A first-of-its-kind human study suggests that cutting calories may help slow the rate of biological aging.
Can cutting calories slow biological aging and help healthy adults live longer? A groundbreaking study in humans suggests that it is possible.
The study, published Feb. 9 in the journal Nature Aging, found that a two-year intervention in which participants had to reduce their daily calorie intake by 25 percent slowed the rate of aging by 2 to 3 percent. According to the researchers, this translates to a 10-15% reduction in mortality risk, roughly the same level of risk reduction as quitting smoking.
These results are important because they provide proof, from a randomized trial, that it is possible to slow down human aging. Although many people may find this level of caloric restriction too difficult, the study supports the concept that behavioral changes, without any medication, can have a measurable impact on the rate of aging. This study paves the way for future studies of other interventions, such as time-restricted eating or intermittent fasting, that may be more scalable and feasible in a broader sector of the population.
Calorie restriction has beneficial effects on metabolism and heart health
The current study is part of an ongoing investigation called CALERIE (Comprehensive Assessment of Long-Term Effects of Reducing Intake of Energy) that began in 2006. Previous studies using data from the CALERIE trial have shown the multiple benefits calorie reduction. A survey found that calorie restriction slowed age-related physiological changes in the liver, kidneys, metabolism, blood vessels, and immune system. Another study showed that calorie restriction reduced risk factors for heart disease and type 2 diabetes and improved cardiovascular and metabolic health. The new study was designed to explore these earlier findings. The researchers wanted to know if the signs of slowing aging at the organ system level were also apparent at the cellular level.
How to measure biological age?
Decades of research using animal models have demonstrated that calorie restriction (without malnutrition) improves lifespan and what is called health span. But is this true for humans? Given the length of human life, it is not possible to perform a rigorous clinical trial to answer this question. Instead, researchers have devoted serious effort to figuring out how to measure a person’s “biological age,” as opposed to their chronological age, in order to spot signs of slowing aging. A promising approach to measuring biological age is to analyze what is called the epigenome. While our genetic code remains largely unchanged throughout our lives, our cells are constantly making reversible changes to our DNA that turn genes on or off. These reversible changes to our DNA are called the epigenome.
Researchers can compare these epigenetic changes to a reference population from previous research to estimate a person’s biological age. Study participants were closely monitored to ensure they were receiving the necessary nutrients.
In the most recent CALERIE study, researchers randomly assigned 220 participants to the calorie restriction group and a control group that had no dietary restrictions. The calorie restriction group consisted of 143 people (44 men and 99 women), while the control group consisted of 75 people (22 men and 53 women). The study population was 76% white, 15% African American, and 9% Asian, Native American, or Pacific Islander, with an average age of 38 years. The participants’ average baseline body mass index (BMI) was 25.1, which would put them into normal weight and overweight categories.
Scientists used sophisticated techniques to estimate how many calories each person needed to maintain their body weight. They then took that baseline and set individual goals that reduced that number by 25%. Thus, if a person’s baseline was 2,000 calories per day, they were expected to consume 1,500. This target level of 25% was chosen because this degree of calorie restriction yielded the best results improvement in lifespan and life expectancy in animal models and was found to be achievable in most participants in the original 2006 pilot study, according to the authors. It is important to note that this was a study of moderate calorie restriction without malnutrition. People who were underweight, depressed or had a history of diabetes, heart disease or eating disorders did not participate in the study.
All study participants received guidance on how to cut calories while still consuming recommended nutrients, and they were given the opportunity to choose eating habits that suited their cultural and individual preferences. Participants in this study were followed closely throughout the study to ensure that they were meeting all of their macronutrient needs, and their weight was closely monitored. If any of them lost too much weight, they were asked to increase their caloric intake.
Maintaining a 25% calorie reduction has proven difficult. The majority of participants did not meet the goal, and the average calorie reduction was 12% at the end of the trial. However, study participants still lost an average of 7 kg over the two years of the study. Furthermore, there was no evidence that calorie restriction had a negative effect on participants’ sleep, cognitive performance or quality of life.
Fewer calories for slower aging
To measure the impact of calorie restriction on biological aging, the researchers analyzed blood samples taken from trial participants before the intervention and after 12 and 24 months of follow-up. They found that calorie restriction slowed the rate of biological aging over time. Additionally, there appears to be a dose-response effect: Participants who reduced their caloric intake to a greater extent saw their biological aging rate decrease more. These results are exciting because they prove that the rate of biological aging is not set in stone, but can be affected by interventions such as calorie restriction.
These findings add to what is currently known about calorie intake and biological aging. Since eating less leads to weight loss (which can have many health benefits), more research is needed to strengthen conclusions about the direct impact of calorie restriction on aging. A follow-up of trial participants is currently underway to determine whether the intervention had any long-term effects on healthy aging.
Why would eating fewer calories slow aging?
Simply put, the current idea is that calorie restriction affects nutrient sensing pathways and energy metabolism in ways that reverse or reduce the effects of aging. These pathways are called “nutrient sensing” because nutrient levels influence their activity. Part of this effect is due to a process called hormesis. When you subject the body or an organism to a stressor, it can, over time, activate certain pathways that ultimately promote health. Take the example of exercise. You’re stressing the body out a bit, and in doing so, some of these key pathways have to change the way they work and signal. Similarly, calorie reduction places mild stress on the body at the cellular level and alters pathways associated with lifespan, including those involving human growth hormone and insulin.
Intermittent fasting or food restriction may have similar beneficial effects.
If calorie restriction isn’t for you, rest assured there is growing evidence that other methods can “trick” the body into producing similar beneficial effects. Although the data on intermittent fasting is mixed as to its effectiveness in reducing caloric intake, time-restricting food seems to have really profound effects, especially in people in their 40s and 50s who want to lose some weight. or who are at a healthy weight and simply looking to improve their biology.
Is it safe to restrict calories for months or years?
Before adopting a calorie-restricted diet, talk to your doctor. It must be done under the supervision and advice of a professional, because it is not without risk. As long as a person is consuming the recommended amount of nutrients, calorie restriction is generally safe, unless they are already underweight or at risk of becoming underweight due to calorie restriction.
Ideally, a person should meet with a dietitian first to help them create a plan and ensure they are meeting all of their nutrient needs. Start by limiting calories from foods and beverages that provide empty calories (very little or no nutrients). These include, for example, sodas, sweetened coffee drinks, lemonades, sweets, pastries and cookies, fast foods, crisps, creamy salad dressings and cream cheese.
