The Concept of CMR
The Obesity and Type 2 Diabetes Epidemics
The Concept of Energy Balance
The growing obesity epidemic is a multifaceted public health problem caused in part by the mechanization and computerization of human labour over the last century. Not only are we now less active at work, we also lead a sedentary lifestyle in which food intake often exceeds energy expenditure. This can lead to overweight/obesity over an extended period of time (Figure). This major behavioural change has had serious repercussions on the body’s energy storage systems. For instance, we are no longer at risk of negative energy balance, which was common in our hunter-gatherer days. Instead, we face a new problem that coincided with the start of industrialization: positive energy balance. Though we may live in the 21st century, humans carry the genes of their ancestors who were naturally selected to store energy for long periods of limited food availability and even starvation. This genetic background protects humans against weight loss and not weight gain, which makes it very difficult for overweight individuals to lose weight. However, the obesity epidemic cannot be explained by changes in our genes, since this phenomenon has only been around for a few decades. Rather, it is our sedentary, affluent societies and individual genetic susceptibility that work in conjunction to affect energy balance and body weight over time. Thus, our ability to store excess energy is interacting with our environment to send obesity rates soaring around the world. A positive energy balance leading to excess fat storage can be caused by various combinations of factors: excess food intake, decreased energy expenditure, or a combination of both, the latter often being observed in obese patients.