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To understand the true size of the American obesity epidemic, we first need to understand what it really means to be overweight. Generally, doctors and nutritionists classify people as either underweight, healthy weight, overweight, or obese. These different classifications are determined by body mass index (BMI), or a measure of body fat based on your height and weight. To get a basic idea, this chart from the CDC approximates what that means for someone who is 5'9" tall.
|5′ 9″||124 lbs or less||Below 18.5||Underweight|
|125 lbs to 168 lbs||18.5 to 24.9||Healthy weight|
|169 lbs to 202 lbs||25.0 to 29.9||Overweight|
|203 lbs or more||30 or higher||Obese|
As for what is driving America's chronic weight problem, there are no definite answers. Scientific studies often reach conflicting conclusions, meaning many theories are out there, but the preponderance of evidence points to the two causes most people already suspect: too much food and too little exercise.
The U.S. Department of Agriculture (USDA) reports that the average American ate almost 20% more calories in the year 2000 than they did in 1983, thanks, in part, to a boom in meat consumption. Today, each American puts away an average of 195lbs of meat every year, compared to just 138lbs in the 1950's. Consumption of added fats also shot up by around two thirds over the same period, and grain consumption rose 45% since 1970.
Research published by the World Health Organization found that a rise in fast food sales correlated to a rise in body mass index, and Americans are notorious for their fast-food consumption ― such food makes up about 11% of the average American diet. Another study demonstrates the full effect added sugars from soda and energy drinks are wreaking havoc on American waistlines. So it is not just how much we eat, but what we eat.
The role of diet in the U.S. obesity epidemic is obviously major, but it's also complex. Consumers are sent wildly mixed messages when it comes to what to eat and how much. One one hand, larger portions, processed packaged food, and drive-thru meals are branded as almost classically American — fast, cheap, filling and delicious. On the other hand, we spend over $20 billion annually on weight loss schemes, from diet books and pills all the way up to last-resort surgeries like lap-bands and liposuction. It's no wonder we're looking for fast food and fast weight loss options, we spend more time at work and less time in our homes and kitchens than our parents did. Sometimes you only have time to pack a leftover pizza slice and a slim-fast for lunch, irony be damned.
This schizophrenic relationship with food is easy to explain in terms of marketing schemes. As decades of soda and tv dinners caught up with our waistlines, the U.S. diet industry grew bigger, faster and smarter. Since the 1970s, popular nutrition wisdom and fad diets have flamed in and out just as quickly as the Arch Deluxe or the McRib. In the 1990s, our big enemy was fat. Low-fat and fat-free products flew off supermarket shelves. It took us decades to learn that when something is fat-free and full-flavored, it's probably too good to be true.
As it turns out, most food companies were just swapping hydrogenated oils and sugar in for the animal fats they removed from low-fat products. Hydrogenated oils are restructured vegetable oils that carry high levels of trans-fats, an amazingly evil type of fat that can raise your bad cholesterol, lower your good cholesterol and increase your risks of developing heart disease, stroke and diabetes. While somewhat less sinister, added sugar can also wreak major damage on a diet. Technically low in calories, high-quantities of sugar disrupts our metabolisms, causing surges in insulin and energy levels and ultimately contributing to weight gain and diabetes.
Lack of exercise is also a major culprit in the obesity epidemic. It's been decades since most Americans worked in fields and on factory floors, a far greater majority of us are sitting throughout our workday. This means less exercise each day. According to one study, only 20% of today's jobs require at least moderate physical activity, as opposed to 50% of jobs in 1960. Other research suggests Americans burn 120 to 140 fewer calories a day than they did 50 years ago. Add this to the higher amount of calories we are packing in, and we get a perfect recipe for weight gain.
But lethargy goes well beyond the workplace. It is also how we get to work and what we do after. Americans walk less than people in any other industrialized country, preferring to sit in cars to get around. And at the end of the day, 80% of Americans don't get enough exercise, according to the CDC.
A number of other factors are thought to play a role in the obesity epidemic, such as the in utero effects of smoking and excessive weight gain in pregnant mothers. Poor sleep, stress, and lower rates of breastfeeding are also thought to contribute to a child's long term obesity risk. Of course, these factors are not explicit or solitary causes of obesity, but they are reliable indicators of the kinds of systemic healthcare failures contributing to this crisis.
In the end, though, we can't lose sight of the big picture. Over the past years, diet fads have come and gone, with people rushing to blame red meat, dairy, wheat, fat, sugar, etc. for making them fat, but in reality, the problem is much simpler. Genetics and age do strongly influence metabolism, but as the CDC points out, weight gain and loss is primarily a formula of total calories consumed versus total calories used.