It is well known that diet and exercise affect health, and research suggestsTrusted Source that it can also affect the speed and progression of aging. Primary aging is the innate process that all people experience; secondary aging is the acceleration of the aging process by excess food intake, lack of exercise, and disease.

It is this secondary aging that may be affected by diet, and studies in animalsTrusted Source have found that restricting calorie intake can slow the process, reduce disease, and prolong life.

Although several mechanisms have been proposed to explain this effect, there is no firm evidence showing why caloric restriction might prolong life.

As cells age, telomeresTrusted Source — the protective lengths of DNATrusted Source at the ends of chromosomesTrusted Source — shorten until, eventually, the cell dies.

Cell death is a feature of aging so, if cell death was delayed by decreasing the rate at which telomeres shorten, might this delay aging? One studyTrusted Source, in mice, has demonstrated this, showing that caloric restriction slows the shortening of telomeres and prolongs lifespan.

Now, researchers from Penn State University have analyzed data from the Comprehensive Assessment of Long-term Effects of Reducing Intake of Energy (CALERIETrusted Source) trial to investigate whether a similar effect might be seen in people.

They found that, initially, caloric restriction accelerated telomere shortening, but after a year, it began to slow the process. At the end of 2 years, the calorie restricted and control group had lost similar telomere length.

Their work appears in Aging CellTrusted Source.

Sebnem Unluisler, chief longevity officer and genetic engineer at the London Regenerative Institute in the United Kingdom, not involved in this research, told Medical News Today:

“The study used a method to track changes in telomere length over time with caloric restriction. Initially, those eating less saw faster telomere shortening, but this slowed down later. Surprisingly, after 2 years, both groups showed minimal difference, suggesting a possible plateau effect. This highlights why long-term studies are vital to understand aging-related processes fully.”

The CALERIE trial recruited 220 participants, of whom 175 were included in this data analysis. All participants were aged between 21 and 50, healthy, and had a body mass index (BMI)Trusted Source of between 22 and 28 kilograms per square meter (kg/m²), indicative of healthy weight to overweight.

Two-thirds of the participants committed to 25% calorie restriction for 24 months, with the rest as controls who continued with their normal diet.

The researchers advised all participants to undertake moderate exercise for 30 minutes, at least 5 times a week, but not to alter their activity levels during the course of the 2-year study. They provided meals to those in the caloric restriction group for the first 27 days to help them with food selection and portion size to ensure adequate intake of essential nutrients throughout the study.

Over the course of the study, the average calorie restriction fell short of the 25% aim, with participants achieving a mean reduction of 11.9%.

At the start, and every 2 weeks throughout the study, the researchers recorded the weight of all participants. During the first 12 months, those on caloric restriction lost weight, then their weight stabilized over the next 12 months. Anyone whose BMI went below 18.5 (underweight) discontinued the study.

Previous analyses of the CALERIE data have shown that caloric restriction had some health benefits, including reductions in total blood cholesterolTrusted Source, blood pressure, and inflammatory markersTrusted Source. However, caloric restriction may have a negative effect on bone density and muscle massTrusted Source.

The researchers measured telomere length from blood samples taken at the start of the study, at 12 months, and at 24 months.

They found that in the first 12 months, telomere length decreased faster in people on caloric restriction. In the second year, the rate of decrease slowed to a lower rate than that of control subjects.

The researchers explained why this might have happened:

“[T]he stress of weight loss that accompanies early-phase CR [caloric restriction] accelerates TL [telomere] attrition, which is thereafter mitigated or ablated altogether as new homeostatic norms are established,” they wrote.

Unluisler suggested that: “Eating less could reduce stress and inflammation in the body, slowing down telomere shortening. It might also help cells repair themselves better.”

Over the 2-year study, there was no significant difference in telomere length change between the 2 groups.