involve the immune system, but IgE antibodies are not present, and the reaction is less severe. Problem foods are recognized by the body as foreign substances that pose a threat and prompt an immune response that releases a myriad of biochemical mediators (such as cytokines and histamines) into the blood stream. These mediators can cause localized inflammation (of the gut or joints, for example), eczema, diarrhea, headaches, migraines, mood swings or behavior problems, excess mucus production, sinus congestion, or general fatigue. Symptoms can arise within a few minutes of exposure and up to two hours later.

Gluten, milk, soy, wheat, seafood, peanuts, eggs, sesame, chocolate, and corn are among the most common food sensitivities, but people can develop one to any food. Food sensitivities are more common than allergies and more prevalent than once believed, occurring in 15 to 20 percent of the population. It’s important to note that food sensitivities are sometimes inaccurately labeled as intolerances. The most common example of this is a “gluten intolerance,” which is technically a gluten sensitivity.

Food intolerances result in localized reactions that do not involve the immune system, but typically interfere with digestion and the absorption of the food. The most common is lactose intolerance–when someone lacks sufficient enzymes to digest lactose (milk sugar). People with a lactose intolerance experience symptoms of gas, bloating, and/or diarrhea after drinking milk or eating foods containing dairy products.

Similar symptoms can result when someone has a bile deficiency and ingests too much dietary fat. Because bile has an important role in fat digestion, individuals with a bile deficiency have difficulty digesting and absorbing fat. This is most common in people who have had their gall bladder removed, but can occur in others as a hereditary disorder. Quite simply, when food can’t be fully digested, it sits in the gut where microorganisms feed on the undigested food and produce bloating, intestinal pain, and flatulence. Additionally, because the undigested food has a high osmolality, the body attempts to dilute it by drawing water into the digestive tract, subsequently resulting in loose stool or diarrhea.

Other substances that are often poorly tolerated include sugar substitutes such as sorbitol, xylitol, and manitol. Likewise, artificial fat replacers such as olestra are designed to resist absorption. Each of these ingredients is touted to be low in calories primarily due to the fact that they are poorly absorbed. Athletes who consume diet beverages, including low-carbohydrate sports drinks or diet foods that contain sugar or fat substitutes, are at increased risk of gastrointestinal (GI) problems during training.


Figuring out whether someone has a food intolerance or sensitivity can be tricky. Figuring out whether an athlete has one can be even tougher. Not all reactions are severe or even very noticeable. And athletes often confuse a food intolerance or sensitivity with the effects of their training regimen.

For example, an athlete may assume the GI discomfort they experience during training is due to the intensity of the work coupled with hot temperatures and high humidity when in reality, they are lactose intolerant. Or an athlete who is chronically tired may just chalk their fatigue up to their demanding practice schedule when they actually have celiac disease (gluten hypersensitivity), which causes inflammation of the intestinal tract and in turn, malabsorption of nutrients–including iron. The malabsorption of iron is usually what’s to blame for their tiredness.

It’s also common for people to have a threshold of tolerance to some problem foods, which allows them to eat the food in small amounts or occasionally without developing a reaction, but if eaten in larger quantities or more frequently, it may cause problems. For example, an athlete who is lactose intolerant may be able to have milk, cheese, or yogurt once or twice a week without issue, but if they eat these foods three days in a row, they begin to develop eczema.

When it comes to an athlete’s tolerance threshold, it’s important to note that other factors can stress the immune system and lower that threshold. For example, an athlete at the peak of his or her training cycle may be less tolerant to some foods than normal because their body is stressed due to the intense training cycle.

If an athlete thinks they may have a food intolerance, there are a number of testing options available to help them identify it. However, they vary in accuracy and none of them are foolproof.

Allergists and immunologists often use skin tests to identify food allergies. While these can easily detect fairly severe food allergies, they usually miss food sensitivities and intolerances.

Another common method involves testing a blood sample for the presence of immunoglobulins (specifically subclasses IgE and/or IgG). However, because immunoglobulins are produced in response to the presence of problem substances (in this case foods), they are not present for a food that has been avoided, and may be present in abundance for a food the patient has only mild sensitivity to, but has been frequently consumed. Food and chemical sensitivities may also have delayed reactions, which means immunoglobulins may not be present at all at the time the sample is drawn. Thus there are often many false negatives and false positives.

The test I feel holds the most promise for helping to identify a food intolerance is the mediator release test (MRT), which measures the size of blood cells and the volume of surrounding fluids after a test substance is added to the blood sample. If the blood cells shrink and the surrounding fluids increase significantly, this suggests an immune response, and therefore an intolerance or sensitivity. The results of an MRT test are then verified with an elimination diet that dietitians guide patients through.


Once identified, food intolerances and sensitivities can be addressed so that they no longer affect an athlete’s performance. The most obvious solution is to completely discontinue eating the offending food. But it’s often not that simple.

The most common mistake athletes make is avoiding problem foods without replacing them with alternative sources of nutrients and energy. Athletes who cannot tolerate certain foods need to find substitutes to meet their body’s nutritional needs.

For example, if an athlete does not tolerate wheat and oats, most nutrition bars are off limits, but alternate sources of energy that can support their training needs include gluten-free pretzels and bananas. While these foods are solutions to immediate energy for training, this athlete would also need to find alternative sources of carbohydrates throughout the day to ensure adequate glycogen stores are maintained. This means substituting other grains such as rice, quinoa, or corn, and/or starchy vegetables like yams and peas.

It is important for coaches, athletic trainers, and other supporters to be positive. No one likes the “food police” telling them what to eat. Athletes are more likely to respond well to encouragement such as “You must be so thankful that you finally know what was bothering you!” instead of “You shouldn’t be eating that!”

For the most part, managing a food intolerance is the athlete’s responsibility, but an athletic trainer or coach can help an athlete who has a food intolerance by planning ahead with the athlete so that there are food and/or beverages at games that the athlete can safely consume. Coaches should also be supportive if an athlete elects to carry different foods with them.

When a team is on a road trip, athletes with food intolerances and sensitivities need to plan ahead and take particular caution to avoid problem foods. Often times it is possible to find allergy-friendly restaurants that are appropriate for the entire team so the afflicted athlete doesn’t feel left out of team meals. A simple Inter-net search can help find those restaurants. However, it is essential that there is a backup plan in place, which may involve bringing along a cooler containing acceptable foods.

Once a food sensitivity or intolerance has been identified, there is usually a period of adjustment while the athlete gets used to a new way of eating. Some may be frustrated by the thought of having to avoid foods they enjoy, so it can be helpful for these athletes to be reminded that this is an opportunity to avoid unwanted symptoms. In the end, most are thankful that they know how to eat to feel and perform better.


The athletic trainer at the beginning of this article did some investigating in order to diagnose the athletes. He had the sprinter keep a food diary for several days, which revealed an increase in his milk consumption. The athlete had started drinking lattes and smoothies, both with milk, which tipped the athletic trainer off to his lactose intolerance. Additionally, the caffeine in the lattes was likely further exacerbating his symptoms. Avoiding milk most of the time and using lactase supplements on the occasions he did consume milk fixed the sprinter’s GI problems.

The distance runner was ultimately diagnosed with a food sensitivity. The athletic trainer was worried about the extra symptoms of chronic fatigue and unresolved muscle soreness, so he had the athlete’s hematocrit and serum iron levels checked and found the athlete had anemia. When anemia is present and accompanied by other food sensitivity symptoms, celiac disease is often the case, which was true for the runner as well. The athlete received diet therapy to learn about a gluten-free diet appropriate for an active individual, and once she removed all gluten from her diet, her symptoms disappeared.

These examples illustrate that the same symptom–in this case diarrhea–could be the result of any number of intolerances or sensitivities. They also illustrate the importance of addressing the symptom and investigating the cause(s). In the end, both athletes were able to return to their previous level of activity by making some fairly simple changes to their diets.


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