The Exercise Myth for Weight Loss

Today, we look at why it’s so hard to outrun a bad diet.

When trying to lose weight, which is more important: diet or exercise? A national survey found that a “vast majority” of Americans trying to control their weight believed that food and beverage consumption and physical activity were equally important. Seven out of ten went with equally important, about two out of ten thought exercise was more important, and only about one out of ten chose diet. The vast majority of Americans are wrong.

It’s easy to understand how people might think diet and exercise play equal roles. After all, our weight is determined by the balance between calories in and calories out. What people may not understand about this energy balance equation is we have much more power over the “calories in” side. In fact, on a day-to-day basis, we have full control—we could choose to eat zero calories or 10,000 calories. But most of the “calories out” tend to be outside of our control.

Unlike wild animals who tend to burn most of their calories on activity, about 60 percent of our daily calories are used up just to keep us alive––what’s called our resting, or basal, metabolic rate, thanks in part to our energy-intensive brains. Even if you stayed in bed all day, you’d still burn more than 1,000 calories just to fuel the basics like thinking, breathing, and keeping your heart pumping. In contrast, even most “active” people accrue less than two hours of exercise a week, which may average out to be less than 100 calories burned off each day. That’s only about 5 percent of the total daily energy expenditure, the “calories out” side of the equation. So, the 2,000 calories we may take in every day from our diet can exert 20 times more influence than exercise over our weight destiny.

Most people believe that exercise is “very effective” as a way to lose weight, but this has been referred to as a myth in the scientific literature. In fact, it’s been labeled one of the most common misconceptions in the field of obesity. Yet, virtually all formal weight-loss guidelines include some sort of physical activity recommendation. Can you outrun a bad diet? Let’s see what the science says.

Population studies have certainly found strong correlations between physical inactivity and obesity. But does a sedentary lifestyle lead to obesity, or does obesity lead to a sedentary lifestyle? It probably works a little bit in both directions. To prove cause and effect, and also quantify the relationship, you really have to put it to the test.

Dozens of randomized controlled trials involving thousands of participants have been published on the effects of exercise on weight loss. Physical activity was not found to be an effective strategy. For example, if you look at the studies that tried using exercise alone to induce weight loss, over an average of about five months, people only lost about three pounds. When you put all the studies together, it looks like it took around six weeks of exercising to get people to lose a single pound. That was exercise alone, though. What about as an adjunct to diet?

If you randomize people into a diet and exercise intervention versus just the diet alone, the added exercise group does do better, but the difference in weight loss only averaged about two pounds. The studies lasted between three and 12 months, and all of that extra prescribed exercise only seemed to translate into a few pounds. The two-pound difference was statistically significant, which means we’re pretty sure it was a real effect. But losing two pounds over a year’s time can hardly be considered clinically significant. As a general rule, researchers like to see at least a five- or six-pound drop.

In a meta-analysis of 18 randomized controlled trials lasting a minimum of six months, the diet-plus-exercise group failed to significantly beat out the diet-only group at all. There appeared to be no long-term benefit to encouraging people to add exercise to their weight-loss regimen. What is going on? Maybe exercise is just better at preventing people from regaining weight. No. The vast majority of randomized controlled trials examining weight-loss maintenance also failed to show an exercise benefit.

Part of the problem is compliance. It’s one thing to tell people to adhere to an exercise regimen; it’s another thing for them to actually do it. When the same randomized controlled trials were re-analyzed to exclude people who flouted the instructions, and analysis was limited to just those who actually put in the time and sweat, a clear advantage to exercise emerges. Exercise only works if you actually do it––though one reason people may become rapidly disillusioned with their new gym membership is their gross overestimation of the capacity of exercise to burn off extra calories.

A slice of pizza has about 300 calories. That converts into an hour of brisk walking per slice—an hour a slice! How many kids are jogging two hours a day to burn off their Happy Meals? Who’s got time to climb 50 flights of stairs to take care of the calories in just one Oreo cookie?

That’s one of the reasons that what we put in our mouths is most important. Public health researchers have been experimenting with including labeling on junk food. Still want that Toblerone if it means you have to walk two hours? Or cookies you’d have to skip rope for 81 minutes for? (I think I’d run an hour just to avoid having to eat shrimp-flavored potato chips.)

Labeling fast food menus with little pictograms of exercising stick figures was found to help nudge people towards lower-calorie options. Seeing that the decision to supersize your fries would mean walking an extra three miles that day, or that choosing the chicken salad over the garden salad could mean having to run nearly three miles, people are more likely to make the healthier choice.

In our next story, we look at how calories burned don’t necessarily equal calories lost.

Most overweight individuals evidently tend to choose exercise as their first approach to weight loss. When unrealistic hopes clash with reality, the disappointment may lead to an abandonment of weight-loss efforts altogether as an exercise in futility (no pun intended). Our false expectations may also give us license to overeat. Our pie-in-the-sky notions about the power of exercise may just be used to justify an extra slice of pie right here on earth. Some researchers warn that labeling menus with calorie equivalents of exercise could be counterproductive, backfiring if people rationalize their indulgences after a workout. This concern has actually been put to the test.

Exercise psychologists took a group of men and women, put them on a stationary bike, and had them cycle until they burned either 50 calories or more than 250 calories. Unbeknownst to them, the researchers manipulated the machines to give false readouts, such that in actuality both groups burned the same number of calories. They just thought they burned more or less. Then, they were offered a meal 10 minutes later, ostensibly to measure the “effects of exercise on taste perception,” but the real purpose was to covertly measure how much people ate. Those who falsely believed they had burned off more calories did seem to demonstrate a greater “license to eat,” ending up eating significantly more calories (mostly in the form of chocolate chip cookies).

After a workout, people may be tempted to treat themselves for their sweaty sacrifice. To prevent this knee-jerk reaction from undermining our efforts, we should strive to make exercise less of a chore. In a paper entitled “Is it fun or exercise? The framing of physical activity biases subsequent snacking,” a study is described in which individuals were randomized to the same amount of physical activity, but just described differently. Half were told they were going on a “scenic walk,” and the other half were told they were going on an “exercise walk.” Afterwards, researchers covertly measured how much dessert everyone took at a subsequent meal. Those in the movement-as-exercise group reportedly served themselves about 35 percent more chocolate pudding than the movement-as-fun group. This is all the more reason to choose activities that are enjoyable, such as walking with friends, while listening to music, or watching a video on the treadmill. Reframing exercise as play rather than work may not only make for a more sustainable regimen, but may make us less likely to consciously or unconsciously feel the need to later reward ourselves at the buffet line.

Even just thinking about exercise may compel people to eat more food. Those randomized to simply read about physical activity went on to serve themselves nearly 60 percent more M&Ms than those in the control group, adding up to hundreds of extra calories. The researchers concluded: “simply imagining exercising leads participants to serve themselves more food.”

Expending energy through exercise may not just psychologically predispose us to eat more, but may physiologically make us hungrier. We evolved in the context of scarcity; so, our body places great value on rapidly replenishing lost fat stores. This helps explain why the average weight loss with exercise training is only 30 percent of that predicted based on the number of extra calories burned. Calories in versus calories out can be complicated by the fact that changes on one side of the equation can affect the other side. In other words, we can work up an appetite.

Carefully controlled studies show that caloric intake tends to rise over time to match any increase in caloric expenditure, making significant weight loss through exercise alone remarkably difficult. This doesn’t happen over a day or two. After a workout, there may not be an immediate increase in hunger, but averaged over the week or weeks, our appetite does tend to increase to balance out most of the extra calories we’ve been burning. This calorie compensation isn’t perfect, though. So, we can end up with a net loss in body fat, particularly at higher exercise levels. So, the secret to weight loss through exercise may be sheer volume––at least 300 minutes a week to achieve appreciable fat loss.

This regulation of our appetite through activity works in both directions. Just as there exists a higher level of exercise where we can start to outpace our appetite and lose weight, there’s a lower level of exercise where our body loses the ability to sufficiently downgrade our appetite, and we gain weight. This sedentary zone where our appetite becomes uncoupled from our activity level appears to start at around 7,100 steps a day.

Let’s say you start out as a really active person, chowing down on nearly 2,900 calories a day, and, for whatever reason, have to cut back on exercise. You’d think you’d gain a lot of weight, but you’re surprised that you don’t. Basically, no increased odds of gaining significant body fat. With your drop in exercise came an inadvertent drop in appetite. But there’s a limit to how far your appetite can drop. Once you cross that threshold, once you dip below logging at least 7,100 steps or so a day on your pedometer, your appetite doesn’t slow much further to match, and the pounds can start to pile on. Your body tries to keep your weight steady by adjusting your appetite, but we just weren’t designed to handle such extreme low levels of movement that sadly characterizes most of the U.S. population.