People who follow calorie-restricted diets have lower core body temperatures, similar to that observed in long-lived calorie-restricted mice, strengthening the idea that eating less helps people live longer, said researchers from the Washington University School of Medicine, in St. Louis, Missouri, USA, in a paper published in the journal Aging recently.

In simple organisms, long-term calorie restriction can double or even triple lifespan. It’s not clear how the practice affects the human lifespan, but those who follow it expect to live past their 100th birthday.

Animal studies have also suggested that reduction of body temperature contributes to increased lifespan in calorie-restricted animals; rodents that consume fewer calories have lower core body temperatures, and live significantly longer than littermates on a standard diet.

However, we know nothing about the long-term effects of calorie restriction on core body temperature in humans, wrote the researchers in their background information.

Following a calorie-restricted lifestyle is not just a matter of cutting calories. It is a disciplined approach where the individual reduces calorie intake to around 75% of what might be considered healthy by more conventional standards, while at the same time keeping careful track of vitamin and nutritient intake order to avoid malnutrition. The most disciplined adherents also track other measures such as BMI and body fat, and plan their meals carefully.

Senior researcher Dr Luigi Fontana, a Research Assistant Professor trained in internal medicine and metabolism, with an interest in nutrition, aging and longevity, and colleagues, compared the core body temperatures of 24 volunteers in their mid-50s who had been following calorie-restricted lifestyles for at least 6 years, with that of 24 age-matched volunteers who ate a Western-style diet, higher in fat and calories.

All the 24 calorie-restricted volunteers were practising members of the CR Society, also known as “CRONies” (short for “Calorie Restriction with Optimal Nutrition”).

The researchers also compared the core body temperatures of the calorie-restricted group with that of 24 age-matched endurance athletes, to see if it was just being lean (as both groups were) or also following a calorie-restricted lifestyle, than linked most strongly to lower core temperature.

Fontana, who is also a senior investigator at the Istituto Superiore di Sanità in Rome, Italy, said they found:

“The people doing calorie restriction had a lower average core body temperature by about 0.2 degrees Celsius, which sounds like a modest reduction but is statistically significant and similar to the reduction we have observed in long-lived, calorie-restricted mice.”

“What is interesting about that is endurance athletes, who are the same age and are equally lean, don’t have similar reductions in body temperature,” he noted.

Core body temperature is the optimum temperature for all the organs in the body to work at their best.

To measure core body temperatures, the researchers asked the participants to swallow telemetric capsules. These then transmitted temperature readings from inside their bodies every minute.

The temperature of the human body is not the same throughout, and internal readings (“core temperatures”) tend to be higher than readings taken closer to the skin.

Ideally, core body temperature is 98.6 degrees Fahrenheit or 37.7 degrees Celsius, but this varies from about 96 to nearly 100 degrees Fahrenheit.

The researchers point out that the study does not reveal whether calorie-restriction itself causes core temperature to go down, or whether something else is involved.

However, Fontana says reduced temperature is a key to longer lifespan in animals: research shows that it is “consistently true that those with lower core body temperatures live longer”, he explained.

Fontana and colleagues referred to evidence from another unrelated study, the Baltimore Longitudinal Study of Aging, that found men with lower core body temperatures lived significantly longer than men with higher body temperatures. The reason for the lower body temperature was probably genetic, they note.

This strengthens the argument that body temperature predicts longevity in humans too, says Fontana.

However, none of these works shed light on how many more years people with lower core body temperatures might live compared to their warmer counterparts.

For now it appears, based on animal studies, that a lower core body temperature is not enough. Rodents whose core body temperature is consistently kept lower by exposure to cold water live no longer than normal rodents.

Fontana says he thinks how you achieve your lower body temperature could be the key.

He reckons that if you spend most of your life overweight, smoking and drinking, and then take drugs to lower your body temperature, you won’t live any longer.

However, he said, if you were to practise “mild calorie restriction”, stick to a good diet, do some exercise, and then take the temperature-lowering drug, then you might see an effect similar to that seen in more severe calorie-restriction.

The National Institute of Diabetes, Digestive and Kidney Diseases, the Insituto Superiore di Sanita/National Institutes of Health Collaboration, the Longer Life Foundation and the Scott and Annie Appleby Charitable Trust, all donated funds and grants to pay for the research.

“Long-term calorie restriction, but not endurance exercise, lowers core body temperature in humans.”
Andreea Soare, Roberto Cangemi, Daniela Omodei, John O. Holloszy, and Luigi Fontana.
Aging, Volume 3 Number 4, April, 2011, pp 374-379.

Additional source: Washington University School of Medicine (press release 10 May 2011).

Written by: Catharine Paddock, PhD