French fries. Pizza. Ice cream. If you think of your favorite foods, there is probably a common denominator: sugar, salt, and fat. Why do humans overindulge in foods we know are unhealthy?

Throughout our evolutionary history, individuals needed high caloric diets to keep up with the rigors of life. Taste buds evolved to favor foods dense in calories, which complemented the energy levels required to function and thrive. Activity was high, as hunting, finding food and water, and escaping predators were full time priorities. Storing fat was necessary for times when food was an uncertainty. 

However, as technology and agriculture expanded suddenly, daily life became increasingly sedentary. Even though humans are wired to crave these foods, few now expend the amount of energy required to keep up with the diets of our ancestors. As such, global obesity is on the rise. As of 2010, 1.4 billion adults around the world are considered overweight or obese. 

But is it really that cut and dry? 

Routinely eating high calorie foods will desensitize dopamine receptors in the brain. This means that over time, a person must eat more to get the same level of satisfaction from eating. While the fact that high fat food can have a drug-like effect is nothing new, it has recently been discovered that this feeling starts in the gut itself, not with the tastebuds as previously thought. Without that satisfied feeling, many people overeat on a daily basis, leading to weight gain. However, this does not have to be a permanent shift. Decreasing the frequency of high fat foods will return the hormone levels to normal. Unfortunately, the problem doesn’t end there.

Fixing the obesity epidemic is not as simple as "calories in vs. calories out." A growing amount of research has shown that epigenetics can influence a waistline. Children of obese fathers are likely to have changes at the gene for insulin-type growth factor 2 (IGF2). Mutations on this gene can lead to colorectal, ovarian, and kidney cancer, though there is no evidence yet that epigenetic markings on the gene will cause disease.

Now the quandary: no matter what is causing the obesity, it isn't healthy. Obesity brings on a host of diseases, including: heart disease, high cholesterol, infertility, cancer, ulcers, skin infections, Type II diabetes, and hypertension, among others. In the United States alone, obesity-related diseases cost a total of $190 billion annually, exceeding the amount spent on diseases related to smoking.