RACHEL MARTIN, HOST:
If you eat less food, can you live longer? Scientists have debated this question for years. Some studies in fish, rats and monkeys suggests that doing so actually can help you live longer. But there have been very few studies in humans. Now, some researchers have found that when people severely cut down calories, they can slow their metabolism and possibly the aging process. Here's NPR's Patti Neighmond.
PATTI NEIGHMOND, BYLINE: The first challenge for this study was finding people willing to take part. After all, they were being asked to look at their typical plate for breakfast, lunch and dinner and cut it by 25 percent - one-fourth of what they normally ate in a day. And clinical physiologist Leanne Redman says none of them needed to lose weight.
LEANNE REDMAN: We enrolled normal-weight individuals.
NEIGHMOND: Redman headed the study at Pennington Biomedical Research Center in Baton Rouge. Fifty-three healthy volunteers took part. One-third ate their regular meals. The rest were on the severe calorie reduction plan. Redman says the volunteers were committed.
REDMAN: I don't know if you understand the rigor of sort of what it means to do calorie restriction every day, which was the goal for two years.
NEIGHMOND: Not surprisingly, in the end, they lost quite a bit of weight - on average, 25 pounds. Those in the control group gained weight, as much as four pounds. But Redman says weight loss was not the point. She wanted to know whether this dramatic reduction in calories could affect how quickly people age. First, she looked at metabolism. For those on the restricted diet, it slowed and became more efficient.
REDMAN: Basically, it just means that cells are needing less oxygen in order to generate the energy that the body needs to survive. And so the body and the cells are becoming more energy efficient.
NEIGHMOND: And if less oxygen is needed to burn energy, then dangerous byproducts of that burning can be reduced.
REDMAN: Oxygen can actually be damaging to tissues and cells. And so if the cells have become more efficient, then they've got less oxygen left over that can cause this damage.
NEIGHMOND: And that damage can accelerate aging. The study also found blood pressure, cholesterol and triglycerides were lower in the group on severe calorie restriction. Now, these findings don't prove drastic calorie-cutting will actually help people live longer. People would have to be followed for their lifetimes to prove that. And in fact, lowering metabolism can cause other problems. Biochemist Valter Longo studies longevity at the University of Southern California. He says severely restricting calories can mean you're more likely to gain weight in the end.
VALTER LONGO: Basically, you have to eat progressively less to maintain the same weight.
NEIGHMOND: And the fact of the matter is most Americans struggle with too much weight, which can cause countless health problems.
LONGO: For most people, if you consider 70 percent of Americans are either overweight or obese, then you can see how, for most people, this will be a big problem - having a slower metabolism that potentially could be carried for years.
NEIGHMOND: Instead of chronic calorie restriction, Longo's a proponent of mini-fasts, reducing calories to just 900 a day for five days every month. It may not lengthen your life, he says, but it certainly can help you maintain a healthy weight. Patti Neighmond, NPR News.
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