As you can see on the Weight Category table on the Definitions page, the weight range that is classified as healthy for your height is pretty broad. For example, someone who is 5 feet 4 inches tall could weigh anywhere from 108 to 145 pounds before he or she would slip into the higher risk category of Overweight. That is a 37-pound range! This is important to notice because one of the common contributing causes of overweight is setting either too low a target weight or too narrow a target weight range.
At the core, there are three forces that come together to determine a person’s body size: biology, psychology, and environment. What makes keeping one’s weight in a healthy range so difficult now-a-days is that the three intertwine — and don’t always cooperate with one another. Biology shapes psychology. Psychology interprets environment which drives biology. And psychology modifies both biology and environment. Having a reciprocally modifying system like this means that no one-dimensional approach (e.g., a diet or a pill) can effectively control one’s weight over the long run. Keeping one’s weight in a healthy range requires a multi-faceted strategy.
Obesity has been the subject of theorizing and research for over a century and there is a rich literature that explores the many facets of this complex phenomenon. Despite the nuances and controversies, we can distill the discussion to a simple concept that helps us to address the problem — specifically, that obesity is the result of a mismatch between our biology and our environment.
Biologically, we are built to thrive in an environment in which food is neither easy to come by, nor calorically dense. We evolved to be able to expend great numbers of calories in search of an unpredictable food supply, and survive well enough to become the dominant animal on the planet. When food is plentiful, we store energy for times of scarcity and, while seeking food, we are able to ignore hunger signals to remain focused on the task. We are also wired not to be very bothered by increasing satiety if good-tasting food is present. (Think about it, if food is hard to come by, it makes good sense to eat as much as you can when it is available!). As recently as a few hundred years ago this design worked well for us. We worked hard for our food, ate heartily, and few people became obese. And one more thing, we are born with a particular body type and size potential. That, along with everything else biological, is a gift from our ancestors.
Today, it is the rare North American who expends much in the way of physical energy to get food. For most of us, hunting and gathering has devolved into driving and ordering. In addition, much of the food we eat has been manufactured in such a way that bite for bite it contains more calories than its natural counterpart did 100 years ago. Thus, our excellent ability to store energy and eat as long as food is available now means that we take in a great number of calories and efficiently store them for a food-deficient future that rarely arrives. Spending few calories to earn our way and having almost eliminated the intermittent famines that thinned our energy stores, we become heavier and heavier. That is at the root of our mismatch problem.
Entwined with our bio-environmental mismatch is that powerful force that sets us apart from the rest of the animal kingdom — our psychology. Influenced by biology and environment, and influencing both of them, our mental apparatus attaches meaning and expectations to food and eating. They are not only essential to our physical survival, but are also part of our social discourse and enmeshed with our emotional experience.
With so many factors influencing what, when, where, why, and how much we eat, it is easy to understand why weight can be so difficult to manage. When we try to juggle the multiple forces that shape our food intake and try to squeeze our bodies into a smaller target weight (range) than our forefathers bequeathed us, it becomes a recipe for deprivation, frustration, and ultimately weight rebound. Hence, careful assessment of a reasonable and healthy target weight range is the essential first step in weight management. That is the key to working with your biology — a task much easier than fighting your biology. For more on learning to manage your weight, click on Treatment for Overweight & Obesity.