What Happens If You Ignore Lactose Intolerance?

Lactose intolerance is one of the most common digestive conditions worldwide, yet many people live with its symptoms for years without fully understanding what is happening inside their body or what the longer-term consequences of leaving it unaddressed might be.

While occasional digestive discomfort after consuming dairy may seem manageable, ongoing exposure to lactose when the body is unable to digest it properly can have effects that extend beyond the immediate symptoms. This article explores what happens when lactose intolerance is ignored, the potential nutritional and gut health implications, and when further assessment may be worth considering.

Understanding Lactose Intolerance

Lactose is a natural sugar found in milk and dairy products. In order to be absorbed by the body, lactose must first be broken down into two simpler sugars — glucose and galactose — by an enzyme called lactase. Lactase is produced in the lining of the small intestine.

In individuals with lactose intolerance, the body produces insufficient amounts of lactase to fully break down the lactose consumed. As a result, the undigested lactose passes through the small intestine and enters the large intestine (colon), where it is fermented by the resident gut bacteria. This fermentation process produces gases such as hydrogen, carbon dioxide, and methane, along with short-chain fatty acids. It is this bacterial fermentation that gives rise to the digestive symptoms most commonly associated with lactose intolerance.

Lactose intolerance is not the same as a milk allergy, which involves an immune system response to the proteins in milk rather than difficulty digesting its sugar content. Understanding this distinction is important, as the underlying mechanisms, risks, and management approaches differ.

Common Symptoms of Lactose Intolerance

The symptoms of lactose intolerance are primarily digestive and typically appear within thirty minutes to a few hours after consuming food or drink containing lactose. The severity of symptoms can vary depending on how much lactose has been consumed and how much lactase the individual produces.

Common symptoms include:

• Bloating and a feeling of abdominal fullness
• Excessive gas (flatulence)
• Diarrhoea or loose stools
• Stomach cramps or abdominal pain
• Nausea

Some individuals may experience only mild symptoms, while others may find them significantly disruptive to daily life. The threshold at which symptoms appear varies from person to person, and some individuals may tolerate small amounts of lactose without noticeable difficulty.

What Happens Inside the Body When Lactose Is Not Digested?

When lactose reaches the large intestine without being broken down, the bacteria that naturally reside there begin to ferment it. This fermentation process is the primary driver of symptoms.

As the bacteria metabolise the undigested lactose, they produce significant quantities of gas. This gas accumulates within the colon and contributes to the sensation of bloating, abdominal distension, and flatulence. The volume of gas produced depends on the amount of lactose consumed and the composition of the individual's gut microbiome.

In addition to gas production, the presence of undigested lactose in the colon draws water into the intestinal lumen through a process known as osmosis. This increased fluid content within the bowel can lead to loose stools or diarrhoea. The combination of gas production and fluid shifts explains why symptoms can develop relatively quickly after lactose consumption and may cause considerable discomfort.

What Happens If You Continue to Consume Lactose?

When someone with lactose intolerance continues to consume dairy products without adjusting their intake or seeking guidance, the digestive symptoms described above tend to recur with each exposure. Over time, this pattern of repeated symptom episodes can become a source of significant daily discomfort.

In the short term, ongoing lactose consumption in a person who is intolerant may lead to recurrent bloating that persists throughout the day, particularly after meals containing dairy. Ongoing digestive discomfort may affect appetite, eating patterns, and overall wellbeing. Altered bowel habits — including fluctuating between diarrhoea and periods of relative normality — may become an established pattern.

For some individuals, the regularity of these symptoms may lead them to accept the discomfort as normal or to attribute it to other causes such as stress or general dietary sensitivity, delaying the identification of the underlying issue.

Possible Long-Term Effects of Ignoring Lactose Intolerance

While lactose intolerance is not typically considered a dangerous condition, ignoring it over a prolonged period may lead to consequences that extend beyond digestive discomfort.

Chronic diarrhoea, if frequent, can contribute to dehydration, particularly in warmer weather or in individuals who do not adequately replace lost fluids. Persistent diarrhoea may also impair the absorption of certain nutrients from the diet, as food may pass through the digestive tract more quickly than usual.

Over time, ongoing malabsorption and dietary avoidance of dairy products — sometimes without adequate nutritional substitution — may contribute to nutritional imbalances. Iron absorption may be affected in some cases, particularly if the overall diet is restricted, which may increase the risk of anaemia. A general lack of dietary variety resulting from symptom avoidance can further compound nutritional shortfalls.

It is important to note that these long-term effects are not inevitable. Many individuals with lactose intolerance manage well with appropriate dietary adjustments. However, those who remain unaware of their intolerance and continue consuming lactose without modification may be more vulnerable to these cumulative effects.

Risk of Calcium and Vitamin D Deficiency

One of the most clinically significant nutritional concerns associated with lactose intolerance relates to calcium and vitamin D intake. Dairy products are a major dietary source of both nutrients in the UK diet, and individuals who significantly reduce or eliminate dairy consumption may be at increased risk of deficiency if suitable alternatives are not incorporated.

Calcium is essential for maintaining bone mineral density throughout life. Inadequate calcium intake over an extended period may contribute to reduced bone strength and an increased risk of osteoporosis, particularly in postmenopausal women and older adults. Vitamin D plays a complementary role by supporting calcium absorption in the gut, and deficiency in either nutrient may compound the effects of the other.

For individuals who avoid dairy due to lactose intolerance, it is important to ensure that alternative sources of calcium and vitamin D are included in the diet. These may include fortified plant-based milks, leafy green vegetables, tinned fish with edible bones, and vitamin D supplements where recommended by a healthcare professional. A GP or registered dietitian can provide individualised guidance on maintaining nutritional adequacy.

Can Ignoring Lactose Intolerance Affect Gut Health?

There is growing interest in the relationship between undigested food components and gut health, and lactose intolerance is no exception. When lactose is repeatedly fermented in the colon over a prolonged period, the ongoing bacterial activity may influence the local gut environment.

Prolonged fermentation can lead to sustained gas production and changes in the acidity of the colonic environment. While the gut is well adapted to handling fermentation to some degree, a persistent and excessive fermentation load may contribute to gut irritation and low-grade inflammation in some individuals.

It is worth noting that the relationship between lactose malabsorption and gut inflammation is not fully understood, and research in this area is ongoing. However, the persistent digestive symptoms associated with unmanaged lactose intolerance may affect the overall comfort and function of the gastrointestinal tract, which in turn may influence general wellbeing.

Could Persistent Symptoms Indicate Another Condition?

One of the challenges with lactose intolerance is that its symptoms overlap significantly with those of other digestive conditions. Bloating, abdominal pain, diarrhoea, and gas are common features of several gastrointestinal disorders, and attributing all symptoms to lactose intolerance without proper assessment may mean that another condition goes unrecognised.

Irritable bowel syndrome (IBS) shares many symptoms with lactose intolerance and is one of the most common conditions that may be confused with it. Some individuals may have both conditions simultaneously, making it difficult to determine which is responsible for specific symptoms.

Coeliac disease — an autoimmune condition triggered by gluten — can also present with similar digestive symptoms. Left undiagnosed, coeliac disease may lead to significant nutritional deficiencies and other health complications. Milk protein intolerance, while less common in adults, is another possibility that may produce overlapping symptoms but involves a different mechanism.

For these reasons, it is important not to self-diagnose lactose intolerance based on symptoms alone. A GP can help determine whether further investigation is appropriate.

Difference Between Lactose Intolerance and Milk Allergy

Lactose intolerance and milk allergy are frequently confused, but they are distinct conditions with different underlying mechanisms.

Lactose intolerance is a digestive condition. It results from a deficiency of the lactase enzyme, meaning the body is unable to fully break down lactose in the small intestine. The symptoms are confined to the digestive system and are caused by the fermentation of undigested lactose in the colon.

Milk allergy, by contrast, involves an immune system response to one or more proteins found in cow's milk, most commonly casein or whey. This immune response can produce a wider range of symptoms, which may include skin reactions such as hives or eczema, respiratory symptoms, and in severe cases, anaphylaxis. Milk allergy is more common in infants and young children and is often outgrown, whereas lactose intolerance tends to develop in older children and adults.

Understanding which condition is present is important because the management approach differs. Individuals with milk allergy need to avoid all milk proteins, while those with lactose intolerance may be able to tolerate certain dairy products — particularly those that are naturally lower in lactose, such as aged cheeses and yoghurt.

Why Identifying the Cause of Symptoms Matters

When digestive symptoms are persistent or recurrent, understanding the underlying cause is an important step toward effective management. Without a clear understanding of what is driving the symptoms, dietary changes may be based on guesswork, which can lead to unnecessary food restrictions or, conversely, continued exposure to the offending substance.

Lactose intolerance may be primary or secondary. Primary lactose intolerance is the most common form and results from a natural, genetically determined decline in lactase production that occurs after childhood. Secondary lactose intolerance can develop temporarily as a result of damage to the small intestinal lining from conditions such as gastroenteritis, coeliac disease, or inflammatory bowel disease. In secondary cases, lactase production may recover once the underlying condition is treated.

Distinguishing between primary and secondary intolerance is clinically relevant because secondary intolerance may point to an underlying gut condition that requires its own assessment and management. A healthcare professional can help determine the most appropriate course of investigation.

How Food Intolerance Testing May Help

For individuals who are experiencing persistent digestive symptoms and are unsure whether lactose or other foods may be contributing, food intolerance testing may provide useful information as part of a broader assessment.

Blood-based sensitivity testing can assess the body's response to a range of food proteins, which may help identify specific foods that could be contributing to symptoms. This type of testing does not replace a clinical diagnosis of lactose intolerance, which is typically confirmed through methods such as a hydrogen breath test or a supervised elimination diet. However, it may provide additional insight, particularly when symptoms are complex or when multiple food sensitivities are suspected.

It is important to understand that food intolerance testing provides information about sensitivity patterns rather than definitive diagnostic conclusions. Results should be considered alongside symptoms and clinical history, and any significant dietary changes should ideally be guided by a registered dietitian or other qualified healthcare professional.

When to Consider Clinical Assessment

While mild and occasional digestive symptoms after dairy consumption may be manageable through simple dietary adjustments, there are circumstances in which seeking clinical assessment is advisable:

• Persistent digestive symptoms that do not improve with dietary modification
• Unexplained weight loss or difficulty maintaining a healthy weight
• Ongoing diarrhoea lasting more than a few weeks
• Symptoms that are severe enough to affect daily activities, work, or sleep
• Concern about nutritional adequacy, particularly calcium and vitamin D intake
• Symptoms that overlap with features of other conditions, such as blood in the stool, significant fatigue, or skin reactions

A GP is the appropriate first point of contact. Further investigation may include blood tests, a hydrogen breath test, or referral to a gastroenterologist depending on the clinical picture. Identifying the cause of symptoms accurately allows for a management plan that is both effective and nutritionally balanced.

Summary: Should Lactose Intolerance Be Ignored?

Lactose intolerance is a common and generally manageable condition, but ignoring it over a prolonged period may lead to consequences that extend beyond digestive discomfort. Repeated exposure to lactose in someone who is intolerant can result in ongoing symptoms that affect quality of life, and long-term dietary avoidance of dairy without adequate nutritional substitution may increase the risk of calcium and vitamin D deficiency.

Identifying the condition and understanding its nature allows for informed dietary choices that maintain nutritional balance while minimising symptoms. It is also important to consider that persistent digestive symptoms may sometimes indicate another underlying condition, and professional assessment can help ensure that nothing is overlooked.

Food intolerance testing, including blood-based sensitivity testing, may offer additional information for individuals seeking a clearer picture of their dietary sensitivities. Any testing or dietary changes should complement, not replace, the guidance of a GP, gastroenterologist, or registered dietitian.

Book a Food Intolerance Test

If you are experiencing persistent digestive symptoms and would like to explore whether food sensitivity testing may be a helpful next step, you can view available test options and book an appointment through the clinic's online booking system.