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

A 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 looked at 493 studies carried out between 1969 and 1994 [5].

Miller and his associates wanted to determine whether adding aerobic exercise to a low-calorie diet accelerates weight loss. And what he found was that diet and aerobic exercise provides only a very marginal benefit (in terms of weight loss) when compared to diet alone.

The 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 study completed at Appalachian State University also shows that aerobic exercise has little effect on body composition over a 12-week period [9].

The research team assigned a group of 91 obese women to one of four groups. Group one followed a restricted calorie diet (1,200 – 1,300 calories per day), while group two performed aerobic exercise for 45 minutes, five days each week. A third group combined exercise and diet. The fourth group acted as controls.

The exercise-only group lost just three pounds. This is despite the fact they exercised for almost four hours each week. Not surprisingly, the women combining diet and exercise got the best results, losing 16 pounds of fat. However, this was only one pound more than the group on the diet.

These disappointing results led the researchers to conclude that aerobic exercise has only a “minor, nonsignificant effect” on fat loss.

A study at Pennsylvania State University shows similar results [4]. A group of men took part in a 12-week program of diet and exercise. Half the men dieted, while the rest used a combination of diet and aerobic exercise.

Despite the fact they trained three times each week for up to 50 minutes, under the watchful eye of certified personal trainers, the exercise and diet group lost only one pound more fat than the diet-only group.

Research carried in the Journal of Applied Physiology also shows that aerobic exercise has a minor effect on fat loss [11]. A group of 24 obese men was assigned to either a low- or high-intensity exercise group for 12 weeks. The men were told to maintain their dietary habits during the study.

The exercise program consisted of cycling at either low-intensity (40% VO2max) or high-intensity (70% VO2max) three times per week. Each workout burned about 350 calories. The duration of each workout for subjects in the low-intensity and high-intensity training program was 57 and 33 minutes, respectively.

After analyzing the results, the researchers conclude that exercise training “did not lead to significant changes in body weight and body composition.”

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 the challenge for researchers is to stop people dropping out. When a research group from the University of Georgia attempted to examine the effect of aerobic exercise on fat loss, more than half the subjects quit before the study was finished [3]!

However, 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 [13].

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 [13].

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 [8].

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 the metabolic rate does not rise at all [2, 8].

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. Moderate-intensity aerobic exercise (such as walking or jogging) has very little effect.

Why does aerobic exercise deliver such small returns?

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

One pound of fat contains the equivalent of roughly 3,500 calories. So, assuming your calorie intake remained static and your weight was stable, you’d need to burn an extra 500 calories per day to drop just one pound of fat over the course of a week.

To lose fat at a decent rate (around two pounds per week) you’d need to burn 1000 extra 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 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 [6].

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.

And that brings us to another problem.

Most modern exercise machines have digital readouts telling you how many calories you’ve burned. Unfortunately, these digital readouts can’t always be trusted.

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.

Another factor that affects the reliability of calorie counters is the difference between net and gross calorie expenditure.

Gross energy expenditure refers to the number of calories you burn during exercise plus your metabolic rate. Net energy expenditure refers to just the number of calories you burn during exercise. Because calorie counters on some exercise machines display gross energy expenditure, the figures they give can be misleading.

In one study, the gross number of calories burned during each workout was estimated to be 255 calories [9]. But the net figure (remember, the net figure represents the “real” number of extra calories you’ve burned) was just 187 calories.

In other words, if you rely on the numbers given by the calorie counters, it might appear that you’ve burned more calories than you really have.

The bottom line

Although it comes as a surprise to many, the majority of research shows that aerobic exercise in the so-called “fat burning zone” is not a very effective way to lose fat.

That’s not to say that cardio is a waste of time, because it isn’t. But in most cases, 30 to 40 minutes of moderate-intensity cardio three or four times a week by itself 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 weight requires both.

About the Author

My name is Christian Finn. I run a private "members only" website designed to help people burn fat, build muscle and get strong. If you want accurate, honest and in-depth reviews on the latest "hot topics" in the world of fitness, you're confused by all the conflicting advice out there, or you just want some training routines that will give you better, faster results, click here now to learn more about how I can help you.

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References

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