The role of exercise in weight loss

Regular exercise can help lower the risk of cardiovascular disease, improve bone density and muscle tone, maintain a healthy weight, improve hemoglobin A1c levels, work wonders against psychological stress and anxiety, lessen arthritis pain and lower the risk of Alzheimer’s disease (1,2,3,4).  It will not, however, make you lose weight (5).


You shouldn’t be.  Think about it:  you can consume 500 calories (a slice of cheesecake or a 10 oz Margarita) in just a few minutes, but it takes an adult of 150 lbs over two hours of fast paced walking, or over one hour of vigorous running, to burn the same amount (1).  If you wish to burn more than 500 calories, to lose weight (as opposed to simply burning off the added calories), it will take an additional hour or so to create the desired negative balance. If the Margarita and the cheesecake slice were both a part of your after dinner indulgence, you’re looking at over 1,000 calories (making up half the daily caloric requirement for most healthy adults) that you must make disappear just to maintain your current weight.

In other words, you can’t outrun your mouth.  Or, to be fair, you can’t outrun your mouth if you have a life which includes a job, commute to work, a household to maintain, child care or other such activities as part of your daily routine.  There simply isn’t enough time in the day to compensate (with exercise) for added calories.  Maybe you can pull it off once in a while but most of the time, it’s a bit of a stretch.

If you have a reasonably healthy body mass index (BMI), regular exercise, which includes endurance as well as weight bearing activities, will go a long way toward keeping all your bits and parts in tip-top shape and your weight in a healthy range.  You will also run a significantly lower risk of gaining unwanted pounds.

You may be wondering:  if regular exercise can have such a positive effect on the body, why even mention that it falls short in terms of weight loss?


When you operate under the assumption that working hard at the gym is going to yield equally impressive results on the bathroom scale, you may be deeply disappointed with the outcome, which, in turn, may translate into disillusionment and very likely, a defeatist attitude.   “Nothing I try works” is a phrase I hear frequently from people who busted their butts at the gym for months, five days a week or more, only to see trivial changes in weight, sometimes, almost against all reason, on the plus side.  That all this work has improved their overall endurance is of little comfort when their pant/dress size has not changed for the better.

It’s not a matter of not having worked out hard enough, or long enough, or regularly enough.  It’s a matter of focusing on the wrong approach then feeling helpless when, after all the time and effort invested in it, the approach fails.

In a trial published in the Journal of American Medical Association in 2003, researchers monitored the weight fluctuations of 184 overweight women participating in various levels of physical activities over the course of 12 months (2).  The women were divided into four groups:

  • vigorous intensity / high duration exercise
  • moderate intensity / high duration exercise
  • moderate intensity / moderate duration exercise, and
  • vigorous intensity / moderate duration exercise.

All the participants benefited from varying levels of improvement in cardiovascular fitness by the end of the trial.   There was no significant difference in terms of weight loss between women at the high end of the intensity/duration exercise spectrum and those at the low end.  High intensity workouts lasting longer periods of time did not yield an advantage, in terms of weight loss, over moderate intensity and moderate duration regimens.

Similarly, the authors of a 2007 study looking at the effects of exercise on cardiovascular fitness divided 464 previously sedentary overweight and obese women participants into four groups: a no-exercise control group or one of three groups in which they expended 4, 8 or 12 calories per kilogram of weight, per week, for a period of six months by engaging in various intensities and durations of physical activity (5). Upon completion of the study, the authors found graded dose response changes in heart fitness across all levels of exercise, but no significant changes in weight.  Exercise alone, regardless of intensity or duration, did not amount to a hill of beans in terms of weight loss, even when routines were maintained for as long as six months.

Several factors account for these somewhat counterintuitive outcomes including increased hunger (and, thus, food consumption) as a result of vigorous exercise, a tendency for people to relax their calorie counting on the days they work out (or they think they can indulge today because they are going to work out tomorrow), the notion that they deserve a reward (read: chocolate lava cake) for all the hard work they’ve completed, and a host of other physiological and psychological factors.  These studies are mere drops in a virtual ocean of evidence that weight loss occurs in the wake of dietary changes, rather than as a result of vigorous exercise routines (6).  “Ah, but muscle weighs more than fat!” you might say, “so, no change in weight doesn’t necessarily mean no change in body size!”  True, but the overwhelming evidence suggests the lack of improvement is not specific to weight, but to overall measurements as well, whenever exercise routines are the only intervention. If study participants ended the trials several dress sizes smaller but weighing the same, there would be no point to having this discussion.

That being said, regular physical activity not only helps keep the weight off, but helps protect against a great number of diseases of affluence (cardiovascular disease, diabetes).  As such, it is an important part of any healthy lifestyle (7,8).

If you are trying to lose weight, it is important to focus on making permanent changes  to your dietary habits.  Popular fad diets don’t work in the long run and exercise alone is not going to help you reach your goals.  There is a sense of helplessness that accompanies the generally disappointing outcomes of making uninformed weight loss regimen choices.  You  may end up feeling as though nothing you try works, therefore, there’s no sense in trying.

A healthy diet that focuses on plant based foods goes a long way toward normalizing caloric intake, body weight and metabolic markers with or without the help of an exercise regimen (9,10).  Talk to a dietitian and/or qualified nutrition counsellor and get the help you need to make permanent lifestyle changes.  Some gyms have dietitians on staff whose services are included in your gym membership.  Work on your dietary habits/choices, and the rest will follow.  It is easier and healthier to watch your caloric intake than to fight an uphill battle while trying to  compensate for added calories by working out.


  1. Centers for Disease Control and Prevention, Division of physical activity and obesity.  Why is physical activity important? 2012. Available at:  Accessed June 2, 2012.
  2. Jakicic JM, Marcus BH, Gallagher KI, Napolitano M, Lang W.  Effect of exercise duration and intensity on weight loss in overweight, sedentary women – a randomized trial.  JAMA 2003; 290(10): 1323-1330.
  3. Church TS, et al. Effects of aerobic and resistance training on hemoglobin A1c levels in patients with type 2 diabetes.  JAMA 2010; 304(20): 2253-2262.
  4. Scarmeas N, et al. Physical activity, diet, and risk of Alzheimer’s disease.  JAMA 2009; 302(6): 627-637.
  5. Church TS, Earnest CP, Skinner JS, Blair SN. Effects of different doses of physical activity on cardiorespiratory fitness among sedentary overweight or obese postmenopausal women with elevated blood pressure. JAMA 2007; 297(19):2081-2091.
  6. Rock CL, Flatt SW, Sherwood NE, Karanja N, Pakis B, Thomson CA.  Effect of a free prepared meal and incentivized weight loss program on weight loss and weight loss maintenance in obese and overweight women.  JAMA 2010; 304(16): 1803-1811.
  7. Hankinson AL, et al.  Maintaining a high physical activity level over 20 years and weight gain. JAMA 2010; 304(23): 2603-2610.
  8. Lee I, Djousse L, Sesso HD, Wang L, Buring JE.  Physical activity and weight gain prevention.  JAMA 2010; 303(12): 1173-1179.
  9. Newby PK, Tucker KL, Wolk A. Risk of overweight and obesity among semivegetarian, lactovegetarian, and vegan women. AJCN, 2005; 81: 1267-74.
  10. Vergnaud A, et al.  Meat consumption and prospective weight change in participants of the EPIC-PANACEA study.  AJCN 2010; 92: 398-407.