No dietary shortcut to longevity?

The less you eat, the longer you’ll live? Maintaining a healthy weight is one thing, but experts have long thought that strictly limiting calorie intake can increase longevity. Before you start making drastic cuts to your diet, beware: a new study has researchers wondering whether caloric restriction increases our lifespan after all.

Caloric restriction (or CR for short) isn’t a new idea — in the 1930s, researchers noticed that lab rats who were deprived of food tended to live longer than their fully-fed counterparts. In the decades that followed, studies in animals and yeast all showed that restricting calories increased lifespan across all species tested. The benefits go beyond extra years of life too. Research suggests that CR can prevent or delay the onset of chronic diseases, help reduce loss of bone mass and strength with aging, and improve immune system functioning. (In animals, at least.)

Still, some humans think the research is promising enough that they’re willing to give CR a try. Caloric restriction involves consuming fewer calories than current recommendations — as much as 30 per cent fewer, in fact. Instead of a 2000 calorie per day diet, someone following a CR regime might only consume 1400 calories. Malnutrition isn’t an issue — the goal is a balanced diet of foods that are high on nutrition and low on calories. No sugars or refine starches allowed!

However, a new study published in the journal Nature suggests that CR might not be worth the sacrifice. The 25-year long study conducted by the U.S. National Institute on Aging (NIA) involved rhesus monkeys — a closer relative to humans than previously investigated. The control group of monkeys was fed a normal diet while the second group consumed a diet of 30 per cent fewer calories. Both diets were low in sugar, contained healthy foods and were even adapted according to the seasonal foods these animals would consume in the wild.

The results? Contrary to previous findings, the CR group didn’t live any longer than the control group. The only benefit researchers could report was lower levels of triglycerides in their blood — an important marker of heart health.

The study seems to contradict a 2009 study at the Wisconsin National Primate Research Center (WNPRC) which found that CR did help extend life. During the 20-year study, only 13 per cent of the monkeys in the CR group died of age-related causes compared to 37 per cent in the control group. In the CR group, none of the animals developed diabetes while 40 per cent of the unrestricted group did — even though the composition of their diets was the same.

Experts note that there are many differences between the NIA and WNPRC studies. For example, the monkeys involved in each of the studies were from different genetic lines. (Conflicting evidence in previous mice studies was also attributed to genetic differences.)  What the animals ate made a big difference too: the diet in the WNPRC was much higher in sugar than in the NIA study, for instance. In the WNPRC study, animals in the control group could eat as much they wanted rather than being fed a specific amount, and they tended to be heavier than the animals in the NIA study.

Confused yet? The contradictions are revealing too: experts say conflicting results point out that our genes and what we eat play a big role in how long and how well we will live, not necessarily how much we consume. That’s not an excuse to eat whatever we want — rather, the study challenges previous CR studies which assumed all calories are considered equal.

And does any of this information actually apply to humans anyway?  There’s a good reason we haven’t heard the results of CR studies involving humans: people live too long.  Even if experiments had been started a couple of decades ago, it would be decades yet before we knew the results. For now, experts can study the long-lived around the world to learn their secrets — but that’s not the same thing as testing the effects of caloric restriction in a controlled setting.

In short, experts still don’t fully understand the role diet and genes play in how we age and how long we will live. There is a lot more research that needs to be done — and answers could be a long time coming.

In the meantime, caloric restriction isn’t something experts say we should try at home. It requires careful supervision from a doctor, and there are short-term risks such as the loss of bone density due to rapid weight loss. CR can impact fertility, and in some animal studies was shown to slow healing and increase risk of infection.

The bottom line: Experts aren’t sure what the long-term effects of caloric restriction will be — good or bad. In the meantime, the usual advice applies. If you’re curious or concerned about a report you see in the news, you should talk to your doctor before making any changes to your lifestyle.

For more information on the study, read the summary in Nature and the article on Time Healthland.