Why Exercise DOES Matter

AAA!! All those gym hours wasted! Whyyyy?!?!

A few weeks ago Time magazine came out with an article saying that exercise didn’t help people lose weight.

It made great headlines.

People in gyms cried heresy. Trainers tearfully defended their jobs. In worldwide riots, millions of people burned their sneakers, then looted La-Z-Boy dealerships. (This may be a slight exaggeration.)

But what if I say:

a) it’s true and
b) this isn’t really news?

The truth is that unless you’re cross-country skiing to the North Pole, exercise alone doesn’t necessarily help people lose weight. JB gave a link in last week’s newsletter to one of his studies showing the same thing. The key is exercise alone without some sort of dietary restriction will not inevitably lead to weight loss.

It makes sense: if you work out and expend a certain amount of calories and then go off and eat just as many or even more — then you’re not going to lose weight.

What about dieting?

So if exercise (alone) doesn’t make you skinny then dieting must make you skinny – right? The study I’m reviewing this week looks at different calorie restrictions (aka diets) and weight loss. It also looks at one more very important thing: metabolic changes.

Redman LM, Heilbronn LK, Martin CK, de Jonge L, Williamson DA, Delany JP, Ravussin E; Pennington CALERIE Team. Metabolic and behavioral compensations in response to caloric restriction: implications for the maintenance of weight loss. PLoS One. 2009;4(2):e4377. Epub 2009 Feb 9.

By the way the E. Ravussin whose lab did this study is the same one quoted in the Time article as follows:

“In general, for weight loss, exercise is pretty useless,” says Eric Ravussin, chair in diabetes and metabolism at Louisiana State University and a prominent exercise researcher.

I don’t want to give anything away, but to say exercise is useless for weight loss is misleading given his own data.

Methods

This study used 48 healthy, overweight (BMI between 25-30) men and women about 38 years old. The average percent body fat was 24.8% for the men and 37.6% for the women. They didn’t smoke, exercise (more than 2 times/week) or have a history of diabetes, cardiovascular disease, eating disorders, substance abuse, regular use of medications or obese (BMI>32). None of the women were pregnant or lactating.

Groups

Participants were randomly assigned to four groups:

1. Control – healthy weight maintenance based on the American Heart Association (AHA) step 1 diet (more on that later)
2. Calorie restricted (CR) – caloric restriction that was 25% fewer calories than baseline requirements
3. Calorie restricted + exercise (CR+EX) – caloric restriction that was 12.5% fewer calories than baseline requirements AND 12.5% increase in energy expenditure from structured aerobic exercise. More about the exercise details a little later.
4. Low calorie diet (LCD) – a 890 kcal/day diet until 15% reduction in body mass was achieved, then the participants followed a weight maintenance diet.

Control – Step I diet

The control group ate a maintenance diet based on the American Heart Association Step I diet, which restricts total fat, saturated fat and cholesterol – kinda the old “fat is bad for you” mentality.

As the AHA describes, “The Step I diet restricted total fat to no more than 30 percent of total calories, saturated fat to no more than 10 percent of total calories, and cholesterol to less than 300 mg/day. It was intended as the starting point for patients who had high cholesterol levels.”

Exercise description for the calorie restricted + exercise group

To reach a 12.5% increase in energy expenditure – i.e. to burn about 403 cals/session for the women and 569 cals/session for the men – the participants did steady state cardio for an average of 53 minutes for women and 45 minutes for men.

Yup, for five days a week these poor souls did cardio for over 45 minutes — totalling about 3 hours and 45 minutes a week for the men and almost 4 ½ hours for the women. Needless to say it’s probably not the optimal way to burn calories, but it does get close to JB’s recommended 5 hours/week of activity to lose weight.

Measuring metabolism

Everybody has heard and uses the term “metabolism”, usually in sentences like: “I have a slow metabolism” or “That skinny bitch can eat whatever she wants — she must have a fast metabolism.”

But what is metabolism, really, and how can you figure out what your metabolism is?

Well, metabolism is a sum of all the enzymatic process, but that’s not what people mean when they say metabolism. What they really want to say is total daily energy expenditure (TDEE), but that doesn’t sound as good. (Try it: “I have a slow TDEE.” Doesn’t really roll off the tongue, does it?)

There are a couple ways to measure TDEE: indirect calorimetry and a high-tech way called doubly labelled water.

Indirect calorimetry

This has been around for a while, and although it works, it’s hard to do. Basically, all the oxygen and carbon dioxide you breathe in and out has to be measured, so that means you either breathe through a mask or in a airtight room. For more details you can go to this link.

Doubly labelled water

This is the not-so-new, but improved, technique that allows you to walk around and do what you normally do without wearing a mask or being in a bubble. Although the doubly labelled water technique has also been around for a while it was pretty expensive. However, in the last few years the cost of the water and the analysis has gone down enough to use regularly.

The technique is based on two types of water isotopes – H₂¹⁸O and ²H₂O. By drinking a given amount of each of the two water isotopes and then measuring how much of the isotope is in the urine, testers can figure out how much energy is expended.

Warning! Science stuff!

After giving two urine samples each participant drank 2g of a 10% enriched H₂¹⁸O (0.2g of H₂¹⁸O) and 0.12g of ²H₂O per kilogram of total body water – based on DXA (dual x-ray absorption). Urine samples were collected after 4.5 hours, 6 hours, 7 days and 14 days. Each urine sample was analyzed for ¹⁸O and ²H (by mass spectrometry) to show the by-products of the isotopic water being broken down.

Why bother with all this water?

Well if you know how much ¹⁸O and ²H show up in the urine after drinking the waters, then you can figure out how much CO₂ is being made by the person. Once you know how much CO₂ is produced you can calculate how much energy they made.

The basic idea is that CO₂ in the body isotopically equilibrates with the O₂ in the body water (meaning the special oxygen, ¹⁸O, from water likes to be equally spread out). Then since some of ¹⁸O is in the form of CO₂ (C¹⁸O₂ ) it gets breathed out. So if you drink some water with special hydrogen, ²H, all the ²H is going to come out as urine, but water with special oxygen, ¹⁸O, will come out as urine and as CO₂. Since you know the ratio of ²H and ¹⁸O going in you can figure out how much ¹⁸O was breathed out as CO₂. If you’re really interested in the technique and equations to calculate TDEE you can read two articles by Schoeller (1,2).

Results

After 6 months the calorie restricted groups and calorie restricted group with exercise lost about 10% of their body weight (control lost 1%). In terms of weight they lost between 8-11 kg on average, with the low calorie restricted diet group losing the most (11kg).

So exercise doesn’t matter – right?

Not so fast.

It turned out that exercise mattered a lot to TDEE (total energy expenditure) or metabolism.

You see, with diet alone, after 6 months on average TDEE went down by 209 cal/day on the 25% calorie restricted diet (CR) and 275 cal/day on the low calorie restricted diet (LCD). Meanwhile, if exercise was added to a 12.5% calorie restricted diet (CR+EX), TDEE went up by 129 cal/day. Note: the values listed in the abstract are nowhere to be found in the results section… weird.

At the 3 month point things were worse for the diet groups, with TDEE being down by 371 cal/day for the CR group and 496 cal/day for the LCD group. Holy cow! That’s a meal. For the CR+EX group they did have slightly lower TDEE, 2 cal/day on average – nothing to write home about.

You can’t explain differences in TDEE by increased muscle mass since there were no differences in body composition (body fat and fat free mass) between the three groups (CR, LCD and CR+EX). You wouldn’t expect much of an increase in muscle mass, given that the exercise was steady state cardio.

Another thing was that the CR and the LCD participants were a lot less physically active after 6 months of dieting compared to when they started. Combining the two groups there was over 100 cal/day reduction in physical activity.

Conclusion

This is your TDEE on caloric restriction without exercise

While the scale may say that exercise doesn’t matter, based on this study it does matter – to your metabolism.

The authors in the study concluded that exercise was key to stopping “metabolic adaptation” or what we would call metabolic slowing. Metabolic adaptation was not only basic biology, but psychological. Biological, because your body becomes more energy efficient in the fact of caloric debt and psychological, because when in an energy deficit, you avoid physical activity to save calories.

The last point in the article is this:

“Furthermore, our data shed some light on lifestyle change interventions that combining diet and physical activities are probably more successful in maintaining weight loss longer term.”

Did I mention this same guy who was quoted in the Time article saying exercise was useless?

Bottom line

In this study, while exercise didn’t make a difference on the scale or even in how much fat was lost, exercise while restricting your diet did matter for maintaining metabolic function. So if you don’t mind being less active and eating 300 calories less a day while being more likely to regain the weight you lost… then sure, exercise doesn’t matter. But if you like your metabolism as it is or want it to burn a few more calories a day then exercise DOES matter.

References

1. Schoeller DA. Measurement of energy expenditure in free-living humans by using doubly labeled water. J Nutr. 1988 Nov;118(11):1278-89. Review.

1. Schoeller DA, Ravussin E, Schutz Y, Acheson KJ, Baertschi P, Jéquier E. Energy expenditure by doubly labeled water: validation in humans and proposed calculation. Am J Physiol. 1986 May;250(5 Pt 2):R823-30.