ExRx.net

Forgive me if this has been answered in other threads - I poked around and didn't see anything directly related.

I’ve been working to understand the physiology/biochemistry behind weight loss (or fat loss to be exact). Finding the reference to the Trembblay research helped me make a lot of sense out of energy system contributions, caloric expenditures, and residual cascades of metabolic “house keeping” that helps burn additional energy.

One topic that I cannot find a SOLID explanation beyond urban-myth postings on weight-loss message boards is: why is weight loss not linear?

If I assume that a person has hit his/her genetic plateau for lean body mass (takes out the concern that muscle, bone, blood volumes, etc. are contributing to the scale) and know for a fact that he/she is in a 500 calorie/day caloric deficit – why doesn’t the scale do a tiny little march day after day after day toward 1 lb./week?

What is more typical is the scale will show the same weight, to the decimal point, for days if not over a week… maybe two weeks – and then suddenly drop 1.5 lbs. overnight. Why does weight come off in step functions rather than a nice little linear slope down? What is happening physiologically to cause a step function????

This question is driving me nuts. Help?!?! 

-SLSorrels

I don't have a reference, but I have a theory. I don't believe that simply being in a deficit works. When you eat less, hormones will tell your body to conserve energy and your expenditure will decrease automaticall. Your body protects the weight it's at. Eventually you will reduce to a point that you get a hormonal change that will adjust your setpoint and your metabolism will increase slightly and you will lose weight. Leptins are invloved in the maintenance of that set point. There is a lag between the reduction in calories and the metabolism slowdown caused by leptins. This is what I believe causes the step effect. You can take advantage of this by including refeeds into your diet. Bodybuilders have been doing this for years, essentially going low carb for a few days, followed by a refeed day, then repeat. This keeps your metabolism high and lowers your bodyfat setpoint at the same time.

I'm not sure but I expect Lyle MacDonald could be a good source for this. Here's his web site: http://www.bodyrecomposition.com/

Stephen Guyenet has been writing about setpoints lately. http://wholehealthsource.blogspot.com/

Very interesting thought... and I'm all into understanding hormonal effects of energy expenditure/storage (a whole other topic, for sure).

But here's my curiosity... I'm such a nerd (come from a science background oh so long ago) that I like to measure things. So, for over two months now I've been monitoring my caloric expenditure via a body monitoring device (they had their own literature on the validity of their algorithms to calculate caloric expenditure via the data inputs of their device... based on 3-axis accelerometer (sp?), conductance, skin temp. etc.) and it charts the data minute to minute. I can see expenditure variations from sleeping to cardio-class to weight lifting - it all looks within reason.

For two months I've maintained a caloric deficit in comparison to my expenditure... as recorded by my food logs and body monitoring device. Basically, given the 2nd law of thermodynamics... the energy to support my daily activity is coming from somewhere and it's not all coming from my food - thus, the deficit.

And, as usual... the WEIGHT comes off in step functions. I'm wondering if the FAT LOSS is actually more linear but the body is making up for the missing volume somehow with something else?? And if so, what is the something else AND why does it do it and HOW does it know how to keep the scale within a decimal point?? (it's actually amazing to ponder)

Sorry for the diatribe... but this really puzzles me!!

-SLSorrels

It sounds like an interesting experiment. Are there any variations in temperature that might correlate with the weight loss? That might indicate a speeding up or slowing down of the metabolism.

Also, instead of searching for Trembblay, try Tremblay.

Well, all solid mass weight loss ultimately comes from using the restroom. Maybe you're a little backed up on the ol' turnpike, so to speak.

likewise water intake and output is likely a factor.

@Stuward
Temperature variations *should* be accounted for via the body sensing device and show up in the daily caloric expenditure data. So I totally agree (and have seen in the data) a decent amount of variation in the daily expenditure (can be upwards of 600-700 calories/day on different days) - and I maintain the caloric deficit even given the variation. But it doesn't help me understand the step function of weight loss.

@ frogbyte and frigginwizard
I've thought of water and "solid mass" - but how can your body maintain a steady weight (on the scale) to the decimal point even if it *is* one or both of those to things? I shudder to think what I'd have to do get measurements on THOSE. Count me out. :-)

I read a message board post (that I disregarded as urban weight loss myth) that fat cells can hold water... I was hoping that someone on these boards would have some sort of journal article or textbook or something concrete to throw at me. It's the plateau/step function of weight loss that has me so puzzled...

-SLSorrels

The "deficit" unless you beleive in violating the first law of thermodynamics HAS TO BE such that 500cals deficit leads to 1 lb/week. In fact, the best way to MEASURE your deficit is from loss rate. It's almost definitional. The confusion comes from people saying they are in deficit, but not having accurate measurement of calories, exertion and basal metabolism. For instance bodybugs are not accurate.

Add on other issues:

-water variation
-metabolism depression when losing (moderate and reversible, but occurs)
-lower needs at lower weight

....and you have the confusion.

@TCO

I hear you on the need to have accurate measures. And I totally agree that the final way to indicate "loss" is on the scale.

I'll also concede that water, and lower caloric needs, and metabolic depression come into play... but what I still do not understand is:

-- How can the body maintain such a specific weight for days on end given the multitude of variables that play into the number on the scale?

-- When the scale does move, it's usually in a step function... how come?

A lower need for calories over time given a smaller body to maintain should make a weight loss curve, not a line or step function... right? Water would be the jumping around everyone tends to see... Metabolic depression would show up as a curve too... or?

It's the step function that blows my mind. It's like a body hangs on and hangs on and hangs on, then suddenly gives up and turns some *weight* loose... then starts hanging on again. I know that's not what's happening... it's just how I describe it.

I don't mean to be argumentative with the people who are trying to help explain the observations... it's just that I'm not completely satisfied with the answers yet. ;-)

-SLSorrels

@Stuward

I found that exact abstract too!! But I can't access the PDF. Do you happen to have it??? (fingers crossed)

-SLSorrels

@TCO

One more tidbit regarding the accuracy of body sensing devices...

I agree that they are not 100% accurate BUT I would believe their % inaccuracy to be randomized across all the data they collect such that relative use is still ok. Like, I agree that I probably didn't burn exactly 2213 calories yesterday 2546 the day before that, but I can feel confident that relatively speaking, I burned MORE two days ago than I did yesterday.

I think it might be a precision vs. accuracy problem. And for my purposes, I'll take precision and hand-wave past accuracy.

Anyway... I digress!

-SLSorrels

Sorry

Lookup Dr. Mike Eades and the other guys I mentioned. There might not be a scientific explanation but they would have it if it existed.

Well mostly the only weight you lose while exercising is sweat/breath water vapor. Technically you're exhaling carbon, but I doubt it's weigh-able.

It's weighable. However, you should be replenishing as you're going along. I drink about 1/5 to 1 litre. that's a lb or 2 of water.