Introduction

Food intolerances stem from the body's inability to properly digest certain foods or their components. Food intolerances are common, affecting an estimated 15-20% of the population, compared to only 2-5% for allergies (immunological reactions to food). Some common food intolerances are gluten intolerance, lactose intolerance, and fructose intolerance. The symptoms of food intolerances vary from person to person but generally include bowel movement abnormalities, bloating, and gas. 

This article will specifically explore stomach pain and excessive sweating as symptoms of food intolerance, providing readers with insights into identifying, managing, and seeking appropriate help for food intolerance-related symptoms.

What are food intolerances?

Food intolerance is when an individual has difficulty digesting a certain food or ingredient, leading to uncomfortable but not life-threatening gastrointestinal symptoms. This differs from a food allergies, which is caused by an immunological response to food that in some cases can be life-threatening.¹ Food intolerances are estimated to affect up to 15-20% of the population, while allergies only affect 2-5%.² 

Food intolerances occur due to enzyme deficiencies (the body lacks the required enzymes to digest a nutrient) or irritant compounds (pharmacological effects).³ Irritant compounds are chemicals present in food that can be involved in chemical reactions, inducing gastrointestinal symptoms. This process is not fully understood, but is thought to involve the gastrointestinal neuroendocrine system.⁴

Common food intolerances 

Some common food intolerances are described in detail below. Many of the listed intolerances can be dietary or hereditary (genetic).

• Lactose intolerance is a reaction to the sugar, lactose, found mainly in milk and dairy products and is one of the most common food intolerances.⁵ Lactose intolerance is caused by reduced levels of the lactase enzyme (also known as lactase-nonpersistence), which leads to unabsorbed lactose buildup in the gastrointestinal tract and subsequent irritation⁴
• Gluten intolerance, also known as non-coeliac gluten sensitivity, is a reaction to the gluten present in foods containing wheat, rye, and barley such as bread and pasta. It is similar to coeliac disease (autoimmune, attacks gut tissues) as reactions can be to the same food types, but patients with coeliac disease present with a very specific genetic genotype⁶
• Some individuals are intolerant to a particular group of carbohydrates known as FODMAPs (fermentable oligosaccharides, disaccharides, monosaccharides and polyols). FODMAPs can bypass the small intestine, moving into the large intestine where they are fermented, causing bloating, gas and abdominal pain.⁷ These symptoms may be exaggerated in individuals with certain gastrointestinal syndromes, such as irritable bowel syndrome (IBS)
• Sulphites found in alcohol, pickled foods, and dehydrated vegetables can also cause symptoms associated with intolerance, including asthma⁸
• Fructose intolerance is caused by malabsorption, similar to lactose intolerance. It is naturally present in fruits, vegetables, and honey⁹

As mentioned previously, chemicals present in foods can induce gastrointestinal symptoms, including:

• Histamine (wine, beer, processed meat products, and cheese)
• Caffeine (coffee, tea, chocolate, and some fizzy drinks)
• Salicylates (coffee, some fruits, including bananas, grapes and apples, herbs and spices, and some vegetables)

Symptoms

Symptoms usually appear a few hours after eating the food an individual is intolerant to and can last a few hours or days. Common symptoms include diarrhoea, constipation or other bowel movement abnormalities, bloating, gas, stomach ache/feeling sick, joint pain or rashes.⁷

Symptoms are very similar in children, and recognising the early signs of food intolerance in children is important to help prevent long-term complications. Similarly to adults, having intolerances to certain foods can result in a diet lacking key vitamins and minerals, so meeting with a dietician is important to ensure children remain healthy and nourished as they grow.

Stomach pain 

Stomach pain is caused by nociceptors (sensory receptors) in the stomach being activated in response to chemical or mechanical stimuli. What we perceive to be stomach pain, may be pain in a different part of the abdomen that we believe is originating in our stomach. The main causes of abdominal pain in adults include gallstones, kidney stones, appendicitis, and gastroenteritis (stomach flu).¹⁰ Other causes of specific stomach pain include indigestion, constipation, and food poisoning. 

The breakdown of certain foods can lead to inflammation or irritation in the gut and its microbiota (microorganisms), resulting in stomach pain. Poorly digested food can also cause bloating and gas, leading to further stomach pain.

Excessive sweating 

Excessive sweating (hyperhidrosis) can occur for a variety of reasons, including anxiety, low blood sugar, infections or as a side effect of medications. It is characterised by sweating more than what your body needs to regulate your temperature, which may include when an individual is cold or at rest. It is diagnosed when the amount a person sweats has a significant impact on their daily routine, causing significant physical, social or emotional discomfort.¹¹

Generalised hyperhidrosis can occur as a symptom of food intolerance. Some people may have a specific reaction to foods high in histamine or those that trigger histamine release.¹² Others may find that spicy foods cause excess sweating.

There is a large volume of scientific studies exploring the relationship between allergies and excessive sweating; however, research specifically looking at intolerances is lacking. As allergies are immunological, the mechanism behind excessive sweating as a response to food intolerance may be completely different to the mechanism in allergies.

Identifying and managing symptoms

First, an individual suspecting a food intolerance will be referred to a specialist who will take a detailed medical history. Those with gastrointestinal symptoms will undergo investigation, including blood and faecal tests or imaging, to rule out other diseases. The availability of clinical tests and diagnostic biomarkers specifically for food intolerances is low, so a diagnosis may be based on ruling out alternative causes. ^3,7

A nutritionist or dietician may ask a patient to keep a diary of the food they eat and their symptoms and they may also put them on an elimination diet for a few weeks. Slowly, foods can be reintroduced to attempt to identify which foods are responsible for causing the symptoms. This trial-and-error approach may work for some people and can help them plan meals, avoiding trigger foods. However, it does not always work for everyone, and it must be completed under medical guidance to ensure the individual receives adequate calories, vitamins, and minerals, in addition to a balanced diet. 

Other options include enzyme supplements, diet modification (e.g., gluten-free diets, low-histamine diets), and over-the-counter treatments for symptoms, such as pain relief. 

When to seek medical help

It is important to distinguish between mild intolerances and serious conditions (e.g., IBS, coeliac disease). Moreover, intolerances may be mixed up with allergies. Unlike intolerances, allergies are immunological responses to food and can be fatal if not treated. Although intolerances and allergies share some symptoms, allergic reactions to food can be identified by itchy skin, swollen or raised rash, wheezing, choking/gasping for air or swelling of the lips, face and eyes.¹ People having an allergic reaction may find that their throat feels swollen and may have trouble breathing.

Other warning signs that require medical attention include persistent symptoms, blood in stool, or extreme weight loss, as the effects of the intolerance may be causing issues beyond manageable symptoms. 

Summary

Food intolerances can manifest in diverse and often uncomfortable ways, with stomach pain and excessive sweating being among the more disruptive symptoms. While these reactions are not life-threatening in the way that food allergies can be, they can still have a significant impact on quality of life. Identifying trigger foods and adopting personalised dietary changes are key steps in managing these symptoms effectively.

Given the complexity of food intolerances and their overlap with other gastrointestinal and systemic conditions, consulting healthcare professionals is crucial for accurate diagnosis and management. There is demand for reproducible, well-designed clinical studies using placebos (inactive substances made to resemble the treatment) and a double-blind design (neither participant nor researcher knows who is taking the placebo). Continued research into the mechanisms of food intolerances will help improve diagnostic methods and therapeutic strategies, enabling individuals to live more comfortably and confidently.