Sunday, July 29, 2012

Research Update: Metabolic Hormones Changes After Weight Loss

Long Term Persistence of Hormonal Adaptations to Weight Loss
New England Journal of Medicine 2011: 365:1597-604.

Objective:  To examine the changes in metabolic hormones for up to a year after weight loss.  We need to learn more about why so many people who lose weight gain it right back.

Methods: 50 overweight subjects were enrolled in a 10 week weight loss program which included a very low calorie diet.  At baseline, after the 10 week weight loss intervention, and 62 weeks, the researchers measured leptin, ghrelin, peptide YY, gastric inhibitory peptide, glucagon-like peptide Y, amylin, pancreatic polypeptide, cholecystokinin, insulin, and subjective ratings of hunger.  Each of these hormones has been shown to have an impact on metabolism and/or energy intake.

Results: After the 10 week low calorie diet, subjects lost an average of 29.7 lbs.  Immediately after weight loss, levels of leptin, peptide YY, cholecystokinin, insulin, and amylin were significantly lower and levels of ghrelin, gastric inhibitory polypeptide, and pancreatic polypeptide were significantly higher.  There was also a significant increase in subjective measures of appetite.

One year after the weight loss, there were still significant differences from baseline in levels of leptin, peptide YY, cholecystokinin, insulin, ghrelin, gastric inhibitory polypeptide, pancreatic polypeptide, as well as hunger.

Discussion: It is not surprising that following weight loss, hormones were changed in a way that promoted weight regain.  We’ve known this for some time.  What is surprising is that they remained that way for a full year after the weight loss!

It is evident that our bodies have amazing defense mechanisms to weight loss.  We evolved in times of drought, famine, and food scarcity.  Those who survived to pass on their genes gained weight quickly, and lost it slowly.  This was most helpful during our early period, but this mechanism has really hurt us in the era of unlimited food availability.

It is becoming clear that the reason so many people regain lost weight is not because they become weak and unfocused with their diet and exercise, but because their body very strongly wants them to put the weight back on.  Weight relapse clearly has a physiological basis.

Take Home Message: After you lose weight, you need to realize that your body starts an all out war to put it back on.  Keep your foot on the gas with your diet, cardio, and resistance training programs.  Your weight loss plan is in no way a temporary thing.  In reality, you need to work just as hard to keep it off as you did to lose it.

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