Calorie Restriction is known for extending lifespan in animals and does so in proportion to the degree of restriction. In a long-running experiment by the NIA, rhesus monkeys were split into groups, where one group would eat ad lib and the other group would be put on 30% Calorie Restriction.
The researchers set up the study so that the control fed animals were actually restricted by 10%, so they wouldn’t become fat or obese. The calorie-restricted group would receive 30% fewer calories.
Unfortunately, unlike the Wisconsin study which showed a significant increase in lifespan, this study showed no increase in mean lifespan in the adult-onset CR group. There could be many reasons for this, which I already discussed in my review of the studies here
It was already known that in certain strains of lab animals, 10% restriction can result in as much lifespan extension as 30% CR. Could the contradictory results of the two monkey studies be explained by the fact that the level of restriction in the NIA monkeys was already enough to elicit the maximum lifespan increase in rhesus monkeys?
I’m not so sure that is the answer because the rhesus monkeys failed to exhibit important changes their health parameters that match rodents and people who do calorie restriction. However, in both groups, the monkeys lived to around 35 years old, which is old for a rhesus monkey when you consider the fact that in previous cohorts, monkeys tend to live to an average of 27-28 years. That corresponds to human years to about 21 years of extra life.
They also noted that 4 calorie-restricted monkeys lived to beyond 40 so far, and only 1 ad lib (10% CR). And out of 3264 rhesus monkeys looked at on record, only 2 monkeys had ever reached this age before. So that tells you something… maybe that aging was indeed slowed.
And we are still waiting for the final results from both studies which will be here in a few years time. And also, cancer incidence reported at the time was zero for the 30% CR group in the NIA study.
The researchers wrote about the monkey studies saying
“The possibility that lower levels of DR are as effective in increasing life span as high levels of DR could help explain the contradictory results reported on the effect of DR in rhesus monkeys in studies that were conducted at the University of Wisconsin and the NIA. One of the major differences in these two studies was body weight and the amount of food consumed by the AL monkeys. Body weight and food consumption were signiﬁcantly greater in the AL monkeys in the study at Wisconsin compared to the AL monkeys at the NIA, suggesting that the AL monkeys at the NIA were slightly restricted compared to the AL monkeys at Wisconsin. Therefore, the lack of an increase in longevity reported by Mattison et al. could be because of the AL rhesus monkeys in this study having achieved a level of restriction necessary for an increase in life span, and a further restriction did not further increase lifespan.”
Study in Rats Comparing 10% CR and 40% CR
In a study conducted in rats, the researchers looked to compare the difference in lifespan and disease in rats fed an ad-lib diet, 10% CR and 40% CR.
What was interesting and what came to my attention before I had finished with the paper was that the mean lifespan was similar for both restricted groups and that there was a significant increase in 10% survival and maximum lifespan for the 40% CR compared with the other two groups.
This is similar to the trend that has been noted in the NIA rhesus monkey study. Because of genetic differences, monkeys may respond differently to varying levels of CR.
You can see that quite a few rats in the study below died earlier than the 10% CR group, but the groups diverged near the end of the lifespan curve and the rats who ate 40% less lived far longer. Adlib group max 1026 | 10% CR max 1180 | 40% CR max 1400.
So for a lucky few who do engage in more strict CR, the pay off might be significant. Although, on average, perhaps even a modest reduction in calories will increase your lifespan by quite a few years.
The rate of declining health for the ad lib and 10% CR group was similar, there was no real difference. However, only in the 40% restricted group was the slope of the Gompertz curve altered, reflecting that the aging of these animals was slower and they remained healthier and had a slower rate of decline in their health.
The earlier deaths of some of the 40% CR group suggests that perhaps it was too much for some of the animals.
Humans who practice calorie restriction have greater control over the level of CR and can micro-manage their diet and supplements. We can also use tests to guide our practice and ease back when it might be too much. This gives us the best chance to see the best possible results from calorie restriction without compromising our health.
You can find the full paper here: http://onlinelibrary.wiley.com/doi/10.1111/nyas.12982/epdf
Reviewed and updated: 08/2018