Friday, September 14, 2012

Science Friday: Calories and Aging

Note: This post doesn't have much to do with running or exercise, but it does talk about staying healthy into old age, which I think is something of interest to most active people

A few years ago I was watching a segment on the Discovery Channel about diets and aging. It was discussing how starvation conditions (a man was trapped in a cave) tell our bodies to shut down the aging process. (When the man emerged from the cave weeks later, he hadn't aged a day.) Fascinating stuff. It went on to suggest that if we reduced our calorie intake we would live longer. Still not too much of a stretch. But then it used an example of someone slashing their normal diet in half, from 4000 calories/day to 2000 calories/day, and (surprise!) that would lead to a longer life.

That's when I turned the TV off. First of all, 2000 calories/day is not near starvation, it's the recommended amount for the typical adult. (Whether or not people are actually eating closer to 4000 calories is besides the point.) Obviously cutting back from overeating will lead to a longer life. But what about reducing a 2000 calorie/day diet? Is there a benefit to that? Ever since the Discovery Channel completely misinterpreted the point, I've cringed a little when I read calorie restriction studies. 

Granted, it's difficult to do these studies in humans. There aren't many volunteers ready and willing to be nearly starving subjects, let alone graduate students who want to wait a lifetime to get the results. The next best thing is primate studies. In the 80s, two groups started putting monkeys on calorie restricted diets (30% fewer calories than normal diets) and then let them age (for 20+ years). One study was done at the Wisconsin National Primate Research Center (WNPRC) and published in 2009. It showed some promise for calorie restriction: the monkeys fed less outlived the monkeys on a normal diet. However, another study, done at the National Institute of Aging (NIA), came out this month and found much the opposite.

The NIA study looked at two cohorts, one that was started on the restricted diet at an old age, and one that started at a young age. The monkeys put on restricted diets in old age had no difference in survival compared to monkeys eating the normal amount of calories. However, there were some health benefits; compared to monkeys on a normal diet, they weighed less and had lower levels of triglycerides, cholesterol, fasting glucose, and oxidative stress. The animals put on a restricted diet at a young age also had no benefit in survival. Furthermore, no other health benefits were observed. Although they weighed less, there were no striking differences between triglycerides or glucose levels. They did have fewer cases of cancer, but diabetes and cardiovascular disease were not prevented.

The results from this study suggest that diet restriction doesn't increase longevity. The major difference between the WNPRC and NIA studies (besides the genetics of the animals, which is a factor, but I won't get into it) is the diets given the monkeys. The diets from the NIA study were healthier: they had less sugar, more antioxidants, and fish oil. (Give the WNPRC some credit; they started these studies in the 80’s when most people were concerned only with total calories.) Additionally and importantly, the control animals in the NIA study weren't allowed to eat as much as they wanted, like the WNPRC animals. They were slightly restricted in order to maintain a healthy calorie intake. The control animals in the WNPRC study may have represented more of an overweight population. So perhaps the WNPRC study was doing more of what I feared these studies would do: just slash the calories of a diet that's too caloric and not very healthy to begin with. Of course you'll be healthier after eating less of a poor diet.

There's a lot more research to be done here.  There may be some benefit to smaller, nutritionally complete (an important point!) diets, but we aren't sure yet. The diets themselves matter, as well as the genetics, the current age, etc. Another study looked at people and found those within a normal weight range (BMI 20.0-24.9) had the lowest mortality rates. So we shouldn't be gorging ourselves, but maybe not starving ourselves either. That sounds good to me.

Dream big,

1 comment :

  1. When I was living and training in Russia before the 2000 trials, the coach in charge of the OTC was big on restricted calorie diets. In my limited Russian vocubulary I gathered from him that he believed that it takes a tremendous amount of energy for your body to metabolize and digest food. Time where it could be concentrating it's energy in repairing muscles from hard workouts. Any calorie beyond replacement was wasting energy. Plus he felt that the more you ate the more toxins you took in and had to process which meant the more chance of one NOT getting processed and becoming carcinogenic.

    When I moved to the Olympic training base I was already a tiny guy and weighed 133lbs and was running around 90miles a week. After 8 months there I was eating significantly less (and drastically less meat, weighed between 122 - 126lbs and running 120miles a week. When you do the math each pound you carry around in a marathon is a big deal. Of course...I can't say if it was the training, being able to dedicate my time to running and not work, or the diet.... but I did improve from 2:28 down to 2:18. Not really fast...but a considerable improvement in one marathon season.

    I did feel consistantly hungry but was assured that hunger was a normal human condition, and also knew myself that often feelings of hunger were due to dehydration.

    Anyways, when I came back to the US it's something that stuck with me and I read many of these same studies. I occasionally chat with that coach when I help recruit for colleges. I should ask him where he came up with this and what conclusions he has about it (now that I speak better Russian).