Up until recently, I thought that the genes I inherited from my parents told my body how to develop into the person I am. You know, brown eyes, 5′ 6’’, reasonable IQ! But I’ve never stopped to think that the way I have chosen to live my life, are actual instructions to my genes, telling them what to do, or what not to do. I never thought that I had some control over my gene function.
But our lifestyle and environment do play a significant role in shaping the way our genes work. In this 5-part blog I want to explore how food and genes interact together and how can we design a lifestyle strategy to help us become more resilient to the effects of ageing.
You will have heard of the Human Genome Project, completed in 2003. It was the mapping of the entire code of 20,000 human genes, of which approximately 1.5% control the making of proteins (these are known as protein-coding or protein-encoding genes). We are going to look at a tiny fraction of those protein-encoding genes and how they interact with our diet to make us each individually unique.
A gene is just a segment of DNA that contains instructions for how and when your cell needs to make proteins. Enzymes are a good example of proteins. Enzymes control many of the body’s processes, particularly digestion. For example “lactase” is an enzyme responsible for breaking down the milk sugar, lactose. The LCT gene part-controls the production of the lactase enzyme from the lining cells of our intestine. For many humans, our ability to make the lactase enzyme naturally decreases with age. As a result, people gradually lose their ability to digest lactose in later life, resulting in “lactose intolerance”. However, some people, particularly those from dairying populations, have developed “lactase persistence”. This means that their lactase-producing genes continue to make lactase and they can enjoy dairy products without digestive upset into adulthood.
Let’s now look at this diagram to help us understand some basic terminology.
The nucleus in the cell contains the X-shaped chromosomes, that you are probably familiar with. Humans have 23 pairs of chromosomes. When you unravel a chromosome, you can see that it is made of smaller and smaller parts that make up the double-helix of DNA. The smallest parts are the coloured blocks that make up the “rungs of the ladder” or in technical terms, the base nucleotide pairs. We only have four base nucleotides, Cytosine, Guanine, Adenine and Thymine. They are represented by the letters C, G, A and T.
The order of these nucleotides is very important. The order is the “recipe”, or set of instructions, for making a specific amino acid which are the individual building blocks of proteins. Different combinations of amino acids will make different proteins. And different proteins have different functions.
Now, the part of the story which explains how we are all different from each other. Humans are 99.5% identical to each other. The tiny 0.5% genetic variation is what makes us different from each other. Part of this variation is due to single changes in the order of the nucleotides. These very common changes are called Single Nucleotide Polymorphisms or SNPs (pronounced “snips”). We each have as many as 5-10 million SNPs. Please don’t be confused with a genetic mutation. Although SNPs and mutations are both changes in the base nucleotides, they are different. SNPs are much more common than mutations. Also, mutations can (but don’t always) impair the function of the genes, like in cystic fibrosis or sickle cell anaemia.
Coming back to SNPs. Many SNPs have no effect on health, while others are potentially very important. They may confer an advantage, like in the lactase example. A person with “lactase persistence” will have a different combination of base nucleotides, which tell the lactase-producing gene to keep making lactase. SNPs can also affect our risk for diseases like diabetes and heart disease; how we respond (positively or negatively) to pharmaceutical and recreational drugs; how effectively we break-down certain chemicals in our environment, that might include alcohol or caffeine; how we respond to the food we eat, including how easily we seem to put on body fat, or not, when we eat certain foods; and how we are affected, or not, by bacteria and viruses. Our individual SNPs can play a role in all these functions and more.
In the next post, we’ll focus on some SNPs that affect how our body responds to our food and also how the food we eat affects our protein-encoding genes.