All about lactose intolerance

When milk or another food or drink containing lactose reaches our small intestine, an enzyme called lactase should break lactose down into sugars called glucose and galactose, which can be absorbed into the bloodstream. If there is not enough lactase, unabsorbed lactose moves through our digestive system to the large intestine, or colon. Lactose in the colon will start to ferment due to the presence of bacteria, leading to the production of various gases and our experiencing the symptoms associated with lactose intolerance such as bloating, flatulence and diarrhoea.  

Depending on the underlying reason why the body is not producing enough lactase, the lactose intolerance may be temporary or permanent. 

Lactose intolerance is a result of a lack of the enzyme lactase that allows the body to digest lactose. Some cases of lactose intolerance are inherited and tend to be permanent. In other cases, the lactase deficiency is a result of another condition, such as an infection in the digestive system. This is known as secondary lactase deficiency, and its effects may be only temporary.  

Most cases that develop in adults have a genetic origin and tend to be lifelong, while cases in children are often caused by an infection in their gut and may last only a few weeks. The permanent cases are usually caused by what is known as primary lactase deficiency, an incapacity to produce the enzyme lactase caused by genetic factors. Secondary lactase deficiency is when a shortage of lactase is caused by another health condition or the use of certain medications. 

Is lactose intolerance genetic or hereditary? Can you develop lactose intolerance? The answer to both of these questions is yes, sometimes. The full answers can be understood by looking at the different types of lactase deficiency, which is what causes lactose intolerance: 

Primary lactase deficiency 

This kind of lactase deficiency is caused by a genetic variation that runs in families. Primary lactase deficiency develops when a body’s lactase production decreases as the person becomes less reliant on milk and dairy products in their diet. This is usually after the age of two, when breastfeeding or bottle feeding tends to have been stopped, although the symptoms of the resulting lactose intolerance may not become noticeable until adulthood

Secondary lactase deficiency 

Secondary lactase deficiency is when a problem in the small intestine causes a shortage of lactase. This can occur at any age, and may be the result of another condition, surgery on your small intestine or a side effect of certain medication. Among the possible causes of secondary lactase deficiency are: 

• Gastroenteritis 
• Coeliac disease 
• Crohn’s disease 
• Ulcerative colitis 
• Chemotherapy 
• Long courses of antibiotics 

The decline in the production of lactase in secondary lactase deficiency can be only temporary, but it could also prove permanent if it is caused by a long-term medical condition.  

In later life it is possible to develop secondary lactase deficiency without any specific condition or reason to trigger it, but simply due to the fact that production of the enzyme naturally reduces as a person gets older.  

Congenital lactase deficiency 

This is a rare hereditary condition that affects new-born babies, in which a genetic fault means the affected child produces very little or no lactase. The genetic mutation that causes congenital lactase deficiency is passed on in an autosomal recessive inheritance pattern. This means that both parents must have a copy of the gene to pass on the condition.  

Developmental lactase deficiency 

Some babies born prematurely (before the 37th week of gestation) have a temporary lactose intolerance because their small intestine was not fully developed before they were born. This condition usually improves as the baby gets older.  

How do you know if you are lactose intolerant? Symptoms of lactose intolerance usually appear within a few hours of consuming a food or drink that contains lactose. These symptoms may include: 

• Flatulence 
• Diarrhoea 
• Constipation (methane can slow the time it takes for food to pass through the gut) 
• A bloated stomach 
• Stomach cramping and pain 
• Stomach rumbling 
• Nausea 

If you think you may have lactose intolerance, it is important to see your doctor to discuss it because the symptoms can be similar to those of other conditions, including IBS and coeliac disease. If you keep a note of what you eat and drink and what symptoms you experience, this will help you and your doctor to have a clearer idea of what is affecting your body. 

Your doctor may suggest removing lactose from your diet for two weeks to see if the symptoms are relieved. There are also tests, typically a hydrogen breath test, which your doctor may want to run to confirm lactose intolerance, find out how much lactase your body is producing, or to try to determine what is causing your lactose intolerance.

Some cases of lactose intolerance caused by another condition such as gastroenteritis will resolve themselves over a period of time.  

If your lactose intolerance is due to primary lactase deficiency, there is no way to try to cure it. But you should be able to control the symptoms by making changes to your diet to cut down on or avoid food and drink containing lactose. To what extent you need to avoid or eliminate lactose altogether will depend on how sensitive your body is to lactose. Some people can tolerate a certain amount of lactose in their diet, while others experience symptoms after ingesting the tiniest amount.  

While there are plenty of lactose-free products to replace traditional dairy foods, eating fewer products with lactose or avoiding them altogether can mean you miss out on certain vitamins and minerals if you are not careful to replace them in other ways. This is particularly the case of calcium and vitamin D, which are important for good bone growth and strength. 

You should discuss the diet that is right for you with your doctor or dietitian. The needs of a child and an older person can vary with regard to certain nutrients.  

Milk and other dairy products contain calcium, protein and vitamins, including vitamins A, B12 and D. Lactose also helps your body to absorb other minerals, such as magnesium and zinc.  

If you are lactose intolerant and sticking to a lactose-free diet or very nearly, getting the right amount of vitamins and minerals can be a challenge. Insufficient intake of these vitamins and minerals can lead to serious health conditions, such as osteopenia, osteoporosis and even malnutrition.  

It is essential to get proper guidance about managing a lactose-free diet.  

Once you have been diagnosed with lactose intolerance, and you know whether you can have a small intake of lactose or must avoid it altogether, it is time to design a diet that means you avoid symptoms and ensure you are getting all the vitamins and minerals you need. 

Lactose comes in milk, be it from a cow or sheep or goat milk, but it is also in a host of dairy products, although it may be a lesser amount that you can tolerate. Products other than milk that typically contain lactose include: cream cheese, yoghurt, ice cream and shakes and smoothies. But beyond dairy produce, lactose can also be present in a host of other foods, including mayonnaise or salad cream, biscuits, chocolate, cakes, some types of bread and bakery products, breakfast cereals, instant soup and other ready meals, and even some processed meats. Read the ingredients carefully to check for hidden lactose. 

Here are some alternatives, which are usually lactose-free: 

• Special lactose free products (milk, yoghurt, cheese,..) Soya milk, yoghurts and cheeses 
• Coconut-based yoghurts and cheeses 
• Almond milk, yoghurts and cheeses 
• Rice milk 
• Oat milk 
• Hazelnut milk 
• All foods labelled “dairy free” or “suitable for vegans” 

For good sources of natural calcium, try to eat plenty of: 

• Leafy green vegetables, such as cabbage, broccoli and kale 
• Soya beans 
• Tofu 
• Nuts 
• Bread and anything made with fortified flour, typical in the US and UK 
• Fish with edible bones, such as sardines 

Your doctor may recommend you take calcium and vitamin D supplements.  

You may also find it helpful to take tablets or drops containing lactase substitutes, which can be added to milk or taken before eating a meal containing lactose.