Many of us gain a few pounds after a party weekend or vacation. Ten years ago I would have blamed my parents for giving me the wrong genes. I’ve completely changed my mind now. I know genetics are the cards I’ve been dealt, but how and where I play them is the deciding factor.
It is now clear to me that eating food that is personalized to improve my microbes and my metabolism allows me to eat more food and still use the same notch on my belt. It’s hard to predict which crap diet or miracle cure will be in vogue as we head into summer, but I can tell you that if it’s based on a test of your DNA or a hair or nail sample, you’re better off a tarot reading as a more fun option.
Think back a decade or two. Remember the flurry of headlines claiming that scientists had discovered the “gene for X”?
Whether it was intelligence, aggression, religiosity, a sense of humor, dementia, heart attacks, or virtually any other human trait, scientists like me were on the hunt for the gene responsible, knowing the papers would love it. We even found that how much you exercised had a genetic component.
There was a wave of excitement when these new scientific tools of the genetic revolution finally allowed us to plumb the depths of the human genome and uncover our previously unreadable manual.
I, and many of my colleagues, hoped that once we worked out which genes did what, we could block the troublesome genes with drugs and solve many of humanity’s ills, especially the modern epidemic of common diseases, such as poor mental health, diabetes and obesity, heart disease and cancer. It was an exciting time to be a researcher.
In 1993 I founded the UK Twin Registry to investigate which diseases had a hereditary component and played my part in this new path to gene discovery.
My early research found that identical twins were much more likely to have similar body weight and composition than non-identical twins. In fact, the place where the excess fat was deposited (i.e. abdomen or buttocks) was inherited even more than the total amount. By the way, it’s healthier to be a pear than an apple, and most women are pears too, if that’s any consolation.
So the hunt for the genetic cause of obesity began in earnest.
I then published several articles on obesity with my team, but it became clear that huge numbers of subjects were needed and we were excited to be part of a consortium that found the first major ‘obesity gene’, called FTO.
But the excitement was short-lived. We soon discovered another thousand genes that were also linked to obesity.
It became increasingly clear that it would not be as easy as we thought. Even FTO, the gene most strongly linked to obesity, explained only one percent of cases. Other factors obviously play a crucial role. However, the work was not a failure and revealed many hundreds of possible mechanisms, unexpectedly not in metabolism but in the brain, often linked to gut hormones and signals for appetite and fullness, such as the GLP-1 pathways targeted by diabetes and obesity drugs . like Wegovy.
So thousands of genes influence weight gain, but they haven’t changed in the last forty years since obesity rates nearly tripled. In the battle between nature and nurture, nurture has gained the upper hand – our environment plays a major role in this story. And often it can overwhelm genetics.
I delved into the role of our environment while studying so-called discordant identical twins. These twins, despite being genetically identical and having lived together for 20 years, were discordant in body weight. For example, one twin weighs three times more than her sister.
We found that lifestyle was often key, especially the choice of their spouse (e.g. a butcher or a lawyer), and had a major impact on their diet and the weight they gained. So when it comes to body weight, the environment you end up in has more influence than your genes.
The crucial role of our changing environment was a good example from twin studies on type 2 diabetes.
Researchers in the 1970s and 1980s wanted to understand whether this relatively rare condition was genetic. At that time, they found many conflicting identical twins – one of whom had type 2 diabetes and their sibling did not – so genetics did not appear to play a major role.
However, when we fast forward thirty years and conducted a similar analysis in European twins in the 2000s, we found that used to be now highly genetically determined, and it was difficult to find conflicting pairs. What had changed? Area.
Genes determine whether you are susceptible to developing type 2 diabetes, but they simply don’t play a role unless the food environment is harmful, which also harms our gut microbes. Only when ultra-processed foods (UPFs) are available in abundance do genes turn on. The genes have not changed, but our food environment has changed dramatically.
Imagine you have 100 people. Half are competent swimmers and the other half cannot swim at all. You can’t tell them apart on dry land. But once they are in deep water, the difference quickly becomes apparent.
In the 1970s and 1980s we were all on dry land. Today, we’re all swimming from the depths through a sea of ultra-processed and hyper-palatable foods that make up about 60 percent of our diets and are designed to make most of us massively overeat.
Ten years ago I was also interested in the question of whether food preferences were hereditary. We asked twins what foods they liked and didn’t like, and we found a fair amount of genetic influence. Even more than I expected. In particular, enjoying stronger bitter and spicy flavors, such as garlic and chili, seemed to have the strongest genetic component.
We even discovered genetically influenced preferences for meat and, to a lesser extent, salads. In the past this may have led to the hunt for the ‘vegetarian gene’, but now we are wiser. These probably suggest that we have different thresholds for liking or disliking foods. But again, it’s your environment that determines whether these genes really make a difference: you’d be hard-pressed to find someone in Italy who doesn’t eat garlic, or someone in Thailand who doesn’t eat chili, because children are exposed to it early. . Here too, your environment determines whether your genes come into effect.
Of course, our food preferences tell us nothing about how our bodies respond to food.
Despite what testing companies claim, useful genetic tests are limited to only a few specific foods. For example, you can get reliable information about your ability to metabolize caffeine, alcohol and lactose. But most of the genetic testing on how you handle other foods, nutrients, or vitamins is completely useless or bogus.
Understanding how you metabolize lactose in dairy products can sometimes be clinically useful, but you probably already know how well you metabolize coffee and alcohol through self-experimentation. If one cup of coffee keeps you up all night or one glass of wine puts you to bed, then you have the answer. How we metabolize food is complex and involves much more than just genes. Zoe’s Predict studies* have shown that even identical twins have very different metabolic responses to fat and sugar consumption. Their reactions are only slightly more similar to each other than to those of a non-relative, despite being essentially genetic clones. We showed that a combination of gut microbes and the structure and nature of the food had greater effects.
I’ve changed my mind about the influence of genes on our personal decisions and choices. And relying on genetics to tell us what foods to eat is a waste of time and money. Genetic testing for selecting your optimal exercise or sport is available, but equally useless, and exercise, while good for you, unfortunately does not help with weight loss.
You can’t change your parents, but we do have greater food options than they do and armed with the right knowledge you can make better nutritional decisions. Whatever your genes, if you improve your food environment and eat the right things, you can reduce those hunger pangs and be as healthy as you want. So ditch the UPFs and eat real food, especially plants.
*Zoe Predict is an ongoing study that Tim Spector leads at King’s College London
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