Last week, the subject of exercise and weight loss was in the headlines again.
The article, titled Exercising but Gaining Weight, was featured in the New York Times.
It describes the results of a study where a substantial number of people taking up cardiovascular exercise ended up with more fat at the end of the study than they had at the start .
Blog comment rage then ensued, with the cardio skeptics declaring they were “right all along” and the cardio activists denouncing the study as “completely ridiculous” and a total waste of time.
When it comes to weight loss, it’s fair to say that aerobic exercise hasn’t performed particularly well over the years.
A 2011 review that looked at 14 studies on aerobic exercise and weight loss also shows less than stellar results, concluding that the value of aerobic exercise as an “independent weight loss intervention for overweight and obese populations is limited.” 
But there are two sides to any story, and this one is no different. Before you force steady-state cardio into a small cupboard under the stairs, lock the door and throw away the key, here are some things to think about.
Steady-state cardio is an umbrella term that can refer to many different forms of exercise, ranging in intensity from low to medium to high.
Putting them all in the same category ignores the fact that 30 minutes of coasting along on the elliptical machine while watching TV and texting requires a lot less energy than the same amount of time spent cycling up Mount Ventoux as fast as your legs will carry you.
Both are forms of steady-state cardio. But the latter is going to have a much greater physical impact than the former.
Most studies out there have looked at low- or moderate-intensity cardio, which in and of itself has only a modest impact on energy expenditure and weight loss [1, 3]. High-intensity steady-state cardio is another story entirely.
As an example, researchers from Appalachian State University found that 45 minutes of high-intensity steady-state cardio (cycling at 85% of your maximum heart rate) burned over 700 calories – 519 during the workout itself and 190 after it had finished . And that was net rather than gross calorie expenditure.
What’s the difference between net and gross energy expenditure?
Let’s say that you jump on the bike in the gym. When you get off, the digital readout says that you’ve burned 500 calories. But those aren’t necessarily 500 extra calories.
Why not? If you’d spent that time sitting in front of the TV doing nothing, your body would have been burning calories anyway.
Gross calorie expenditure refers to the number of calories you burn during exercise plus resting energy expenditure for an equivalent time. Net calorie expenditure refers only to the extra number of calories you burn during exercise.
How much of a difference is there between the two numbers?
In one study, the gross number of calories burned during 45 minutes of aerobic exercise was 255 calories. But the net figure, which represents the “real” number of extra calories burned, was just 187 calories .
Here’s something else that’s very important.
Most studies report only the average results for a group of people. But this can mask large differences in individual results.
When some people increase the amount of exercise they do, they get very hungry. This leads them to eat more, which ends up reducing the calorie deficit created by exercise.
Researchers have labeled them compensators, because they compensate for the calories burned during exercise by eating more.
Take a look at the figure below, which comes from a study looking at the variability in weight loss following 12 weeks of supervised exercise . It shows individual changes in both weight (BW) and fat mass (BF).
Don’t pay too much attention to the changes in body fat. It was measured using BIA (the technology used in body fat scales), which is not a reliable way to track changes in body composition over time.
When the data from all the subjects was pooled, the average drop in weight was eight pounds.
However, there was a large variability in the amount of weight lost. One subject lost 32 pounds. But another subject taking part in the exact same study gained almost four pounds.
The non-compensators – that is, the people who didn’t compensate for the calories burned during exercise by eating more – reduced their calorie intake by an average of 131 calories per day. But the compensators ended up eating more, increasing their calorie intake by an average of 268 calories per day.
Many studies show that cardio produces little in the way of weight loss. But that doesn’t mean everyone in the study got the same results. Weight loss in one set of subjects may simply have been “cancelled out” by weight gain in another
To give you an idea how exercise can vary in its effectiveness as a tool for weight loss, I’m going to compare two people, both of whom are doing exactly the same thing in the gym.
The first is a 250-pound overweight male. He’s a non-compensator, and doesn’t get extremely hungry when he does more exercise.
The second is a 150-pound overweight female, who tends to compensate for the calories burned during exercise by eating more. She gets very hungry whenever the amount of exercise she does exceeds a certain threshold. Keeping her food intake under control is a constant struggle.
They both go to the gym 4-5 days a week, for around 45 minutes. Most of that time is spent walking on a treadmill set on a slight incline.
The male has one big advantage that makes exercise a lot more effective where weight loss is concerned. Namely, that he’s carrying around an extra 100 pounds.
Simply going for a walk burns off a large number of calories. It’s the equivalent of someone with a normal BMI walking on the treadmill with a heavy rucksack strapped to their back.
What’s more, he doesn’t find that exercise makes him significantly hungrier than before. So he’s able to create a much larger energy deficit, which in turn means a faster rate of weight loss.
Our 150-pound overweight female burns fewer calories during exercise. She also ends up either partially or completely compensating for the calories burned during a workout by eating more food. As a result, her rate of fat loss will be significantly slower.
So even though we have two people, both with the same goals, and both following the same exercise routine, the potential exists for them to experience very different results.
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ABOUT CHRISTIAN FINNChristian Finn holds a master's degree with distinction in exercise science, is a former personal trainer and has been featured on BBC TV and radio, as well as in Men's Health, Men's Fitness, Fit Pro, Zest, and Perfect Body magazine.
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