Calorie restrictive eating for longer life? The story we didn’t hear in the news
This should have been the lead:
The long-awaited research on the effects of calorie restriction on aging in rhesus monkeys from the University of Wisconsin and Wisconsin National Primate Research Center have just been released. It found no statistically significant difference in the number of deaths among the monkeys who’ve been eating a calorie-restrictive diet for more than 20 years compared to the monkeys who’ve been allowed to eat ad lib all day as much as 20% over their normal calories.
But that’s not what made the news, of course. Instead, we’ve been bombarded with a thousand news stories all reporting in lockstep that low-calorie diets have been proven to add years to our lives.
We are, once again, witnessing marketing and media reporting from press releases — in this case, one from the University of Wisconsin-Madison and lead researcher, Dr. Richard Weindruch; and another from the magazine, Science, where the results were published (and are viewable for $15.). You’ll find no critical examinations of the study in the press releases, no careful evaluations weighing the risks and benefits of caloric restriction, or any mention of downsides at all. The study was presented as providing “compelling evidence” that calorie restriction extends lifespans and slows aging, and suggesting that genes may be responsible.
What’s up?
As we know, whenever we hear a health statistic, the first question we should ask ourselves is how a statistic is defined. Definitions are everything. Only by reading critically can we begin to decipher the wordsmithing, the art of marketing. Read carefully what Dr. Weindruch said in his press release:
We have been able to show that caloric restriction can slow the aging process in a primate species. We observed that caloric restriction reduced the risk of developing an age-related disease by a factor of three and increased survival.
A stronger clue came from this quote in the press release:
There is a major effect of caloric restriction in increasing survival if you look at deaths due to the diseases of aging.
The lower mortality claimed among the monkeys on the calorie restricted diet were achieved only after eliminating 37% of the monkey deaths. They defined mortality as “age-associated deaths” and eliminated any cause of death they didn’t believe was associated with aging. As the supplemental data explains, 16 deaths from “non-age-associated causes were censored and their age of death used as the time variable in the regression.”
Science doesn’t really work that way. Researchers can’t simply ignore the evidence that doesn’t support their hypothesis. That would be the difference between research done to build evidence to support a hypothesis, from science that is objectively studying a hypothesis.
Only one mainstream news article noted this technique. If readers searched diligently, they found it buried about 460 words into a New York Times article, while this finding wasn’t even mentioned in nearly all the other news stories. The Times article noted:
If caloric restriction can delay aging, then there should have been significantly fewer deaths in the dieting group of monkeys than in the normally fed comparison group. But this is not the case. Though a smaller number of dieting monkeys have died, the difference is not statistically significant, the Wisconsin team reports.
No statistical difference. It was a null study that to date has failed to support the calorie restriction hypothesis.
The non-aging-related causes of death included monkeys who died while taking blood samples under anesthesia, from injuries or from infections, such as gastritis and endometriosis. These causes may not be aging-related as defined by the researchers, but they could realistically be adverse effects of prolonged calorie restrictions on the animals’ health, their immune system, ability to handle stress, physical agility, cognition or behavior.
As we know, the most important endpoint in medical interventions is all-cause mortality. Selectively looking at only one cause of death, while ignoring that more patients died from something else, is not evidence to support the efficacy of a treatment. “The treatment worked, but the patient died” is not good medicine that considers the whole patient.
The researchers also used age-related causes of death as meaning the age-associated diseases most prevalent in humans, cancer and heart disease. But, the authors explained, “typically, cardiovascular disease is not detected in caged animals, though on physical exam, a heart murmur may be noted.” So, they used noninvasive techniques to evaluate murmurs, as well as monitor the animals for the presence of tumors.
Another misconception repeated in mainstream media coverage was that the calorie restricted monkeys were eating 30% fewer calories than normal. Again, few people read carefully or went to the study methodology to understand that the monkeys were really eating about 30% less than the control monkeys. In actuality, the control animals were overfed 20% more than their usual diet, while the CR monkeys’ diets were adjusted to keep them about 30% less than the control monkeys. As an earlier report on this study’s methodology explained:
Since 1989, we have been studying the effects of a moderate (30%) adult-onset dietary restriction (DR) in a nonhuman primate model. We chose a rhesus monkey (Macaca mulatta) model… The effects of aging and DR are being analyzed longitudinally in adult male rhesus monkeys, ranging in age from 8 to 14 years (average 9.3 years) at study onset… The 30 rhesus monkeys used in this study were born at and have lived their entire lives at the Wisconsin National Primate Research Center… [In 1994, an additional 30 females and 16 males were added to the study.] Prior to the start of the study, animals were monitored for individual baseline food intakes of a purified diet (10% fat, 15% protein) for 3 months. Animals were then randomized to either Control or Calorie Restricted groups based on their baseline food intakes. Food allotments for the CR animals were then reduced by 10% per month for 3 months to reach the intended 30% DR. Control animals were fed 20% more than their average daily intake…
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