Impact of Weight Loss on NEAT

You may have noticed that after some time dieting, you hit a weight loss plateau in which you stop losing weight; well, this is due to a variety of reasons, some known and others unknown. In this article, we will investigate if non-exercise activity thermogenesis is a cause of decreased weight loss when in a calorie deficit, and if so, a series of reasons for why this may or may not be the case.

What is Non-Exercise Activity Thermogenesis?

Non-Exercise Activity Thermogenesis (NEAT) is the amount of calories (energy) used during activity, movement outside of exercise activity [3]. So, any movement structured, competitive, and/or measured is typically classified as exercise, everything other than that falls under the umbrella of NEAT – this includes walking to and from the car, fidgeting in a chair, texting on a phone, and an innumerable number of other large and small activities.

Metabolism is made up of a few main components, and one of those is Thermic Effect of Physical Activity (TEPA) which encompasses all activity; which means, it includes exercise activity and non-exercise activity. Now, while most people in the western world focus on exercise activity, in a direct sense, non-exercise activity uses the most calories of the two. So, while the Thermic Effect of Physical Activity makes up a good 20% of total metabolism, it is non-exercise activity (NEAT) that makes up the vast majority of that 20% of total metabolism, not exercise – although, again, most people focus on exercise [1][4].

 

Does Losing Weight Lead to a Decrease in NEAT?

Yes [1].

Could two people of the same body weight have different NEAT?

Absolutely – there are many factors that play a role in NEAT and the amount of difference between two people, even at similar bodyweights, can be severe (even as high as a 2000 calorie difference) [6].

Understanding the Physiology?

In terms of why Non-Exercise Activity Thermogenesis decreases with weight loss is still a matter of debate in a few respects; however, some reasons are quite clear.

The more reasonable and proven understanding of why NEAT decreases with weight reduction is simply due to the weight change, itself. One such understanding is the shift in energy cost of movement [1]. If a person is 200lbs before going on a diet, then diets and loses 30lbs, then the energy necessary to move the same person will decrease as the energy required to move a 200lb person is more than that necessary to move the same person at 170lbs.

Another possible reason is simply the necessity to be in a calorie (energy) deficit to lose weight, so if energy is harder to come by in the body, the body will catabolize its stored energy – this we know. However, as a consequence, it could also dissuade movement, if not in a planned manner, then in an unplanned, unconscious manner by decreasing the amount of fidgeting or other unconscious, “spontaneous” activity a person normally does [5].

 

Other possible mechanisms relate to the biochemical occurrences in the cell, specifically muscle cells. It is thought that Type II muscle cells (those used in heavy weight lifting, for example), have the ability to decrease or increase their energy use; so, in a way, they could be considered “energy efficient” [2]. Not only that, all muscle cells may have the ability to be more efficient in terms of enzymatic activity [1]. Both of these possible mechanisms need further research, however, as most of the studies done on the subject have been in non-human trials.

These are three of the possible reasons for why non-exercise activity thermogenesis can adapt or lead to a decrease in caloric expenditure, therefor possibly aiding in slowing or stopping weight loss. Again, there is far more research needed on the subject, but what data is available makes these conclusions relatively sound – we will see if this holds true in the future, especially in relation to aspects like genetics, enzymatic efficiency, etc.

SUMMARY

With non-exercise activity thermogenesis making up a majority of total activity, defined as thermic effect of physical activity (including exercise and non-exercise), it seems that any adaptation thereof would have some impact on calories used by the body, especially since activity accounts for 20% of total calories used throughout the day. Well, it seems that non-exercise activity thermogenesis does decrease as weight loss occurs (the result of a calorie/energy deficit). The reasons are still largely unknown, but one of a few plausible reasons are attributed to a decrease in energy expenditure due to a loss of weight; less weight to move, less energy used. So, could NEAT be a contributor to stalls in weight loss? Absolutely.

Writer: Nicolas Verhoeven

                                                                                                          Citations

[1] Levine, J. A. (2004). Non-Exercise Activity Thermogenesis (NEAT). Nutrition Reviews, 62, S82-S97. Retrieved from http://www.ncbi.nlm.nih.gov/pubmed/12468415

[2] Wendt, I. R. (1973). Energy production of rat extensor digitorum longus muscle. American Journal of Physiology, 224, 1081-1086. Retrieved from http://ajplegacy.physiology.org/content/224/5/1081

[3] Levine, J. A. (2006). Non-Exercise Activity Thermogenesis. Arteriosclerosis, Thrombosis, and Vascular Biology, 26, 729-736. Retrieved from http://atvb.ahajournals.org/content/26/4/729.full

[4] Physical Activity: Energy expenditure. (2002). Retrieved from http://apjcn.nhri.org.tw/server/courses/12345phys-act/p2.php

[5] Trexler, E. T., Smith-Ryan, A. E., & Norton, L. E. (2014). Metabolic adaptation to weight loss: implications for the athlete. J Int Soc Sports Nutr, 11(1), 7. Retrieved from http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3943438/

[6] Von Loeffelholz, C. (2014). The Role of Non-exercise Activity Thermogenesis in Human Obesity. MDText Inc. Retrieved from https://www.ncbi.nlm.nih.gov/books/NBK279077/

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