Calorie restriction slowed biological aging by initially accelerating it
In a new study, a team of American and Canadian scientists looked at how reducing caloric intake affects human telomeres - a kind of "protective caps" at the ends of chromosomes that protect them from damage and "sticking" to other chromosomes. The effect was not as unambiguous as expected.
Animal experiments have repeatedly shown that limiting calorie intake by 20-60 per cent has a positive effect on longevity and the biology of ageing. A long-term research project called CALERIE is underway in the US, in which medical researchers are studying whether the results of calorie restriction experiments in animals hold true for humans.
CALERIE participants are healthy, obese men and women between the ages of 21 and 50 with a body mass index of 22 to 27.9. As part of a paid experiment, their caloric intake was restricted by 25 per cent for two years.
Previous analyses of the CALERIE participants' blood composition, immunological and epigenetic data confirmed that after two years of this dietary regime, their biological ageing process slowed. The new work, recently published in the journal Aging Cell, is an extended study in which the authors looked at how calorie restriction affected telomere shortening (which is linked to biological age and body aging).
"The reasons why caloric restriction of food may prolong human lifespan are numerous, and the topic is not yet fully understood. One of the main mechanisms that provide such an effect is related to cell metabolism. When a cell consumes energy, waste products are produced, causing oxidative stress that can damage DNA or otherwise "break" the cell. When human cells consume less energy due to caloric restriction, there is less waste and the cells break down more slowly," explained one of the study's authors, Dr Waylon Hastings of the University of Pennsylvania.
Using data from 175 CALERIE participants taken at the beginning of the experiment, one year after the start and at the end (after 24 months), the researchers compared the length of their telomeres. About two-thirds of the subjects were from the calorie-restricted group and one-third were from the control group.
In the end, the scientists found that telomeres shortened differently over the course of the study. During the first year, when the calorie-restricted participants lost weight, the length of their telomeres shortened faster than in the control group. This indicates more active cellular aging processes in the body. After 12 months, the participants adapted to the calorie restrictions and their weight stopped dropping. After that, in the second year of the experiment, their rate of telomere loss slowed significantly compared to the control subjects.
As a result, after 24 months, participants in the two groups came to the end of the study with roughly the same results - their telomere lengths were not statistically different.
"The study shows that the effect of calorie restriction on telomere loss is a complex mechanism. <...> Contrary to expectations, people who consumed fewer calories initially lost telomeres faster. The process slowed down when their weight stabilised," said Professor Idan Shalev, another co-author of the paper.
According to the scientists, their results raise many important questions. In particular, how did telomere length change later in life? The project plans to collect data from 10 years of observations, and the researchers are already waiting to analyse them.
Despite the mixed preliminary results, previous research papers based on the CALERIE data suggest the health benefits of calorie restriction. In particular, it may help lower levels of "bad" low-density lipoprotein (LDL) cholesterol and blood pressure. As for the effect on telomeres, a two-year experiment is not enough for any definite conclusion, the scientists concluded.