Caloric Restriction: Comment and Response

by Nina and Brad

Brad’s post on caloric restriction (see Caloric Restriction and Longevity) prompted an interesting comment from Kathleen Summers MD PhD that I thought it worthwhile to share with you. Rather than having Brad respond in the comments section (I'm not sure how many of you actually read the comments), I asked him to reply to her comment at the end of this post. So have a look! This debate is a very good example of how little scientists currently understand about the aging process (a theme we return to periodically) and provides a hint of some of the many issues surrounding the controversy regarding the best diet for healthy aging.

Posted by Kathleen Summers MD PhD to YOGA FOR HEALTHY AGING

The biggest lesson here is that an excess of energy intake brings disease, disability, and early death. Restricting intake protects against cancer - and also diabetes, arthritis, and heart disease to some degree, although the numbers in the latest study didn't reach significance for the latter (potentially due to limited sample size). Teasing out just what the optimal amount of intake is takes time and research. And it's complicated - there's nutritional, environmental, mental/emotional health, and genetics among other factors playing a role.

The monkeys in both groups of the Wisconsin study ate more and weighed more than the NIH monkeys. The researchers used different sources for their proteins, fats, and carbs as well as a different approach to vitamin and mineral supplementation.

We have one primate study showing extended life span with calorie restriction and one not showing the same but yet other positive results. Let's not jump to absolute conclusions about what the latter study means.

Response from Brad Gibson PhD

Kathleen,

You make some good points, and I agree that this most recent NIA caloric restriction study needs to be considered within the context of other published work. There are undoubtedly many nuances in experimental design and interpretation that future experiments will need to address. That said, my major point is that the data for CR in primates is weak at best.  Many of my colleagues were very critical of the earlier Wisconsin study on two counts: the fact that they fed the control group a fairly high caloric diet and that they removed animals from their final analysis on the basis that they died from non age-related reasons. The removal of animals in the final statistical analysis was a very dubious call. And, as it was pointed out in the NYT article—and by many critics of the Wisconsin study—if those animals were included there was no difference in longevity between the two primate groups. Combined with other studies on more diverse genetic backgrounds in mice that show very mixed effects of CR, one really has to wonder how much traction the CR models has left in it, at least in mammals. Oddly, the data on other model organisms (flies, worms etc.) remain strong.  But one can only push these conserved evolutionary arguments so far.

While there may be benefits in a CR diet as you indicate (e.g., cancer and heart disease), one needs to make a distinction between a low calorie diet and caloric restriction. Many years ago a very prominent scientist in the field of aging who practiced the CR diet stated at the end of his seminar that "we scientists" needed to make a case to the public about the benefits of CR. I challenged him on this assertion, saying that American's relationship to food is so screwed up as it is, that to send a message that food is your enemy is not good advice. There is no evidence that CR in humans is beneficial. In contrast, there's plenty of evidence that a sound, balanced, healthy, low-to-moderate caloric diet (especially one that limits or avoid meat and dairy) is good for you. I suspect we are in agreement on that point.

I also agree that we are still far from drawing a final conclusion on the benefits of CR on human longevity. I was a bit flippant on this point in my last blog post. Guilty as charged. And there is little doubt that there will be more NIH studies examining CR and longevity in various mammalian and primate models as there is still compelling and interesting evidence that needs to be sorted when all animal models of CR and longevity are considered. However, I for one, will be placing my bets elsewhere.

Caloric Restriction and Longevity

by Nina and Brad

You may have noticed that we’ve been talking about yoga for healthy eating this week (see Yoga for Healthy Eating) without defining what “healthy eating” entails. To be honest, we’ve intentionally been avoiding getting too specific about dietary recommendations because there is so much controversy these days about what a healthy diet is. However, one thing we can now say with confidence is that the best diet for healthy aging does not mean starving yourself. In today’s New York Times, the results of a 25 year study at National Institutes of Health on caloric restriction was announced, disproving the somewhat popular theory that a low-calorie diet will prolong our life span. See Severe Diet Doesn’t Prolong Life, at Least in Monkeys.

Photo from National Institutes of Health

Since we just happen to have a bona fide scientist who studies aging on our staff, we decided to ask him to weigh in. Here’s what Prof. Bradford Gibson (aka Brad) has to say about this news and about caloric restriction in general:

"The data demonstrating that caloric restriction (CR) increasing longevity is impressive, at least for yeast, worms and flies. It was generally thought that this link between CR and longevity was evolutionarily conserved in mammals as well, as evidence from several mouse and rat studies seemed to indicate. (However, even the mouse data has come under scrutiny as the CR effect does not seem to work nearly as well in when these studies are carried out on mice with more diverse genetic backgrounds, you know, like the ones in your attic as opposed to the inbred lab strains.)

"The primate studies, however, have been obviously more problematic to carry out, considering the cost and time required to get the results can be 20 years or more. This, of course, has not discouraged some people, including some very prominent scientist, to adopt this seriously restrictive diet by choice. Personally, I thought they were nuts to do so; but the field of aging research has always attracted extreme positions and is littered with false or exceedingly thin claims and snake oil salesmen, despite the general field of aging research becoming more mainstream. So what have we learned? Hypothesis fail. Experimental designs are flawed. Things are more complicated than we thought. And I can assert that my own small number of encounters of people on the CR diet suggest that they don't look so good, i.e., pale, gaunt, and a bit listless. So enjoy your meal, wine and chocolate, and maybe the field of aging research will move on to a more interesting and scientifically compelling hypothesis to spend our NIH dollars on."