Lactose intolerance is a common condition affecting approximately 65-75% of the global population. Lactose is a carbohydrate found in milk and dairy products, and it is digested by the enzyme lactase. The concentration of this carbohydrate varies among different types of animal milk: 6-7 g/100 ml in human milk, 5-6 g/100 ml in cow’s milk, and 4-5 g/100 ml in sheep, goat, and buffalo milk. In yogurt, this amount is reduced to 1-3 g/100 ml.

Lactose intolerance, also known as hypolactasia, occurs due to a deficiency in lactase production, leading to inefficient digestion of lactose (milk sugar) in milk and dairy products. This can result from insufficient or absent lactase enzyme production in the small intestine. Lactase breaks down lactose into glucose and galactose, allowing it to enter the bloodstream and be utilized by the body. The most common form of lactose intolerance is primary deficiency, which occurs when lactase production decreases after weaning. Secondary deficiency, on the other hand, can develop due to external factors such as gastrointestinal diseases, malnutrition, or surgical interventions. A rarer form, congenital lactase deficiency, is caused by the inheritance of two defective lactase genes.

• Primary (adult-onset) lactase deficiency is the most common form worldwide, occurring naturally as lactase production decreases with age.
• Secondary (acquired) lactase deficiency can develop due to conditions affecting the small intestine, such as celiac disease, Crohn’s disease, or severe gastroenteritis. This type is often reversible through dietary adjustments, including temporarily eliminating lactose for two weeks and then gradually reintroducing it. Since lactase activity can decrease over time without lactose exposure, individuals in Turkey with secondary lactose intolerance may permanently lose enzyme activity if they do not receive proper guidance.
• Congenital lactose intolerance is a rare genetic disorder in which infants are born without lactase enzyme production, preventing them from digesting even breast milk.
• Developmental lactose intolerance occurs in premature infants whose intestines are not yet fully developed to produce lactase. This condition is usually temporary and resolves as the intestines mature.

Symptoms and severity vary among individuals based on factors such as lactase concentration, gut microbiota composition, lactose intake, gastrointestinal motility, and personal sensitivity.

• Since most of the global population experiences lactose intolerance, it often leads to excessive avoidance of dairy products, potentially resulting in nutritional deficiencies. Proper diagnosis and management can prevent unnecessary dietary restrictions.
• Congenital lactose intolerance requires a lactose-free diet until symptoms subside, after which tolerated amounts may be reintroduced.
• Secondary lactose intolerance necessitates a temporary lactose-free diet until the underlying condition is treated (usually two weeks).
• Adults can consume lactose-free dairy products or those labeled as "lactose-reduced," but these may not be suitable for children with congenital or primary lactose intolerance since they still contain about 20% of lactose.
• Most adults can tolerate up to 12 g of lactose in a single sitting. When combined with other foods, tolerance may increase to 15-18 g.
• Spreading dairy consumption throughout the day or diluting dairy products may improve adaptation.
• Yogurt and aged cheeses (e.g., cheddar, parmesan) are better tolerated than milk.
• Gut microbiota, influenced by diet and environmental factors, plays a role in lactose digestion. Beneficial bacteria like Lactobacillus and Bifidobacterium can help reduce bloating and diarrhea. Increasing dietary fiber (prebiotics) and consuming probiotic-rich foods (e.g., kefir, yogurt) may alleviate symptoms.
• Regular, low-level lactose exposure can improve tolerance by promoting lactase enzyme activity.

• Plant-based milks offer a digestible and nutritious alternative for lactose-intolerant individuals. These include almond, soy, oat, coconut, rice, cashew, and hazelnut milk.
• They are suitable for those with lactose intolerance, milk allergies, or vegan dietary preferences.
• Nutritional content varies depending on the plant source, and some are fortified with calcium, vitamin B12, and vitamin D.
• While soy milk is high in protein, almond and rice milks have lower protein content, which may be a drawback for individuals with high protein requirements.
• Some plant-based milks are processed and may contain added sugars or artificial flavors, making label reading essential.
• Coconut milk is high in saturated fat, which may negatively impact heart health if consumed excessively.
• Certain plant-based milks contain allergens; for example, soy milk is unsuitable for those with soy allergies, and almond milk may pose risks for individuals with nut allergies.
• Since plant-based milks do not provide all essential nutrients required for child growth, they should not be a primary nutritional source for young children.

• Lactose-intolerant individuals can consume certain dairy products as they often tolerate small amounts. Hard cheeses and fermented dairy products (e.g., yogurt) contain lower lactose levels and are easier to digest.
• Lactose intolerance is different from milk allergy. Lactose intolerance involves the inability to digest lactose, whereas a milk allergy is an immune reaction to milk proteins.
• Symptoms vary among individuals. Some people can tolerate small amounts of lactose, while others experience symptoms even with minimal intake.
• Proper management and dietary choices enable lactose-intolerant individuals to maintain a balanced and nutritious diet without unnecessary restrictions.