Complicating the Picture for Calorie Restriction and Fat

A survey of calorie restriction in many mouse breeds finds that it doesn't work to extend healthy life in all, and that difference appears to be related to the degree to which calorie restriction results in fat loss. This presents an interesting complication, given that it has been clearly demonstrated that surgically removing visceral fat extends life in mice, and the human studies of calorie restriction show unambiguously positive results on health: "Since the 1930s scientists have proposed food restriction as a way to extend life in mice. Though feeding a reduced-calorie diet has indeed lengthened the life spans of mice, rats and many other species, new studies with dozens of different mouse strains indicate that food restriction does not work in all cases. ... [Researchers] studied the effect of food restriction on fat and weight loss in 41 genetically different strains of mice. The scientists then correlated the amount of fat reduction to life span. The answer: Mice that maintained their fat actually lived longer. Those that lost fat died earlier. ... Indeed, the greater the fat loss, the greater the likelihood the mice would have a negative response to dietary restriction, i.e., shortened life. This is contrary to the widely held view that loss of fat is important for the life-extending effect of dietary restriction. It turns the tables a bit."



This was also observed in older studies, i.e., CR longevity effect is greatest in lab animals losing least weight. Looks like researchers are stuck in a loop.

Posted by: Lou Pagnucco at May 5th, 2011 8:53 AM

What if there are two types of lab animals -- those that respond to caloric restriction by reducing their metabolic rate, and those that continue at the same metabolic rate. The ones that reduce metabolic rate conserve their fat and age less rapidly because their body is performing fewer operations per unit time and have less metabolic stress per unit time. The ones that continue at the same metabolic rate lose their fat, become stressed because they are malnourished, and therefore appear to age normally despite the reduced caloric intake.

Posted by: Parker at May 5th, 2011 4:36 PM

Very strange. I'd be interested to see the details of this study. I wonder if this fat to longevity ratio also holds in humans? If find it difficult to believe that a body fat % in the low but healthy range would reduce longevity. Regardless, I think Cronies should be heartened by the fact that the main long-term CR study I know of in humans, the Honolulu Heart Study, showed those who restricted calories were among the longest-lived in their population.

Posted by: Kim at May 6th, 2011 2:32 PM

I'd be interested in seeing the results also. On the surface this is discouraging, but it isn't even clear to me that any new testing was done here, the use of the term 'survey' implies to me that they just reprocessed data from pervious tests. The more reports I read, the less import I put on any one report. I'd bet there are large flaws here.

Posted by: JohnD at May 9th, 2011 10:13 AM

A somewhat related thread you might find interesting over at the Immortality Institute.

A few studies have shown lower mortality rates in overweight people.

Posted by: Justin at May 10th, 2011 10:18 AM

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