What everyone got wrong about "eat less to live longer"

The Question

I know you are a big advocate of eating more, and I’ve read all of your articles about it. But I have a really hard time bringing myself to do it. I know it would help me achieve my goals of getting stronger, but I’m having a hard time reconciling it with other things I know about eating food. Isn’t eating, not even “less” maybe but restricting your intake to certain hours for instance, supposed to help you live longer? And it improves memory? I’m sure that’s not everything. But how do you square that science with your approach? —Joan

The Answer

It’s hard to explain how popular the idea of “caloric restriction to live longer and be smarter” felt when I was in college. I bristle at it now because, for me at the time, it definitely became a cornerstone in my rationale for many a disordered behavior.

Eating regularly and normally had no defenders or proponents, that I could see; everyone was trying to score points on the negative-calorie meter, from cutting out snacks to “working off” or “earning” food with exercise. But calorie restriction specifically as the secret to eternal life was was everywhere. At least in my emotional memory. This is to say, I feel like I know exactly what you are talking about. But it made me curious to get on my little science-reporter hat and revisit what exactly people were saying, and how they were saying it, that it became such a sticky set of rules we felt obligated to live by. (And many still do, in some form, but we will get to that.)

Where did it all come from? It turns out there is probably enough for a whole book, so I can’t say possibly cover it all here. But as best as I can tell trying to reconstruct it in the year of our lord 2023, it seems like it began with a sudden minor avalanche of studies that came out between 2003 and 2009, on the topic of caloric restriction and how long things lived. Scientists had started studying the effects of reducing energy intake among populations of various short-lived things: yeast, fruit flies, rats, rhesus monkeys. They were surprised by what they seemed to find: Moderately reducing energy intake (calories) seemed to extend the lifespan of all these creatures.

The study avalanche was then amplified by waves of increasingly breathless media coverage. These studies were covered by CNN, multiple times by the New York Times and Scientific American, Wired, in professional publications and daily local newspapers. There were two spear tips to all of the coverage: the CALERIE studies, and something called the Calorie Restriction Society[^1].

It’s difficult to say exactly what the real-life shape of the Calorie Restriction Society was. It started as a Usenet group (sci.life-extension, archive here) in 2003 and hit the big time when founders including Brian M. Delaney, Lisa Walford, Roy Walford, MD, and others published a couple of books on eating less as the key to living longer.

The Calorie Restriction Society enjoyed a wide-ranging, years-long press tour, and was featured in media appearances including Good Morning America, The Today Show, 20/20, and CBS News. (NYTimes: “There are now books about calorie-restriction methodology like 'The C.R. Way'… On a recent ‘60 Minutes’ segment about a group of calorie-restricting Argonauts, a dinner party began with hors d’oeuvres of flour-free bread smeared with baby food.”)

The Calorie Restriction Society seemed to crop up any time any of the caloric restriction studies, and especially the CALERIE studies, were covered. The CALERIE (Comprehensive Assessment of Long-term Effects of Reducing Intake of Energy) studies were a series of trials that set groups of people about the task of eating less (mostly 12-25% less than their total daily energy expenditure), and then tested them for various health biomarkers, including things like insulin sensitivity, oxidative stress, cholesterol, and quality of life. The studies, as you might guess, showed promising results: People’s markers largely improved.

What’s fun about this whole swirl of scientific studies is that they were published in what now feels like a heyday of breathless reporting from mainstream writers who were, frankly bad at science. They seemingly knew very little about how to identify red, or at least pink, flags in scientific research. S, the studies that were trumpeted from the high hills by all the newspapers and newsmagazines and daily digest TV shows of the land all suffered from at least one of a few flaws:

The “in mice” (or monkeys, or fruit flies, or yeast) problem. Pre-CALERIE, publications were very excited about the calorie restricted animal studies. I credit the “in mice” Twitter account with really popularizing this, but we used to have a real problem with breathless reporting on studies that freely extrapolated results achieved in mice (or any other creature) right onto the human population.

Lest it need to be said, mice are not people, and nor are monkeys, fruit flies, or yeast. Much of the initial furor about calorie restriction concerned these non-human studies and became a launching pad for future calorie restriction reporting.

Extremely selective study population. The participants in the human CALERIE studies were not only few in number, but even before the study got going, the researchers hyper-controlled for people who were predisposed to do well under caloric restriction. People were screened out for age, weight, medical history, psych profiles (including whether they had risk factors for eating disorders), and whether they exercised or smoked. Because of this, there’s precious little the studies could say about “humans in general.” This is kind of fine because the authors were not trying to speak to the general population; more on this in a minute.

Small study size. It’s extremely hard to study people, as I’ve written about before. But in one of the CALERIE studies conducted in Baton Rouge, only 12 of 48 people studied actually underwent the calorie restriction everyone ultimately got so excited about (others were controls, additionally exercised, or ate an extreme low-calorie diet). There were only 132 people who participated in this 2009-ish phase of the trial, total.

Reproducibility matters. Academic publishing has gone through something of a crisis in the last several years, when people started to realize that many of the individual studies on which we had started to hang a lot of our operations could not be separately recreated by different scientists and labs. Unreproducibility is a pretty bad sign for scientific conclusions; sometimes it just happens, but sometimes it’s due to deliberate manipulation of data or parameters by the authors.

In 2009, this problem hadn’t yet taken hold in public consciousness, so we still saw a lot of publications’ longform magazine writers running out of their shoes leaving flame tracks behind them to cover any given study that claimed to have solved aging, unhappiness, people’s relationships with their in-laws, poverty, whatever. Just for instance, it seems like one of the very early studies people got excited about, on calorie restrictions for yeast, is not as rock-solid as the headlines made it sound.

The studied didn’t even… prove what the stories (or studies) purported they did. Virtually all of these studies were trying to relate two biological factors: how long things live, and how much they eat. The earlier non-human studies had a more reasonable claim to this, because it doesn’t take that long to study the whole life cycle of a mouse or fruit fly; even the calorically restricted mice only lived a few years.

But the CALERIE studies on humans didn’t run even remotely long enough to say anything really concrete about longevity. At the longest, they went on for a couple of years. The actual findings mostly focused on various biomarkers of health that are correlated with lower mortality, but they didn’t even remotely definitely prove anyone actually lived longer as a result of calorie restriction.

In 2009 or so, most editors and writers weren’t yet really aware of this stuff. So when studies came out tentatively finding that there may be some positive correlations between modest caloric restriction and health biomarkers, plus there was a seemingly sizeable and growing community of adherents to this strategy? Everyone went bonkers. The dim layperson-magazine-writer’s summation of this research was perfectly engineered to capture the imagination and go viral: Eat less, weigh less, live longer. Defy death itself and become hotter by not even really doing anything, via a good solid dose of Puritanical restriction and denial of bodily needs? We love that!

One thing about coverage of these studies is extremely funny to me, in hindsight. While most of the studies include information about participants’ body weight, the researchers weren’t targeting loss of body weight as the goal. They were trying to study the effect of caloric restriction itself on health, not the effect of restriction-induced weight loss. Quoth one CALERIE study: “The primary goal of the CR (calorie restriction) intervention is to achieve and maintain a sustained reduction in caloric intake rather than a specified weight loss, with weight change being a proxy indicator of sustained CR.” Quoth another:

“The objective of the current study therefore was to determine if CR induces a reduction in free-living energy expenditure that is larger than what can be explained by changes in body weight and body composition (i.e. metabolic adaptation). Furthermore we wished to examine whether CR induced a change in energy expended in physical activity. As a secondary analysis we determined if metabolic adaptation occurred only during weight loss or if it persisted after the lower body mass reached stability. We hypothesized that similar to sedentary energy expenditure, total daily energy expenditure would be reduced by CR partly due to metabolic adaptation and partly due to decreased physical activity. Such metabolic and behavioral adaptation can explain the variability in the rates of weight loss even in well controlled studies as well as the propensity of relapse after weight loss.”

But even as many of the media stories written started out purporting to be also about longevity and caloric restriction, they found themselves steered as if by an invisible hand into talking about the body weights of the restrictors, especially how much weight they had lost in the course of modestly restricting their calories (NY Times: “Peipert began at 174 pounds and had just hit 151; by Week 52, the chart projected he would plateau at 147 pounds, which ideally he would maintain for a full year”).

It seems like many of the participants, too, joined the study not with the goal of furthering science, but in hopes of losing weight (also NY Times: “The majority of subjects in Calerie have so far succeeded in achieving their weight-loss goals. The ones I spoke with seemed to think the most effective tool for sticking with the diet is simply the study’s accountability factor: they not only have to produce their food diary each week; they also have to be weighed in.”) Even though the studies weren’t about weight loss per se, diet culture took the damn wheel and made them about it.[^2]

Another reason these studies seemed to stick in the craw of media coverage despite their shakier-than-presented foundation was that the participants in these studies were mostly of “normal” to “overweight” BMI. This meant that, if you want to play the dubious game of “the higher the BMI the higher the health risk,” these people weren’t even in the group that supposedly most benefits from weight loss. These studies seemed to hit the public consciousness extra hard because they ominously implied that even the already-thin had a duty to remain vigilant about their caloric intake, lest they shorten their lifespans. The message was that everyone is responsible, always, for policing themselves; no one is ever truly safe from the specter of “possibly eating too much.” Again, these wrong conclusions to imply, let alone draw. But the reporting warped the picture until everyone saw what they wanted to see: Virtuous-seeming deprivation that would give us control over our unwieldy bodies.

Like the studies, the Calorie Restriction Society also turned out to have little substance. Its founders’ books were sold to big-name publishers presumably in part off the back of the popularity of their online club. But New York Times describes the Calorie Restriction Society as a group of “several hundred men and women,” while Science magazine let founder Delaney speculate the group is frequented by “thousands” of people. It’s very hard in this day and age to imagine anyone covering any group of people numbering in the “several hundreds,” unless it was to talk about how fringe they are, versus being the next wave of lifestyle design. All the C.R. books now have middling Amazon ratings; per the reviews, they lack substance, and readers are dissatisfied that the books have no more granular directions than “just eat less.” Here’s a great one star review of The CR Way by an epidemiologist.

Nowadays, people are somewhat more aware how problematic it is to tell people to ambiguously restrict calories. In our modern times, the caloric-restriction pushers now know they need to dress caloric restriction up in a number of fancy outfits, such as “one meal a day” (OMAD); intermittent fasting; or as Gywneth Paltrow fav Andrew Huberman calls it, “time-restricted eating.”

In the time between the first big surge of caloric-restriction coverage and now, the fasters and restricters got a few years where they got to play around with a new toy that seemed to support calorie restrictoin, called "autophagy": Basically, a limited number of studies seemed to suggest that restricting food in amounts or for certain periods of time allowed our bodies to do more cellular cleanup, which provided a possible mechanism for all the health benefits cited in the caloric-restriction studies. But as with the earlier round of calorie restriction studies, those findings have not proved solid enough to base anything on.

What about the "calorie restriction improves memory" thing? It seems there were similar studies about this around the same time. As far as I can tell, the reporting carries many of the same issues: small size, super specific population, conclusions that aren't remotely sound enough to base one's lifestyle around .[^3]

So what remains? I’m not saying that there is absolutely nothing to any of this science at all. The CALERIE studies are still being conducted, and continue to show that a very small amount of restriction (12%) shows improvement in “aging related biomarkers” in a very small group of people over the course of two years.

But scientists don’t agree in hindsight whether the CALERIE study approach and its offshoots were even meant for wide public consumption. As one researcher told Scientific American in 2017, “we really study this as a paradigm to understand aging. We’re not recommending people do it.” True to that, a lot of the coverage of the studies mentions participants carping about how annoying it is to have to watch what they eat. (”They were tired of conflating meals and mathematics; they looked forward to a day when they wouldn’t need to check the caloric content of every course.”)

It is relatively common in the general lifting-weights space to sometimes reduce food intake, though we do it with pretty strict guardrails on how much and for how long if we don’t want to put our well-being or hard-won muscle at risk. When I’ve done this, I’ve tracked my food precisely because it’s hard to nail a modest calorie deficit just by eyeballing everything. But as the participants in these studies said, keeping track of your food all the time, especially for years at a time, sucks and is tedious. (Many strength training pros also use calorie restriction because they have long presumed that cutting body fat, as we call it, was a necessary part of the strength-building process; recently, some have started to question whether that is strictly true.)

My big takeaway is that, even if we were to allow that it’s a certainty that caloric restriction makes us a little bit healthier and helps us live—let’s shoot the moon and say a couple of decades longer—science could hardly have picked a more supremely annoying, tedious, and laborious method for achieving those results than “daily overriding worry about whether I’m eating just barely too much.” I’ve lived with both healthy and unhealthy caloric restriction, and I’ve gotten all the promised results. If you told me I had to live that way for the next 40 years, and all it would get me is another 20 years of living like that, I’d say keep your 20 years. Maybe I’ll be singing a different tune in 40-some years, so I say this with apologies to my 76-year-old self in the year 2063. (If you’re not currently sheltered against nuclear winter or actual biblical flood accompanied by the 140-degree surface temperature of the earth, you are doing better than I was imagining).

It would have been a great kicker to this piece to say that, in a turn of dramatic irony, any or all of the people involved in pushing caloric restriction many years ago had now died, their caloric restrictions having failed to save them. I checked, and this is not the case. But most of them, who were in their late 50s to early 60s back then, are around 80 now. The clock ticks ever louder.

[F1] [Two-drink-minimum open mic night voice] Calorie Restriction Society? What is this, my high school lunch table?

[F2] More on this topic from me.

[F3] A bonus fact about this linked story about calorie restriction and memory is that it was edited by disgraced science writer Jonah Lehrer.