Lactose intolerance

Do we really know what our eating habits are driven by?

Does the information provided by our genome influence the development of food intolerances? What did the first hominids eat and how did we evolve to our current eating habits?

We often tend to view our dietary choices as a cultural matter, not directly linked to our biological past. However, dairy consumption in our society has gone beyond culture to become something purely biological. We have always considered the benefits of breast milk essential for infant survival. In fact, milk production is precisely what defines a mammal—a species to which humans belong. For proper infant development, babies consume breast milk, which contains 3.8% fat, 1.0% protein, 7% lactose and 87% water, and/or infant formulas designed for the same purpose.

We must bear in mind that almost all of us are born with lactase, the enzyme that allows us to properly digest lactose, the sugar in milk; without lactase, a baby could not breastfeed. In general, most adult mammals develop lactose intolerance—an ironic fact, given that humans continue to consume dairy beyond infancy. In other mammals, a gene is activated that directly affects milk consumption once they have grown enough to eat other foods.

What changes occurred throughout human history that allow our bodies to tolerate this sugar in adulthood?

As reported by a study published in the scientific journal Nature, humans underwent genetic changes with the arrival of agriculture and livestock farming. These changes enabled the consumption of animal milk as a survival strategy around 8,500 years ago.

Humans transitioned from gatherers and hunters to hunters and herders. Animal domestication shaped new dietary habits and, consequently, altered our internal biology. Changes affecting diet were also reflected in the immune system and even in height. One key change was the ability to digest and tolerate milk consumption during adulthood. In addition, genetic variants emerged that prepared the immune system to protect against new pathogens, such as those arising from close coexistence with livestock and larger, denser settlements.

Despite this evolution, could it be that our genetics still do not allow us to tolerate lactose properly?

We understand that the development of lactose tolerance or intolerance depends largely on our genetic inheritance, among other factors.

By learning from our genome whether we have a genetic predisposition to lactose intolerance, we can decide whether to consume dairy products, reduce intake, combine them with lactase supplementation, or avoid them altogether.

How does lactose intolerance affect us?

Lactose intolerance presents a characteristic set of symptoms that vary depending on each individual, their genetics and their level of lactose tolerance.

In adults, lactose intolerance is caused by reduced production of the enzyme lactase. Lactase is highly expressed during infancy, then gradually decreases to minimal levels or may become inactive, even if the gene is still present.

One of the most common symptoms is abdominal bloating and pain, followed by what is commonly described as poor digestion: diarrhoea, nausea, gas and vomiting. We should also remember that there is a less widely recognised list of symptoms associated with poor metabolism of certain foods, such as migraines. Feeling well should be the norm, and in many cases a symptom is a sign that something is not working properly in our diet.

One way to better understand ourselves is to take a nutrigenetic test and base our new routine on its results to achieve a personalised diet. If two polymorphisms or single-nucleotide variants (SNPs) in the MCM6 gene—which is associated with lactose intolerance—are present, they can be detected through genetic testing.

How can we face life without dairy in a society where it is generally considered essential?

If we do not consume dairy, will we lack calcium?

In principle, dairy products do not need to be completely eliminated; this depends on individual tolerance. Fortunately, proper diagnosis can significantly improve quality of life, and there are many non-dairy foods that are rich in calcium. According to the National Institutes of Health (NIH), calcium can be found in high amounts in:

– Legumes such as chickpeas and beans.

– Nuts such as almonds, hazelnuts, pistachios and walnuts.

– Broccoli, cauliflower, chard and spinach.

– Seeds.

– Certain canned products, such as sardines and salmon with bones.

For cheese lovers, it is worth noting that more mature cheeses contain less lactose but also higher fat content. Including these foods should be guided by a nutrition professional once the degree of lactose intolerance is known.

This also affects our grocery shopping habits. A simple tip to identify whether a product contains lactose is to read the label. Fortunately, allergens and common intolerances such as lactose are highlighted in bold, making them easier to spot.

At first, eliminating or reducing a specific food such as lactose-containing products can be challenging. We are talking about a change in habits, which is never easy. That is why seeking support from a trusted professional can make the transition smoother and help you achieve overall wellbeing through a diet tailored to your genetics.

References

1. Martin CR, Ling PR, Blackburn GL. Review of Infant Feeding: Key Features of Breast Milk and Infant Formula. Nutrients. 2016;8(5):279.
2. Kuhlwilm M, Gronau I, Hubisz M et al. Ancient gene flow from early modern humans into Eastern Neanderthals. Nature 530, 429–433 (2016).
3. Olalde I, Allentoft M, Sánchez-Quinto F et al. Derived immune and ancestral pigmentation alleles in a 7,000-year-old Mesolithic European. Nature 507, 225–228 (2014).
4. Swallow DM. Genetics of lactase persistence and lactose intolerance. Annu Rev Genet. 2003;37:197–219.
5. Anguita-Ruiz A, Aguilera CM, Gil Á. Genetics of Lactose Intolerance: An Updated Review and Online Interactive World Maps of Phenotype and Genotype Frequencies. Nutrients. 2020;12(9):2689.