MADELEINE BRAND, host:
Scientists have studied whether an extremely low calorie diet could mean a longer life, and they've come up with some interesting results. Here to parse them is our medical expert, Dr. Sydney Spiesel. He writes for the online magazine, Slate, and teaches at the Yale Medical School. Welcome, Syd.
Dr. SYDNEY SPIESEL (Medical Columnist, Slate Magazine): Hi, thank you.
BRAND: What did these researchers find? These were researchers at Louisiana State University.
Dr. SPIESEL: Well, they found a couple things. One is that there're a bunch of factors that we know are present in people who live a long time. Their insulin levels are lower. Their body temperature is lower. They have a slightly elevated level of a certain hormone that's produced by the adrenals. Their DNA seems to be more stable. So the question that the researchers addressed, and they addressed it by dividing their subject into groups who had diets with normal amounts of calories and diets with very dramatically reduced amounts of calories.
What they did was they just looked at which of these factors that we know are associated with longevity were influenced by the decreased level of calories in the diet, and what they found were subjects who had decreased calories had lower insulin levels, had lower body temperature. Their metabolism turned down. They made more efficient use of calories, and, in addition, there was less damage to their DNA.
And that was quite interesting, because one of the things that we believe, or many people believe is that DNA breakdown, in all of us, is, in some way, related to the aging process.
BRAND: How many calories are we talking about with an extremely low-calorie diet?
Dr. SPIESEL: Well, in terms of the study, they determined what the baseline caloric need was for each of the people in the study. And then, for some of the people, they just took that baseline caloric need and reduced it by 25 percent.
BRAND: So we're not going to know--this was a six-month study, Syd. We're not going to know whether or not these people will live longer.
Dr. SPIESEL: We actually may never know that. There's no way that I can imagine, although I've been thinking about it, that we could really do a study that would determine what dietary effects really make people live longer, because the only really scientific way to do the study would be to take two groups of infants, right? You put one of them in one room, and one group in another room, and you feed them--one group a normal diet and the other group, a calorie-reduced diet, and you just watch them for, oh, 70, 80 years.
(Soundbite of laughter)
BRAND: There is a group called the Calorie Restriction Society, and they're advocating a 900-calorie-per-day diet. That sounds pretty extreme.
Dr. SPIESEL: Well, it sounds very extreme, and 900 calories a day, anybody will lose weight dramatically, and there are a lot of negative things that happen. And to be fair, in their very own Web site of the organization, they list a lot of the risks, of which one of them is that people just don't look as good when they're terribly sort of cadaverous, and that's what happens to people on very reduced diets.
Their bones may weaken. They become quite sensitive to cold. Women will gradually lose their periods. That's something we see in anorectic youngsters. There's a little, sort of subtle things. When we sit down, some of what we're protected against is by the natural fat that we have, which is padding. There is a loss of that kind of cushioning.
The other thing is a very subtle thing. You're hungry all the time. I mean, my own guess is that people--I don't function very well if I'm hungry all the time. I might live longer, or maybe it would just feel longer.
BRAND: Dr. Sydney Spiesel writes for the online magazine, Slate, and he's also a Yale Medical School professor. Thank you, Syd.
Dr. SPIESEL: Thank you. Nice to be here. Transcript provided by NPR, Copyright NPR.