The skull of Bison antiquus in Mark Mullins's living room looks like something Conan the Barbarian might wear to make a fashion statement. To picture this extinct animal, imagine an American bison—2,000 pounds of pissed-off, top-heavy bovine capable of hitting 30 miles an hour on a flat stretch of prairie—and add about 500 pounds and longer horns. Then amp up the intimidation factor by several times.



Now picture humans roaming the plains of Paleolithic era North America 15,000 years ago, people just like us in nearly every way except for the fact that they haven't gotten around to inventing much of the stuff we now eat, wear, operate, or live in. You or I wouldn't approach a Bison antiquus armed with anything less than a bazooka, but the first people to populate North America tracked, killed, and consumed the beasts using nothing more than simple tools, like pointy sticks and flaked stones.



"It was their ability to outsmart these megamammals that allowed humans to successfully kill the animals, which were so much stronger," Mullins says. "People understood the animals' movements and behavior."



Mullins is 40 years old, slim, and obviously fit. He's been collecting spear points, arrowheads, and other ancient tools since he was a teenager. His home in Colorado Springs houses one of the world's largest private collections of artifacts from the Ice Age, a period that ended about 10,000 years ago. He's spent his life working to piece together the story of the people who once populated our hemisphere.



And yet I'm surprised to learn that Mullins is a recent convert to the paleo diet, a system of eating that's based on foods that would have been available to our ancient ancestors before the invention of agriculture.



"I just went to what I thought these people ate," he tells me, adding that in the 2 years since he and his wife, Marisa, made the switch, he's lost 70 pounds. So now he might be too much of a lightweight to tackle a ton of raging bison.



But the surprise isn't so much that Mullins follows the ancestral diet but that he waited so long to go paleo.



EVOLUTION OF A DIET

The name "paleo diet" was coined by Loren Cordain, Ph.D., author of The Paleo Diet for Athletes and a professor of health and exercise science at Colorado State University in Fort Collins, where I meet with him the day after I met with Mullins. Cordain shows me a wall of file cabinets packed with studies on various aspects of the diet, which today goes by many names, from "caveman diet" to "ancestral nutrition" (the preferred generic) to "evolutionary nutrition" (a term used in some published research). They all describe the same concept.



"Seventy percent of the typical U.S. diet is foods that our Stone Age ancestors wouldn't have consumed," Cordain says. According to him, these include grains, dairy, peas and beans, processed oils, added sugars, and alcohol. "What we've tried to do is replace these calories with real foods—fruits, vegetables, meats, seafood." (And although some paleo advocates don't like to admit it, research suggests that early humans were processing and eating wild grains many thousands of years before they actually figured out how to grow them as crops.) (If you know you need more real food in your diet, . We'll deliver recipes from top chef right to your inbox weekly.)



The diet took a while to reach its current level of popularity, and you can see why. In a world in which most of us have grown up to think of whole grains, dairy, and beans as vital parts of a healthy diet, Cordain and his like-minded compatriots had a hard time convincing the rest of us that we should give up those foods.



The whole thing started with a 1985 study published in the New England Journal of Medicine. Titled "Paleolithic Nutrition: A Consideration of its Nature and Current Implications," the paper argued that the human genome, which has evolved over millions of years, simply hasn't had enough time to adjust to foods like grains, dairy, and beans (not to mention candy corn and Cheez Whiz), which were not staples in the human diet before the advent of agriculture 10,000 years ago. The notion reminded Cordain of a famous observation from the evolutionary biologist Theodosius Dobzhansky: "Nothing in biology makes sense except in the light of evolution."



Cordain came across the study in 1987. Coincidentally, that same year the scientist and author Jared Diamond published an article in Discover magazine in which he called agriculture "the worst mistake in the history of the human race." In my interviews for this story, more people mentioned that 25-year-old article than any book or study published since, including Diamond's Pulitzer Prize–winning book Guns, Germs, and Steel, which came out a decade later.



Here's the money passage from the article: "Skeletons from Greece and Turkey show that the average height of hunter-gatherers toward the end of the ice ages was a generous 5'9" for men, 5'5" for women," Diamond wrote. "With the adoption of agriculture, height crashed, and by 3,000 B.C. had reached a low of only 5'3" for men, 5' for women." (And let's not get started on their lifespans. Click here for 5 Ways to Add 22 Years to Your Life.)



Because height is frequently considered a marker of a society's overall health, many paleo advocates use the post-agricultural decline in human stature as one argument for their position. Diets based on foods that humans hadn't evolved with can often result in malnutrition, they say.



Why does this matter? The starting front court for the Miami Heat didn't seem to have a nutrition problem, though it made the Thunder look a bit sickly. And don't we live in a country where few people starve or do backbreaking labor, and where modern medicine offers quick fixes for the diseases we pick up from one another? And more to the point, why should food crises in prebiblical times affect what we eat today?



To answer that last question, it's helpful to see what hunter-gatherers did better than we do now. That requires a quick field trip to our distant past.



KILLER ELITE

The Lindenmeier archaeological site, just north of Fort Collins, is one of the few places where you can see the world almost exactly the way nomadic hunter-gatherers would have seen it when they camped here 11,000 years ago. The site overlooks a vast expanse of grassland; on a clear day it would have offered miles-long vistas. And because back then was an ice age, the prairie was covered with abundant snow in winter, which made the hulking Bison antiquus as easy to spot as a chocolate chunk in ice cream.



I'm standing on the overlook with two archaeologists: my friend John Williams, Ph.D., a lecturer at the University of Colorado at Denver, and his friend Jason LaBelle, Ph.D., a professor at Colorado State University and the leader of the team exploring the area. This region has been studied and excavated on and off since the 1920s.



Lindenmeier is best known as the burial ground for hundreds of artifacts from the Folsom period, the height of Paleolithic culture in North America. I knew from looking at Mullins's collection that these people took extraordinary care in crafting their tools. Ice age people came up with the most complex way to create each piece, taking extra steps to show off their ability, Mullins says. Moreover, "They went to extremes to find the most precious and semiprecious stones," bypassing stones that were more common—and equally lethal—but just not as beautiful.



A prehistoric Steve Jobs would've fit right in.



LaBelle agrees, noting that the Lindenmeier archaeological site has offered up scores of sewing needles, along with complex jewelry pieces. "These guys had plenty of downtime to take care of lots of things beyond subsistence," he says.



What gave them all that time? Their food. In addition to bison, they also ate deer, pronghorn, rabbits, hares, turtles, and the occasional camel. These are all signs that Ice Age North Americans were living high on the hog (even though there were no hogs on the continent back then—a shame if you've tried this Tasty Pork Burger Recipe).



Their diet also included plenty of carbohydrates. In summer, "they could munch their way through the landscape, like Pac-Man," LaBelle says. They would start low, where the first nuts and berries were ripening, and then climb to higher elevations to find the same plants reaching maturity later in the season.



Standing on the Lindenmeier overlook, you can imagine a time when there was boundless food, water, and fresh air; when everyone got plenty of exercise; when people had the time to create objects that were beautiful for beauty's sake; and when there was no such thing as organized warfare. (That's not to say violence wasn't a fact of life back then; assholes existed long before Jersey Shore.)



"People remained hunter-gatherers until they were forced to change," LaBelle says, which leads to the obvious question: What forced prehistoric humans to give up such a productive, satisfying, and—more to the point—nourishing way of life?



THE STORY OF US

Here's a condensed history of the human species: Six to 7 million years ago, the human evolutionary line became separated from the great apes. A human ancestor, Australopithecus anamensis, began regularly walking upright some 4 million years back, even though he was still somewhat chimpishly long-armed and short-legged.



The Paleolithic, marked by the first use of stone tools, started about 2.6 million years ago. Around this time, Team Hominid figured out that the ability to hit soft things with hard objects presented exciting new culinary options. Thus, our guys started consuming meat, first probably only scavenging and later hunting, and providing themselves with an unprecedented supply of protein, along with fat from brains and bone marrow. This infusion of nutrients played a great role in our evolutionary history. The human brain of Homo habilis around 2 million years ago grew 50 percent larger to become the Homo erectus brain just 300,000 years later, and it would grow another 50 percent in modern humans, who emerged around 200,000 years ago. With the bigger brain came the first true hunter-gatherer lifestyle. (The love of meat endures to modern times. Check out the Men's Health Guy Gourmet Cook the Cow series for all the beef recipes and tips you—or Grok the Caveman—could ever want.)



Good times, right?



Not really. Life often would've sucked hard for those first Homo sapiens. Scientists believe a prolonged ice age until about 70,000 years ago may have reduced the human population to a mere several thousand.



The stretch of the Paleolithic in which humans hit the top of the food chain and lived large was surprisingly brief, roughly 25,000 to 10,000 years ago. It was the true sweet spot of human evolution: We had the world to ourselves, having outcompeted (or bred with) the Neanderthals who occupied the same areas in Europe and Asia. We had plenty of game to hunt and relatively few predators. (Giant cave bears, for example, were mostly extinct by then.)



But then the planet warmed up and it all went to hell. Animal migration routes changed, leaving the humans in Europe with more mouths to feed but less prey to hunt (and smaller prey at that). Fishing made up for some of the reduction in available game, but when agriculture arrived in what we now call the Neolithic, it wasn't because people were tired of hunting. It was because, for the first time in eons, the planet was warm enough and wet enough to provide actual growing seasons, and our ancestors were smart enough to take advantage of that. (To this day, following the growing seasons will allow you to sample the best, freshest fruits and vegetables. Click here to learn How to Pick the Best Produce.)



The shift from hunting and gathering didn't happen all at once. It took thousands of years for the first farmers in the Middle East to cultivate the wheat and bean plants that had been growing wild in that region, and to turn them into crops that could be reliably planted, harvested, stored, and eventually transported. Around this time people also started domesticating animals like cows and sheep. People in some areas turned to farming and herding as soon as they became exposed to it, while others stayed with hunting and gathering until, as LaBelle says, they were forced out of it. A dwindling few remain hunter-gatherers to this day.



Most of us today hunt and gather all our food in supermarkets, and our average height has returned to about a preagricultural 5'9". But we're also older and fatter, and many of us live with chronic conditions that, the paleo advocates say, are a self-inflicted consequence of diets filled with foods our species isn't meant to eat.



"What kills everybody now in the Western world is heart disease, cancer, and autoimmune diseases," Cordain tells me. (How come? Click here to read the Men's Health special report Obesity in America.) In fact, according to the CDC, heart disease and cancer are the two leading causes of death in the United States, while a landmark University of Connecticut study found that autoimmune conditions, which include lupus, rheumatoid arthritis, and thyroiditis, are significant contributors to mortality among young and middle-aged women. "There's a common process that drives all of those. You can't have heart disease—or cancer—without inflammation. You can't have autoimmunity without inflammation."



Inflammation, he says, often starts with digestive problems. Grains and legumes, in particular, contain antinutrients—chemicals that, because they're indigestible, may lead to inflammation that spreads from the digestive system until it becomes systemic.



Some diseases have an obvious connection to diet. Celiac disease, for example, is an autoimmune condition triggered by gliadin, a protein found in gluten, a natural component of wheat and other cereal grains. Lectins are other problematic proteins found in high concentrations in beans, legumes, and cereal grains. But others have no known connection to diet, and that's where I find myself wondering if the paleo advocates are pushing their basic idea too far.



Two big problems emerge here. One is logical, the other factual. "Here is a group of people who claim to take an evolutionary approach to life, yet show that they do not understand evolution," says Mathieu Lalonde, Ph.D., an organic chemist at Harvard. "Just because we have the same genes as our Paleolithic ancestors doesn't mean we're meant to eat the same things. There have been adaptations."



Among them are increases in enzymes that help us digest starches and lactose (the sugar in milk). These adaptations are unevenly distributed among various populations around the world. What matters is whether a particular food is tolerated. The simplest way to figure this out, Lalonde says, is to stop eating a food or food group for 30 to 60 days and see what happens.



There's also a problem with the idea that "diseases of Western civilization" are all or mostly related to diet, or that they're even new.



Take for example Otzi the Iceman, whose frozen (thus preserved) 5,300-year-old corpse was discovered in the Italian Alps in 1991. Otzi was in his 40s when he was shot in the back with an arrow, which probably killed him. But if the arrow hadn't done him in, his clogged arteries suggest that he might not have lived much longer. (He also suffered from arthritis.) According to a recent study in Nature Communications, Otzi had several genetic markers that nearly doubled his risk of heart disease. In other words, a man who lived thousands of years before the mythical Trojan War had genes that strongly suggested he might eventually die of the number one cause of death afflicting 21st-century Americans.



The genes that show up on Cordain's disease checklist may not be exactly new either. In The Blue Zones, author Dan Buettner's study of the places where people live the longest, we meet residents of an isolated, mountainous region in Sardinia, an island off the coast of Italy. The people who live in that area have genes with origins that date back to Paleolithic times. The good news is that the people there seem wired to live for a very long time. The bad news is that they're also at high risk for a pair of autoimmune diseases: type 1 diabetes and multiple sclerosis.



So yet again we find "diseases of Western civilization" encoded in ancestral genomes. Another inconvenient fact comes to light in studies of the healthiest, longest-living people in places like Sardinia; Okinawa; and Nicoya, Costa Rica: They all eat cereal grains like wheat, corn, and rice—lots of cereal grains, in fact—along with legumes. The Sardinians are also fond of their wine and dairy.



The agrarian diet is typically low in protein and fat but high in plant-derived carbs, while the paleo diet is high in protein and fat but relatively low in carbs. If one is "ideal," then the other must be completely wrong. Right?



It's not so simple. Lalonde believes the paleo camp is winning, and he says he's seen the studies to prove it. But plenty of lab work needs to be done before we can point to the modern diet alone as the root of all evil, or to the paleo way of eating as a cure for metabolic syndrome and other modern ills.



WHEN LESS IS MORE

Right about the time I started working on this story, a friend who lives "off the grid" in an undisclosed location told me about his most recent fitness discovery: By doing hard physical labor and living without central heat and air conditioning, he'd become leaner than he'd ever been when he'd used conventional diet and exercise. His story brought to mind a 2006 study in the International Journal of Obesity, which listed a series of reasons why our population may have gained so much weight in the past 30 years. Among them: In 1923, the "thermal standard for winter comfort" in U.S. homes was a brisk 64°F. By 1986, the average thermostat was set to a balmy 76. It's natural for us to "upregulate" our metabolism in winter to keep warm while downshifting in summer, when heat slows our appetite. Living in a climate-controlled world can mess with that balance, potentially leading to weight gain over time.



So, as an experiment, I turned our thermostat down to 66 for the winter as I switched to a kinda-sorta paleo diet. That is, I eliminated almost all grains after breakfast, which was a lot harder than it sounds in a family of five. (Try eating meatballs without the spaghetti.) I went from having a nightly beer to maybe a couple of drinks on weekends. I added a salad every evening and ate fruit throughout the day. I also tried to take a nightly walk with my wife or one of our kids. The rest of my life, including three gym workouts a week, stayed the same.



By mid-March I'd lost about 10 pounds. When the weather warmed up, I noticed that shorts that had fit me the previous summer were hanging off my hips.



Since I changed three things at once—diet, exercise, and ambient temperature—I can't say which was most effective. But I bet it was mostly the diet. Good things tend to happen when you replace processed foods with fruits, vegetables, eggs, lean cuts of meat, and the occasional baked potato.



"I disagree with how paleo is justified," Lalonde says, "but they get the food mostly right. They're nutritious meals of whole foods."



BRAIN CANDY

Let's return to the Paleolithic, or at least the part of it in Mark Mullins's home in Colorado Springs. Once I notice that Bison antiquus skull, it's hard to focus on anything else.



On the back of the skull is a fist-sized hole, where the top of the skull was smashed out with a large stone. Mullins says that whoever killed this ton-and-a-quarter beast would've eaten its fat-rich brains first. Ancient humans, who did hours of exercise a day and whose bodies had to keep warm through long, frozen winters, needed far more calories than we do. Bison brain would've been an antediluvian delicacy.



Today this authentic aspect of Paleolithic cuisine isn't recommended. Most humans stopped eating brains long before we invented zombies to eat them for us. We simply didn't need the calories anymore, once we figured out how to get them from other sources.



That's always the way it has been for Homo sapiens. We figure out how to do one thing; then we figure out how to do something better. "We are and have been a very dynamic population for hundreds of thousands of years," says Stephen Phinney, M.D., Ph.D., a professor emeritus of medicine at the University of California at Davis and coauthor of The Art and Science of Low Carbohydrate Living. Take, for example, the idea that food processing is inherently bad. "Very early on, there is evidence that humans learned to process food," Dr. Phinney says. "They were very strategic in what they hunted and what they saved."



Today, of course, we have the opposite problem. There are so many ways to process and preserve food for transport and consumption that our biggest challenge is trying to avoid the excess calories that are cheap, tasty, and rarely far away. (Click here for your complete guide to the 125 Best Processed Foods for Men.)



My toes-in-the-water experiment with the paleo diet showed me that it's a simple system for limiting calories. To keep weight off, I'll probably have to stick with the plan for life, and that brings me back to the original question that the paleo diet claims to answer. Are grains really so bad? Are we all better off if we avoid them whenever possible? The only way to know for sure is to cut them out of your diet for a month or two.



You may or may not feel better (I feel about the same as I did before), but you'll probably end up lighter—exactly what you'd expect from any diet based on either eliminating or overthinking. If your diet works, it's because you've learned to follow a set of rules that keep you from eating stuff just because it's there.



In that sense, we are still cavemen. The right foods in the right volume were a matter of life or death for them. Survival often meant finding new sources of calories. For us, the problem is reversed. Staying lean means deciding what we can live without.



Lou Schuler Lou Schuler, CSCS, is a National Magazine Award-winning journalist and editorial director of the Personal Trainer Development Center

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