Differences between lactose and milk protein: Complete guide
Differences between lactose and milk protein
Although they are often confused in everyday language, lactose and milk proteins are completely different components in both structure and function. Lactose is a natural sugar found in milk. In order to digest it, the human body needs an enzyme called lactase, which breaks down lactose into two simpler sugars: glucose and galactose. If a person does not produce enough lactase, they develop what is known as lactose intolerance, a digestive problem that can cause uncomfortable but not dangerous symptoms. At Beurrespa, we promote informed and healthy eating by offering content that helps you better understand these types of digestive disorders and make more conscious decisions in your daily life.
On the other hand, milk proteins, such as casein and whey proteins (lactalbumin and beta-lactoglobulin), can trigger a disproportionate immune response in susceptible individuals. This reaction is known as milk protein allergy and can affect the digestive system, skin and breathing, and can even lead to anaphylaxis. Unlike intolerance, which allows for some consumption, this allergy requires avoiding even minimal amounts, as a product labelled ‘lactose-free’ may still contain milk proteins.
Origin and mechanism of each disorder
The differences between intolerance and allergy lie not only in their chemical origin, but also in how the body processes them. Lactose intolerance is a matter of digestion, not the immune system. It occurs when the small intestine does not produce enough lactase, which prevents lactose from being broken down. As a result, this undigested sugar reaches the colon, where it is fermented by bacteria, causing gas, bloating and diarrhoea. This problem can be genetic (present from birth) or acquired over time, especially from adolescence or adulthood onwards.
Milk protein allergy involves a response from the immune system, which mistakenly identifies certain proteins as dangerous agents. The body responds by releasing histamine and other chemicals that trigger allergic symptoms, ranging from mild to very severe. This type of allergy usually appears in childhood, in the early years of life, although it can persist into adulthood in a small proportion of the population.
While intolerance is a chronic condition that can be managed with diet, milk allergy is life-threatening in cases of accidental exposure. That is why people with allergies must be much more careful about what they eat, read labels thoroughly and, in many cases, carry emergency medication such as auto-injectable adrenaline.
Symptoms and severity
The symptoms of lactose intolerance are mainly digestive. They usually begin between 30 minutes and 2 hours after consuming products containing lactose. The most common symptoms are abdominal pain, gas, bloating, diarrhoea and, in some cases, nausea. The intensity of these symptoms varies depending on the amount of lactose consumed and the person’s level of lactase deficiency. Although uncomfortable, these symptoms do not pose a serious health risk.
In contrast, milk protein allergy can present with a wider range of symptoms and affect different systems of the body. In addition to gastrointestinal discomfort, it can cause hives, skin redness, difficulty breathing, nasal congestion, vomiting, swelling of the lips or eyelids, and even anaphylaxis, which is a severe generalised allergic reaction that can be fatal without urgent treatment.
Therefore, the severity of the two conditions is very different. Intolerance causes discomfort that can be anticipated and controlled, while allergy can be unpredictable and requires constant vigilance, even with processed foods, contaminated utensils, or products with traces of milk.
Diagnosis and treatment
Proper diagnosis of these conditions is essential to establishing the correct treatment. In the case of lactose intolerance, diagnosis is usually made through tests such as the hydrogen breath test, which measures the amount of hydrogen expelled after consuming a dose of lactose. Lactose tolerance tests or genetic analysis may also be used to confirm lactase deficiency.
Treatment for intolerance consists of dietary modification, which can range from completely avoiding lactose-containing products to reducing their intake or supplementing with oral lactase supplements. In many cases, people with intolerance can consume fermented products such as yoghurt or mature cheeses, which contain less lactose.
On the other hand, milk protein allergy is diagnosed through skin allergy tests (prick tests), blood tests to detect specific IgE, and, in controlled cases, oral provocation tests. The only effective treatment is the total elimination of milk and dairy products, including baked or processed products where milk proteins may be present. In emergency situations, injectable adrenaline (EpiPen) is used, especially if the person has a history of severe reactions.
Permitted and prohibited foods
In a diet for people who are lactose intolerant, there is quite a wide variety of foods available if precautions are taken. Today, there are numerous lactose-free products: milk, yoghurts, cheeses and other modified dairy products that allow you to enjoy the taste and nutrients of milk without suffering its side effects. There are also lactase enzymes in tablet or drop form that can be taken just before consuming foods containing lactose, which helps many people to avoid having to restrict their diet so much.
However, in the case of people who are allergic to milk proteins, the restriction must be absolute. Even products labelled ‘lactose-free’ may contain casein or whey, which can trigger an allergic reaction. In addition, foods that do not contain milk as a main ingredient but may be contaminated during processing, such as sausages, industrial sweets, sauces, ready-made products or commercial breads, should be avoided. Therefore, correct labelling is crucial for these people.
Affected population and epidemiology
Lactose intolerance is extremely common in adults worldwide. It is estimated that more than 65% of the world’s population has some degree of intolerance, with it being more prevalent in Asian, African, Native American and Mediterranean populations. In northern Europe, lactase persistence is higher, so the incidence is lower, around 10–15%.
In contrast, milk protein allergy mainly affects young children, especially during the first year of life, when cow’s milk is introduced into the diet. In most cases, this allergy disappears between the ages of 2 and 5, although a minority retain it throughout their lives. In adults, milk allergy is much less common, with an estimated prevalence of less than 1%.
The difference in prevalence also influences how the two conditions are managed. While intolerance is usually assumed to be part of adult digestive diversity and is managed flexibly, food allergy requires a more clinical approach and continuous monitoring, especially in childhood.
Frequently asked questions about the difference between lactose and milk protein
Can you develop lactose intolerance as an adult?
Yes. It is common for lactase production to decrease with age, which can lead to symptoms even if milk was tolerated without problems in childhood.
What happens if an allergic person consumes traces of milk?
Even small amounts can cause serious reactions. Therefore, cross-contamination should be avoided and each label should be read carefully.
Are there any home tests to detect lactose intolerance?
Although not a substitute for a medical diagnosis, some people experiment by eliminating lactose for a few weeks and then gradually reintroducing it to observe symptoms.
Are plant-based products safe in both cases?
Plant-based products such as soya milk, oat milk, almond milk, and rice milk are safe for people with intolerances and allergies, provided they do not contain milk-derived additives.
Is it possible to have both conditions at the same time?
Yes, although rare, there are people who are both lactose intolerant and allergic to milk proteins. Their diet must be very carefully controlled.