You are what you eat, it’s true. But you also eat what you are, in the sense that your DNA determines – to an extent – what you like, what you need, and how your body reacts to food. This is why the same diets and dieting tricks don’t work for everyone. Sometimes people are simply going to be fatter, slimmer, more muscular or skinnier than other people.
Based on this logic, two dietary theories have arisen.
The first is that we can look at human DNA in general to determine the best diet for us as a species. The paleo diet, for example, posits that the human body never really evolved to digest lots of carbohydrates, since our earliest ancestors gobbled meat, nuts and berries instead of farmed wheat and rice.
The second theory says that you can crack your own personal genetic code to determine the perfect diet for you. Some companies offer “DNA diets” that tell you what, exactly, you should eat based on a DNA test (in exchange for cash, of course!). They claim to be able to advise whether you should eat more or less carbs than your mates, or the amount of cholesterol you can get away with.
Both of these theories have merits, but there are also serious doubts about their efficacy.
First: The human-species, DNA-based diets. These diets tend to follow the logic that natural is better, because, after all, our bodies evolved in the natural world without MSG, refined sugar and other industrially processed modern foods. There is a lot of wisdom there. Indeed, we have access to higher quantities of food and in far more refined forms that mother nature could ever dream of. Obesity and diabetes have been around since the dawn of time, but they have been mainly limited to the wealthiest kings and merchants who could sit around and snarf on sausage and wine all day. Now, however, basically, anyone can buy as much salt, flour and Coca-Cola as they want. Sticking to a natural diet has indeed been shown to maintain a healthy weight and metabolism, and to prevent diseases like diabetes and heart disease.
Another big takeaway from research into human physiology is that our DNA is not our friend anymore. Or rather, it’s not a friend to our efforts to stay healthy in the modern, industrialised world. Your body wants you to gobble up as much carbs and cholesterol as possible because it thinks you’re still running down gazelle on the Serengeti.
Unfortunately, research here mostly deals with the broad strokes on how the body consumes and digests certain nutrients, not specific dishes. In fact, beyond the basic macronutrients, the research is a lot less conclusive – multivitamin supplements, for example, seem to have no effect on the body, and nobody is sure why. Thus, diets like paleo that postulate what our bodies might have evolved to prefer to go far into the weeds. The truth is that we can still only make vague guesses about what our Stone Age ancestors were munching on, and some new archaeological evidence – such as the revelation last year that humans might have been baking bread 15,000 years ago – is challenging what we thought we knew. Compounding this, the way our body metabolizes food is also way too complex to make sweeping generalizations about, say, cutting out dairy products.
But what about our individual DNA? Your personal DNA does indeed have a big effect on our body and metabolism. If you are prone to weight gain, for example, you might have to diet more faithfully than others to maintain your target weight. There are also some food-related genetic conditions. About 90% of people of East Asian descent are lactose intolerant, for example, versus only about 5% of northern Europeans. Obviously allergies and conditions like celiac disease have genetic roots, and a tendency towards alcoholism, too, can be inherited.
On the other hand, you can’t simply crack open your genetic code and automatically discover what you should and shouldn’t be eating. Research by Stanford University suggests that adults following diets tailored to their genes aren’t any healthier than people following ordinary diets. Furthermore, the way your body handles food is also affected by things like your level of physical activity, sleeping patterns and other lifestyle choices. And again, science has not managed to untangle the relationship between nature and nurture.
So, yes, turn to science to help learn what’s best for your body (and by science, we mean real studies by real researchers, not faddists and amateur-nutritionists). But also remember that legitimate scientists, of all people, understand that science has limits, and any diet plan or nutrition tip that goes into the nitty-gritty of our DNA and evolution is probably hogwash.