It is heavily influenced by my experience as a personal trainer in the early 1990's. During that time, I saw literally hundreds of people try — and fail — to speed up weight loss with a program of regular aerobic exercise.By aerobic exercise, I mean things like cycling, walking, rowing or jogging, usually performed for between 20 and 60 minutes in the so-called "aerobic training zone." Interval exercise, on the other hand, especially when you get the length of the work and rest intervals right, is another story entirely.
Despite what we've been told, aerobic exercise has very little effect on weight loss. There's been enough research over the last 25 years to convince almost anyone that aerobic exercise programs are not a very effective way to promote weight loss.
Weight loss
Most people begin an exercise program designed for weight loss with the intention of sticking with it. Unfortunately, the majority give up after six months, deciding they simply don't have the time to exercise regularly.
There are usually two reasons behind any decision — the real reason, and the one that sounds good! Individuals claiming, "they don't have the time" are often hiding the fact that their expectations were not met. Simply put, they were not making the progress they were promised. For many people, the benefits of aerobic exercise are not enough to justify the time and effort you put in.
On an intellectual level, most people know they "should do more exercise." However, any good salesperson will tell you that we don't make decisions based on intellectual reasoning. We base them on emotion.
Most of us exercise because, at a very basic level, we want to look and feel better. We exercise because it appeals to our sense of vanity and pride. We want to look and feel good.
The problem comes when there is a conflict between the results you expect from aerobic exercise, and what you actually get. Many people starting an exercise program are told they can expect to lose around two pounds of fat each week. 
Some people do. But the majority doesn't.
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?
Although it comes as a surprise to many, the majority of research shows that aerobic exercise has only a minor effect on weight loss.
Some evidence for this comes from a review of several hundred weight loss studies conducted by Dr. Wayne Miller and colleagues at The George Washington University Medical Center [5].
The team examined 493 studies carried out between 1969 and 1994. Miller and his associates wanted to determine whether adding aerobic exercise to a low-calorie diet accelerates weight loss. Twenty-five years of weight loss research shows 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 [7].
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 were exercising 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 [10]. 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 [21].
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."
Aerobic exercise again failed to deliver any meaningful results when the training frequency was increased to five times per week. A team of Canadian researchers, publishing their findings in the Journal of Applied Physiology, followed a group of men and women for four months [16]. Half the group followed a restricted calorie diet, while the rest combined the diet with five days a week of cross training (a mixture of treadmill walking, cycling and stepping).
At the end of the program, scientists were at a loss to explain why the diet and exercise group had lost just one-half pound more than the diet-only group, describing their findings as "perplexing".
In one 1997 study carried in the journal Medicine and Science in Sports and Exercise, group of adult males lost just four pounds in weight — despite three hours of exercise every week for 14 weeks [11]. Hardly the dramatic results we're promised when joining a gym.
Many people believe they need to spend six hours or more in the gym each week to get the results they're looking for [9]. And it's true that for aerobic exercise to be effective, you need to do a lot of it. Scientists from Canada report that three months of aerobic exercise was enough to cut body fat levels by an average of 13 pounds [15]. However, the brave souls who volunteered for this study trained for more than one hour, every single day, for three whole months.
Personally, all that aerobic exercise would bore me silly. The exercise program I use to shed fat requires that I spend no more than five hours in the gym each week. It's virtually identical to the program you'll read about elsewhere on this site. That's not because I'm lazy. It's just that I don't have the time (or the motivation) for the marathon workouts that all the "experts" tell me I need.
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. The challenge for researchers is trying 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 [12]!
This shouldn't come as a surprise, especially when you consider the fact most subjects make such little progress.
In an attempt to make their study more reliable, researchers designed the HERITAGE Family Study, describing it as the largest, well-controlled training study of its kind [13]. A large group of 557 men and women was followed 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.
Calorie counters
This isn't surprising when you consider how many calories are contained in a pound of fat — the equivalent of roughly 3,555 calories. The most fundamental aspect of any fat loss program is to create a calorie deficit — to burn more calories than you eat. Unfortunately, aerobic exercise burns around 187 calories per session [7]. Based on this estimate, you'll need 19 workouts, each lasting 45 minutes, to lose just one pound of fat.
This figure might come as a surprise if you use the calorie counters on exercise machines to monitor calorie expenditure during a workout. Unfortunately, these digital readouts are not always accurate. 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. Without directly measuring oxygen consumption, it's difficult to get an accurate estimate of energy expenditure during a workout.
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 (but not all) exercise machines display gross energy expenditure, the figures they give can be misleading.
A good example comes from a trial carried in the International Journal of Sport Nutrition [7]. A group of overweight women took part in an aerobic exercise program. The program involved 45 minutes of aerobic exercise, performed in the so-called aerobic training zone (70-80% of maximum heart rate).
The average number of calories burned during each workout was estimated to be 255 calories. However, this figure doesn't take into account the difference between net and gross caloric expenditure.
The gross number of calories burned was 255. In contrast, 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.
Muscle loss
When you lose weight from dieting alone, some of the weight lost comes from lean muscle tissue. Some experts believe that aerobic exercise prevents this reduction in muscle mass. But the facts tell a different story. Several studies show that diet and aerobic exercise both lead to a drop in muscle tissue [10, 15]. Aerobic exercise won't offset the loss in lean muscle caused by dieting.
When you lose weight by dieting, roughly seven of every 10 pounds lost over a 12-week period come from fat. Adding aerobic exercise doesn't prevent the loss of muscle. But it does reduce it slightly. You'll get better results when you combine the right diet with aerobic exercise and resistance training. Virtually all of the weight you lose with this kind of program will come from fat [10].
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 has no effect on resting metabolic rate [13].
Some studies do show that elite athletes do have a higher metabolic rate than weight-matched controls. However, scientists have been unable to establish whether this is due to a high calorie intake, a superior level of fitness or if it exists simply as an after effect of their last training session [6]. Furthermore, when an increase in physical activity results in a calorie deficit, there is evidence to show that the metabolic rate does not rise at all [6, 14].
Another popular misconception is the idea that aerobic exercise increases caloric expenditure 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 (the name given to the increase in caloric 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 on post-exercise metabolic rate.
Does this mean that aerobic exercise is a waste of time? Definitely not.
Weight gain
There is evidence to show that aerobic exercise helps to prevent the gain in weight that often happens following a period of dieting [2]. It's extremely difficult to stick to the kind of diet needed to maintain weight loss. As a result, many people soon return to their original weight.
Aerobic exercise plays a vital role in helping you maintain a healthy body weight. The National Weight Control registry contains a listing of subjects who have lost at least 30 pounds of weight, and kept it off for at least 12 months.
Although the people on the register use a number of different strategies to reduce body fat, the one thing they have in common is a commitment to regular exercise [4]. Scientists from George Washington University also report that regular exercise helps to maintain higher levels of weekly fat loss 12 months after starting a diet [5].
Researchers at Maastricht University have shown that just ten weeks on a very low-calorie diet actually reduces the number of fat calories your body burns each day [8]. This post-diet drop in fat oxidation could explain why many people find it difficult to stop the weight coming back once they've lost it.
A group of 40 overweight men took part in the study. They were assigned to one of two groups. One group dieted, while group two combined the diet with a program of regular aerobic exercise. The men in the exercise group completed three sessions per week, consisting of walking and underwater exercise. Each workout lasted for around one hour.
During the first six weeks of the study, subjects in both groups were given a very low-calorie diet providing just 500 calories daily. From weeks 7 to 10, they gradually increased their food intake.
Both groups lost roughly the same amount of fat and muscle. However, the subjects who didn't exercise had a reduced capacity to burn fat, both at rest and during exercise. The good news is that exercise served to prevent this decline.
What this means is that the benefits of low-intensity aerobic exercise are more apparent when you're trying to keep the weight off. The exercise doesn't have to be particularly vigorous or demanding. Just three hours of walking each week is enough to prevent the post-diet decline in fat oxidation.
Physical activity as part of a fat loss strategy also appears to encourage healthier eating patterns. Individuals who exercise frequently may perceive food as "activity fuel", and place greater importance on the quality of their diet.
Californian researchers have identified a direct link between physical activity and various markers of dietary quality [3]. They found that physical activity was associated with healthy eating habits, such as eating fruit and vegetables. More physically active individuals are also less likely to eat foods with a high calorie content.
That said, there are also people who eat what they want, then do hours and hours of exercise in an attempt to burn it off again. This is mistake. When it comes to shedding fat while preserving lean muscle, one of the most important hormones is testosterone. Although testosterone is considered a muscle-building hormone, there are studies showing that it also helps to cut body fat.
Unfortunately, too much exercise can lower testosterone. Endurance-trained men, for example, have lower testosterone levels than men of the same age who never exercise [19]. Men with low testosterone levels are also more likely to develop a pot belly [17].
In short, trying to make up for a poor diet by doing a lot of aerobic exercise is not a good idea.
Subcutaneous fat
Publishing their findings in Medicine and Science in Sports and Exercise, Japanese researchers have shown that dieting leads to a greater reduction in visceral fat [1]. Exercise, on the other hand, has a greater impact on subcutaneous fat. Subcutaneous fat (pronounced sub-cue-tain-ee-us) is stored just under your skin. Visceral fat (pronounced viss-er-al) surrounds and protects your internal organs.
The women in the study took part in a 13-week program that combined exercise with a restricted-calorie diet. One group followed the diet, combined with 1-2 days per week of exercise. Group two made no change to their diet, but exercised 3-4 days each week.
Both groups lost roughly the same amount of fat. In the group who exercised more frequently, six of every 10 pounds of fat lost came from subcutaneous fat. However, in the group who exercised less frequently, less than three of every 10 pounds of fat lost came from subcutaneous fat.
Energy flux
Aerobic exercise also allows for a higher energy flux, which refers to the flow of calories (or energy) through your body.
A high energy flux means that you're eating a large number of calories, but balancing that with an equally high volume of exercise. A good example of someone with a high energy flux would be a cyclist taking part in the Tour de France. Despite the fact these athletes eat thousands of calories each day, they're still able to remain lean simply because they're doing so much exercise.
An example of a low energy flux would be someone following an extremely low-calorie diet while doing little or no exercise.
A high energy flux is linked with a high metabolic rate. Endurance-trained males, for example, in a high state of energy flux have a higher metabolic rate compared with a low energy flux state.
As they age, people are generally less physically active. The result is that they burn fewer calories each day. Unless they eat less to compensate for this reduction in calorie expenditure, weight gain is the inevitable result.
The good news is that you can minimize the age-related drop in basal metabolic rate by maintaining a high energy flux — balancing a higher calorie intake with an equally high volume of exercise. Not only will this help you to stay lean, it's also a great way to provide your body with more of the vitamins, minerals and other nutrients it needs.
The bottom line
Many people starting an exercise program are told they can expect to lose around two pounds of fat each week. Some people do. However, the majority doesn't.
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.
Although it comes as a surprise to many, the majority of research shows that aerobic exercise — such as waking, jogging, cycling or rowing — in the so-called "aerobic training zone" is not a very effective way to lose fat.
At best, you can expect to lose between one-quarter and one-half pound of fat per week, depending on how much aerobic exercise you do.
Regular exercise is important because it promotes the loss of subcutaneous fat. Subcutaneous fat is stored just under your skin. Visceral fat surrounds and protects your internal organs.
Aerobic exercise also allows for a higher energy flux, which refers to the flow of calories (or energy) through your body. This lets you balance a higher calorie intake with an equally high volume of exercise. Not only will this help you to stay lean, it's also a great way to provide your body with the vitamins, minerals and other nutrients it needs.
References
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2. Buemann, B., & Tremblay, A. (1996). Effects of exercise training on abdominal obesity and related metabolic complications. Sports Medicine, 21, 191-212
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7. Utter, A.C., Nieman, D.C., Shannonhouse, E.M., Butterworth, D.E., & Nieman, C.N. (1998). Influence of diet and/or exercise on body composition and cardiorespiratory fitness in obese women. International Journal of Sport Nutrition, 8, 213-222
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9. Timperio, A., Cameron-Smith, D., Burns, C., Salmon, J., & Crawford, D. (2000). Physical activity beliefs and behaviours among adults attempting weight control. International Journal of Obesity, 24, 81-87
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12. Evans, E.M., Saunders, M.J., Spano, M.A., Arngrimsson, S.A., Lewis, R.D., & Cureton, K.J. (1999). Body-composition changes with diet and exercise in obese women: a comparison of estimates from clinical methods and a 4-component model. American Journal of Clinical Nutrition, 70, 5-12
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16. Ross, R., Rissanen, J., Pedwell, H., Clifford, J., & Shragge, P. (1996). Influence of diet and exercise on skeletal muscle and visceral adipose tissue in men. Journal of Applied Physiology, 81, 2445-2455
17. Tsai, E.C., Boyko, E.J., Leonetti, D.L., & Fujimoto, W.Y. (2000). Low serum testosterone level as a predictor of increased visceral fat in Japanese-American men. International Journal of Obesity and Related Metabolic Disorders, 24, 485-491
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