Is Exercise Really Necessary to Lose Weight?


  1. Exercise is good for your health, but what about losing weight?
  2. Some reasons to doubt the weight-loss benefits of exercise
  3. Energy expenditure and intake are closely linked
  4. Evidence that exercise has no effect on weight loss was ignored
    The bottom line


"Imagine you're invited to a celebratory dinner.

The chef's talent is legendary, and the invitation says that this particular dinner is going to be a feast of monumental proportions. Bring your appetite, you're told—come hungry.
How would you do it?

You might try to eat less over the course of the day,—maybe even skip lunch, or breakfast and lunch. You might go to the gym for a particularly vigorous workout, or go for a longer run or swim than usual, to work up an appetite. You might even decide to walk to the dinner, rather than drive, for the same reason.

Now let's think about this for a moment. The instructions that we're constantly being given to lose weight–eat less and exercise more —are the very same things we'll do if our purpose is to make ourselves hungry, to build up an appetite, to eat more.

Now the existence of an obesity epidemic coincident with half a century of advice to eat less and exercise more begins to look less paradoxical."
(Gary Taubes. Why We Get Fat. New York: Anchor Books, 2011, Page 40.)

1. Exercise is good for your health, but what about losing weight?

“It's now commonly believed that sedentary behavior is as much a cause of our weight problems as how much we eat. And because the likelihood that we'll get heart disease, diabetes, and cancer increases the fatter we become, the supposedly sedentary nature of our lives is now considered a causal factor in these diseases as well.
Regular exercise is now seen as an essential means of prevention for all the chronic ailments of our day.

(*snip*)Faith in the health benefit of physical activity is now so deeply ingrained in our consciousness that it's often considered the one fact in the controversial science of health and lifestyle that must never be questioned.(*snip*)

But the question I want to explore here is not whether exercise is fun or good for us or a necessary adjunct of a healthy lifestyle, as the authorities are constantly telling us, but whether it will help us maintain our weight if we're lean, or lose weight if we're not.
The answer appears to be no. (*snip*)

Malathon runner

The ubiquitous faith in the belief that the more calories we expend, the less we’ll weigh is based ultimately on one observation and one assumption.

The observation is that people who are lean tend to be more physically active than those of us who aren't. This is undisputed. Marathon runners as a rule are not overweight or obese.

But this observation tells us nothing about whether runners would be fatter if they didn't run or if the pursuit of distance running as a full-time hobby will turn a fat man or Woman into a lean marathoner."
(Taubes. Why We Get Fat. Page 41, 46.)

2. Some reasons to doubt the weight-loss benefits of exercise

In the following article, I believe I mentioned that adding exercise to a conventional calorie-restricted diet has not been very effective, and I will try to explore why. I would like to address the following five points.
【Related article】  Dieting Doesn’t Work in the Long Run

(I)Overweight among the poor

"In the United States, Europe, and other developed nations, the poorer people are, the fatter they're likely to be. It's also true that the poorer we are, the more likely we are to work at physically demanding occupations, to earn our living with our bodies rather than our brains. (*snip*)

They may not belong to health clubs or spend their leisure time training for their next marathon, but they're far more likely than those more affluent to work in the fields and in factories, as domestics and gardeners, in the mines and on construction sites. 

manual labor

That the poorer we are the fatter we're likely to be is one very good reason to doubt the assertion that the amount of energy we expend on a day-to-day basis has any relation to whether we get fat.

If factory workers can be obese, as I discussed earlier, and oil-field laborers, it's hard to imagine that the day-to-day expenditure of energy makes much of a difference. "
(Taubes. Why We Get Fat. Page 41-2.)

(II) Exercise makes you hungrier

Many people have probably realized that exercise and manual labor will make them feel "hungrier" and have a greater appetite than in a sedentary life such as a desk job. Some of you may have exercised to lose weight, but ended up eating chocolate or other sweets because you were tired and then regretted your own weak will and "lack of self-control.”

However, I believe that these are the correct mechanisms for humans. I will explore this issue in more detail in the next section 3.
(III) Increased absorption rate

The effect of aerobic or anaerobic exercise on body fat loss is said to be different, but either way,  I believe the energy once expended through exercise will basically come back

Energy circulates

When we exercise, our muscles need energy. Depending on the intensity of the exercise, energy is produced mainly from blood glucose, muscle glycogen, and fatty acids from fat cells. Of course, energy expenditure will increase once, but then I believe the body will increase its absorption rate to absorb more nutrients from food in the intestines to compensate for those lost nutrients.

Increased absorption rate” might be difficult to understand but think of it this way: When a person drinks alcohol on an empty stomach or drinks alcohol after exercising, it will make them more intoxicated or a person turns redder than usual (AKA the Asian glow)

And, if you are not a drinker, eating or drinking something sweet after exercise may cause your blood sugar to rise more rapidly than usual.

(IV) Become less active at other times

It is said that when people increase their amount of exercise, they naturally tend to become inactive the rest of their lives.

For example, after completing a thirty-minute jog, one may end up relaxing on the couch for a couple of hours because of the fatigue, or may become less active than usual over the course of the day.[1]

relaxing on a couch
(V)Small amount of body fat burned

Body fat is a stored form of energy, so it is not used immediately. Therefore, in the case of high-intensity anaerobic exercise that stresses the muscles, ATP and creatine phosphate stored in the muscles are used as an energy source for about 15 seconds from the start. After that, what is being expended is blood glucose and glycogen, the fast-acting energy source stored in the muscles.

In aerobic exercise such as jogging, which is said to burn more body fat, there is a concept of a fat-burning zone (low-intensity exercise that keeps your heart rate between 60 and 69 percent of  maximum heart rate), but even in this case, about fifty percent of the calories burned come from fat.[2].

Even if the calories burned in thirty minutes of jogging are two hundred kcal, that does not all translate into a reduction in body fat.

3. Energy expenditure and intake are closely linked

In section [2] above, I explained about increased absorption rate, having a bigger appetite, and becoming inactive after exercise, but I will quote again from "Why We Get Fat" for a more scientific explanation.

"The very notion that expending more energy than we take in-eating less and exercising more-can cure us of our weight problem, make us permanently leaner and lighter, is based on yet another assumption about the laws of thermodynamics that happens to be incorrect. 

The assumption is that the energy we consume and the energy we expend have little influence on each other, that we can consciously change one and it will have no consequence on the other, and vice versa. (*snip*)

Intuitively we know this isn't true, and the research in both animals and humans, going back a century, confirms it. People who semi-starve themselves, or who are semi-starved during wars, famines, or scientific experiments, are not only hungry all the time but lethargic, and they expend less energy. And increasing physical activity does increase hunger; exercise does work up an appetite. (*snip*)

In short, the energy we consume and the energy we expend are dependent on each other. Mathematicians would say they are dependent variables, not independent variables, as they have typically been treated. Change one, and the other changes to compensate. (*snip*)

Anyone who argues differently is treating an extraordinarily complex living organism as though it were a simple mechanical device. (*snip*)

In 2007, Jeffrey Flier, dean of Harvard Medical School and his wife and colleague in obesity research, Terry Maratos-Flier, published an article in Scientific American called “What Fuels Fat.”

In it, they described the intimate link between appetite and energy expenditure, making clear that they are not simply variables that an individual can consciously decide to change with the only effect being that his or her fat tissue will get smaller or larger to compensate. "
(Taubes. Why We Get Fat. Page 77-8.)


4. Evidence that exercise has no effect on weight loss was ignored

"As it turns out, very little evidence exists to support the belief that the number of calories we expend has any effect on how fat we are.

In August 2007, the American Heart Association (AHA) and the American College of Sports Medicine (ACSM) addressed this evidence in a particularly damning manner when they published joint guidelines on physical activity and health. (*snip*) Thirty minutes of moderately vigorous physical activity, they said, five days a week, was necessary to “maintain and promote health.”

But when it came to the question of how exercising affects our getting fat or staying lean, these experts could only say: “It is reasonable to assume that persons with relatively high daily energy expenditures would be less likely to gain weight over time, compared with those who have low energy expenditures. So far, data to support this hypothesis are not particularly compelling." (*snip*)

From the late 1970s onward, the primary factor fueling the belief that we can maintain or lose weight through exercise seemed to be the researchers' desire to believe it was true and their reluctance to acknowledge otherwise publicly. 

Although one couldn't help being “underwhelmed” by the actual evidence, as Judith Stern, Mayer's former student, wrote in 1986, it would be “shortsighted” to say that exercise was ineffective, because it meant ignoring the possible contributions of exercise to the prevention of obesity and to the maintenance of any weight loss that might have been induced by diet. (*snip*)

As for the researchers themselves, they invariably found a way to write their articles and reviews that allowed them to continue to promote exercise and physical activity, regardless of what the evidence actually showed. 

One common method was (and still is) to discuss only the results that seem to support the belief that physical activity and energy expenditure can determine how fat we are, while simply ignoring the evidence that refutes the notion, even if the latter is in much more plentiful supply."
(Taubes. Why We Get Fat. Page 43-4, 53-4.)

[1]Dr. John Briffa. Escape the Diet Trap. 
London: Fourth Estate, 2013, Page 222.

[2]University of Hawai‘i at Mānoa Food Science and Human Nutrition Program.「Fuel Sources for Exercise」. 2018.

The bottom line

(1) The idea that the more calories we burn, the lighter we weigh is based on the observation that "lean people tend to be physically more active than those who are not." However, there is little evidence to support this.

(2) Everyone would probably agree that "lean people tend to be more physically active than those who are not." However, it is not as simple as, "if you increase caloric expenditure through exercise, you will lose weight.” The relationship between exercise and weight is more complex.

【See more】Misunderstanding of the Relationship Between Diet, Exercise and Body Weight

(3) Calories consumed and calories expended are interconnected, and if you exercise more, you will feel hungrier and have a bigger appetite. Even if you keep your caloric intake the same, your body will try to regain lost energy source and nutrients due to increased absorption rate after exercise.

(4) The problem with being overweight is that one's base weight value is elevated, and while energy expenditure through exercise may lead to temporary weight loss, it is not effective in the long run. 
As we’ll see in more detail in the following blogs, it is more important to improve dietary balance and intake methods (when or how often you eat, etc.) in combination with exercise.

【Related article】   For Dieting, Meal Improvement Rather than Exercise