The discovery of the structure of DNA by Watson and Crick in 1953 marked the start of a new era in medicine. Heredity could explain the origin of some diseases. However, subsequent advances in research have shown that the environment has a decisive influence on our health. Genes or habits?

TTEXT: ÓSCAR PICAZO Dietitian-nutritionist with a degree in chemistry. Fundación MAPFRE


It was in 1953 that James Watson and Francis Crick published their great discovery – the structure of DNA. This molecule, present in all the cells of our body, stores all the information needed to “build” a human being. From basic traits such as our eye color or height, through to our predisposition to baldness or to suffering cancer.

The DNA revolution led to a certain degree of euphoria and was partly responsible for “genetic determinism”, i.e. the belief that our future health is written in our genes and there is little we can do to change it. However, something did not tally. It was observed that some people with a predisposition to developing a certain disease did not do so and, on the contrary, others who were not predisposed did become ill.

The relevance of habits

When we speak of predisposition, we are referring to the so-called noncommunicable diseases – obesity, diabetes, cardiovascular diseases, etc. – all of which are on the increase in the Western world. Although attempts were initially made to explain this in terms of our genes, science has shown that our habits have a lot to do with aspects such as our body weight. One example is a gene called FTO. Its discovery in 2007 sparked great enthusiasm, as it appeared to be closely linked to body weight gain (a 70 percent greater risk in those individuals with two copies of the gene). However, subsequent studies examined in greater detail its interaction with our lifestyle. It was thus found that, while someone may be a carrier of the obesity-related variant of this gene, their eating habits will be the determining factor.

Our lifestyle can, in some way, turn certain genes “on or off ”

This is what is called epigenetics, the interaction between genes and the environment. Our lifestyle – including habits such as our diet, physical activity, rest patterns, stress, consumption of alcohol or tobacco – can, in some way, turn certain genes “on or off”. Dr. Elliot Joslin summed this up well in his phrase: “genetics loads the gun, but the environment pulls the trigger.”

The force of destiny

Nonetheless, we are not including here some metabolic diseases, marked by one or several genes, which can have an irremediable effect on our health. These could range from alterations such as lactose intolerance or PKU (phenylketonuria), controllable through our diet, to others such as Huntington’s disease, which appears progressively and for which there is currently no treatment other than palliative measures.

In other cases, there are genes that do not necessarily lead to the development of the disease, yet they are so clearly associated with it that some people make drastic decisions. This is the case of the famous actress Angelina Jolie, who decided to undergo a mastectomy after discovering she was a carrier of a variant of the BRCA gene that increases the risk of breast cancer.

The heredity of habits

Maintaining healthy lifestyle habits is always worthwhile. We cannot fall back on such excuses as “it’s in my genes.” Moreover, we would be doing our children a disservice.

Our way of life also leaves epigenetic marks on them, which can affect the health of the next generations.

Recent studies have shown that not only do we pass on to our offspring the genetic information contained in our DNA sequence or instill bad habits in them. Our way of life also leaves epigenetic marks on them, which can affect the health of the next generations.

This has been seen in mice treated with certain substances, whose effect was still present up to two generations later, even though they had not been exposed to them. These discoveries are leading to a resurgence of Lamarckism, the idea that organisms can pass on to their offspring characteristics acquired during their lives, in their interaction with the environment. This theory was abandoned in favor of Darwin’s theory of evolution.

The question is therefore obvious: are some of the epidemics we currently suffer the result of a snowball effect? Are we predisposing future generations to these scourges? It is still too early to tell, but we cannot wait for the answer or it will be too late. Let’s not pull the trigger.


The market for tests

In 2007 the American company 23andme launched its genetic test targeting the general public, a test which estimated the genetic predisposition to certain diseases. A few years later, in 2013, the FDA (U.S. Food and Drug Administration) requested the withdrawal of the test, given its doubts about the reliability of some results. In particular, there was concern about the possibility of a false positive or false negative, which could lead to some people making poor decisions about their health, such as preventive mastectomies, or the modification or abandonment of treatments on the basis of the test results. Currently 23andme is authorized to market tests which indicate the risk level for ten diseases very clearly linked to different genetic variants.