We are what we eat. In the 19th century, the German philosopher and anthropologist Ludwig Feuerbach coined this famous phrase, meaning that humans need to live on more than just bread and water. Although Feuerbach was criticising the classical vision of the church, today the phrase has taken on different connotations, at least from the standpoint of biology. Or, more specifically, epigenetics.
The epigenetic mechanism can be understood as a complex system that allows genetic information to be used selectively by activating and deactivating certain functional genes. In 1957, Conrad Waddington presented his 'epigenetic landscape' to illustrate a series of concepts in developmental biology. In this landscape there is a ball at the top of a hill. When it begins to roll down, it can go down one valley or another. Once it arrives at its destination, the ball will probably remain there unless we do something to it.
In Waddington's model, the ball at the top represents the zygote and those rolling down the hill, heading into their respective valleys, represent the different cells that make up the body. In this process of differentiation, which occurs during embryonic development, epigenetics plays an important role. So much so that each cell type carries unique epigenetic characteristics, as if each of them had its own identity card.
Although there are several types of epigenetic modifications, without doubt the best understood is methylation - the introduction of the methyl chemical group - of cytosine nucleotides. Today we know that when these nucleotides are methylated, they prevent the expression of the affected genes. When they are not, they allow expression. In this way, DNA methylation operates like a switch that turns genes on and off selectively.
Continuous exposure to our surroundings introduces epigenetic markers into our DNA which may result in genes being turned on or off erratically, causing the development of diseases. So it is not the same living in Beijing, where pollution levels are above the maximum recommended by the WHO, as in the idyllic Swiss Alps where Heidi and her goat used to run around.
Equally harmful are such bad habits as smoking, excessive consumption of alcohol, physical inactivity and stress. But, fortunately, the footprints we leave in our DNA throughout our lives are not totally irreversible. Unlike mutations, which are permanent changes in our DNA, epigenetic markers can be 'written' and potentially 'erased'. By taking up a healthy lifestyle, we can have a positive impact on our health.
So it is clear that we are not, as Feuerbach said, just what we eat. We are the result of everything we experience. This can be seen in studies carried out in identical twins.