Why it can sometimes pay to be realistic about the impact of exercise on weight loss

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January is not that far away now and when it comes around at least some people will turn their thoughts to shedding surplus pounds through diet, exercise or both. I came across a report this week of a recently-published study which compared the effects of aerobic exercise with resistance training on weight and fat loss. The report stated that aerobic exercise was the clear winner, but neglected to give any actual amounts of weight lost. I have to admit I was a little suspicious because previous evidence has shown that aerobic exercise has limited effect on weight, generally speaking. I went to find the actual paper [1] to see if the devil was in the detail.

In this study, sedentary overweight and obese adults were randomised to one of three exercise groups for a period of 8 months.

  1. aerobic exercise (treadmill, cross trainer machine, stationary bicycle) for a total of 12 miles a week at 65-80 per cent maximal intensity.
  2. resistance training on 3 days per week designed to burn the same number of calories as the aerobic exercise of group 1.
  3. both aerobic exercise and resistance training combined (group 1 exercise plus group 2 exercise)

The results revealed that both groups 1 and 3 lost weight and fat, and group 3 lost no more weight and fat than group 1 (despite doing twice as much exercise). Group 2 did not lose weight. All this led the authors to conclude that aerobic exercise is superior for weight loss. But what I (and perhaps other people) really want to know is just how effective the aerobic exercise was in terms of weight loss.

It turns out that individuals in group 1 lost a total of 1.66 kg (about 3.5 lbs) of fat. Remember, though, this is over an 8-month period, so the pounds were not exactly dropping off. Now, let’s factor in the amount of exercise the amount of exercise required to achieve this weight loss result…

Individuals exercised for a total of about 2 hours a week which means that the total amount of exercise over the study period came to about 70 hours. For each hour of exercise individuals lost about 1 ounce (or about 30 grams) in weight.

Let me be clear and say I am not writing this to dissuade individuals from taking exercise and being active. I am an enthusiastic advocate of physical activity, and believe it has the capacity to benefit health in many ways. However, my experience tells me that many people use exercise to regulate weight and that this is particularly the case in January. I also know that many are disappointed with the results they achieve, feel something is ‘wrong’ with them, and can give up altogether when they don’t feel they’re getting a return on investment.

I think it helps some to know that substantial weight loss is unlikely to come from exercise, so that expectations are aligned with the likely results. Then, individuals may not be so disappointed when they don’t get the ‘expected’ results from exercise with regard to weight loss.

So, I encourage individuals to exercise if they can, but to focus on benefits they are likely to experience such as improved physical and psychological wellbeing and improved fitness.

It occurs to me that this latest study may cause some to conclude that there’s not much point to resistance exercise. Actually, I think there is. It can strengthen the body, which can improve mobility and reduce frailty, which is particularly important for the elderly. It also can improve the aesthetics of the body, which some are grateful for.

Being realistic about the likely impact of exercise on body weight and focusing on whatever else it has to offer can, I think, help motivate us to be active and stay active.


1. Slentz A, et al. Effects of aerobic and/or resistance training on body mass and fat mass in overweight or obese adults J Appl Physiol 2012;113:1831-1837

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