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Reduced metabolism/TDEE beyond expected from weight loss

So several studies have pointed to this effect of adaptive thermogenesis, some of which is expected. But found a nice recent one that covered several effects at once nicely.

First, the totally expected part. I'll try not to use the term metabolism as an all day type thing including all activities when that is really TDEE. Metabolism is mainly the lower level functions, some base and required though can be slowed down, some higher level functions like cell replacement for skin, hair, nail, muscle growth which can really be slowed down or skipped, and even higher level stuff like processing foods which probably shouldn't be considered metabolism normally, but some do ("kick start your metabolism by eating breakfast" misunderstanding).

Your TDEE is composed of your BMR (Basal metabolism) + NEAT (Non-Exercise activity) + TEF (energy burned processing food eaten) + EAT (Exercise activity).

If you eat less, your TEF burn (usually about 10% of what you eat) goes down, so TDEE goes down. So eating 2000 TEF is 200 of that, go to eating 1600 TEF is 160, so loss of 40 calories to TDEE, not much.

As you start to weigh less, NEAT and EAT (if pace & intensity kept the same) go down since you are moving less mass around, so TDEE goes down. What may happen though is you move more since you weigh less, and exercise harder. So perhaps no adjustment to TDEE, but probably lowering.

As there is less body mass for functions, the BMR will go down slightly. If mainly fat mass lost, not that bad since it didn't require much energy anyway (2 cal/lb a day). But muscle mass lost, while resting energy use isn't much (6 cal/lb a day), that lost muscle being used daily could impact TDEE badly. Along with less mass is perhaps less LBM which includes blood volume, less muscle is also less glucose stores (with water), and water management is a decent calorie burn too. So as weight goes down, BMR goes down somewhat depending on what is lost, and therefore TDEE will lower too.

So outside all those known and expected reasons for your metabolism and TDEE to burn less as you diet and lose weight, there is the one that could be avoided, and perhaps you want to avoid it to make maintenance easier.

And that is a drop in TDEE unrelated to any of the above, and is just the body getting more efficient with BMR, TEF, NEAT, and EAT altogether, metabolic adaptation is what it's usually called. Sometimes called metabolic damage, if you consider lower than what it was and could be damage, or merely the body doing what it has to do.

Here's the 6 month study in full if you want to dig in to it, I thought I'd point out some tidbits.

Participants had to be between BMI 25-30, overweight category, but healthy otherwise. They were excluded if they smoked, exercised more than twice a week, were pregnant, lactating or post-menopausal, had a history of obesity (BMI>32), diabetes, cardiovascular disease, eating disorders, psychological disorders, substance abuse or regularly used medications except for birth control. So that may have a bearing in comparison.

Diet was 55 / 15 / 30 for C / P / F. 

CR (Calorie Restriction) was 25% deficit from TDEE, so not massive.

CR + EX (EXercise) was 12.5% deficit plus 12.5% calories burned in cardio exercise 5 x week, each session being 403-569 calories for 45-53 min (women and men difference).

LCD (Low Calorie Diet) was 890 cal/day until 15% of weight was loss, then back to maintenance calories by month 3, whatever it was then. That's a tad massive

DEXA scans for body composition of LBM (Fat Free Mass (FFM)) and Fat Mass (FM). Sedentary TDEE measurements in a metabolic chamber for 23 hrs. SMR (Sleeping Metabolic Rate (BMR)) measured chunk of night no movement.

Several formulas related to measured Sedentary TDEE at baseline based on all available stats, to compare down the road when stats changed.

At 3 month check, sedentary TDEE had dropped by the following amounts, below what the formulas would have indicated for new measured LBM and FM, and SMR. In other words, it lowered the expected amount, and an additional...

CR - 371

CREX - 2

LCD -  496

At 6 month check, there was some recovery to be had, and reminder the LCD was at maintenance this entire time from 3-6 months...

CR - 209

CREX - 129 over expected

LCD -  275

So notice that even after 3 months maintenence level eating, the initial LCD group still had a TDEE 275 below what was expected for their current LBM and FM. Perhaps more time at maintenance it would have recovered?

The CR group slightly recovered, but still 209 lower than expected. 

The CR+EX group actually had an increased TDEE.

Now that was Sedentary TDEE in the lab that was compared.

Daily TDEE with all activity was also compared to their SMR, TDEE/SMR for physical activity rate (PAR).

At month 3, CR and LCD had significant drops in PAR below what would have been expected for their current LBM and FM, by CR 350 and LCD 497, with CR-EX having none. At month 6, CR 215 and LCD 241, so again some recovery.

So the NEAT part of their day decreased as expected because of lower weight, but even more than expected because of less movement, resulting in lowered figures above.

So, that is how much their TDEE dropped along with their lower eating level and weight.

Now imagine during your weight loss, is your TDEE being lower going to help or hinder you for sticking to an eating level? May depend on how little you really want to eat.

They lost in total CR - 8.3, CR-EX - 8.4, LCD - 11.2.

So while the LCD did lose the most (in 3 months too compared to 6), their TDEE had only recovered from 496 to 275 below what it could be, perhaps more recovery was coming. So no wonder the first few months of maintenance could be the hardest, you have the most suppressed TDEE then.

And notice that even the great results of the CR-EX group, still meant 8.4 lbs in 6 months of dieting, with a 25% deficit in essence, 12.5 created by diet, with additional 12.5 by extra exercise. But no loss of TDEE, in fact increase, and mere decent level of cardio.

Other point to keep in mind - no more than 2 x exercise a week was being done prior - so they had a lot of room for improvement. No weight loss prior, so full burning metabolism. And in overweight range, not obese where these effects might not be so bad.

Thought it was interesting info to know. So when you are talking about metabolism slowing down, it's more correctly your TDEE slowing down with all the components of it to some degree, beyond what was going to happen anyway. And recovery to expected levels could be well over 3 months when at maintenance. They reference another study where it took 6 years to.

HBO documentary Weight of the Nation discussing similar study, and the hormones causing the above effect. 

Here is another study reference alot like the one above, this one trying to come up with a formula to take in to account this more than expected downgrade in metabolism/TDEE. 

60 votes + -


michellekicks wrote 103 months ago:
This should be required reading. Thanks for compiling it and making it understandable to the normal person :)
Hadabetter wrote 103 months ago:
Excellent summary, and very interesting findings.
rides4sanity wrote 103 months ago:
Thanks! This was a good summary.
bluelena wrote 103 months ago:
I'll take a higher TDEE at endgame ANY DAY. Thanks for putting this together!
itsallyson wrote 103 months ago:
This was really informative! Thanks for posting :)
EvgeniZyntx wrote 103 months ago:
Excellent excellent write up. Can you also post it to the adaptive thermogenesis thread? I'd love to see it there!
Yasmineh_ wrote 103 months ago:
Really interesting and well put together. Thanks for posting it.
Phaedra2014 wrote 103 months ago:
Very useful. Thank you!
Buddhasmiracle wrote 103 months ago:
Thank you for posting, analyzing the study and summarizing the results. As one poster said above, this should be required reading along with "the roadmap" by helloitsdan.
GymRatGirl13 wrote 103 months ago:
Excellent! Bravo!
prairiewalker wrote 103 months ago:
I concur with all the above praise/ thank you!
RaspberryKeytoneBoondoggle wrote 100 months ago:
Thank you!! (As usual)
OliviaCeed wrote 98 months ago:
I have never heard of this TDEE before. Thank you for the synopsis. I am presently printing the information and since I'm going to see the Wharton Clinic tomorrow for a resting metabolic rate test, this is going to be a topic of discussion! Very interesting information.
MandaLeigh123 wrote 89 months ago:
great read and helps me understand things more!

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