How disappointing. After years of self-imposed semi-starvation, you find that you will not outlive your relatives or neighbors who have been happily eating without worrying about calories, portion sizes or when they might exit the world. Last week’s report of the failure of low-calorie diets to extend the lives of monkeys must have been a source of frustration and confusion to many who believed eating less would gain them a longer life.
Two studies were started about 25 years ago to see if reducing food consumption was associated with an increased life span. Early indications that this might be the case came from studies done with mice and rats. Calorie restriction extended the life of these rodents beyond their normal limits (not a happy conclusion for those of us living in cities with a poorly fed rat population). The next step was to extend the study to animals more closely related to us, i.e., primates. The Wisconsin National Primate Research Center in Madison found that limiting calories below what the monkeys normally would be eating did indeed prolong survival, compared to control monkeys.
But before you give up eating breakfast, lunch and dinner on a regular basis, consider the results of the second study, done at the National Institute of Aging (NIA). As reported in the journal Nature, monkeys were given a diet with 30% fewer calories than control monkeys for about 25 years. The difference in calorie intake was substantial; it was as if your normal consumption of 2500 calories a day was reduced to 1750 for most of your life. Alas, no marked difference in lifespan was found between the two groups.
Instead, according to an editorial in Nature.com by Steven Austad (Nature 2012 11484 online 29 August), we should be looking at what the control monkeys were fed to understand the discrepancy in results between the two monkey studies. In the NIA study, the control animals were fed a healthy diet calculated to prevent obesity. However, that was not the case in the Wisconsin diet. Those monkeys went to the primate equivalent of a food court. They could eat as much as they wanted and more than 25% of their diet consisted of sucrose. In all good humour, of course, were they drinking slurpees or eating cotton candy?
That last question notwithsanding, it is actually comforting to learn these results, because they reinforce the traditional approach to dietary practices, that is, moderation. The NIA control animals followed a moderate diet and they lived as long as their semi–starved counterparts. The Wisconsin monkeys, who overfed themselves, lost the competition for longevity to their underfed colleagues and probably would not have lived as long as moderately-fed monkeys.
There is another take-away message not mentioned in all the hype surrounding these studies. These monkeys lived more or less in cages. Compared to monkeys in the wild, they were quite sedentary. Would monkeys in a natural environment live longer or shorter lives, depending on their food supply? (This is assuming, of course, that the monkey’s natural enemies were removed from their environment.)
Yet doing the study with caged animals denied the possibility of spending their lives running around treetops makes the outcome more applicable to our lives. Few of us spend our days in vigorous physical activity. In a sense, we are like the monkeys in the study. We don’t live in cages but we do spend time in equally sedentary environments: cars, offices, dens, classrooms, libraries and bedrooms. So even though it looks as if a drastic cut in our calorie intake may not be necessary to live out our normal life span and perhaps beyond, the NIA study shows us that maintaining a normal weight and eating a healthy diet may be the best way we may reach the biblical promise of four score and twenty and beyond.