After weight loss, natural human biology powerfully drives weight regain.  Thus, many people who have weight loss success with lifestyle changes struggle to keep weight off over the long term, often resulting in a ‘yo-yo’ pattern of weight fluctuation over the course of their life.


We know that weight loss is associated with many metabolic health benefits, but what is the effect of yo-yo weight cycling on health over the long term?  If weight is regained, are the health benefits from the prior weight loss maintained?  Are we back to Square One with the same metabolic health that we had before the last yo-yo? Could metabolic health be worse, compared to before the last yo?


Human studies on this topic have shown conflicting results.   It is very difficult to answer this question with human studies, as people need to be followed for years to a lifetime, and controlled clinical trials are very difficult (dare I say impossible) to conduct rigorously for that period of time.  (Regular readers may recall a small study I blogged on previously, which did provide some very interesting insights.)


Given the challenges of large, long, human studies, a recent systematic review and meta-analysis looked at the available animal studies on this topic.


Authors identified 29 studies, all of which were conducted in rats or mice. They evaluated data on two questions:


1.  How does metabolic health compare between animals who have been weight cycling (yo-yo), vs animals who have always carried elevated body weight?


2.  How does metabolic health compare between animals who have been weight cycling (yo-yo), vs animals who developed obesity later in life?


They found that there were no differences in health outcomes between weight cycled animals and those with lifelong obesity, despite the fact that weight cycled animals had a lower body weight.  If we extrapolate these results to humans, the message here is that metabolic health improvements with lifestyle-induced weight loss disappear when weight is regained.  (Actual human studies show conflicting results on this.  Some human studies show continued metabolic health benefits after weight regain, which may be related to long lasting lifestyle changes that are independent of their weight, such as healthier food choices or exercise.)


The second key finding was that weight cycled animals had worse metabolic health than animals who developed obesity for the first time later in life.  Weight cycled (yo-yo) animals had higher body weight, which may have something to do with their metabolic health being worse. However, some studies have observed that inflammatory changes with obesity are more pronounced with weight cycling.  Changes in gut bacteria with an obesity-promoting diet, towards those which favor weight regain and metabolic disease,  may persist despite weight loss. Finally, a reduction in energy burn in brown fat in weight cycled animals may contribute.


An additional parameter for which data was assessed was the effect of weight cycling on liver inflammation, with some studies showing greater liver inflammation in weight cycled animals than those who always had obesity.  In humans, we know that weight loss improves fatty liver disease.  If weight regain could damage human liver health, this speaks to the paramount importance of maintaining weight loss long term.


BOTTOM LINE: In these animal studies, metabolic health benefits of weight loss disappear when weight is regained. Yo-yo weight fluctuations may result in worse metabolic health later in life, compared to those who develop obesity later in life for the first time.   If these findings are also true in humans, this speaks to the importance of maintaining weight loss long term.  As the authors note,

Pharmacologic treatment (weight management medication) and metabolic (bariatric) surgery may need to plan a greater role in the management of obesity, to achieve long-lasting health benefits. 


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