Rapid Weight Loss Tanks Metabolism? The TBL Study

Thanks to Yoni Freedhoff of Weighty Matters blog for providing me with the full text of this one.  Check out his take on the results.  Update 11/11/13:  Full text now available free HERE.

Context: An important goal during weight loss is to maximize fat loss while preserving metabolically active fat-free mass (FFM). Massive weight loss typically results in substantial loss of FFM potentially slowing metabolic rate.

Objective: Our objective was to determine whether a weight loss program consisting of diet restriction and vigorous exercise helped to preserve FFM and maintain resting metabolic rate (RMR).

Participants and Intervention: We measured body composition by dual-energy x-ray absorptiometry, RMR by indirect calorimetry, and total energy expenditure by doubly labeled water at baseline (n = 16), wk 6 (n = 11), and wk 30 (n = 16).

Results: At baseline, participants were severely obese (×± sd; body mass index 49.4 ± 9.4 kg/m²) with 49 ± 5% body fat. At wk 30, more than one third of initial body weight was lost (−38 ± 9%) and consisted of 17 ± 8% from FFM and 83 ± 8% from fat. RMR declined out of proportion to the decrease in body mass, demonstrating a substantial metabolic adaptation (−244 ± 231 and −504 ± 171 kcal/d at wk 6 and 30, respectively, P < 0.01). Energy expenditure attributed to physical activity increased by 10.2 ± 5.1 kcal/kg·d at wk 6 and 6.0 ± 4.1 kcal/kg·d at wk 30 (P < 0.001 vs. zero).

Conclusions: Despite relative preservation of FFM, exercise did not prevent dramatic slowing of resting metabolism out of proportion to weight loss. This metabolic adaptation may persist during weight maintenance and predispose to weight regain unless high levels of physical activity or caloric restriction are maintained.

Now, the results in the abstract sound daunting and a lot of people point to the techniques used on The Biggest Loser to blame the relapse of a good number of contestants.  In a 2010 podcast with Jimmy Moore, Dr. Michael Dansinger who works on TBL  gave some unscientific stats that roughly 1/3rd kept the weight off, 1/3rd gained back significant amounts -- like half, and 1/3rd relapsed to starting weight (or higher?).  Even if these are a bit "off" this is no worse and likely better than the general population track record, and that includes all the millions who have shed buku poundage on Atkins, etc.   More thoughts on that later.  So they took 16 participants and "linear regression analysis was used to generate an equation for predicting RMR based on FFM, FM, age, and sex at baseline".  Here is the plot of adjusted RMR's and the equation for the regression line used to predict RMR at reduced weight and the table of results:

Now the first thing that stuck out to me was the amazing RMR's!!  I mean at Week 30, at ~ 190 lbs average weight and 27% body fat, the average RMR was 1763 cal/day.  I know without having it checked that my own RMR at ~200 lbs (I logged intake and weighed for a pretty decent stretch in 2009) had to be quite a bit lower as I maintained at roughly 1500 cal/day.   As if 1763 weren't enough, their TDEE was 2900 cal/day -- an enormous amount of food!  I'd say that it's really hard to justify any sort of assertion that TBL "damages" let alone "destroys" contestants' metabolisms.  Now I imagine the TDEE maintenance calories would go down w/o the 4-6 hrs/day of exercise, but if one picks the right foods, the 1763 cal/day RMR translates to roughly 2350 cal/day for a very sedentary person (using RMR as 75% of TDEE).  When one considers that Mark Sisson's full sample menu (which he states he rarely eats in its entirety) is around 2500 cal/day, I think making excuses for regain based on some differential from predicted reduction in RMR is bogus.  That's two 1000 cal meals and a 500 cal meal.  If one of those 1000 cal meals is breakfast, that's 5 eggs fried in butter and a large bagel with cream cheese.  Then one could go to McD's for a light lunch for 500 calories and eat 3 Lean Cuisines for dinner.  I mean really ....

Frankly as I've been working on my RMR post, I must say I was shocked to see how high their RMR's were.  Their initial RMR's are also phenomenal so it's fair to say these contestants did not get obese because their metabolisms were hopelessly slow or they had dysfunctional mitochondria or whatever.

So, is there any other useful information to be gleaned from this study and/or TBL in general?  Well, for one, overtraining -- and I don't subscribe to this part, but it IS a competition reality show after all -- and whatever cortisol that produces does not prevent *massive* weight loss.  Secondly, from the use it or lose it category, high volume exercise -- the bulk of which is "cardio" -- does appear to be quite effective in maintaining lean body mass.   Now, here's my rub with how this study was presented.  They say:

Despite relative preservation of FFM, exercise did not prevent dramatic slowing of resting metabolism out of proportion to weight loss.

And yet the plot was for adjusted RMR and then the regression line used to predict the post-weight loss intervention took other factors into account.  Yet RMR is know to correlate rather tightly with FFM (fat-free mass aka LBM = lean body mass).  I would love to have seen a regression of measured RMR vs. FFM.  Perhaps this would produce the same conclusions, but body weight does NOT correlate all that well with RMR.  If you're looking at how an intervention impacts metabolism, and you're going to "call out" preservation of lean mass, it would be more appropriate to present that analysis (if it was even done, and if not, why not?) than the analysis they did.

The results of this study demonstrate that despite a relative "tanking" of metabolism, participants were able to shed boatloads of fat with admirable preservation of lean mass.  That perhaps the rapidity of the intervention is  insufficient to allow for adjusting to the NORMAL food intake required to maintain the losses.