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Understanding Food Intolerances for Better Performance

Whether you are dealing with food intolerance or sensitivities, for an athlete, feeling even marginally better can translate to improved training.

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The terms allergy, intolerance, and sensitivity are used interchangeably throughout the medical and nutrition world as well as in more popular articles and health reviews. While there are important distinctions to be made between all three and the physiological responses that accompany them, it’s important not to get too wrapped up in defining exactly what is meant by intolerance, at least in terms of you as an individual and what it means for your diet on a day-to-day basis. The bottom line is this: You have an intolerance for a specific food if you feel better and notice a decrease in symptoms when you avoid it. You have a sensitivity to specific foods and ingredients when you are able to tolerate them, but only in limited amounts. In this case, you can decide whether to avoid these foods or eat them in moderation. Whether you are dealing with intolerance or sensitivities, for an athlete, feeling even marginally better can translate to improved training, better recovery, increased mood, and ultimately superior results come race day.

RELATED: Could Your GI Problems Actually Be a Food Intolerance?

You do not need scientific reasoning, a test, or a diagnosis to make this judgment. If you feel better after eliminating a specific food, you don’t need a doctor, nutritionist, or lab technician to confirm your findings. Unless you are dealing with an allergy, which requires vigilance and a thorough understanding of potential sources of contact, it is more important for you to simply avoid certain foods rather than fully understand the scientific reasoning. In some cases, reliable, proven tests or a knowledgeable nutritionist can be very valuable in providing support and helping you navigate the process of identifying problematic foods, pointing out hidden sources and eliminating them while maintaining optimal nutrition. However others simply cannot experience what you are feeling and reporting, so the onus is always on you. There is also no reason to think that any one food is mandatory for you to meet your nutritional goals, so don’t be alarmed at having to avoid certain foods or groupings of food. History has demonstrated that humans are very good at surviving and thriving on very different diets. This will guide you through the process of choosing the foods that are best for you and eliminating those that inhibit performance and optimal health so you can put together your best diet. Just as your training plan will be different from that of your training partner, so too your diet will be unique to you.

Identifying the Signs of Food Intolerance

Food intolerances may not have the same sense of urgency as allergies do, but the seriousness of a food intolerance shouldn’t be underestimated. Over the course of many years or countless exposures, the effects of a food intolerance on your health and body can be uncomfortable, embarrassing, and in some cases, extremely debilitating. We are also seeing increased recognition that inflammation resulting from poorly tolerated foods may contribute to or exacerbate obesity and diseases including heart disease, depression, diabetes, and some cancers.

Gastrointestinal issues are typically considered evidence of a food intolerance. When problems arise, our logical assumption is that “it must be something I ate.” However, for the majority of people with food intolerances, gastrointestinal complaints are not present. In these instances, it becomes more difficult to identify the problem or make an association between diet and physical issues that are seemingly unrelated. Food and stomach issues are easily linked, but it’s more of a jump for most people to consider that food can impact the brain or the skin or the respiratory system. Instead, they look to other possibilities to explain their symptoms.

Cravings can also be a sign of food intolerance. Sometimes problematic foods give you a “high” because your body becomes somewhat addicted to the hormones histamine and cortisol that are released in response to the aggravating foods. Inevitably, what goes up must come down, and you are likely to experience a very low point after you consume these foods, for example headaches or negative changes in mood. Those feelings, of course, can only be rectified by consuming more of the problem food in order to experience that “high” again. This is the cycle of cravings in motion.

It can be difficult to reconcile that these “feel-good” foods are potentially not good for you. We see this when people go on an elimination diet and initially feel worse. The highs they were getting from problem foods are not there any more. The good news is that if you are truly able to avoid the problematic foods, the associated cravings subside relatively quickly after you remove them from your diet and mood swings and other symptoms are alleviated. One way to pinpoint your own feel-good foods? Be on the lookout for things you consume daily and feel anxious about giving up.

All foods contain chemicals—either natural or artificial or both—and some intolerances are the result of a chemical buildup; in other words, a small amount of the problem food may not produce any adverse effects, but over time and with exposure to either that same food or other foods containing similar chemicals you are sensitive to, a threshold may be reached and symptoms may appear.

It’s something akin to “the straw that breaks the camel’s back.” Adding to the chemical load can be sensitivity to nonfood items, such as soap, detergent, or pesticides. This is important to keep in mind. Intolerances caused by chemical buildups can be much trickier to identify. It’s not always a simple cause-and-effect relationship.

Food intolerances are highly individual, but many are genetic—they just manifest themselves in different ways. So grandma’s eczema, your dad’s irritability, and your own gut pain may in fact be related to the same food intolerance, even though at first glance the symptoms have nothing in common.

Table summarizing various gastrointestinal, respiratory, urinary, or cardiovascular symptoms that could be indicators of food intolerance

When I began exploring my own food intolerances, I shared my experiences and knowledge with my family, encouraging them to also try making some changes. My parents are world-champion masters rowers, so they were already eating a very healthy diet and maintaining an extremely high level of fitness. But my dad has suffered from gut issues all his life. Although he realized his problems were probably not normal, he had fully accepted them as his normal. When he eliminated gluten and other grains from his diet, he felt worlds better. Today there is no way you could convince him to eat a piece of bread or tempt him with a cookie. My mum, on the other hand, never had gut issues and was less obviously reacting to any foods in particular. As the cook in their house, it made things easier for her and Dad to be eating the same foods, so she also embraced a diet free of gluten and grains. She was surprised to find that her lifelong reflux suddenly disappeared. She also dropped considerable weight and went from being a very fit, strong lady to an even stronger, svelte world-champion rower in her sixties, competing at her high school weight.

It is beyond the scope of this article to detail all the factors that can cause, contribute to, or confound suspected food sensitivities, but it’s a wide-reaching list that reveals just how intricate our bodies are. When investigating your own food intolerances, you might find that hormones, stress, temperatures, seasons, and other environmental factors play a role.

When considering symptoms and possible intolerances, it’s important to keep in mind that food intolerances and allergies can present at any age and can change over time, which is another reason they’re sometimes difficult to identify and address. Consider instances where children grow out of certain allergies or a food intolerance or allergy is introduced by a parasite or after a severe illness. Food intolerances can also occur during or after pregnancy, likely due to hormonal changes in the body.

How External Factors Exacerbate or Cause Intolerance


The strong connection between the gut and mind plays an important role in the presentation and severity of symptoms. Consider stress management and other lifestyle factors along with dietary changes.


Irritants such as alcohol can increase permeability of the gut wall, changing how we are able to deal with foods.

Weakened Immunity

Because the gut is the command center for the body’s immune defenses, any time the immune system is challenged by infection or illness, the gut’s ability to cope with digestion and maintenance of the gut barrier may be compromised.


Exposure to unsanitary conditions or poor hygiene will introduce lots of foreign and unwelcome critters that place stress on the immune system, again affecting how smoothly the gut functions. On the flip side, our obsession with cleanliness as a society means that our immune system can be kicked into overdrive when it encounters something that should actually be considered harmless.

Vitamin D

Research shows that vitamin D may influence how the immune system functions and the health of the cells in the gut as well as the body. This is why we see a direct correlation between low levels of vitamin D and many conditions and diseases.

Gut Bacteria

The types and size of bacterial colonies in your gut can change as a result of your diet and use of antibiotics. As gut bacteria evolves, it will affect how food is digested and how healthy the mucosal barrier is, potentially leading to new symptoms or changing the severity of existing symptoms.


Physical damage and changes to gut bacteria can also be caused by parasites, which can be very hard to identify and get rid of. This is a concern that should be addressed with a medical professional.

Adapted from The Athlete’s Fix: A Program for Finding Your Best Foods For Performance & Health by Pip Taylor with permission of VeloPress.