In the great diet debate, every argument counts. Whether you’re talking about keto, paleo, intermittent fasting, Weight Watchers, or intuitive eating, there’s one prevailing idea that seems to repeat on a loop: Human beings are wired to fast. It’s part of our nature and built into our biology.
"Wouldn’t it be better if we just went back to the way things were?
The argument posits that our prehistoric ancestors would go days, even weeks without food, yet remained healthy. In today’s world, as “diseases of civilization” — obesity, diabetes, cancer and heart disease — rapidly grow, wouldn’t it be better if we just went back to the way things were?
To an extent, this story rings true. Brianna Stubbs, Ph.D., lead translational scientist at the Buck Institute for Research on Aging, says “there would’ve definitely been periods during human evolution when we just wouldn’t have been able to eat for a day or two.”
But the idea that it might be better to stop eating three meals a day, and instead, return to ancient eating patterns is still being debated. Historians question how much stock we should put in the “caveman diet,” and the inadvertent intermittent fasting of our predecessors.
“Just because it’s a dietary practice that our ancestors had in the past, does that mean, A) it was something that was beneficial, and B) it was something that we should return to because it would be good for us today?” Briana Pobiner, Ph.D., paleoanthropologist at the Smithsonian, tells Inverse.
Paul Freedman, Ph.D., a food historian from Yale University, says that argument is all wrong. “We exaggerate the poverty of hunter gatherers,” Freedman says. “There were good days and bad days but for the most part, people had more choice and security than we think.”
Freedman questions the historical and cultural argument that hunters and gatherers were regularly fasting. “Scientists trot out our ancestors as a way of framing and making their findings appealing, but they don’t know what they’re talking about. They know a lot about physiology but nothing about history.”
“Leave our ancestors out of it,” Freedman says.
The Starving Caveman Myth
In today’s food-abundant context, most people’s eating choices are shaped by their desire to feel fit, eat what tastes good, or optimize health. But our ancestors ate for one main reason: survival.
Up until about 12,000 years ago, all humans got their food by hunting, gathering or fishing. As foragers, they would fast until they found, caught or killed their food. There was no breakfast upon waking,, or leftovers for lunch. They ate opportunistically, Freedman and Pobiner say, consuming anything they could get their hands on.
Contrary to what Paleo diet enthusiasts might say, there was no single diet that prevailed; the diets of hunter-gatherers depended largely on location, season, and opportunity. In the polar regions, Eskimo communities relied on wild animal protein, while the Juǀʼhoansi in Southern Africa ate mostly wild plant foods. There was no neighborhood bodega or Trader Joe’s to pick up mango during winter.
"There is no scientific basis for our current “three meals a day plus snacks” eating pattern.
At the time, humans did not eat as much as we do now.
Mark Mattson, Ph.D., a professor of neuroscience at the Johns Hopkins University School of Medicine and former chief of the Laboratory of Neurosciences at the National Institute on Aging, says there is no scientific basis for our current “three meals a day plus snacks” eating pattern.
For the majority of human history, people ate one or two meals per day. The current time-restricted eating patterns like the 16:8 or one meal a day diet (OMAD) mimic this ancient phenomenon.
During periods without food, the body evolved to tap into fat stores for energy. Some research shows this capability makes us metabolically and nutritionally flexible — able to maintain a sporadic diet.
While cavepeople may have eaten less in total, Freedman disputes the notion that hunters and gatherers would go days or weeks without food on a regular basis, calling into question the idea that fasting is natural.
“In the Stone Age, when everybody was a hunter gatherer and when the streams were full of fish, and yes, it depended on climate, but the places where people settled tended to have enough stuff going on to support a regular diet,” he says.
Hunter and gatherer societies were egalitarian, so there was no ruling elite or large-scale hierarchy dictating consumption, says Freedman. Communities were small and resources were relatively abundant.
"A lot of missing meals in history is not from nature, it is from oppression.
“A lot of missing meals in history is not from nature, it is from oppression,” he says. “I would test the assumption that because hunter gatherers are cast as uncivilized people they do not live in cities; they do not have writing; they must therefore be eating worse.”
When humans did go days without eating, he says, it was usually from disaster or famine, which ultimately led to starvation. So from his perspective, cavemen weren’t intermittently fasting; they were starving to death.
"It is not part of some kind of routine that our ancestors got used to.
“People who were going for days without eating not only didn’t like it, but found it was not helpful,” Freedman says. “It is not part of some kind of routine that our ancestors got used to.
“And then even if they did, which I doubt, the notion of going back to the things that they did, or the idea that we are hard-wired for intermittent fasting is, to me, not proven. Actually I think what’s hardwired in us are things that don’t work anymore.”
He’s referring to the ancient tendency to consume tons of fat and sugar — foods that were rare in prehistoric times, but are pervasive in modern day.
Pobiner agrees that we should be cautious in looking to what she calls the “deep past” for dietary knowledge. “A lot of people died in the past due to things like starvation and disease. Most humans did not live past reproductive age. I don’t think we necessarily want to emulate that,” she says.
Pobiner is right: Most humans lived to approximately 35 to 40 years old in the pre-agricultural era. “If you lived to 45 or 50, you were pretty old,” she says.
“I think there is this kind of romanticization of the past and the idea that we should eat like our ancestors ate because they were healthy and they lived long lives and they were disease free. And probably none of those things were the case,” Pobiner says.
Why We Eat Three Meals a Day: From Foragers to Farmers
After the era of hunter-gatherers came the Neolithic, or agricultural revolution about 10,000 years ago, which triggered tremendous health and social changes. Suddenly, growing crops, raising livestock, and storing surpluses created a predictable source of food. No longer were humans covering miles per day hunting big game or spending hours spearfishing in the local stream. Now, they could till the land, cultivate food, and eat more than ever before. With greater food security, people no longer fasted from lack of access to food.
“My understanding of how the three meals a day started was when farming became prominent,” Mattson says. “This became the eating pattern. People were able to store food and wake up in the morning and have food, which previously they didn’t.”
But predictability did not come without a cost, Freedman says.
“So that’s what the agricultural revolution does: It creates a reliable staple. But in return for reliability, you get a less varied diet and probably a less healthy population and more controllable population too.”
Many societies made a single staple crop like rice, cassava or potatoes, along with some flavoring or vegetables, the basis for their diet. Their diet narrowed, and research shows that that this change caused their health and height to suffer. People got shorter, and had nutrient deficiencies that potentially led to disease.
With this newly stable food supply, however, populations boomed, and farmers began to outnumber foragers. The shift in population put huge stress on the environment, Pobiner says.
“Most of what people were eating in the past was what was locally available, what was sustainable, and what they could get their hands on,” Pobiner says. “And the real change has been the incredible increase in population in the recent past.”
Our current dominant eating pattern emerged as our ability to store food increased and our working routines evolved. In the mornings, people would often eat a meal before heading out for the day’s work. Sometimes, they’d eat a midday meal or “lunch” as it came to be known, but they would always have dinner with family. Social rituals grew around these mealtimes, establishing the modern three-meals-a-day pattern. Timing and quantity of meals varied geographically.
Even though they were not foraging for food, they were still much more active than we are today. They spent the day cultivating crops in the fields and tending to livestock, so they were still experiencing drops in insulin and accessing fat stores. According to Mattson, they still went longer periods without food, a sort of unplanned “intermittent fast.”
Something to Give Up
Only when people had reliable access to food did they ever contemplate giving it up. After the agricultural revolution, humans did begin voluntarily intermittently fasting, but not for health reasons, for spiritual ones.
For thousands of years, Muslims have fasted sun up to sun down during Ramadan, Catholics have abstained from meat during Lent, and Jewish people have fasted on Yom Kippur. In more recent history, intermittent fasting has been used as a form of political protest, like Gandhi’s fasts during India’s freedom movement.
But now, intermittent fasting is the diet du jour, selling millions of diet books and sparking heated conversation online and among scientists. Freedman sees this trend as a replacement for religious fasting.
"Intermittent fasting, and dieting in general, is a modern phenomenon that is the result of some kind of search for meaning in a society that seems spiritually dead but materially sated.
“Intermittent fasting, and dieting in general, is a modern phenomenon that is the result of some kind of search for meaning in a society that seems spiritually dead but materially sated,” Freedman says.
In the absence of direction from organized religion, diet culture thrives as people find identity and community in their food choices, he explains.
“Once you don’t have a religion that may be liberating in a way, but it also forces you to seek meaning in something else. That could be science, it could be personal growth, it could be achievement. It may include a quest for people to control their body or listen to their body or get in touch with something. Who am I to say that this is not the right way of going about it?” Freedman asks.
Evolutionary Discordance: Real or Not?
As work shifted from farm to factory during the Industrial Revolution, the human eating schedule shifted to the three-meals-per-day routine that now dominates Western society. Today, most people do not go more than four hours without eating.
Unfortunately, this current rate of food consumption, along with the popularity of processed foods, contributes to the astronomical rates of obesity, diabetes, heart disease, and cancer seen today.
"Evolution changes faster than we think.
One argument says that disease rates have exploded because of an environmental mismatch — or what scientists call environmental discordance. The idea is that modern human bodies are still caveperson bodies, and therefore ill-adapted to modern diet.
Pobiner says this is wrong — evolution changes faster than we think.
“This idea of the evolutionary mismatch is that human evolution proceeds really slowly, and that we haven’t had enough time to adapt to current diets,” she explains. “But what we see is that in situations where there is very strong selection pressure, there can be adaptations to changes in diet over a very short amount of time.”
She refers to the Andean people in the highlands of Peru who adapted to a high-starch diet after potatoes became a staple crop. Another example is how approximately a third of the human population is now adapted to digest dairy products, something previously unheard of earlier than 7,500 years ago.
In response to an increasingly problematic and industrialized food system, it can be tempting to turn towards our prehistoric ancestors for wisdom. But maybe, she says, humans have evolved farther from our paleo-ancestors than we think.
“We are not the people that lived on the planet 10,000 years ago or 50,000 years ago and 300,000 years ago with the origin of our species,” she says. “We shouldn’t necessarily be eating like them.”
What Worked Then Might Not Work Now
Pobiner says intermittent fasting may have potential benefits but we should not be trying it because we think our pre-agricultural ancestors had something figured out health-wise.
“Just because a dietary practice existed in ancient times, doesn’t necessarily mean it is good or healthy today,” she says.
"People love to hear that our ancestors had some kind of wisdom and they’re not interested in whether it’s true or not.
Our tendency to look toward the past says more about our nostalgia or sense of inadequacy than about anything they actually did, Freedman says. “People love to hear that our ancestors had some kind of wisdom and they’re not interested in whether it’s true or not.”
Pobiner suggests examining more recent food-related shifts in history, and potential ways to minimize their harmful effects.
“People will ask all the time what diet is healthy,” Pobiner says. “It depends on what your health goal is and if your health goal is weight loss, that may be one kind of diet. If your health goal is cardiovascular health, that may be another kind of diet. I think it is useful to look at current diets and the rise of processed food and industrial agriculture, which are very recent developments. Whether those things are good for us or not are big questions. and you know, they probably are not.”
So if your health goal is to lose weight, stabilize your blood sugar, or potentially protect your brain and body from disease, those may be valid reasons to try intermittent fasting, not because our ancestors may have done it.