Weight Loss and Exercise: Why Cardio Alone Won’t Cut it

weight loss exerciseA lot of people are told they can expect to lose up to two pounds of fat each week with a program of regular aerobic exercise.

Some do. But a lot of people fail to see anything in the way of meaningful results, even after months of trying.

It’s easy to think the problem lies with you. Is it because your metabolism is slow? Are you getting older and burning calories at a slower rate? Is it in your genes? You stick to the program, and still you don’t lose any weight.

What’s going on?

If you’re not losing weight, it’s probably not your age, your metabolism, or your genetics that are causing the problem. It’s simply the fact that conventional aerobic exercise programs are not a particularly effective way to drop the pounds.

By aerobic exercise, I mean things like cycling, walking, rowing or jogging, usually done 3-4 times each week for 20-60 minutes in the so-called “fat burning” zone.

Despite what we’ve been told, this type of program has only a minor effect on weight loss. There’s been enough research over the last 25 years to convince almost anyone that aerobic exercise alone is not a very effective way to lose weight.

Let me give you a few examples…

In a review of several hundred weight loss studies, Dr. Wayne Miller and colleagues at The George Washington University Medical Center set out to determine if adding aerobic exercise to a low-calorie diet accelerates weight loss.

What they found was that diet and aerobic exercise provides only a very marginal benefit (in terms of weight loss) when compared to diet alone.

Average weight loss after a 15-week program of regular aerobic exercise was seven pounds. Over the same period, dieting cut weight by roughly 17 pounds. When exercise and diet were combined, average weight loss was 20 pounds — just three pounds more than diet alone.

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.”

One of the main criticisms of weight loss studies is the small number of participants they use. The more people that take part in a study, the more reliable the results. But even with a large number of subjects, the results aren’t much better.

As part of the HERITAGE Family Study, one of the largest well-controlled training studies of its kind, researchers followed a large group of 557 men and women as they embarked on a 20-week exercise program.

Each subject was required to exercise three times per week for an average of 42 minutes. Researchers even went to the trouble of having each bout of exercise monitored by an exercise technician and a computer.

Following a grand total of 60 exercise sessions over a period of almost six months, the average amount of fat lost was slightly less than two pounds, prompting scientists to admit that aerobic exercise “is not a major factor” in weight loss.

What about your metabolic rate?

One popular claim is that aerobic exercise leads to an increase in your metabolic rate. However, researchers conducting the HERITAGE Family Study found that almost six months of aerobic exercise had no effect on resting metabolic rate.

Some studies do show that elite athletes have a higher metabolic rate than weight-matched controls. However, scientists have been unable to establish whether this is due to a higher calorie intake, a superior level of fitness or if it exists simply as an after effect of their last training session.

Furthermore, when an increase in physical activity results in a calorie deficit (which it’ll need to if you want to lose weight) there is research to show that your metabolic rate won’t rise at all.

Another popular misconception is the idea that aerobic exercise increases caloric expenditure for several hours after a bout of exercise, thus making a further contribution to fat loss. Unfortunately this is not always the case.

Excess post-exercise oxygen consumption (EPOC), which is the name given to the increase in calorie expenditure following a workout, is more likely to occur after high-intensity exercise.

Lance ArmstrongAppalachian State University researchers found a large increase in EPOC after subjects cycled for 45 minutes at around 85% of their maximum heart rate, which led to a net calorie burn of 519 calories.

For 14 hours after the workout, subjects burned an extra 190 calories, which represents 37% of the net calories burned during the workout itself. Moderate-intensity aerobic exercise at 60-70% of your maximum heart rate is not going to have anything like the same impact.

Why does aerobic exercise deliver such small returns?

The most fundamental aspect of any fat loss program is to create a calorie deficit. Unfortunately, you just don’t burn off that many calories with a typical aerobic exercise program.

Let’s say that your workout creates a daily calorie deficit of 500 calories. That comes to 3,500 calories per week (500 x 7 = 3,500). If all of those calories came from fat, you’d lose just one pound in weight.

To lose fat at a decent rate (around two pounds per week) you’d need a deficit of 1000 calories per day. And the type of workout that burns 1000 calories, in terms of both time and effort, is not a realistic goal for most people.

For moderate-intensity aerobic exercise to be effective, you need to do a lot of it. Scientists from Canada, for example, report that a walking program was enough to cut body fat levels by an average of 13 pounds over three months, or just over one pound per week.

Although this is a lot more than some of the other studies we’ve looked at it, the people taking part in this trial trained for more than one hour, every single day. And not everyone has that much spare time to devote to exercise.

They were also obese, with an average body mass index (BMI) of 31. For people like this, steady-state cardio is often the ideal form of exercise. They’re storing so much extra weight that just going for a walk expends a massive amount of energy. It’s the equivalent of someone with a normal BMI walking around with a 75-pound rucksack strapped to their back.

Which brings me to another problem.

Most modern exercise machines have digital readouts telling you how many calories you’ve burned during your workout. But they can’t always be trusted to give you an accurate figure.

The most reliable way to assess energy expenditure during exercise is to measure oxygen consumption. Each liter of oxygen that you consume generates approximately five calories of energy.

For example, if you exercise for 30 minutes and consume 30 liters of oxygen, you’ll have burned 150 calories. But without directly measuring oxygen consumption, it’s difficult to get an accurate estimate of how many calories you’ve really burned.

Something else to consider is the difference between net and gross calorie burn.

If you jump on the exercise bike for an hour and burn 500 calories, you haven’t actually burned 500 extra calories.

Why not?

If you’d spent that hour lying in bed doing nothing, your body would have been burning calories just to keep you alive. To get an accurate idea of how many extra calories you’re burning during your workout you’ll need to subtract the calories your body would have burned anyway.

In other words, you’ll want to know the difference between net and gross calorie burn.

  • Gross calorie burn refers to the number of calories you burn during exercise plus resting energy expenditure for an equivalent time.
  • Net calorie burn 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 (70-80% of maximum heart rate) was 255 calories. But the net figure (remember, the net figure represents the “real” number of extra calories you’ve burned) was just 187 calories.

That’s a big difference. In fact, the gross calorie burn was over 35% higher than the net calorie burn.

If you rely on the calorie counts provided by exercise machines and online calculators, chances are you’ll come away with the impression that you’ve burned a lot more calories than you really have.

That’s not to say that cardio is a waste of time, because it isn’t. A program that combines regular strength training with a proper diet AND cardiovascular exercise is still the best way I know to get in shape.

But by itself, 30 to 40 minutes of moderate-intensity cardio three or four times a week isn’t going to deliver the results you want.

People often ask me how much of your weight loss success comes from diet and how much comes from exercise. My answer is always that it doesn’t matter. What’s more important is to accept that losing fat requires both.




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About Christian Finn

Christian FinnChristian Finn holds a master's degree in exercise science, is a certified 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. You can contact Christian using Facebook, Twitter, Google+ or via e-mail.