Wow!  I just read a fascinating study directly related to rapid weight loss and metabolism.  I hope you find it as interesting as I did!

In 2012, Darcy L. Johannsen and colleagues reported on the effects of rapid and massive weight loss, even when a large reduction in calories was accompanied by vigorous exercise.  I’m going to summarize the study for you here:

1.  All participants were severely obese, with an average body mass index of 49.4.   (A body mass index of 30 or higher is considered obese.)

2.  After 30 weeks of caloric restriction and vigorous exercise, the subjects lost an average of one third of their initial weight.

3.  Even with vigorous exercise (at least 90 minutes a day, 6 days per week), not all of the subjects’ weight loss was due to the loss of fat.  About 17% of the weight loss was due to the loss of fat-free mass (FFM), including muscle tissue.

4.  Even with vigorous exercise, the subjects’ resting metabolic rate dropped significantly, and this wasn’t just due to a loss of weight.  (A smaller person will generally have a lower resting metabolic rate than a larger person due to less body mass to maintain.)  In other words, the drop in metabolic rate was too large to be explained by the amount of weight lost alone.

5.  This drop in resting metabolic rate was due to a phenomenon called metabolic adaptation.  The brain changes the amount of hormones it secretes, telling the body to slow down the rate of chemical reactions in response to a rapid loss in body weight.

6.  The subjects who lost the most weight had the largest drop in resting metabolic rate.

7.  The researchers cited other studies which suggest that this drop in resting metabolic rate will persist over time, requiring the subjects to continue with vigorous exercise and a reduction in calories to maintain their weight loss.

I was surprised that the subjects lost non-fat tissue, even while exercising an hour and a half to four and a half hours per day.  Their bodies were unable to utilize only fat stores for energy when calories were severely restricted, so some non-fat tissue was lost, despite their exercise regime.  I assume that this loss of non-fat tissue would have been even more marked if the subjects hadn’t been exercising and relied on caloric restriction alone.

The moral of the story–lose weight slowly, unless your doctor recommends rapid weight loss to manage a serious health condition.  While it can be discouraging to see the numbers on the scale change ever so slightly, rapid weight loss, at least in this study with obese subjects, appears to wreak havoc with a person’s metabolic rate.  This means that maintaining a weight loss that was achieved quickly will be very challenging, particularly if the drop in metabolic rate persists.  It’s important to know, however,  that this study used a relatively small amount of subjects (16), and that weight loss was extremely rapid.   It’s quite likely that results would be different if the weight loss wasn’t so rapid.

I’m going to try to find credible research that looks at the effects of slow weight loss on metabolic rate and will post it as soon as I can.  In the meantime, most experts seem to think that a weight loss of one to two pounds a week is the best way to preserve muscle mass and to avoid a large drop in a person’s resting metabolic rate.

If you want to read the entire article, click on this link.

Reference:  Darcy L. Johannsen, Nicolas D. Knuth, Robert Huizenga, Jennifer C. Rood, Eric Ravussin, and Kevin D. Hall.  “Metabolic Slowing with Massive Weight Loss Despite Preservation of Fat-Free Mass”, Journal of Clinical Endocrinology and Metabolism.  2012 July; 97(7), 2489-2496. Published online April 24, 2012.  Retrieved from http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3387402/ on Jan. 31, 2014.

Holly Trimble, MS, LPT

Disclaimer:  This blog is for informational purposes only.  Readers should discuss any specific health concerns with their physicians.