What is food intolerance?
Food intolerance and food intolerance symptoms occur due to the difficulty in digesting (or breaking down) certain kinds of food. This is associated with an unpleasant physical response but does not involve the immune system.
Food intolerance and the symptoms associated, are a relatively common condition. It is estimated that around 15-20% of the population may be affected by it. Food intolerances should not be confused with food allergies.
Intolerance to lactose found in the milk is the commonest example. Other common food components that trigger food intolerance symptoms include:
- Gluten (present in pasta, pastries cakes, and biscuits)
- Caffeine (Coffee, tea, cola drinks, caffeine drinks, and chocolates)
- Histamine (sausages, tuna, anchovies, cheese, eggplant, avocado, spinach, red wine, beers, champagne, etc.)
- Fructose (sugar, honey, and some vegetables)
- Glutamates (tomatoes, cheese)
- Natural and added food chemicals (soft drinks, oils, margarine, bread, confectionery, etc.)
What are the food intolerance symptoms?
Most people with food intolerance report symptoms of digestive upset. However, food intolerance symptoms are not always obvious.
Here we take a detailed look at 30 food intolerance symptoms that may surprise you!
If you suffer from migraine or headaches and have not yet discovered a triggering factor, your food intolerance may be behind them.
Some studies have indicated that foods such as cacao, banana, eggs, and hazelnuts may be triggers for migraine headaches. Other foods such as wine and aged cheese are also known to cause headaches due to specific chemical components that alter the blood flow in the brain.
2. Trouble sleeping
People with chronic digestive disorders as a potential result of a food intolerance often sleep less and have trouble sleeping.
Lactose and gluten may negatively affect the production of hormones. This in turn disrupts the biological clock. Furthermore, food containing specific amino acids like histamine promotes the production ad release of stimulant neurotransmitters that are going to keep you up at night.
3. Feeling tired, lethargic, and sluggish
Adverse reactions to food can often lead to symptoms of fatigue. Many of us may have experienced feeling tired, lethargic, and sluggish after a dinner party or remember falling asleep after the food has been cleared away.
But when you have a food intolerance, this could happen frequently. Your body works in overdrive to process and digest the meal, resulting in exhaustion and sleepiness.
4. Rectal bleeding
Rectal bleeding or hemorrhoids can occur due to food sensitivity and this particularly affects children more frequently.
Intolerance to certain food may lead to chronic constipation. When you are constipated, you are more like to push hard. This will make the veins around your rectum and anus swell. These swollen veins are called hemorrhoids, which may burst to cause bleeding.
5. Numbness and Tingling
Dietary intolerance can cause several physical reactions. Numbness in the hands and feet and tingling sensation in the tongue are responses that can be triggered by gluten, dairy, and other culprits.
These symptoms usually begin within a few hours of eating the food that you are intolerant to. Sometimes they can appear for up to 48 hours.
6. Tonsil stones
The tonsils are located at the back of the throat and contain small spaces where bacteria can accumulate. Tonsil stones are small stone-shaped balls that form in the tonsils. They are a result of trapped debris and germs that builds up in the tonsils.
Dairy contains lactose, a form of sugar that makes it easy for the bacteria to grow. It thickens the mucous and contains calcium which allows the formation of stones. Resulting in a food intolerance symptom of sore throat which may eventually lead to “tonsil stones.”
7. Bad breath
Bad breath is caused by the accumulation of the excess amount of toxins in the blood.
Food that is not digested well, due to intolerances, passes through the disrupted intestinal lining. These then enter the bloodstream and cause the accumulation of high quantities of toxins. The presence of these toxins persistently in the blood leads to bad breath.
8. Feeling cranky and irritable
Many people, especially children, become irritable and cranky after eating dairy. These could be due to the resulting stomach discomfort, which they are not able to vocalize.
Even for adults, feeling cranky and irritable after a meal is your body telling you that you have stumbled upon food that you are intolerant to, resulting in food intolerance symptoms affecting our mood!
9. Trouble staying focused and concentrating
Brain fog is characterized by a lack of focus and mental clarity which can be sometimes a hidden symptom of food intolerance. Research has suggested that some food (like modern refined wheat found in pizza crust, crackers, and bread) can trigger chronic inflammation. This in turn can lead to trouble staying focused and concentrating.
10. Joint and muscle pain
Chronic inflammation not only affects your brain's focusing ability but can also lead to joint and muscle pain. When you eat foods that your body cannot handle, it raises the insulin levels in the blood. This can promote inflammation which causes discomfort and an aching sensation in the muscles and joints.
11. Mood disorders
People who have gluten sensitivity have reported higher levels of depression and anxiety. While it is not clear why it leads to mood disorders, researchers have speculated that gluten-related intestinal damage can lead to nutritional deficiencies. This can lead to depression and anxiety. The gut and the brain are linked (also called the “gut brain axis”) via the vagus nerve. The vagus nerve sends signals from the gut to the brain and vice versa. Food intolerance symptoms do not just affect the gut but can also affect the brain, potentially causing mood disorders.
12. Unpleasant body odor
What you eat can directly affect how you smell, and in more ways than just your breath!
When your body is having a hard time digesting certain food it can cause excess bloating and gas. Research has shown that men who ate a healthy diet consisting of fruits and vegetables had better-smelling sweat, regardless of how much they perspired.
13. Skin problems
We commonly tend to assume that food intolerance affects our digestion, but it can reflect on our skin too. If you have never had problems with your skin in your teen years but are suddenly breaking out in adulthood, its time to think about how they may be linked to food intolerances and symptoms.
Acne and eczema are two problems encountered in food intolerance. Because of the chronic inflammation in the gut, skin health-boosting vitamins and minerals are not absorbed properly. Moreover, undigested food particles, bad bacteria, proteins, and toxins also enter through the leaky gut.
As the body tries to fight these bad substances, it pops up as acne!
14. Food cravings
If you've ever had cravings for sugary foods after a meal, it could be due to an inability of your body to effectively break down food like carbohydrates.
This is because your body has become used to a regular supply of these foods and if you haven’t eaten any for a while, there will be withdrawal symptoms. It can then lead to binge eating.
15. Runny nose and congested sinus
If you occasionally get a runny nose after eating a meal, it could be due to a triggering food. Gustatory rhinitis is when you have a thin nasal discharge after eating certain foods. Sometimes you may also experience watery eyes and sneezing.
Spicy food, black pepper, chili powder, curry, hot sauce, and onions are some foods known to trigger a runny nose.
Intolerant food can also lead to a congested sinus. Excess mucus created in the sinuses can cause post-nasal drip, the constant dripping in the back of the throat that can lead to bad breath.
16. Back pain
If you are intolerant to a certain food, this reaction may upset the digestive system and, in turn, cause pain along the back. If you already have back pain, the inflammation can make the symptoms worse.
17. Flu-like feeling
People with intolerances to certain foods may experience inflammation after eating them leading to stomach pain or cramps, vomiting, and diarrhea that can mimic symptoms of the flu.
18. Chest pain
If you have lactose intolerance, and if you end up eating dairy, it will cause an excess buildup of gas. This can sometimes lead to chest pain.
19. Shortness of breath
Bloating as a result of food intolerance can affect the diaphragm, the muscular partition between your stomach and chest. Because the diaphragm assists in breathing, it can lead to shortness of breath.
While very uncommon, intolerance to certain food can trigger seizures. People who are lactose intolerant have certain enzyme deficiencies that may also cause mental retardation and seizures.
21. Weight gain
When you eat food that your body is not able to break down, your body becomes inflamed leading to increased insulin resistance. Because insulin is a fat-storing hormone, this causes excess weight gain and obesity.
Diets that promote inflammation are high in sugar, refined starches, saturated and trans-fats, and low in natural antioxidants, omega-3 fatty acids, and fiber from whole grains, fruits, and vegetables.
22. Ringing in the ears
Dairy products like milk, cream, and cheese products are filled with different fats.
Fats cause weight gain and cardiovascular issues such as limited blood circulation and high blood pressure both of which are known to cause tinnitus or the constant ringing in the ears.
Intolerance to foods like lactose can cause a range of symptoms including palpitations, or the awareness of the heart beating in your chest. It can also feel like your heart pounds, flutters, or skips a beat.
Palpitations could be due to the increased flow of blood to the gut for digesting difficult food. The resulting increase in heart rate can sometimes feel like it is pounding. Food intolerance symptoms do not always just affect the gut!
24. High blood pressure
Dietary intolerance damages the gut that decreases your ability to absorb nutrients (such as Vitamin B12 and folate). These are required to control homocysteine. When the levels of homocysteine increase, it can cause high blood pressure.
25. Stomach gurgling
The growling gut may be a sign of lactose intolerance. Also known as Borborygmi, the loud gurgling sound of the stomach occur as the undigested food particles move through the gastrointestinal tract.
26. Menstrual pain
If you are suffering from some form of dietary intolerance, chronic inflammation can contribute to dysmenorrhea or menstrual pain. Milk and other dairy products, caffeine, and artificial colorants used in candies can trigger such kinds of severe pain. Menstrual pain can be associated with a food intolerance symptom due to the inflammatory response the body sends, which can cause a hormonal imbalance.
Eating wheat or gluten in intolerant people can stimulate the bladder. The insides of the bladder can be slightly irritated and inflamed resulting in frequent urination and bedwetting in children. If your child is continuously wetting the bed with n
Excessive sweating is caused by stimulation of the sympathetic nervous system, which is a result of the body working hard to digest food particles.
Dietary intolerance is detected as a stressful condition by the sympathetic nervous system. It then activates the mechanisms that help you during stressful situations, like sweating.
29. Mouth ulcers
Mouth ulcers can occur from food additives and can appear as late as 12 to 24 hours after eating the said food.
Early diabetes may be linked with celiac disease, a gut disease caused by intolerance to gluten. Genetic tests have revealed that both diseases share similar regions that were not seen in healthy people.
What is the difference between food allergy and food intolerance?
Food allergy is a response given by the body’s immune system to a protein present in the food. The body mistakes the food protein as a threat and reacts vigorously to it. It usually involves antibodies like immunoglobulin E (IgE).
Food intolerance usually causes symptoms that aren’t life-threatening and may not occur if you eat small amounts of the said food. The symptoms begin a few hours after eating as the food passes through the digestive tracks.
How to diagnose food intolerance?
Food intolerance is most often diagnosed through a trial-and-error method. You may be asked to keep a diary to log what you eat through the day and then look for the common triggering food.
Eliminating the suspected food from the diet is another way for diagnosing food intolerance. You begin by completely avoiding the food until you are symptom-free, then reintroduce the food one at a time. This can help pinpoint which food is causing your symptoms.
Lactose intolerance can be detected by a hydrogen breath test.
Symptoms of food intolerance are often straightforward like bloating, abdominal cramps, and constipation. Sometimes it may not be. Awareness of the varying presentation of dietary intolerance can help you avoid the triggers and ease your condition.
- Lomer, M C E. “Review article: the aetiology, diagnosis, mechanisms and clinical evidence for food intolerance.” Alimentary pharmacology & therapeutics vol. 41,3 (2015): 262-75.
- Tuck, Caroline J et al. “Food Intolerances.” Nutrients vol. 11,7 1684. 22 Jul. 2019,
- Manu, P et al. “Food intolerance in patients with chronic fatigue.” The International journal of eating disorders vol. 13,2 (1993): 203-9.
- Guariso, G et al. “Emicrania e intolleranza alimentare: studio controllato in età evolutiva” [Migraine and food intolerance: a controlled study in pediatric patients]. La Pediatria medica e chirurgica : Medical and surgical pediatrics vol. 15,1 (1993): 57-61.
- Domínguez-Ortega, G et al. “Extraintestinal manifestations in children with gastrointestinal food allergy.” Journal of pediatric gastroenterology and nutrition vol. 59,2 (2014): 210-4.
- 6. Vernia, Filippo et al. “Sleep disorders related to nutrition and digestive diseases: a neglected clinical condition.” International journal of medical sciences vol. 18,3 593-603. 1 Jan. 2021.