Thrifty Gene Hypothesis

The thrifty gene hypothesis is the idea that humans can efficiently store nutrients that were limited in supply 10,000–15,000 years ago (known as the Paleolithic era) and that this increased efficiency in storage is related to many of the metabolic problems observed today. This hypothesis was first proposed by James Neel in 1962. Unfortunately, it takes a significant amount of time for genes to evolve into more desirable traits (approximately 5,000–10,000 years). Therefore, our current genetic information is helpful for an environment which no longer exists.

One component of the thrifty gene hypothesis is the ability of humans to store fat very efficiently. The [Page 744]idea is that during the Paleolithic era, humans would often go long periods of time without sufficient food intake (i.e., only when large animals were caught), and subsequently, these humans became very efficient at storing the calories; the stored calories would be used during times of famine. In modern times, unfortunately, there is a plethora of food available to the residents of many developed countries. Therefore, when humans eat today, they store their extra calories very efficiently. This efficient storage system, combined with a decrease in physical activity, may contribute to the current obesity epidemic and all of the diseases that are associated with obesity (i.e., insulin resistance, Type 2 diabetes mellitus, heart disease, and high blood pressure).

In regard to the development of Type 2 diabetes mellitus, it is believed that early humans rarely consumed simple carbohydrates (sugars) and that the actions of insulin were different 10,000–15,000 years ago. Currently, humans require a large amount of insulin to handle the requirements of the modern-day diet. This increased demand of insulin in people who are also overweight increases the likelihood of developing insulin resistance and eventually Type 2 diabetes mellitus.

In addition to this hypothesis about body weight, the thrifty gene hypothesis includes speculation about high blood pressure. Early humans consumed a diet low in sodium chloride (table salt) and thus established an efficient ability to store sodium. Today, the food supply contains much greater sodium content and thus when people consume sodium, their bodies do their best to hold on to it. This is the believed mechanism for why people get salt-induced high blood pressure.

It has been viewed that storing sodium efficiently is a genetic defect. In fact, according to the thrifty gene hypothesis, the opposite would be true. People who do not get the rise in their blood pressure in response to sodium intake might have mutated their thrifty gene to adapt to the modernized world. Alternatively, because our ancestors consumed a diet high in potassium (found in many fruits and vegetables), humans have not developed a good method to conserve excess potassium. Therefore, it has been suspected that low potassium levels from current diets may also be a factor in the development of health problems in developed countries.

Another component in regard to the link of obesity and the thrifty gene hypothesis is the decrease in physical activity. During the Paleolithic era, humans were extremely physically active. They exerted a great amount of energy in acquiring food. During the last 100 years, physical activity has significantly diminished. Not only do humans have easy access to large quantities of food, but there has also been a significant decrease for other physical tasks (i.e., travel is no longer limited to the legs). The increased food intake in combination with decreased physical activity is unfavorable for the thrifty gene environment.

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