# Physiology of weight loss
**URL:** https://boards.straightdope.com/t/physiology-of-weight-loss/601758
**Category:** Factual Questions
**Created:** [November 3, 2011, 4:45pm UTC](https://boards.straightdope.com/t/physiology-of-weight-loss/601758 "2011-11-03T16:45:21Z")
**Posts on this page:** 10
**Page:** 1
### Author:  [@Rhythmdvl](https://boards.straightdope.com/u/Rhythmdvl)
#### Post date: [November 3, 2011, 4:45pm UTC](https://boards.straightdope.com/t/physiology-of-weight-loss/601758/1 "2011-11-03T16:45:21Z")
Help! I’ve been locked in a room for some time now. Mad scientists have poked, prodded, and maniacally laughed as they determined that my daily caloric expenditure is exactly 2,500 calories. Further, through monitored adjustments of People Chow, they have established that my body metabolizes one pound of fat every 3,500 calories.
These (and more) baselines established, they have changed my daily routine such that I’m now expending an additional 250 calories per day; my ration of People Chow has been decreased by 250 calories per day. There is no additional exercise per se, in that no muscle-building takes place. It is primarily a mild cardiovascular expenditure of calories spread out over the course of a day, accompanied by a slight caloric restriction.
What happens, physiologically-speaking?[sup]\*[/sup]
[sup]\* I hope I have the term correct. I mean the bio-mechanical/physical interactions that occur—hormone levels signalling fat cells to do their thing, mini-aliens bursting out of fat cells’ chests, that sort of thing.[/sup]
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### Author:  [@Al\_Bundy](https://boards.straightdope.com/u/Al_Bundy)
#### Post date: [November 3, 2011, 8:47pm UTC](https://boards.straightdope.com/t/physiology-of-weight-loss/601758/2 "2011-11-03T20:47:07Z")
So you will be burning 3,000 counting the extra burn and reduced intake. You don’t say how many calories you take in so calculating the outcome is not possible. If you were already losing weight, you should lose an extra pound per week (500\*7=3500). If you were gaining weight, you will gain less or maybe lose some. Without your weight and intake, I can’t say more.
What I can say is the there is more going on then raw numbers. A person can plateau for many days while seemingly taking in less than burned. All of a sudden when the plateau is broken, you can shed more than the deficit. Breaking a plateau can be tricky. Sometimes it requires eating MORE calories. All I know is that it works. In my own case I have found that certain foods put on weight more than others regardless of the calorie count. Chocolate milk adds weight for me and it seems to be rather lean too, which should be a good thing. If I don’t drink chocolate milk I tend to lose 2# per week eating anything else I want until I’m ready to bust. I suggest to you that experimentation could pay big dividends when you discover those trigger foods for you.
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### Author:  [@Rhythmdvl](https://boards.straightdope.com/u/Rhythmdvl)
#### Post date: [November 3, 2011, 9:04pm UTC](https://boards.straightdope.com/t/physiology-of-weight-loss/601758/3 "2011-11-03T21:04:16Z")
You’re right about everything (AFAIK), but these Mad Scientists have already done all the legwork. Through much poking and prodding, and by keeping me on a completely controlled diet of People Chow, they know all the end results.
The additional exercise component is very mild. All movement has been strictly controlled. For months now, a light would go on and I need to walk across the room or up the stairs to turn it off (yay operant conditioning!). Through meticulous calculation of energy expended (via heart rate monitors, oxygen sensors and magic doohickies), they were able to determine exactly how much to move the walls by in order to increase my caloric output. They carefully spread things out such that I only expend an additional 15.6 calories per hour (over my 16-hour day).
The People Chow never varies. Except that when this phase of the experiment began, the calorie count of the three portions per day decreased by a little over 83 calories per meal.
These are mad scientists we’re talking about—well versed in the Cube movies and big fans of Skald the Rhymer. They have controlled for everything, they know the expected results.
I’m asking about what’s going to happen on the physical level. What triggers the fat cells to … to … to what, exactly? And what happens to the product of whatever they do? I know (or pretend to know) how weight loss/gain happens at the macroscopic level, I’m wondering what’s going on under the hood.
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### Author:  [@DSeid](https://boards.straightdope.com/u/DSeid)
#### Post date: [November 4, 2011, 4:18am UTC](https://boards.straightdope.com/t/physiology-of-weight-loss/601758/4 "2011-11-04T04:18:42Z")
Hormones react to the energy deficit. Insulin goes down, cathecholmines go up. Together that triggers a cascade that results in an fat cell (adipocyte) enzyme, called hormone-sensitive lipase, moving from the adipocyte cytosol into the fat globule. There it cuts off one of the three fatty acids that are the “tri” of triglycerides. After that other lipases are at the ready to cut off the other two. The fatty acids travel through the blood to cells that need energy and get into the mitochondria where they are oxidized. You can read the details of the biochemistry [here](http://www.biochem.arizona.edu/miesfeld/Miesfeld-Fall2008Lecs/Lec34-Fall08/Lec34-F08-Handout.pdf) if you want.
The fat cell with less in it now produces less leptin (a hormone produced by fat cells). That causes less energy expenditure. Your mad scientists will need to increase your activity to keep you burning the same amount. In addition to leptin fat tissue also produces the hormones acylation stimulating protein (ASP) and adiponectin (see [here](http://diabetes.diabetesjournals.org/content/53/suppl_1/S143.full) for details about all three) which work to maintain fat stores.
Hopefully the scientists have enough muscle building built in to off set the muscle that is broken down for energy along with the fat. (Losing gradually like your scientists have you doing it should not need be much.)
I hope that helps.
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### Author:  [@Keeve](https://boards.straightdope.com/u/Keeve)
#### Post date: [November 4, 2011, 10:39am UTC](https://boards.straightdope.com/t/physiology-of-weight-loss/601758/5 "2011-11-04T10:39:24Z")
Here’s the part I don’t understand:
> [@DSeid](#):
>
> That causes less energy expenditure. Your mad scientists will need to increase your activity to keep you burning the same amount.
I am convinced that there are certain things that can happen in the body chemistry, which will cause the body to burn up a larger or smaller number of calories for the same amount of activity. This is commonly referred to as a “higher metabolism” (where the same amount of activity causes the body to burn more calories) or as a “lower metabolism” (where the same amount of activity causes the body to burn fewer calories).
Can someone explain to me how this works? It sounds like a perpetual motion machine to me.
How can it be that a person burns 2000 calories doing a certain amount of activity, while another person – or even the same person on another day – can do the exact same activity and burn only 1000 calories? Doesn’t this violate the Law of Conservation of Matter and Energy? Where does the extra activity come from, without burning extra calories?
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### Author:  [@DSeid](https://boards.straightdope.com/u/DSeid)
#### Post date: [November 4, 2011, 12:22pm UTC](https://boards.straightdope.com/t/physiology-of-weight-loss/601758/6 "2011-11-04T12:22:54Z")
Nope, no violations. More a consideration of the _Second_ Law - which crudely means that every machine coverts energy into work with varying degrees of inefficiency. Think along the lines of how two models of the even the same exact car, same exact weight, can have different gas mileage, depending on factors like tire pressure, recent tune up, accessories on the hood, etc. One car might run a little faster while stopped at lights (have a higher resting metabolic rate). One driver might have different habits that they do not even realize that decrease efficiency.
The machines that are our bodies do that and adjust themselves all the time. Resting metabolic rate changes. We add in little movements just sitting there that burn calories without realizing it as well (Non-exercise activity thermogenesis - NEAT). We burn calories just processing our food and can even do that with different levels of efficiency.
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### Author:  [@Rhythmdvl](https://boards.straightdope.com/u/Rhythmdvl)
#### Post date: [November 4, 2011, 12:49pm UTC](https://boards.straightdope.com/t/physiology-of-weight-loss/601758/7 "2011-11-04T12:49:48Z")
Thanks for the awesome batch of reading to do–it’s exactly what I was looking for!
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### Author:  [@Keeve](https://boards.straightdope.com/u/Keeve)
#### Post date: [November 4, 2011, 1:07pm UTC](https://boards.straightdope.com/t/physiology-of-weight-loss/601758/8 "2011-11-04T13:07:34Z")
> [@DSeid](#):
>
> The machines that are our bodies do that and adjust themselves all the time. Resting metabolic rate changes. We add in little movements just sitting there that burn calories without realizing it as well (Non-exercise activity thermogenesis - NEAT). We burn calories just processing our food and can even do that with different levels of efficiency.
Ditto what **Rhythmdvl** said. Thanks!
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### Author:  [@DSeid](https://boards.straightdope.com/u/DSeid)
#### Post date: [November 4, 2011, 2:47pm UTC](https://boards.straightdope.com/t/physiology-of-weight-loss/601758/9 "2011-11-04T14:47:44Z")
You’re welcome!
I wish I could say I remember all those biochemical steps (although I did have them memorized for a test once a few decades ago! :)) or completely comprehended the hormonal interplays - especially the newer emerging understanding of the importance of adipose tissue as an endocrine gland, and its hormones interactions with other fat, metabolism, and appetite regulating hormones like ghrelin. But hey, so long as those mad scientists laughing manically do, that’s all that matters.
For your further reading pleasure, [more about NEAT](http://www.ajcn.org/content/72/6/1451.full) and about how non-obese individuals automatically increase it in response to overfeeding and how much fidgeting is a part of it.
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### Author:  [@DSeid](https://boards.straightdope.com/u/DSeid)
#### Post date: [November 4, 2011, 11:35pm UTC](https://boards.straightdope.com/t/physiology-of-weight-loss/601758/10 "2011-11-04T23:35:45Z")
Sorry for the doublepost, but you two will definitely find [this article](http://www.ajcn.org/content/88/4/906.full) interesting. It appears that your mad scientists really exists:
> [@](#):
>
> We have conducted studies of energy metabolism before and after weight reduction in obese and nonobese subjects whose physical activity is monitored, whose weight stability is clearly documented, and who ingest only a liquid formula diet for months at a time while living in a clinical research center (CRC). Using this design, we have been able to control for possible differences in diet composition, subject compliance, and physical activity and to stabilize weight to levels of constancy not possible in out-patient studies. We are also able to avoid assumptions regarding physical activity.
>
> Within our subject population of \>100 persons, 7 subjects have maintained a weight loss of ≥10% for ≥1 y before entry into this study, and those subjects are designated here as Wtloss-sustained). We contrasted their EE with the EEs of sex- and weight-matched subjects who had been admitted to the study at usual body weight (designated here as Wtinitial) or who had been admitted to the study at usual body weight and then reduced to ≤90% of their starting weight (designated as Wtloss-recent).
(EE = Energy Expenditure)
Not even People Chow … “only a liquid formula for months at a time” … whoa.
What did they find?
> [@](#):
>
> Total EE for 24 h (TEE) was assessed on the basis of precise titration of fed calories of a liquid formula diet necessary to maintain body weight with a variance of \<10 g/d over ≥14 d (3). … Resting energy expenditure (REE) was measured by indirect (hood) calorimetry sampling every 30 s for a period of ≥30 min at 0900 while subjects were in bed and in a postabsorptive state (6). …
>
> … the thermic effect of food (TEF) … was calculated … NREE, defined as energy expended above resting and TEF in physical activity, was calculated …
>
> … Absolute values of TEE and NREE were significantly greater in the Wtinitial group than in the Wtloss-sustained and Wtloss-recent groups … The negative energy balance required for the dynamic loss of body energy stores (mainly FM) is accompanied by reductions in EE per unit of metabolic mass that are reversed by refeeding (9, 16, 36). The question of whether this disproportionate decline in EE persists after dynamic weight loss has ended, but while body weight is being maintained below initial body weight, is critical to an understanding of the biological basis for the very high recidivism to obesity seen in otherwise successfully treated patients (28, 29). We previously reported persistent reductions in EE—corrected for metabolic mass and age—in subjects maintaining a reduced body weight for periods of ≈3 mo after cessation of weight loss (3-6, 37). These reductions in EE could reflect transient carryover of the metabolic consequences of negative energy balance or could be a reflection of physiologic responses to reduced body fat per se (or both). The distinction between these 2 possibilities is critical to an understanding of weight homeostasis in human subjects.
>
> The major finding of the present study is that there are similar, significant declines in TEE, NREE, and, to a lesser extent, REE in subjects maintaining a reduced body weight, regardless of whether that reduced weight has been maintained for weeks or years. In other words, bioenergetic responses to maintenance of a reduced body weight do not wane with time. …
>
> … Elsewhere, our group has presented data indicating 1) that the changes in systems regulating both the energy intake and energy output that occur during reduced-weight maintenance act coordinately to favor the regain of lost weight and 2) that many of these changes are reversed by the restoration of circulating leptin concentrations to pre-weight-loss levels and are therefore the consequences of persistent relative hypoleptinemia long after weight loss has ended (4, 39-41). The long-term persistence of weight-reduced phenotypes after weight loss suggests that leptin signaling is important not only in systems affecting both energy intake and output but also in both short-term and long-term regulation of body energy stores. …
IOW someone who was an obese adult loss who has lost weight MUST make a commitment to have both _fewer calories and more activity_ than others their size and fat percent do in order to maintain their weight loss.
I was looking to see if I could find an article showing that leptin levels renormalized to a new weight norm after a while … apparently no such luck. It is still unclear to me if changing the macronutrient composition of the diet would have some effect. Anecdotally I have seen that help get through weight loss plateaus.