Sports nutrition and supplements are widely used for performance enhancement, muscle building as well as weight loss. There is a broad range of products available, with differing levels of evidence regarding effectiveness and safety. This discussion will only deal with intolerances and allergies and not with issues of toxicity, appropriateness and effectiveness (see e.g. ABCD classification of the Australian Sports Commission).
Sports nutrition and supplements include many of the usual components of food, such as carbohydrates, fats and protein, in high concentrations and athletes may have any of the known intolerances or allergies to these nutrients. Please see the corresponding sections of this website for this information, or use the Food Intolerance Finder. Some of the most common intolerances to sports nutrition and supplements are secondary to reactions to fermentable sugars, such as fructose, lactose, maltose and polyols (sorbitol, xylitol, mannitol). Gluten, protein (food allergy) and fats (bile acid malabsorption / fat intolerance) in sports nutrition and supplements can also cause symptoms.
Allergies to flavoring, color and preservative agents (see non-allergic non-specific additives), as well as spices and milk protein (e.g. whey, casein) deserve a special mention, as they are often present in sports nutrition products.
It should be noted, some allergies only appear when food components are consumed shortly before or after, or during exercise. These are called food-dependent exercise-induced allergies or anaphylaxis (severe allergic reaction).
Exercise-induced wheat and crustacean (shellfish) allergies are most common. Further allergic reactions include alcohol, tomatoes, cheese and celery. The use of certain medications, such as aspirin and nonsteroidal anti-inflammatory drugs (NSAIDs) before exercise increase the risk of these reactions. The underlying cause of exercise-induced allergy is most likely the activation / degranulation of allergy-linked immune cells called mast cells. Very severe life-threatening reactions can rarely occur, with breathing problems and dangerous changes in blood pressure.
Frequency in population and natural history
Itching skin with a rash (urticaria) is the commonest manifestation of allergies, affecting 10 to 20 percent of the population. Asthma (breathing problems, cough) and blood pressure changes directly related to food are much less common, and asthma directly due to exercise rather than food itself is much more frequent.
Intolerances to fermentable sugars, such as lactose or fructose (FODMAPs) can be present in between 10 to 15 % of the younger general population, but no special relationship to exercise is known.
The most common exercise-induced allergic reaction is an itching skin with a rash (urticaria) or hives. The range of possible reactions is quite wide, including diarrhea, nausea, vomiting, bloating, abdominal cramps and pain, swallowing problems or reflux. Tingling, swelling, itching of the mouth, lips, tongue and throat, edema or swelling of the face or limbs, and respiratory problems, such as runny nose, sneezing, sinusitis, difficulty in breathing, cough and asthma are further possible signs of an allergy. Nervous system reactions, such as loss of ability to concentrate, tiredness and headaches are reported. At the extreme end of the spectrum, life-threatening anaphylactic shock can ensue. These reactions are most common in adolescents with co-existing asthma and with peanut allergies.
Symptoms relating to sugar and fat intolerances are similar to those of functional gastrointestinal disorders, including bloating, abdominal cramps and pain, diarrhea or constipation, increased intestinal sounds and gas production, reflux (e.g. acid taste in mouth, heartburn), nausea and vomiting. It should be borne in mind that endurance exercise itself can lead to similar symptoms.
Testing and diagnosis
As with all food allergies, diagnosis of exercise-induced food allergies is based on careful interview, skin and blood tests and doctor-monitored exposure challenge
Sugar intolerances are diagnosed using breath tests
There are no specific tests for fat intolerance.
If allergy treatment is necessary, allergy, antihistamines, corticosteroids and adrenalin (epinephrine) may be administered. Prophylaxis aims to prevent a recurrence; the patient should be given an emergency kit with self-injectable adrenaline (e.g. Epipen) to deal with any recurrent episode. After the food allergen has been identified, it should be avoided for at least 4 to 5 hours before any exercise. The use of aspirin and non-steroidal anti-inflammatory agents should be avoided during this time.
Most common reactions to sports nutrition or supplements
Sports bars: Fructose, milk components, gluten, fruit extracts, malt, nuts, barley, cocoa, additives (flavor, preservatives)
Sports gels: Fructose, additives (flavor, preservatives, e.g. sodium benzoate, potassium sorbate), kola nut, ginger
Sports drinks: Fructose, additives (flavor, color), whey protein
Caffeine is a stimulant to the central nervous system and is common as a sports supplement. Regular use of caffeine does cause mild physical dependence. This does not cause a problem for most people at recommended daily doses up to 400mg per day (adolescents up to 100mg / day; black coffee: 200mg, Red Bull: 80mg / can). However, some individuals react very sensitively to even small doses of caffeine, with possible symptoms being interference with sleep, nervousness, anxiety, dizziness, increased thirst, headache, irritability, fever, behavioral changes, marked blood pressure increases, diarrhea and further signs of gastrointestinal upset. Severe caffeine overdose can lead to trouble breathing, vomiting, hallucinations, confusion, chest pain, irregular or fast heartbeat, uncontrollable muscle movements and even convulsion. These severe reactions require medical treatment.
Ephedrine, often used in the form of the ma huang herb, is a popular supplement used for energy enhancement, fatigue reduction, increased strength, power, and speed, decreased reaction time, as well as to improve body composition. Many side effects are known and are fairly frequent. Some individuals are much more likely to experience these effects, which include tremors, palpitations, headache, restlessness, anxiety, and sleeplessness. More serious effects on the heart and blood pressure do occur regularly, especially in individuals with pre-existing blood pressure problems or heart disease, and can result in seizures, severe blood pressure increases, irregular heartbeat, psychological changes, liver inflammation, stroke, damage to the heart muscle and bleeding in the brain. The adverse effects do not always depend on the dose consumed and can occur at low doses in intolerant individuals. The danger of side effects in increased with physical exercise and dehydration. If any of the above symptoms occur, medical treatment should be sought.
Further general reading on sports nutrition