It's been more than 70 years since the discovery that reducing the number of calories fed to rats could nearly double their lifespan. In the 1980s, research intensified on the possible life-prolonging properties of reduced caloric intake, and the correlation has held in virtually every corner of the animal kingdom studied—from single-celled yeast to worms to insects to mice—that eating less translates into longer life.

This research has inspired many people to actively reduce their caloric intake in hopes of living longer, healthier lives. Most prominent among these undereaters is the Calorie Restriction Society ("Fewer Calories, More Life" is the society's motto).

The CR Society was established in 1994 to provide support and information to those interested in pursuing the "CR lifestyle," as they call it. The website www.calorierestriction.org contains a lot of published research data supporting the benefits of the CR lifestyle, as well as press clippings of CR in the media. But the results of one recent study are absent. This omission is especially conspicuous given that Calorie Restriction Society members were a focus of the study.

The study, "Long-Term Effects of Calorie or Protein Restriction on Serum IGF-1 and IGFBP-3 Concentration in Humans," conducted by Luigi Fontana, et al., and published in the journal Aging Cell, investigates the relationship between dietary calories and protein on the body's IGF-1 levels. IGF-1, which stands for "insulin-like growth factor 1," is a protein-based hormone. IGF-1 has been shown to promote tumor development, and because of that, and for other reasons too, it's widely believed in biomedical research circles that IGF-1 regulation is a key factor in determining the life span of many organisms.

Reduced caloric intake in rodents has been shown to cause a dramatic reduction in IGF-1 levels, and this is presumed to play a role in the mechanism by which caloric restriction extends rodent lifespan. But when Fontana and company measured the IGF-1 levels of members of the Calorie Restriction Society, after an average of six years of caloric restriction, they found, to their surprise, IGF-1 levels nearly comparable to those eating a typical Western diet. This suggests that eating less might not give humans the same life-prolonging benefits it gives mice.

Another dietary group in this study consisted of vegans. As they eat no animal products, vegans tend to eat less protein, while consuming more calories and weighing more, on average, than the calorie restrictors. And while calorie restrictors didn't show dramatically lower levels of IGF-1, vegans did.

The researchers then tweaked the diet of the calorie-restriction group, holding calorie intake low and reducing their protein intake as well. After three weeks, these people showed a dramatic reduction in IGF-1 levels, leading the researchers to conclude that in humans, caloric restriction alone isn't enough to lower IGF-1 levels; it must also be coupled with protein restriction.

Interestingly, these results have not made it to CalorieRestriction.org, which continues to promote high levels of protein consumption in the CR diet. Perhaps this blow to the fundamental pillar of the CR Society's dogma was more than they cared to acknowledge. Such is the way of cultish behavior.

This research also shoots a big hole in many of the trendy low-carb/high fat/high protein diets like Atkins, the Zone and South Beach. While it doesn't dispute that these diets may indeed help you lose weight, this research does suggest that they aren't good for you.

Kudos to Michael Pollan, whose 2008 book In Defense of Food argues that the healthiest diet consists of smaller portions of high-quality plant-based foods.

The book's central creed reads, "Eat food. Not too much. Mostly plants." And while his "eater's manifesto" is supported by the IGF-1 study, Pollan maintains a level of skepticism toward using reductionist science to study diet, a practice he calls "nutritionism": "The widely shared but unexamined assumption [of nutritionism] is that the key to understanding food is indeed the nutrient. Put another way: Foods are essentially the sum of their nutrient parts."

While Pollan is by no means anti-science, he argues that nutritionism has sent dietary guidelines on a roller-coaster ride in recent decades, with foods like margarine coming in and out of favor. The deluge of low-fat foods on the market, meanwhile, has done more to increase obesity rates then curb them, because, as we know now, dietary carbohydrates make people gain more weight than fat.

Pollan argues that there is an ecology to food that makes it greater than the sum of its parts. It includes where the nutrients are from and what they are consumed with. The first part of his eater's manifesto, "Eat food," draws a distinction between industrially produced food and ecologically correct food, with only the latter truly qualifying as food.

In the IGF-1 study, there is little mention of where the protein comes from, aside from the obvious fact that the vegans got all of their protein from plants. But the processes by which different proteins are created have different health implications on the eater.

Protein from 100 percent grass-fed beef, for example, may be similar to protein from factory-farmed beef, but the factory-farmed beef is fed a diet of grain, which literally creates a different animal. Since cows didn't evolve to eat grain, grain-fed cattle tend to get sick more often and are thus injected with more antibiotics. While I can't say how these differences might affect IGF-1 levels in the blood of the cow eater, a relationship isn't inconceivable.

The fact that the IGF-1 study made no attempt to standardize the sources of the proteins in question is a big deal, I believe. Plant protein vs. animal protein; wild meat vs. domestic; free-range vs. confinement—these all have major bearing on the ecology of a meal, as would the presence or absence of a nice glass of wine along with it.

So while I read with interest the results of studies like this one, I'd be more interested if the study distinguished between the protein in a Whopper and the protein in a piece of grass-fed beef. Nutritionism might not value the difference between clean, local food and industrially produced food, but I agree with Pollan. It matters.

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