A scientist at Washington University in St. Louis worked with Calorie Restriction Society members (known as CRONies - Calorie Restriction with Optimal Nutrition) to see whether calorie restriction (CR) would extend life as well in humans as it does in rats and mice. Well, among the CRONies calorie restriction did not lower the level of a growth factor called IGF-1 as well as CR does in mice. This suggests that human calorie restriction might not extend life as much as it does in mice.
St. Louis, Sept. 24, 2008 — Calorie restriction, a diet that is low in calories and high in nutrition, may not be as effective at extending life in people as it is in rodents, according to scientists at Washington University School of Medicine in St. Louis.
Previous research had shown that laboratory animals given 30 percent to 50 percent less food can live up to 50 percent longer. Because of those findings, some people have adopted calorie restriction in the hope that they can lengthen their lives. But the new research suggests the diet may not have the desired effect unless people on calorie restriction also pay attention to their protein intake.
Biogerontology theorist Aubrey de Grey already does not expect CR to extend human life by double digit percentages like it does in rodents. Aubrey argues that CR might extend human life by a year or two as a way to help people live longer to reproduce after a couple of bad growing seasons. The selective pressure on humans about how their metabolism should respond to CR probably didn't produce a capacity for human metabolism to reduce the rate of aging by such a large amount. Besides, we already have many life-extending mutations that mice do not have as we live much longer than they do.
In an article published online this month in the journal Aging Cell, investigators point to a discrepancy between humans and animals on calorie restriction. In the majority of the animal models of longevity, extended lifespan involves pathways related to a growth factor called IGF-1 (insulin-like growth factor-1), which is produced primarily in the liver. Production is stimulated by growth hormone and can be reduced by fasting or by insensitivity to growth hormone. In calorie-restricted animals, levels of circulating IGF-1 decline between 30 percent and 40 percent.
"We looked at IGF-1 in humans doing calorie restriction," says first author Luigi Fontana, M.D., Ph.D., assistant professor of medicine at Washington University and an investigator at the Istituto Superiore di Sanità in Rome, Italy. "For years, we have been following a cohort of people from the CR Society who have been on long-term calorie restriction. We found no difference in IGF-1 levels between people on calorie restriction and those who are not."
Fontana decided that since vegans have much lower IGF-1 levels that perhaps lowering protein intake in CRONies would work to lower IGF-1. Well, yes, it did. So here's the bottom line: maybe reducing protein consumption will allow us to live longer.
Again, Fontana had a ready-made study group. His team has been following a population of strict vegans for several years. They tend to eat less protein than the CRONies from the CR Society, so he compared IGF-1 levels between the two groups.
"The vegans had significantly less circulating IGF-1, even if they were heavier and had more body fat than CRONies," he says. "Protein in the diet seemed to correlate with the lower levels of IGF-1. The strict vegans took in about 10 percent of their total calories from protein, whereas those on calorie restriction tended to get about 23 or 24 percent of calories from protein."
The investigators wanted to take one more look at the relationship between dietary protein and IGF-1, so Fontana asked a group of CRONies to eat less protein for a few weeks. He says it was not easy to cut protein because those on calorie restriction have to do a lot of calculating and juggling to ensure they take in very few calories and still get adequate nutrition. Increasing dietary protein is one way many CRONies guard against becoming malnourished.
"But six of them agreed to lower their protein intake," Fontana explains, "and after three weeks their circulating IGF-1 declined dramatically."
Cutting back on your protein consumption is easier than cutting back on your calories.
By Randall Parker at 2008 September 25 12:13 AM Aging Diet Studies | TrackBackActually CR does not increase life spans, what it does is make the same amount of time seem like forever.
My basic take on all of this is that we don't really know enough about how diets affect our metabolism to generate a useful plan of action.
Fat was bad, then saturated fat, then transfats. Now protein may kill us sooner... or it may not. Sugar is bad, especially the high fructose kind etc...
We only have three sources of calories; fats, proteins and carbohydrates. Now that they are all bad for us what are we to eat?
Nutrition science is roughly where medicine as a whole was when we were casting out evil spirits. Eat what you like.
Studies of Seventh Day Adventists show that those that follow a vegan regimen have nearly a decade additional longevity compared to S.D.Adventists who eat meat. Studies also indicate that protein from milk adds to the negative effect.
Cheers,
Dave
Does low meat consumption increase life expectancy in humans?1,2,3
Pramil N Singh, Joan Sabaté and Gary E Fraser
Background: Since meat products represent a major source of protein in the Western diet, findings on whether meat intake significantly contributes to the burden of fatal disease have important clinical and public health implications.
Objective: The objective was to examine whether a very low meat intake (less than weekly) contributes to greater longevity.
Design: We reviewed data from 6 prospective cohort studies and report new findings on the life expectancy of long-term vegetarians from the Adventist Health Study.
Results: Our review of the 6 studies found the following trends: 1) a very low meat intake was associated with a significant decrease in risk of death in 4 studies, a nonsignificant decrease in risk of death in the fifth study, and virtually no association in the sixth study; 2) 2 of the studies in which a low meat intake significantly decreased mortality risk also indicated that a longer duration ( 2 decades) of adherence to this diet contributed to a significant decrease in mortality risk and a significant 3.6-y (95% CI: 1.4, 5.8 y) increase in life expectancy; and 3) the protective effect of a very low meat intake seems to attenuate after the ninth decade. Some of the variation in the survival advantage in vegetarians may have been due to marked differences between studies in adjustment for confounders, the definition of vegetarian, measurement error, age distribution, the healthy volunteer effect, and intake of specific plant foods by the vegetarians.
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5 R. Popham, W. Schmidt, and Y. Israel, "Variation in Mortality From Ischemic Heart Disease in Relation to Alcohol and Milk Consumption," Medical Hypotheses, 12, No. 4 (1983), 321-329.
Researchers studying 19 Western countries concluded that heart disease mortality rises as consumption of milk protein rises. The researchers noted, "Multiple regression analysis confirmed the importance of the milk factor … as a determinant of variation in ischemic heart disease mortality rates."
Fat Man,
Yes, I couldn't stand to live in a perpetual state of hunger. If I didn't have to work maybe I could do it. But I need to be able to concentrate and CR would cut into that.
Ben Franklen,
The research results on diet have become more refined in what they tell us. The old fat-bad message has been replaced by more precise advice. Yes, trans fats really are bad for you. Some fats are beneficial (omega 3 fatty acids) or at least neutral (monounsaturates).
Dave Gobel,
Thanks for that highly relevant study.
Confounding influences: A typical person eating a vegetarian diet certainly makes many other nutrition-improving choices. Maybe the sure advice is to eat a Seventh Day Adventist vegan diet based on what they say they eat. Plus B-12 tablets.
Milk: I wonder if hormones or fat in milk are the culprits.
Two points first to address the comments made to this post
- I have never been able to think more clearly, concentrate and memorize things better than anytime in my life before I went on CR.
- Calorie Restriction has never caused me more significant hunger, in fact, I eat more food (volume wise) that I did ad lib, and more variety
Now as for the article and whether or not CR will extend lifespan in humans. If you refer back to some old studies done on rodents you will find that increasing protein intake, in the context of a CR diet, leads to 'longer life' in the CR group, and less disease. I'm unsure whether the protein increase (upto 50% of the diet) attenuates the reduction of IGF-1 normally seen in CR mice, but I assume it does to some extent. This is not evidence against CR at all, pretty much all previous results on humans have been beneficial. To name a findings; Virtually no risk of heart disease, diabetes or stroke. Little risk of autoimmune disease, no inflammation, less DNA damage, up regulation of genes involved in longevity (SIRT1), biomarkers that correlate with longevity such as very low fasting insulin and glucose, low body temperature, and overtime we expect less decline in DHEA. We see the same hormonal, metabolic changes. Doctor Fontana even found that those on CR have hearts that function 15-20 years younger than their ages! This is big news. We hypothesis why centenarians become 'centenarians', why they make it to that big number of 100. Well if anything is going to give you that chance it HAS to be CR right? The common characteristics that are thought to enable people to reach 100 are being found in those that go on a CRON diet. We put genetically identical mice on CR and they live upto 50% longer, this is because the longevity gene resides in us, it's just about epigenetics, turning on those genes. Right?
Most deaths in humans is caused by cardiovascular disease, IGF-1 plays a big role in cancers and rodents DO die of cancer much more frequently than humans. I believe that this is not a negative finding at all, and people on a CR diet should really think carefully before reducing their protein intake to such low levels while on CR.
If you want to live long enough to see real anti aging therapies. Be smart and practice some form of CR, whether it be just cutting out snacks or being on a more moderate diet. CR, not supplements or anything else is going to give the biggest chance of staying alive.
Matt,
My very strong suspicion is that people who can do CR diets have a lot less hunger than the people who can't keep weight off.
Far more people try to lose weight than try to do CR. We know from lots of studies of those who try to control their weight that few can sustain weight loss. Now, would they do better if they took their weight way way down? I'm curious to know whether more radical weight reduction results in an easier time keeping off the weight.
Matthew,
Can you recommend some web resources for starting a CRON program?
Randall,
"We know from lots of studies of those who try to control their weight that few can sustain weight loss. Now, would they do better if they took their weight way way down?"
I think so, if only because people on CRON diets accept that they will have to pay detailed attention to everything they eat. Most dieters pay that kind of attention during the diet, and relapse when they go back to "real life".