Chapter 5 Exercise

"Run Forrest, run." - Forrest Gump 1994

Now that the all that calorie arithmetic is crystal clear let's look at exercise, the other side of the energy equation. Maybe there's something we can do here to change our weight and shape. When we say "getting into shape" we mean "getting fit" in English. But that's a misnomer as we will see, exercise won't help you change your shape unless you're talking about body building which is a different matter. Aerobic exercise, like running or swimming or biking, will not help you lose weight. Body building will make you gain weight.

Fat muscles

The muscles in your body are formed from muscle cells that have banded together to form spindles. Like nerve cells, mostly, and fat cells, maybe, you can't increase the number of muscle cells or spindles that you have. You can increase the size and strength of each spindle though and thereby the muscles they go to make up.

What happens when you build up your muscles? You gain weight because muscle weighs more than fat. You also can increase your basal metabolism because basal metabolism depends on your lean body mass. You might think that that would be good because you can eat more to service that basal metabolism without getting fatter. This is the point of a book, Fit or Fat? by Covert Bailey (1978, Haughton Mifflin Co., Boston) that was a best seller for awhile. As soon as you quit the body building routines however you shrink back down. Also there are other mitigating effects as we will see, that don't let body building be any more effective for weight loss than aerobic exercise.

When you lose weight by dieting, about 75% of the weight lost is fat and 25% is lean body mass, mostly muscle since this is the most chageable part of your lean body mass. It is has also been shown that obese people who lose weight just by dieting alone gain much efficiency during their activities. Weigle(1) for example reported that the resting metabolic rate was 97+% of predicted for subjects who lost more than 20% of their usual weight. This is a big weight loss but these subjects didn't change their basil metabolism. This is somewhat hard to believe because when you lose weight your heart rate goes down and your blood pressure goes down. Never the less, since the erstwhile obese subjects needed to eat 25 to 30% fewer calories to maintain the weight loss, almost all of the saving must have occured from activity efficiency. It could be that they slowed way down or that the decreased payload took less work to schlepp around or it could mean that they somehow got metabolically more efficient during exercise. That is they looked like someone who had done an exercise program. They got fit. Weigle concludes that, "a substantial increase in the physical activity would be necessary in any weight-loss maintenance program to overcome the energy savings of the reduced obese state." This is discouraging. To burn the same calories after you lose weight that you used to before you lost weight, you have to exercise more. To keep from gaining back the weight you have to continue to eat a lot less.


We can examine the issue of exercise and weight loss by looking for studies that show that exercise doesn't produce weight loss, there are lots of those. We can examine this issue by finding studies that show that exercise does produce weight loss. There are none. That was easy.
But why does everybody think that exercise will help you lose weight?
People who win marathons are small and skinny. You never see winners who are big and fat. Also it is well established that generally if you put a big person on a treadmill he will not do as well as a lean person. But that's not the same as saying that exercise will make you lose weight. Or that those people are fat because they don't exercise. There are other intrinsic things about an obese person that makes it unlikely that he or she is a good athlete, especially in the pole vault.

Even training for the Boston Marathon won't change your shape or weight. NOVA, the science series for PBS, recently had a show titled Marathon Challange (October 2007). They asked the question, "Can a group of sedentary non-athletes be transformed in nine monthes into a team that can complete the Boston Marathon?" The answer by and large was "Yes." Conducting this experiment were top flight trainers and experts in exercise physiologys.
One surprising thing was the finding that among these sedentary volunteers there was a wide range of fitness as measured on their high tech fitness measuring machines. People who are thin are automatically fitter than fat people, even if they don't exercise regularly. It's intrinsic and genetic like obesity.
Before and after their training, these candidates underwent a DEXA scan, which is a kind of soft tissue X-ray of their bodies. You can see all the bulges and the overall shape and the size of the fat deposits on a DEXA scan. The DEXA scans showed no change in shape and percentage of body fat after the training. The before and after DEXA scans can be overlayed and matched up. The ones who were overweight to start with were still overweight and had not shed any pounds except for Betsy who was dieting. How did they explain this?
Narrator:"Part of the problem is that running doesn't consume as many calories as one might hope, not even the 26.2 miles of the actual marathon."
Miriam Nelson (a commentator for this show and a well known exercise specialist):"People might be surprised at how little energy you need to expend to actually run a marathon. For my size runner, around 115 pounds, it's only about maybe 2,600 calories to 3,000 calories - only about twice as much energy as I need in the day to just maintain my body weight."
Their point is that since it doesn't cost very much, calorie-wise, to train for a marathon or run in one, it would not take much extra eating to make up for it. The reality is more complicated than that. As we will see, the calorie cost of the exercise is beside the point.
Another comment during this show by Miram Nelson after the evidence of the DEXA scans: "Diet may even be more important than the exercise for the active weight loss component. But for weight maintenance and for the prevention of weight gain, physical activity - and a fairly high volume of physical activity - is absolutely crucial."

The exercise gurus have finally begun to admit that exercise won't help you lose weight but now the party line is - if you do lose weight somehow, exercise will help you keep it off. Why would exercise help you maintain weight loss if it can't help you lose weight? I don't understand.
In Novemver, 2009 I attended the 4th annual Cleveland Clinic Obesity Summit where Timothy Church MD, PhD, MPH, (John S. McHenry Endowed Chair in Health Wisdom, Pennington Biomedical Research Center, Baton Rouge, LA) gave a talk. He is an exercise expert of some renown. During his talk he said that exercise is "indispensible for maintaining weight loss" after you accomplish it by dieting. So I raised my hand and asked what's the evidence for this? He said that I could contact him by e-mail and he would show me the evidence.
This I did and he sent me 4 articles and this e-mail:

"I apologize for the barrage of emails but it was the most efficient way to send you the information. While I just send you a few things. I literally could have sent you hundreds. I disagree on many of your points. Exercise alone CAN be effective for weight loss but it clearly is not as effective as diet + exercise and as evidenced by the papers I send exercise is critical for long term weight maintenance. It is really an efficiency issue. Most individuals are not interested in the slower approach of exercise only to promote weight loss (I do not blame them) but it certainly does work for some individuals. Clearly it is much more efficient to reduce caloric intake in order to produce quick meaningful weight loss. Over time after the individual has lost a significant amount of weight the daily energy (non exercise) will come down to the same level as the daily caloric intake and it is at this point that the calories expended from exercise become so important (weight maintenance). I hope this makes sense. Tim"

These are the articles he sent:

  • -Wing RR, Phelan S. Am J Clin Nutr 2005:82(suppl):222S-5S. and -Klem ML + al. Am J Clin Nutr 1997;66:239-46.

Both of these reports use the experience of the "more than" 4000 people in in the National Weight Control Registry (NWCR) who have managed to lose an important amount of weight and keep it off for an important amount of time. Almost all of them say that exercise is part of their secret. Despite the optimism of Wing and Phelan these people are rare birds. If you use their optimistic numbers, 80% of us never manage this feat. It is instructive to look at these people and study their success. This is interesting and can generate hypotheses but it's like studying the lives of people who have gone from rags to riches. It's anecdotal and not worth too much as evidence. I can't believe they are not hungry and miserable. How many people could you find in a national registry of anorexics?

  • -Jakicic JM et al. Arch Int Med 2008;168(14):1550-1559.

The result of this study, shown in the (corrected) figure 2 and stated in the first line of the "Results" in the abstract, is that there was no benefit of exercise for the maintenance of wt loss.
However the conclusion in the abstract says the opposite. It is based on "Post hoc analysis (that) showed that individuals sustaining a loss of 10% or more of initial body weight at 24 months reported performing more physical activity (leisure time physical activity LTPA) compared with those sustaining a weight loss of less than 10%." (This LTPA averaged more than an hour a day for the >10% loss sustainers and was on top of the exercise prescriptions that were administered.)
This post hoc finding is undermined by the observation (p1558 last line of the comment) "..Moreover, continued contact with the intervention staff and the ability to sustain recommended eating behaviors also may be important contributing factors to maintaining significant weight loss that exceeds 10% of initial body weight, which suggests that physical activity does not function independently of these other behaviors."

  • -Donnelly JE + al. Med Sci Sports Exerc. 2009 Feb;41(2):459-71.

In the abstract it says, "However, no evidence from well-designed randomized controlled trials exists to judge the effectiveness of physical activity for prevention of weight regain after weight loss"

  • -Shaw K + al. Cochrane Database Syst Rev. 2006 Oct 18;(4):CD003817.

These guys conclude: "When compared with no treatment, exercise resulted in small weight losses across studies." and "The results of this review support the use of exercise as a weight loss intervention, particularly when combined with dietary change."
This is wrong but it is not about weight loss maintenance.

To this Dr. Church replied that he basically accepted all that but....
To which I replied with a quote from Bertrand Russell. British author, mathematician, & philosopher (1872 - 1970) "In all affairs it's a healthy thing now and then to hang a question mark on the things you have long taken for granted."

To which he has not replied.

Prevention of obesity with exercise

How about exercise to prevent weight gain in the future? This is a slightly different question, but why would exercise prevent weight gain in the first place if it can't help with weight loss or weight loss maintenance? There is this study of exercise to prevent weight gain: The March 24/31 issue of the Journal of the American Medical Association has a report of a study about exercise and weight gain prevention, at least according to it's title. (2) It was conducted with 34,000 middle aged women followed for 13 years. It seems to be a little late in the game to do a project like this with women at 54 years of age, but this study is an addendum of the Women's Health Study that was started in 1992 to test a different question - whether aspirin and vitamin E could help prevent heart disease and cancer.
At the beginning they weighed the women and asked them how much they exercised. They divided them according to the exercise they said they did into 3 groups - greater than 1 hour/day, less than 20 minutes/day, and in between. They rechecked the exercise reports 5 more times during the 13 years. Their figure 2 shows that the highest exercise group weighed the least at the start and the lowest exercise group weighed the most, but then they all gained the same amount over the 13 years. There's an interesting dip in the weight gain at year 10 in all 3 groups. What was that from?
Anyway, the women who were normal weight at the start, and who said they exercised at least 60 minutes per day for the whole 13 years, were less likely to gain the 5 lbs that everybody else gained no matter how much they exercised. It's impossible to say whether the normal weight people who did not gain at least 5 lbs/year were just more likely to be able to exercise >60 mins per day or whether exercising that much prevented the weight gain in this select group. It's perfectly reasonable to think it's the former. Why would this much exercise only help normal weight people?
Maybe older women and the rest of us should be exercising 2 hours, or 3 or 4 per day. But 60 minutes a day of moderate intensity exercise, like running, biking or swimming, is a lot, even though 35% of these women said they did that much. I run triathlons and I don't average more than 1 hour per day. I am also fat and slow.
I think we can safely add "prevention of future weight gain" to our list of things that exercise won't do except maybe for women who are normal weight at age 54 and exercise a lot. But less than and hour a day won't even help them.

What about if you diet and exercise at the same time?

This might seem like a good strategy to try and preserve muscles relative to fat. Exercise and diet together are no better than diet alone. Demonstrating this is a ancient study (3) where 12 overweight patients were brought into the hospital for 4 weeks and given a very low calorie diet of liquid protein and coarbohydrate. Six of these study subjects sat around and 6 performed an exercise program. Both groups lost the same amount of fat and lean body tissue. So exercise contributed nothing to the weight loss. More important was the finding that resting oxygen consumption fell in the exercise group 17% more than in the sedentary group. Oxygen consumption is an indirect measure of calorie consumption and metabolism. So this is different than the evidence from Weigle mentioned above. When you lose weight by dieting only your activity energy cost goes down. But if you diet AND exercise your resting energy costs go down too.
These authors, ever enamored of the idea that exercise is supposed to help somehow, said that maybe 4 weeks isn't long enough to benefit from exercise in a weight reduction program or maybe exercise programs should come after the weight loss from dieting. If a little exercise doesn't help maybe a lot more will.

Exercise is good

It is a bright and shining lie to say that exercise will help you lose weight. But maybe we should keep that a secret, as apparently it has been for awhile, because exercise is so very good for you.
Exercise will improve you blood pressure and cholesterol. Exercise will make you live a lot longer. It even makes you happier and smarter.
Demonstrating how exercise can improve psychological wellbeing is a study from the United Kingdom. (4)
They divided 81 obese adolescents into three groups. The first third did an 8 week exercise program. Another third did stretching and played sedentary games; that was the "exercise placebo." The final third were just followed for the same 8 weeks on a waiting list.
They found significant improvements in self-worth, and self-esteem and physical activity in the daily lives of the exercised adolescents. There was no change in BMI from exercise.
These authors point out that obese children have a poor quality of life that is similar to that of pediatric cancer patients. Some of their subjects were even suicidal. So in the treatment of obesity, improving self esteem is important and exercise is good for that.
They also point out that compliance with the exercise program was good "which suggests that obese adolescents are motivated enough to engage in regular exercise when they are provided with opportunities and support to do so." What they don't say explicitly was whether these kids thought that the exercise program would help with their obesity. Still these kids were much happier at the end even though they didn't lose any weight. Maybe we don't have to lie.

Exercise magic

Ok, how about this idea.
We know that calorie restriction increases longevity in mice and dogs and every animal so far tested and so probably in humans too. The increase is quite amazing - 20 - 50%. For humans that would mean living to age 130 or so.
Exercise has also been shown to make you live significantly longer (though not as long as calorie restriction) and the life extending benefit of exercise has actually been demonstrated in humans.
What does exercise and calorie restriction have in common?
Well, calorie restriction - eating barely enough to survive, but not so little that you starve to death, because that wouldn't increase longevity - lowers your your heart rate and your blood pressure and lowers the energy cost of activity. One theory for how it works to increase longevity is that it sort of slows down the clock.
Regular exercise and getting fit does those same things. So eating less makes you live longer and exercise makes you eat less. You will use a few extra calories while you're exercising but unless you race in the Tour de France or you are Micheal Phelps in training, on balance you're burning a lot less.
The difference is that calorie restriction is worse than death, but exercise, though temporarily painfull during your run or swim, is nowhere near as stressful. Exercise actually takes less time too. Calorie restriction makes you hungry and tired and miserable and impairs your productivity. Exercise does the opposite. Also exercise can be done while learning Chinese.
For those of you sitting in the back row and not paying attention, there is one other big difference: calorie restriction will make you lose weight but exercise will NOT help you lose weight or keep it off.

1. Weigle DS. Weight loss leads to a marked decrease in nonresting energy expenditure in ambulatory human subjects. Metabolism 1988;37:930-6.

2. Lee I-m, Djousse L, Sesso HD, Wang L,Buring JE. Physical activity and weight gain prevention. JAMA. 2010;303(12):1173-9.

3. Phinney SD et al. Effects of aerobic exercise on energy expenditure and nitrogen balance during very low calorie dieting. Metabolism 1988;37:758-65.

4.Daly JD, et al. Exercise therapy as a treatment for psychopathologic conditions in obese and morbidly obese adolescents: A randomized, controlled trial. Pediatrics 2006;118:2126-34.