Health risks of being overweight – the difference between “calories in” and “calories out”
THE “SECRET” TO EASY WEIGHT LOSS is well-known—so well-known, in fact, that everyone has one. It’s eating less fat . . . or fewer carbs. It’s exercising at low “fat-burning” intensity . . . or at maximum intensity. It’s consuming fewer calories . . . or burning more calories. It’s lifting weights . . . or doing cardio. The contradictions are endless, and the real message is that there’s no single tactic that makes losing weight easy for everyone.
But that doesn’t mean we don’t know anything about weight loss. On the contrary, researchers are teasing apart the complex links between diet, physical activity, hormones, and fat storage.
Understanding how different types of exercise and eating patterns affect the body will help you plot a weight-loss strategy tailored to your needs and avoid common misconceptions like the myth of the “fat-burning” zone. More importantly, it’s now clear that being thin and being healthy aren’t always the same thing—so the success of your exercise regime should be measured by aerobic fitness, not the bathroom scale.
Is it possible to be fat and healthy at the same time?
Fat is bad and obesity is an epidemic—that’s the message we hear on a daily basis. That’s why the unexpected results of a 2009 study published in the journal Obesity created a mini-sensation. A team of Canadian and American researchers used data from Statistics Canada’s National Population Health Survey to follow 11,326 adults for 12 years. They found that subjects who were overweight (body mass index of 25 to 30) were 17 percent less likely to die during the study period than those of normal weight (BMI of 18.5 to 25).
Does this mean we’ve been wrong all along about the links between weight and health? That our mantra should be, as newspaper headlines put it, “Get fat, live longer”? In truth, the results weren’t surprising to obesity researchers, joining a growing pile of evidence that body weight is not the absolute indicator of health we once thought. But don’t quit the gym yet. It turns out that physical fitness is a far better barometer of your long-term health than weight is—and that holds true even for thin but inactive people who thought their fabulous metabolism meant they didn’t need to exercise at all.
Steven Blair, a professor at the University of South Carolina, has performed a series of studies dating back to 1994 that try to distinguish between obesity and physical inactivity as causes of health problems. “When we look at obesity and properly adjust for fitness, the obesity risk goes away,” he says. “It just disappears.” In fact, he says, obese people who are physically fit are half as likely to die as people of normal weight who don’t exercise.
This message is particularly crucial for people who start exercising and soon get frustrated—and perhaps quit—because they don’t succeed in losing weight. As long as they’re meeting basic exercise goals such as half an hour of moderate to vigorous exercise five times a week, Blair says, they’re gaining important health benefits no matter what the scale says. Seen in this light, the Statscan results are less shocking—in fact, they closely mirror the results of a similar U.S. study from 2005, which also found that those carrying a few extra pounds into old age lived longer.
“As you age, you start to lose weight and become frail,” notes one of the Statscan study’s authors, David Feeny of Kaiser Permanente Center for Health Research in Portland. For the elderly, among whom most of the deaths in the study occurred, a few extra pounds may provide a margin of error to help them through the illnesses and accidents that become common at that age. In addition, a more vigilant health care system that watches for warning signs such as high blood pressure may have actually succeeded in lowering the penalty for being obese over the past few decades, Feeny says.
The study doesn’t give obesity a free pass—those with a BMI above 35 were 36 percent more likely to die during the study than those of “normal” weight. But researchers also point out that BMI isn’t the most effective way to measure risky fat build-up. “It’s most useful in population studies,” says Travis Saunders, a researcher at the Children’s Hospital of Eastern Ontario Research Institute in Ottawa whose blog Obesity Panacea covers the latest findings in obesity research. “But if you try to apply it to individuals, it doesn’t work.” That’s because where you store fat is as important as how much you have. Fat in the abdominal region, particularly the visceral fat that accumulates between internal organs rather than fat stored just beneath the skin, is particularly problematic. In contrast, Saunders says, fat on the hips, buttocks, and lower body appears to be less of a concern. For that reason, many doctors now measure waist circumference as a proxy for visceral fat. Ideally, men should be less than 40 inches (102 centimeters) and women should be less than 35 inches (88 centimeters).
It’s also worth remembering that (strange as it may sound) death isn’t everything. The average lifespan is now long enough that conditions like heart disease, hypertension, and diabetes—all of which are strongly linked to being overweight—can have a serious impact on quality of life in your final years. The message of the Statscan research, ultimately, is not that weight is irrelevant but that your focus should be on the ongoing process of living healthily, rather than the potentially misleading endpoint of reaching a certain weight.
BODY MASS INDEX
To calculate your body mass index (BMI), divide your mass in kilograms by the square of your height in meters. For example, a man who is 1.75 meters tall and weighs 75 kilograms would have a BMI of 75 / (1.75)2 = 24.5. (Alternatively, multiply your weight in pounds by 703 and divide by the square of your height in inches.) A BMI between 18.5 and 25 is considered normal weight; below 18.5 is underweight and above 25 is overweight, while above 30 is defined as obese.
Is weight loss simply the difference between “calories in” and “calories out”?
In theory, managing your weight is simplicity itself. If you take in more energy (in the form of food) than you burn (through physical activity and metabolic processes), those extra calories are stored as excess weight. If you burn more than you eat, you lose weight. Calories in minus calories out. From a physicist’s perspective, this is inarguably true, since nature forbids you to either create or destroy energy. In practice, though, it’s a little more complicated—because the “calories out” part of the equation doesn’t behave as we expect.
Consider what would happen if you added one 60-calorie chocolate-chip cookie to your daily diet. Since a pound of fat contains 3,500 calories, simple math suggests that you’d pack on about half a pound a month, or six pounds a year, for the rest of your life.
But, as a 2010 paper in the Journal of the American Medical Association explains, this isn’t what happens. As you begin to gain weight, your body has to spend metabolic energy repairing, replacing, and supporting the cells in this new tissue. You start burning more calories without any change in physical activity.
As a result, the weight gain slows down and eventually levels off after a few years at a total of six pounds—even if you keep eating that extra cookie for the rest of your life.
Unfortunately, the opposite happens if you start eating 60 fewer calories per day. Initially, you’ll lose weight. But now the body doesn’t have to expend any energy maintaining the lost tissue, so you burn fewer calories, and the weight loss levels off. If you now revert to your normal diet—which is what people usually do once they achieve their weight-loss goals—you’ll simply regain the weight.
It’s not just the weight you gain or lose that conspires to keep your body weight constant. For more than a decade, researchers at Columbia University have been performing painstaking experiments in which volunteers check into a controlled hospital setting for months at a time.
They’re fed only a liquid diet (40 percent of the calories come from corn oil, 45 percent from glucose, and 15 percent from the protein casein) so that their daily caloric needs can be computed exactly. With both obese and normal-weight subjects, the researchers control food to reduce or increase body weight by 10 percent and observe the metabolic consequences.
The most recent study, published in 2010 in the American Journal of Physiology, tested how the subjects responded to physical activity. When they lost weight, their muscles became about 15 percent more efficient—not simply because they were carrying less weight around, but because of changes in the ratio of enzymes responsible for burning fat or carbohydrate as fuel.
While greater efficiency sounds like a good thing, it means they were burning fewer calories, making it harder to maintain the low weight. In contrast, their muscles became 25 percent less efficient when they gained weight, once again pushing them back toward their starting weight.
These findings provide a sober reminder of how hard it is to slim down once you’ve gained weight. But there are also some practical lessons we can draw from the Columbia research. The biggest change in muscular efficiency was observed at the lowest levels of exercise intensity, equivalent to the activities of day-to-day life as opposed to exercise.
As a result, the researchers suggest, “the weight-reduced individual might ‘escape’ this increased efficiency by altering the intensity of exercise.” Exercising harder rather than longer might be the most effective strategy for keeping weight off.