Dubai, United Arab Emirates (CNN) — People of normal weight may be able to extend their lives by restricting the calories they consume, according to a new study that attempted to measure the pace of aging in people who were asked to reduce calories by 25%, over the course of two years.
“We’ve known for about 100 years that calorie restriction can extend the healthy lifespan of a variety of animals in the laboratory,” said senior author Daniel Belsky, associate professor of epidemiology at Columbia University’s Mailman School of Public Health.
“It does this by altering biology in ways compatible with slowing down the aging process, but the exact mechanisms of how this happens are still being investigated,” added Bielski, who studies longevity.
The study used “biological clocks” to determine the rate of aging in its participants, and was designed to measure people’s biological age compared to their actual age.
“Our study found evidence that calorie restriction slowed the rate of aging in humans,” said Caline Ryan, co-lead author and associate research scientist at the Robert N. Butler Center on Aging at Columbia University.
But longevity scientist Dr Peter Attia dismissed the study’s findings as “noise”.
In an email, Attia, who was not involved in the study, said: “I just don’t see any evidence that any of the biological clocks work.”
The scientist hosts a podcast called “The Drive” dedicated to explaining and applying longevity research to everyday life.
Tools to predict biological age are controversial, according to Pankaj Kapahi, a researcher in the field of calorie restriction and a professor at the PAK Institute for Research on Aging in California, USA.
“At best, it tells you something about a very small aspect of aging,” said Kapahi, who was not involved in the study.
For example, the strength of your grip and how active you are are biological indicators of age. “We all know people who break down physically, but who are healthy cognitively. And so you also need to test for cognitive aging,” Kapahi explained.
CALERIE study
A study conducted in the 1950s asked people to reduce their caloric intake by 50%, which led to malnutrition, or a lack of key micronutrients, in the participants.
Subsequent research often focused on reducing calories in people whose BMI indicates obesity.
The first clinical trial of calorie restriction in people of normal weight began in 2007 and was called CALERIE.
Because of the malnutrition caused by the previous study, CALERIE asked 143 adults between the ages of 21 and 50 to reduce 25% of their normal caloric intake for two years.
Another group of 75 people maintained the usual diets as a control group.
During the trial, several tests were conducted over 6-month intervals to gather information on weight loss, change in resting metabolic rate, effect on cognitive function, inflammatory markers, cardiovascular health, and insulin sensitivity.
The CALERIE results published in 2015 found that, on average, people in the restricted group were able to cut their calories by 14%, or about half the target of 25%.
However, this amount reduced their fat mass by about 10%, while lowering risk factors associated with heart disease, with no negative effects on quality of life.
There was also a decrease in tumor necrosis factor alpha, a protein that promotes insulin resistance and obesity-induced type 2 diabetes.
Other studies have used blood samples and other data collected from participants in the CALERIE study to explore other ways that moderate caloric restriction might benefit the body.
For example, researchers at Yale University found that calorie restriction increases the health of the thymus gland, the T-cell-producing organ of the immune system.
Results differ
The new study, published Thursday in the journal Nature Aging, extracted DNA sequences from white blood cells taken from CALERIE participants at 12-month intervals.
Bielski’s team analyzed signs of epigenetic changes in the DNA, looking for signs of aging.
In the new study, the researchers used the epigenetic clock PhenoAge, another called GrimAge, and a new tool Bielski recently developed with Duke University.
The third biological clock, DunedinPACE, attempts to determine the pace of aging with a single blood test, Bielski said.
Belsky, also a scientist at the Robert N. Butler Center on Aging at Columbia University, noted that PhenoAge and GrimAge showed no signs of reversing aging in blood samples from participants in the CALERIE trial.
But DunedinPACE found a 2-3% reduction in the rate of aging, which is equivalent to a 10-15% reduction in the risk of death, according to other studies.
Controversy about biological clocks
This did not impress the study’s critics, however, as Attia noted that the performance of the DunedinPACE test was mediocre at best.
Kapahi stated that the fact that the PhenoAge and GrimAge watches did not find any specific anti-aging benefits was not surprising. “These biological age predictors don’t agree with each other, and they don’t necessarily agree with other biological indicators,” he explained. “It will confuse the public, and unfortunately people buy these tests even though there is very little useful information coming out of them.”
Does calorie restriction benefit humans?
Regardless of the debate over how to measure slow aging, calorie restriction does have a role in actually extending life, especially in “overnourished” individuals, according to Attia.
“I don’t want the reader to think that this intervention (calorie restriction) is worthless, but only that it (the study) does not prove a reduced rate of aging,” Attia explained in an email.
