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Have you ever wondered why some people eat a lot and don’t put on weight? And conversely, why some people, despite a controlled diet, gain weight easily? As you can imagine, a good part of the reason lies in their genes. Although we don’t know the total number of genes involved, knowledge is growing. Here we explain everything you need to know.

Genes and diet: the discipline of nutrigenetics

The way people metabolise, absorb and use food varies greatly from person to person. For example, the same diet can cause one person to lose weight while another person maintains or even gains weight. There are individuals who have a low BMI (Body Mass Index) despite eating mainly hamburgers and fries. Certain foods and drinks do not affect everyone in the same way. For example, coffee can have a completely different influence on blood pressure in different people. This is why it is not possible to make a general statement about the effect of food on our bodies. 

For some years now, researchers have been able to explain these discrepancies. It is not only what you eat that matters, but also who eats it. This is the birth of nutrigenetics.

People’s DNA is virtually identical, differing by only 0.3%, but it is precisely this small percentage that is responsible for the differences we observe between us: from the colour of our hair to the way we absorb and use nutrients. This is because genes are our instruction and construction manual. They determine how, when and where the proteins that function in the body are built. A small change in genes can make them work completely differently. For example, depending on the genetic variants of the FTO gene, there can be on average a difference of about 3 kilos body mass index (BMI), so the information in your genes determines your risk of obesity.

Why are there differences in metabolism?

As mentioned above, these differences in food metabolism are due to genetic variants.

Some of these variants are common in some populations and rare in others. The best known example relates to the enzyme lactase, the enzyme responsible for breaking down lactose, the milk sugar. As in all other mammals, the expression of this enzyme decreases in humans after weaning. No other mammal consumes milk or milk products as an adult.

However, about 7,500 years ago, a genetic mutation (variant) occurred in Central European cattle breeders that allowed its carriers to digest milk even as adults. This variant gave them an evolutionary advantage, as it allowed them to incorporate nutritious and abundant food, thanks to animal husbandry. There is also the possibility that the benefit went beyond energy intake: providing vitamin D in areas lacking sunlight, having a relatively unpolluted drink (useful in times of polluted water) and developing a stronger immune system in children.

In Southeast Asia, on the other hand, this genetic variant hardly exists. There, 98% of the inhabitants cannot digest the milk sugar, lactose, because in adulthood they lose the enzyme, which is less active. They get flatulence or diarrhoea as soon as they consume dairy products.

As a rule, however, it is individual factors that determine how we metabolise nutrients. For example, there are many people who, due to their genetic profile, absorb substances such as calcium or vitamin C from food less well than the rest of the population. 

Genes and coffee

Caffeine is one of the most widely consumed stimulants in the world. It is found naturally in the leaves and seeds of many plants such as tea, coffee and cocoa, and artificially in some soft drinks, energy drinks and some painkilling drugs. Caffeine is metabolised in the liver by the enzyme cytochrome P450 1A2.

What do your genetics say?

One of the known relationships in nutrigenetics is between coffee and the CYP1A2 gene, which is responsible for caffeine metabolism in the liver. A polymorphism (genetic variant) in this gene could explain why some people can drink coffee all day without being particularly bothered (carriers of the A allele). While others start to get a racing heart after just one cup (carriers of the C allele). Carriers of the A allele are fast metabolisers, their CYP1A2 enzyme works faster and therefore caffeine does not stay in the body for a long time and only has a short-lived effect. In slow metabolisers (carriers of the C allele) the process takes place at a slower rate. Caffeine stays in the body much longer, during which time it increases the release of hormones such as adrenaline and cortisol, which speed up the heartbeat and increase blood pressure.

What dietary strategy can I use?

The health benefits of coffee are not universal. The positive effects of caffeine include increased responsiveness and concentration, stimulation of adrenaline and free acid release, and muscle contraction. This can be advantageous for some sports. Fast metabolisers soon clear caffeine from their systems, allowing the antioxidants, polyphenols and other healthy compounds in coffee to have a positive impact without the adverse effects of caffeine. However, in addition to genetic factors, the body’s ability to metabolise caffeine also depends on other factors related to lifestyle habits, such as the amount of coffee ingested per day, smoking habits or treatment with oral contraceptives. Because these and other factors can speed up or slow down caffeine metabolism, the most sensible advice is to maintain a moderate caffeine intake. For slow metabolisers there is an increased exposure to the risk of high blood pressure and heart attack, so this stimulant should be reduced or eliminated from the diet if possible.

Your DNA is unique, why shouldn't your diet be?

The GensalutFit nutrigenetic test takes your genetics into account to offer you a personalised, adapted, healthy and effective diet. From a saliva sample, we can analyse a whole series of scientifically validated genetic variants in your DNA that are associated with fat accumulation and increased BMI, appetite regulation, and other variants important for the development of a personalised diet such as those related to:

● Fatty acid metabolism.

● Folic acid

● Presence of metabolic disturbances in the newborn.

● Caffeine

● Vitamin A

● Vitamin D

● Hypersensitivity to alcohol

● Lactose intolerance

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What your genes say about your ideal diet
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