Hungry Mice Live Longer, Hungry People Might, Too

Can you starve your way to a long life and great health? According to several studies on calorie restriction in mice, possibly so.

Obviously, that's a plan that can go too far. Anorexia kills. And the consequences are dire even among the cured. Canadian researchers have calculated that girls who were anorexic at age 15 and recovered would cut 25 years off their life span.

But for those of us well above the anorexic level, what about all those studies that show calorie-restricted (CR) diets are linked to living longer? 

It's a pertinent question because roughly 40% of Americans are obese. And, 70% of us are at least a little overweight. People whose weights are “normal” on height-weight charts are actually a minority.

There are plenty of logical reasons for us to shed pounds. Obesity is highly correlated with some kinds of cancer, diabetes, heart disease, knee and back pains, asthma, sleep apnea...

Yet, Americans keep getting heavier. And those of us who do shed a few pounds almost always regain them.

Except for those who believe in CR. The CR advantage probably comes down to attitude:

•                     Why diet to lose weight: Eat less to gradually get skinny because if you're fat you might get sick from one of many possible things (some of which could happen to you whether you diet or not) some day in the future.

•                     Why CR: Eat less so you will live longer. Getting thin is a nice bonus.

CR can be approached in many ways. Some people just cut calories by a significant amount every day. That can range from 10% less than your normal intake to 30% less. Others choose to eat regularly for 5 days a week and fast or drastically reduce their calories on the other two.  Yet others fast on a different schedule.

The CR idea is so widely touted and has been “proven” so many times:

•                     Nematodes (worms) lived longer when their calories were restricted and they were receiving resveratrol at the same time.

•                     Another experiment on yeast and flies also showed they lived longer on restricted calories, again results were best when the subjects were fed resveratrol.

•                     A new experiment just showed that mice also lived longer when fed only once a day, presumably because that meant they fasted longer as well as receiving fewer calories overall.

Over the years, CR experiments have focused on mice, flies, worms, and fungi because their short lifespans make it easy to follow subjects through whole generations.

We don't know nearly as much about the effect on humans. There has never been an experiment where researchers began restricting the calories of dozens of children, kept them on restriction for the rest of their lives, and followed them all the way from cradle to grave. There never will be. 

The best we have are some correlations. Based on data from 900,000 western European and North American adults body mass is strongly associated with lifespan. Among the morbidly obese, half died by age 70. Among the lean, less than a quarter had died by age 70.

There have also been some short-term experiments. Valter Longo at USC had subjects cut their calories in half five days per month. After three months, they managed to lower their triglycerides, cholesterol, and body mass. Their blood glucose levels improved, too.

That seemed promising. Alas, the diet wasn't popular. A fourth of the subjects dropped out of the experiment before the three-month mark. The odds that millions of us would use this approach for our entire lives, as Longo suggests we should, are somewhere between dismal and impossible.

Now the good news... Everything we know about CR so far doesn't suggest you should go that route if you don't want to. While the disadvantages of obesity are real, the advantages of CR are still in question.

Let's start with the obvious. You are not a mouse.

Murine—mouse—studies are significant and very helpful, but they're limited. It's one thing to test the chemistry and physiology of a drug on mice with their similar biology. It's quite another to use mice to test lifestyle choices when their lives differ so greatly from ours.

Those long-living mice existed in a highly protected environment with no predators, food shortages, crummy bosses, bills due... you get the idea. So far there are no perfectly controlled studies that prove any one of us will live longer with a CR lifestyle. All we know for sure is that being obese is not good.

Second, there is definite support for the importance of resveratrol in life extension, and it seems especially helpful when cutting calories.

And finally, newer research with primates and studies on human data sets expand the story. Longevity may have a better relationship to maintaining muscle mass than it does to maintaining the waist you had when you were 18 years old and in your physical prime.

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