Low-Calorie Diet Doesn't Extend Life In Monkeys
August 30, 2012

Restricted Calorie Diet Shown To Have No Effect On Increased Lifespan

Connie K. Ho for redOrbit.com — Your Universe Online

Researchers recently discovered that, while calorie restriction has short-term health benefits for monkeys, it doesn´t necessarily increase their life span.

According to the Wall Street Journal, in the past, calorie restriction was thought to increase longevity by 30 to 40 percent in experiments done with lab mice and rats. In 2009, the idea of caloric restriction became more popular when a study by the Wisconsin National Primate Center with rhesus monkeys demonstrated a trend that showed increased longevity based on a calorie-restricted diet. As such, there has been the long-reigning belief that cutting calories leads to living longer. Some people reduce their food to as much as 30 percent below the recommended 2,200 calories a day for adults and pharmaceutical companies are looking into drugs that might be able to copy the effects of a reduced diet.

The theory by scientists was that cutting calories was similar to when the body had to adapt when there was a shortage of food. However, the new study proposes that the theory might not be able to be applied to humans. The results were recently published in the journal Nature.
"One thing that's becoming clear is that calorie restriction is not a Holy Grail for extending the life span of everything that walks on earth," lead author Rafael de Cabo, a gerontologist at the U.S. National Institute on Aging, told the Wall Street Journal.

AFP reports that the study was launched by the National Institute on Aging (NIA). Over a 23-year period, scientists studied two groups of monkeys who were given 30 percent less food than what they normally should eat. Their results were compared to a control group of monkeys that had been fed the recommended amount of food for normal monkeys in their age group. The monkeys, who were between the ages of one and 14 in one group and between 16 to 23 in another group, did not live longer than the control group of monkeys.

“It will be valuable to continue to compare findings from ongoing monkey calorie restriction studies to dissect the mechanisms behind the improvement in health that occurred with and without significant effects on survival,” the researchers wrote in the report.

There were other varied health results from the reduced calorie diet. Male animals had lower cholesterol levels, but this result was not found in females. Also, while reducing calories decreased likelihood of cancer, it increased the chance of developing cardiovascular disease. Furthermore, a variety of age-related diseases appeared later in the animals who were given less food. Various studies on low-calorie diets have helped scientist better understand how aging happens in humans.

"However, these effects did not translate directly to a beneficial effect in longevity," commented Cabo in the AFP article.

Furthermore, the researchers note that there are differences between the Wisconsin study and the NIA study.

“These monkeys were healthier than really healthy control counterparts,” Julie Mattison, a staff scientist at NIA, told Bloomberg News. “So it´s quite possible that we´ve maximized our lifespan effect.”

As well, one difference was the control monkeys´ diets in the NIA project. The animals in the Wisconsin study were able to eat freely throughout the day, while the ones in the NIA study were under a more-controlled diet. The foods in the diets were also somewhat different.

“We have shown in the Wisconsin study, in which the control animals can eat as much as they choose during the daytime, more like a ℠normal´ human diet, that there are benefits to caloric restriction,” commented Ricki Colman, senior scientist at the Wisconsin National Primate Research Center, in an e-mail to Bloomberg News. “Perhaps these are harder to detect when compared to animals eating a diet more like an ´ideal´ human diet.”

Another difference was the genetic makeup of the animals. The Wisconsin study included Indian rhesus monkeys, while the NIA study featured mixed Indian and Chinese monkeys. These slight differences could have explained the different results.

Even with these findings, investigators believe that people may have different responses to calorie restriction. The results of calorie restriction will also depend on the weight of individuals when they start the diet (i.e. if they are overweight, underweight, etc.). However, the researchers believe that the new findings will not deter people from pursuing low-calorie diets.

"They see their blood pressure go down, their fasting glucose go down, their cholesterol go down, and they feel better," remarked Brian Delaney, president of Calorie Restriction Society International, in the Wall Street Journal article. "They believe it will enable them to live youthfully into their 70s, 80s and even 90s."