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Why do humans crave sugary foods? Shouldn't evolution lead us to crave healthy foods?
Category: Health
Published: August 17, 2015
By: Christopher S. Baird, author of The Top 50 Science Questions with Surprising Answers and physics professor at West Texas A&M University
Sugar is actually quite healthy when consumed in moderate amounts and in its natural form. The main natural source of sugar is fruit. In prehistoric times, vegetables were the most abundant foods and fruits were scarce in comparison. However, vegetables carry little energy compared to fruits. Therefore, the pre-human primates who consumed the most calories were the ones best able to stave off starvation and pass on their genes. Since fruits were relatively rare, the primates who ate the most of them were best positioned to win the battle of evolution. For this reason, genetic mutations that caused some of our ancient ancestors to crave sugary foods, and to be able to convert the sugar to body fat for future use, ultimately caused them to flourish. Simply put, early primates evolved to crave fruits precisely because these foods are so healthy in the small amounts that were available to them. Because it is more difficult to retrieve a fruit from a high tree than to just eat whatever grass or leaves are sitting around, an intense, innate craving for sugar was needed to drive early primates towards this food.
Now fast forward millions of years to our modern age. With improved agricultural technology, rich countries became able to grow fruits cheaply and in abundance. Instead of being rare caches of calories that could boost survival, fruits became staple foods that could be consumed anytime. The innate craving for sweet foods was still present in humans, but the scarcity of such foods was no longer a problem for many people, leading to over-consumption. This situation still holds true today in affluent nations. In short, the advancement of technology has made it easy for many of us to eat far more sweet foods than our bodies are able to handle. Craving and eating sugar in the amounts and forms that our ancient ancestors encountered is quite healthy. Craving and eating sugar in much larger amounts and in extracted forms is what is unhealthy.
Technology has not only enabled us to grow fruits in abundance, it has also enabled us to extract and concentrate the sugar in the fruits. If a raw orange tastes good mostly because of its sugar content, then the sugary juice squeezed out of the orange should taste even better. It does! If sugar is mostly what makes the orange juice taste so good, then boiling off some of the water from the juice should give you a sugary lump of gummy candy that tastes even better. It does! The problem with this extraction and concentration process is that each step along the way makes it easier for a person to eat too much sugar. It is possible to eat your way to obesity by consuming only oranges as your treat, but doing so requires eating dozens to hundreds of oranges a day. In contrast, it's much easier to eat a few bags of orange candies every day, or drink a pack of orange soda pop every day, and end up obese. In this way, concentrating sugar into sweet treats makes it very difficult to eat as much as you please and still stay healthy. Another problem is that the sugar which has been extracted from fruit is no longer bound to fiber, making it a spike-and-crash source of blood sugar rather than a steady source of blood sugar. Even freshly-squeezed orange juice is less healthy than a whole orange because the sugar has been separated from the fiber.
If you want to be healthy, you shouldn't completely ignore your evolutionary craving for sugary foods. Rather, direct this craving towards eating moderate amounts of whole fruits, while cutting back on candy, fruit juice, soda pop, and sugary baked goods.
Now, this thought process may lead you to ask, "If eating too much sugar is unhealthy, shouldn't evolution eventually lead us to instinctively avoid eating too much sugar?" The answer to this question is complicated. First of all, you are indeed right that humans are still evolving. However, genetic evolution is a very slow process that requires many generations. Humans have only been manufacturing sweets in abundance for a few hundred years, which may not yet be long enough for any kind of evolutionary change to be noticeable. Secondly, evolution is not a guiding hand that automatically forces organisms to want to do what is healthy. Rather, evolution is simply a description of the process by which groups with certain genetic changes that enable them to better survive their particular environment tend to cause these changes to spread in succeeding generations. There are many factors which could affect a modern human's ability to survive. For this reason, it is hard to predict what direction human evolution will take in the future. With that said, since over-consumption of sugar can ultimately lead to an early death, it's certainly plausible that over-consumption of sugar will be naturally selected against in the coming millennia. This could lead to humans that innately no longer want to over-indulge in sweets. There are a few ways humans could evolve to avoid over-indulgence. For instance, the genes that produce a craving for sugar could simply disappear. Or, the human body could develop a mechanism whereby eating too much sugar triggers a painful or uncomfortable sensation, similar to how breathing in some water triggers an unpleasant choking feeling that drives you to cough. Whatever form the mechanism takes, it is certainly possible that future humans will evolve such that they no longer have a desire to over-indulge in sugar.