It is possible to develop new food intolerances at any point in life. A food intolerance is a non-immune adverse reaction to a food or component, causing digestive distress. This phenomenon often results from gradual shifts in the body’s chemistry and the environment of the digestive tract. Unlike immediate reactions seen in allergies, an intolerance involves the digestive system’s inability to properly process a substance. The reaction is typically delayed and dose-dependent.
Food Intolerance Versus Food Allergy
The fundamental difference between an intolerance and an allergy lies in the biological mechanism. A food intolerance involves the digestive system and is generally not life-threatening. Symptoms are typically confined to the gastrointestinal tract, including bloating, gas, abdominal pain, and diarrhea.
A food allergy involves the immune system and the production of Immunoglobulin E (IgE) antibodies in response to a food protein. When IgE antibodies are involved, the reaction can be rapid and severe, potentially leading to anaphylaxis, which affects multiple bodily systems. Because an allergy is an immune response, even a microscopic amount of the trigger food can cause a reaction. An intolerance is often dose-dependent, meaning small amounts of the food may be tolerated without symptoms.
Physiological Reasons for Adult Onset
The development of food intolerances in adulthood is due to natural, age-related changes and external factors that alter the digestive environment. One common physiological change is a reduction in the body’s production of digestive enzymes. For example, the enzyme lactase, which breaks down the milk sugar lactose, often declines naturally after childhood, leading to an inability to fully digest dairy products.
The health and composition of the gut microbiota play a role in adult-onset intolerances. Shifts in the balance of intestinal bacteria, known as dysbiosis, can be triggered by chronic stress, antibiotic use, or long-term dietary changes. When beneficial bacteria are depleted, the remaining microbes may ferment undigested food particles in the colon. This fermentation produces excess gas and causes symptoms like cramping and bloating.
Changes in the integrity of the intestinal lining, sometimes called increased gut permeability, can allow larger, incompletely digested food molecules to pass through the mucosal barrier. This may contribute to systemic inflammation or trigger reactions to substances that previously posed no problem. Damage to the intestinal lining can also impair the cells responsible for enzyme production, leading to secondary deficiencies.
Specific Intolerances That Emerge in Adulthood
Several specific food intolerances tend to emerge later in life. Lactose intolerance is the most prevalent example, stemming from the progressive decline in lactase enzyme activity. This makes it difficult to process the disaccharide found in milk and many dairy products, resulting in classic gastrointestinal symptoms.
Sensitivities to Fermentable Oligosaccharides, Disaccharides, Monosaccharides, and Polyols (FODMAPs) frequently appear in adulthood, often coinciding with the onset of Irritable Bowel Syndrome (IBS). These short-chain carbohydrates, found in foods like wheat, onions, beans, and certain fruits, are poorly absorbed in the small intestine. They then travel to the colon where they draw water in and are rapidly fermented by gut bacteria. This process causes significant gas production and distension.
Histamine intolerance is linked to a deficiency in the Diamine Oxidase (DAO) enzyme, which breaks down histamine ingested through food. Since the DAO enzyme is produced in the intestinal lining, its deficiency can be secondary to inflammatory bowel conditions or the use of certain medications. This enzyme deficit leads to an accumulation of histamine from foods like aged cheese, cured meats, and fermented beverages, causing a wide range of symptoms.
Identifying and Managing New Intolerances
Consulting a healthcare provider, such as a doctor or a registered dietitian, is the first step to rule out other medical conditions. The gold standard method for identifying the specific trigger is a supervised elimination diet. This process involves strictly removing the suspected food or food group for a period of weeks, followed by a systematic reintroduction phase to observe the return of symptoms.
Specific diagnostic tests are available for certain conditions, such as the hydrogen breath test, used to diagnose lactose and fructose malabsorption. This test measures the amount of hydrogen gas produced by intestinal bacteria after consuming a specific sugar. Management of an identified intolerance centers on dietary modification, including controlled avoidance or substitution with alternative foods. Depending on the specific enzyme deficiency, management can also include targeted supplementation.
Individuals with lactose intolerance can take over-the-counter lactase enzyme supplements before consuming dairy products. Those with histamine intolerance may benefit from taking a DAO enzyme supplement to aid in the breakdown of histamine from food.