Lactose Intolerance Explained


What is Lactose and what is Lactase?

All mammals are weaned on their mother's milk, which provides for them easily digestible and adsorbable nutrients (protein, sugar, fat, vitamins, minerals). Different species of mammals have different amounts of these nutrients in their milk (such as percentage of fat or protein), and sometimes different constituents of each of these (such as different types of protein within the protein fraction) — but they all share one thing in common: the sugar present is always lactose.


Lactose is a (disaccharide) sugar made from two smaller (monosaccharide) sugar units: glucose (commonly found in foods), and galactose (which is more rare in our foods). Lactose is not useable by humans as a disaccharide and needs to be broken down into these two monosaccharides, which can then be used within the body. The stomachs of newborn mammals contain a protein whose job it is to break up this lactose into useable glucose and galactose.

This 'enzyme' is called lactase (or b-galactosidase).

Lactase Persistence and Lactose Intolerance

During the period after birth, glucose and galactose are very important - for producing energy to power the development of the body (glucose), and for incorporation into molecules in the brain to help construction of neurons (galactose).

After approximately, the age of two, the expression of the lactase gene is turned off, leading to no production of the lactase enzyme, and therefore our inability to directly digest lactose. This is the situation for 95% of the human population.

If this population consumes a significant amount of lactose, in the absence of lactase to break it down, the lactose is used by bacteria in our stomachs. Mammalian stomachs naturally contain a vast number of bacteria (called our gut microbiome), which should play beneficial roles in out health, although with modern diets, can also cause issues.

When, in the absence of lactase, we consume large amounts of lactose, the bacteria can use the lactose themselves to produce energy and gas (carbon dioxide), which is why we can get bloated, or to produce other small, slightly toxic molecules, which is why we can get cramps and diarrhoea. These symptoms are rarely life-threatening but can causes severe discomfort and pain.

A small percentage of the global population are able to produce lactase throughout life — this population show 'lactase persistence', and in Western Europe and Northern America, this population is actually in the majority.

The Evolution of Lactase Persistence


In Western Europe and North America, it is the minority of the population who have the 'usual' biology, and the marjority show the characteristic of 'lactase persistence - the continuing production of lactase into adulthood. This allows them to consume diary products.

The appearance of lactase persistence represents an example of gene-culture co-evolution (or a niche construction), where a gene evolved due to a cultural shift — that of consuming milk and cheese.

Archaeological sites in the fertile crescent have revealed that humans started to live a herding and dairy-based existence around 10,000 BC. Milk was consumed, and cheese was made. Due to the geography, the first dairy products were likely to be sheep-milk based, only a few thousand years later did goats and cows become dairy animals.


The benefits for humans to be able to process milk and other dairy products, even in adulthood, are clear - the energy and nutrients from milk are significant and are still important to our lives today. The proteins help build strong bodies, the calcium help bone structure, and the fats together with lactose provide stored or instant energy.

Genetic analysis of samples from Mesopotamia show that at around the same time as herding, and the pastoral existence arose (as compared two a hunter-gatherer society), a particularly relevant genetic mutation can be identified.

This genetic 'point mutation' (T−13910) changes the character of a region outside the lactase gene. This change in sequence now attracts more 'activators', which promote the reading of the gene and the production of the lactase enzyme throughout adulthood.


Genetic evidence has now shown that this mutation 'upstream' of the lactase gene has occurred, and remained in the population, at least three distinct times — once Mesopotamia and twice in Africa.

The survival of genetic mutations within a population require that they be 'selected for' as they confer some form of advantage to the carrier. We have already established some of these: the extra energy and protein from milk, and even the extra calcium to provide strong bones.

As humans migrated north from the cradle of civilisation, one can easily see how a population carrying this altered gene would quickly out compete any resident population who were unable to benefit from the advantages of liquid milk — and this is why so many Western Europeans and their descendants contain this genetic variation.

Lactose Intolerance - What to do?

This story of lactose persistence is fascinating, but it doesn't help if you have lactose intolerance.

So what should one do?

Dairy products are still an import part of a balanced diet, as they provide calcium, fats and the rare galactose sugar, as we established. Therefore, it is not wise — nor necessary — to eliminate these from your diet completely, even if you are lactose intolerant.

Lactaid milk is cow's milk that has been treated with lactase, and therefore is lactose-free. Tablets which contain the enzyme can also be purchased and taken at the time of consumption, which helps to remove the lactose from food.


But it's usually not necessary to complicate your meal times with these solutions. Every individual has a different level of intolerance to lactose, and it is for every individual to find their own tolerance.

Experts at the National Institutes of Health, Bethesda, MD, suggest that those with lactose intolerance can still consume at least 12 g of lactose per day (contained in about 1 cup of milk), with little or no symptoms. This amount can be increased by consuming the lactose with other foods.

The key to eating full dairy products with tolerable levels of lactose is to eat fermented products, such as yoghurt, and, of course, cheese. Fermentation is the process by which friendly microbes, such as lactobacilli (using their own versions of lactase), breakdown lactose to glucose, galactose and carbon dioxide.

Yoghurt is a partially-fermented product of denatured milk protein, and therefore will contain less lactose than regular milk. The amount present, however, varies brand to brand, product to product, and since there is no requirement for an indication of lactose levels on packaging, it can be hit and miss to find a yoghurt that can be consumed easily. Food scientists performed analysis of lactose in yoghurt within the Israeli market, and found the lactose content varied from 3.8 g to 5 g per 100 ml.

It is surprising to know that a portion of fresh cheese, such as cottage cheese or mozzarella, contains less then the limit of 12 g per day - 0.3 g to 1 g - since most (but not all) of the lactose is lost in the drained whey, and not retained in the cheese. However, some suffered of lactose intolerant symptoms find that even these fresh cheeses and their levels of lactose are too high, and in this situation, the best course of action is to choose an aged cheese.


Aged cheeses provide more time for the lactobacilli and other microbes to breakdown the remaining lactose in the cheese, thus lowering its amounts to undetectable levels — and rendering it safe to eat for those with lactose intolerance. It's generally accepted that after one year of ageing, the level of lactose has reached zero.

Everything in Moderation

So there we have it. Having some level of lactose intolerance is not the end of your cheese, or other dairy, eating habits. Rather, be wise, be informed, and ask your local, independent cheese monger for help, if you need to find the right cheese for you!