The obesity epidemic has quickly become one of the greatest health challenges humans have ever faced, and the weight loss industry is now a billion dollar market that provides dieters with supplements, surgeries, and diet plans that promise instant fat loss. However, it hasn’t always been this way. We don’t have to go back more than a couple of decades to understand that the obesity epidemic has evolved over an extremely short period of time. The most recent estimates suggest that the number of overweight and obese people worldwide has risen from 857 million in 1980 to 2.1 billion in 2013, which represents an increase in both adults (28% increase) and children (47% increase) in the past 33 years (1). While it’s often believed that high-income developed nations have the highest obesity rates, several low-income countries actually surpass the stereotypical fat nation United States. Today, about 62% of the world’s obese population live in developing countries which have adopted the western dietary pattern (refined, calorie-dense, and highly palatable food) (1).
A person is considered obese when body mass index is 30 or over, a level of body fat accumulation that has negative effects on health. As excess fat tissue releases many inflammatory mediators and goes hand-in-hand with metabolic disturbances, hormonal dysregulation, and an altered gut microbiota, it’s no surprise that obesity is associated with an increased risk of several types of chronic disorders, such as type-2 diabetes, cardiovascular disease, and different types of cancers (2). Besides the obvious individual challenges that come with being obese, the obesity epidemic is also a major economic burden for the society at large.
However, the obesity epidemic hasn’t taken root everywhere. Some traditional populations which are still largely unaffected by the western lifestyle have low obesity rates, and among hunter-gatherers who still eat ancestral diets and live in an environment that closely resembles that of our paleolithic ancestors, obesity is virtually unheard of (3,4,5). This observation has led to the characterization of obesity as a disease of civilization, also sometimes called a mismatch disease.
This label as a mismatch disease is based on the idea that our genome was forged in the ancestral natural environment, an environment that demanded for a physically active lifestyle, periods of food shortage, diets rich in nutritious whole foods, and other factors that are common features of the hunter-gatherer lifestyle. When we divert too far away from this environment, as we’re now seeing in the industrialized world where we have easy access to cheap and palatable food, don’t need to expend a lot of energy to acquire food and shelter, and in general have disconnected ourselves from the natural human environment, disorders such as obesity emerge.
It’s generally accepted that obesity is caused by a combination of environmental and genetic factors, and few people with a general understanding of thermodynamics will disagree that the reason we gain fat is because we expend less energy than we consume. This is also consistent with studies which show that the rapid surge in obesity rates goes hand in hand with an increased energy intake (6). However, the fact that we’re now eating more food than we used to doesn’t really provide that many answers. The questions we should really be asking ourselves are; why are we eating more food than before, and why do some people gain more fat on a identical diet than others?