Research unearths another reason why exercise is not particularly effective for the purposes of weight loss

Despite repeated calls for us to be more active in order to counter rising rates of overweight and obesity, the evidence suggests that activity has, generally speaking, very modest effects on body weight. I wrote quite recently about this here and here.

Generally, two main reasons for why exercise does not promote significant weight loss are cited: the calorie burn during exercise is generally quite small, and people who exercise more tend to eat more too. The result? It’s generally difficult to get into caloric deficit through exercise alone. A recent piece of research appears to have unearthed another reason why exercise has generally little impact where weight loss is concerned.

In this study, 34 overweight and obese sedentary women (average age 31) were put on an exercise programme for a period of 8 weeks. The women were instructed to exercise for a total of 150 minutes a week at a heart rate of 135-145 beats per minute (about 75 per cent of maximum heart rate for these women). The women were assessed for a number of things including weight, body mass index and fat mass.

Overall, average weight loss was 0.15 kg (1/3 of a pound). Fat loss was an average of 0.0 kg. Basically, for the group as a whole, the exercise turned out to be thoroughly ineffective from a weight and fat loss perspective.

The authors of this study noted, however, that while average fat loss was negligible, it varied from a loss of 3.2 kg to a gain of 2.6 kg (yes, that’s right, some women gain quite considerable quantities of weight on their exercise regime). So, the authors of the study then decided to do further analysis by splitting up the group into those who lost more weight than expected (the ‘responders’) and those who lost less weight than expected (the ‘non-responders’).

Further analysis, including measurements of resting metabolic rate and total energy expenditure revealed that the lack of response to exercise was mostly explained by a reduction in activity generally. In other words, some women upped their formal exercise, but then just slowed down when they were not exercising (the ‘responders’ actually increased their activity outside of the formal exercise programme).

This study was hampered somewhat by not having a proper control group (i.e. a group not exercising). However, it again provides evidence to support the notion that, generally speaking, aerobic exercise is not very effective for the purposes of weight/fat loss. It should be said, however, that in this study did find that exercise appeared to promote fat loss in some women. And, it should perhaps be noted, women in both responder and non-responder groups saw a reduction in waist circumference, which suggests that even in those not losing fat, some healthy fat redistribution is going on.

This research also provides another potential explanation for why aerobic exercise has generally been found to be ineffective for the purposes of weight loss: in addition to relatively small calorie burn and a tendency to cause individuals to eat more, upping exercise may lead some to become more sedentary in their daily lives.


1. Manthou E, et al. Behavioral Compensatory Adjustments to Exercise Training in Overweight Women Medicine & Science in Sports & Exercise 2010;42(6):1121-1128

12 Responses to Research unearths another reason why exercise is not particularly effective for the purposes of weight loss

  1. Pål Jåbekk 25 May 2010 at 7:23 pm #

    Very interesting.

    I haven’t read the study yet, but I would think it highly likely that the two groups differed in fat oxidation ratios. It is not unlikely that exercise promotes a greater fat oxidation in some than others. Those who experience the largest increase in fat oxidation (a greater availability of oxidizable fuel from adipose tissue) would likely experience this as increased energy levels accompanied by increased voluntary activity.

    If fat oxidation on the other hand is not increased the subjects might experience this reduced energy availability as an increased need to rest.

    Just a thought.

  2. Mallory 25 May 2010 at 9:14 pm #

    good post and good points! i think running is whack…strength training hard a couple times a week for a short time is all that is needed

  3. Sharon Stiles 25 May 2010 at 11:37 pm #

    If you go from very little exercise to a regular exercise regime then you are likely to be increasing muscle. Muscle weighs more than fat so it is common for people to initially weigh more. It would be the physical measurements that would give the noticeable change at this stage which was documented here as their waist measurement changed. When I do weight loss with clients often it is the dress size that they go for rather than what the scales say.

  4. Jamie 26 May 2010 at 2:34 am #

    I’ve seen this so often over 15+ years of working in gyms. Typically individuals will put all their eggs in the exercise basket and the attitude becomes “I did some exercise today so I don’t have to take the stairs”. It is very similar to the “I’ve done some exercise today so I have earned this cake” mentality.

    Energy conservation is also very common in body builders who have gone both low carb & low fat simultaneously. They get through their workouts but shut themselves down either side of those. They will sleep more & lie on the couch more. Most would be better going high fat & low carb and maintaining the higher activity levels in order to lean out.

  5. Jamie 26 May 2010 at 2:54 am #


    The full paper is available here if you haven’t already seen it:

  6. Will 26 May 2010 at 7:26 am #

    Type of exercise is surely important in these comparisons? Many weight lifters will attest, as well as a good diet, resistance training is by far the fastest method of fat loss. Faster than just dieting alone. Not weight loss per se, but fat loss (which is obviously more important) Long distance cardio is terrible for fat loss, this has been known for years.

  7. Bob Blick 26 May 2010 at 2:34 pm #

    Most fitness people will tell you the key to losing weight is exercise combined with a healthy diet. High intensity aerobics is also being touted. Short periods of sprints, for instance, using a slow run period to recover, and repeating about 8 times.

    My problem with studies of this sort is it gives people a reason not to exercise. They point to one study they find and ask why should they exercise when this study shows they are not going to lose weight.

  8. Dr John Briffa 26 May 2010 at 2:53 pm #


    I take your point that evidence showing aerobic exercise is not generally effective for weight loss might discourage individuals to take exercise. However, I’d like to add two things to this:

    1. I believe in reporting the truth, and I think we’ve been generally misled about exercise and weight loss.

    2. There are some people who might have found exercise did not help them lose weight and ‘gave up’, who might be encouraged to know they didn’t do anything ‘wrong’ and might come back to exercise for other benefits.

  9. Doug Dew 28 May 2010 at 8:34 pm #

    My personal experience of several years of Ironman Triathlon training, which involves many hours of aerobic exercise each week, is that no significant weight loss occured… I carried excess fat all the way through this period…

  10. alexandra 29 May 2010 at 1:11 pm #

    I have known for years that exercise does not bring wight loss. But it does bring muscle tone, a feeling of fitness and agility and a physical sense of well being (in addition to psychological effects). Only diet can bring weight loss and in my case only a very low calorie diet over a prolonged period has proved successful in bringing my weight down and re-calibrfating my metabolism. After such a diet – when I got to 66 kilos – I found my weight stayed stable very easily for about five years while eating “normally” i e avoiding carbs. I kept the weight off that way. Once you have lost weight exercise is easier and more pleasurable, more rewarding because you are better at it. You are more agile. But it’s fitness exercise brings – not weight loss.

  11. Kevin 6 June 2010 at 9:02 pm #

    The best way to lose fat is to follow the nutritional regime of a bodybuilder or a fitness model. Look at their physique, they dont follow a high fat diet and they exercise useing cardio and a heck of a lot of resistance training.
    I have never seen or heard of anyone creating an athletic body by training for 12 minutes a day and walking for 30 mins 3 times a week. If anyone knows someone who has i would be interested to know. Real world testing is the proof surely?


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