Exercise & Weight Loss

When people want to lose weight, we typically jump to two behaviors – diet hard and hit the gym with a renewed resolution. Now, obviously there is reason for this sudden trend to focus on these two activities, but is one being given a bit too much credit? In this article, we will examine how exercise directly and indirectly impacts our weight loss, as well as its effectiveness – buckle up, we may be in for a surprise.

What types of Exercises?

For the purpose of this article, we will cover resistance training and cardio training.

Direct impact of exercise on weight loss?

First, let us take on the question of what happens when we compare isocaloric conditions between groups among various exercise modalities (cardio and resistance training).

It seems that, if we use oxygen as our measure (and we can do this due to our understanding of the Respiratory Exchange Ratio), we see that compound resistance training at moderate intensity (75%1RM) leads to about 8.83 calories used per minute if a person were to exercise for 30 minutes [1]. If we focus on isolation exercises (curls, for example), however, we get an even smaller number at a hollow 3 – 6 calories used per minute; keep in mind, as well, that these numbers are reflective of men, as women tend to expend significantly less (between 1 – 6 calories per minute, with the lower range being for lower intensities and isolation exercises) [2]. Meanwhile, moderate-vigorous (70%HRmax) cardio exercise uses about 9.2 – 9.5 calories per minute [1]. This leads to, approximately, 265 calories and 280 calories per 30 minutes, respectively.

It seems relatively clear that while exercise certainly expends calories, and in a direct sense, cardio uses a bit more energy than resistance training, the numbers are still rather low. From another perspective, even in obese individuals undergoing vigorous (65-80%VO2) exercise, for 20 miles a week, with isocaloric conditions over 8 months, there was only a 7 – 8 lb drop in weight (some may be accounted for by minor recomposition and indirect impact) [3]. You would expect, if exercise is as powerful weight loss method, to see significant weight loss in people primed for weight loss.

Indirect impact of exercise on weight loss?

Now is where things get more interesting and may have some interesting perspectives to offer – indirect impact. Indirect impact is anything that is influenced by exercise, but is not attributed to the energy used to move the body. So, that defined, we know that energy (calories) are used for muscle growth, repair [4]. Since that is the case, the indirect impact can be increased based on the amount of muscular remodeling the body undergoes because of intense exercise (generally, the more intense exercise, the more muscular remodeling). It is difficult to say how much caloric expenditure would increase with increased protein synthesis and protein breakdown over the period both are elevated, but what we do know is that the increased muscle mass leads to, roughly, a 4.5 – 7 calorie per lb gain in metabolic rate [4][5]. While this number may not be extensive, even if a person gains 20 lbs of muscle (140 calories a day, maximum), it does symbolize a relatively permanent increase in expenditure due to exercise’s effects and those effects could help lead to weight loss.
Another possible area is excess post-exercise oxygen consumption (EPOC), where we see an elevated level of energy use even after exercise. This could be considered a “recovery” of sorts, but as this effect can last many hours post exercise, it is also difficult to quantify. That said, a number between 24 – 45 calories, the higher end with increased intensity, is probably appropriate, per 500 calories expended via direct exercise [6]. Regardless, the impact is not massive on caloric expenditure and therefor will have little impact on weight loss, itself.

Exercise Impact on Satiety?

While looking at exercise’s impact as a whole is an almost complete view on the subject, it would make sense to investigate if exercise has an impact on physiological hunger cues, because if it does, then that could be another indirect means by which exercise could impact weight loss. That said, it does seem that exercise may have an impact; I say “may”, because studies were done on populations that may have impaired regulatory capacity (leptin levels, for example). Anyway, assuming there is a generalizability, very intense exercise seems to have a blunting effect on hunger and increase satiety in some individuals [7][8]. Again, the research is not accepted widespread for all individuals, so read into this selectively [9].

SUMMARY

All in all, the direct impact of exercise on weight loss is relatively small with small levels of weight loss over long periods of time (even with calories controlled). However, there may be some unique benefits via indirect impact of exercise on weight loss by increasing caloric usage through the increase in muscle mass, as one example. Overall, however, without nutrition as a staple for weight loss, exercise alone is unlikely to lead to great reductions in weight.

Writer: Nicolas Verhoeven
References

[1] Falcone, P. H., Tai, C., Carson, L. R., Joy, J. M., Mosman, M. M., McCann, T. R., … Moon, J. R. (2015). Caloric Expenditure of Aerobic, Resistance, or Combined High-Intensity Interval Training Using a Hydraulic Resistance System in Healthy Men. Journal of Strength and Conditioning Research, 29(3), 779-785. doi:10.1519/jsc.0000000000000661

[2] Reis, V., Júnior, R., Zajac, A., & Oliveira, D. (2011). Energy Cost of Resistance Exercises: an Uptade. Journal of Human Kinetics, 29A(Special Issue). doi:10.2478/v10078-011-0056-3

[3] Slentz, C. A. (2005). Inactivity, exercise, and visceral fat. STRRIDE: a randomized, controlled study of exercise intensity and amount. Journal of Applied Physiology, 99(4), 1613-1618. doi:10.1152/japplphysiol.00124.2005

[4] Bier, D. M. (1999). The Energy Costs of Protein Metabolism: Lean and Mean on Uncle Sam's Team. In The Role of Protein and Amino Acids in Sustaining and Enhancing Performance. Retrieved from https://www.ncbi.nlm.nih.gov/books/NBK224633/
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[5] Kinucan, P. (n.d.). Controversies in Metabolism. Retrieved from https://www.unm.edu/~lkravitz/Article%20folder/metabolismcontroversy.html

[6] Vella, C. A. (n.d.). Exercise After-Burn: Research Update. Retrieved from https://www.unm.edu/~lkravitz/Article%20folder/epocarticle.html

[7] Prado, W. L., Lofrano-Prado, M. C., Tenório, T. R., Balagopal, P. B., Oyama, L. M., Botero, J. P., & Hill, J. O. (2014). Effect of Aerobic Exercise on Hunger Feelings and Satiety Regulating Hormones in Obese Teenage Girls. Pediatric Exercise Science, 26(4), 463-469. doi:10.1123/pes.2013-0200

[8] King, N. A., Caudwell, P. P., Hopkins, M., Stubbs, J. R., Naslund, E., & Blundell, J. E. (2009). Dual-process action of exercise on appetite control: increase in orexigenic drive but improvement in meal-induced satiety. American Journal of Clinical Nutrition, 90(4), 921-927. doi:10.3945/ajcn.2009.27706

[9] Martins, C., Morgan, L., & Truby, H. (2008). A review of the effects of exercise on appetite regulation: an obesity perspective. International Journal of Obesity, 32(9), 1337-1347. doi:10.1038/ijo.2008.98

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