The paleo diet gets a lot of things right. First and foremost, it’s a simple and effective system for reducing your daily calories without starving or depriving yourself of important nutrients. The recommended foods include most of the best protein sources—meat, fish, poultry, eggs—along with plenty of fruit, vegetables, nuts, and seeds.

Related: 20 Healthy, Protein-Packed Smoothie Recipes

It’s hard to go wrong with a diet in which 100 percent of the foods are unprocessed, with no added sugar or salt.

But no one should ever claim with a straight face that it represents what people actually ate in the Paleolithic, an era that started roughly 2.5 million years ago and lasted until the rise of agriculture about 10,000 years ago. Or what more recent hunter-gatherer tribes ate, and in some cases still eat, according to historians and anthropologists.

Some of their culinary choices seem like they’re straight out of your worst nightmare, if your nightmares resemble zombie movies, giving you a whole new appreciation for our modern food industry. Bring on the candy corn!

(For more must-know health tips—and 2,000+ awesome life hacks to help you become stronger, happier, and healthier—check out The Better Man Project, the brand-new book from the editor in chief of Men’s Health.)

1. Rumen noodles

“Chyme” is a sweet word for a food source that’s objectively sour: the semi-digested stomach contents of animals. It’s not just a meal ready to eat. It’s already eaten.

Why stomach stew? Imagine you’re a caveman living in an ice age. You have zero access to plant food for months at a time. Along comes an unsuspecting herbivore, looking for moss and lichen and whatever else it can scrape off rocks or bark. After you kill it, those stomach contents give you the first hot meal of the day—no microwave required—and provide nutrients you wouldn’t otherwise get, including active live cultures to aid digestion.

Related: 6 Disgusting Things on Your Body Right NOW!

Nearly every pre-modern society had a thing for it, and not just for food. The Kuria in East Africa would rub the chyme of cattle, goats, and sheep all over their bodies, using it as a magical perfume to protect them from bad people. (Maybe it’s just us, but we can’t imagine it would take a lot of magic to persuade bad guys to stay away from someone slathered in goat guts in the boiling African heat.)

Closer to home, Inuits of the 19th and 20th centuries were observed eating partly fermented, pre-digested mush from the rumen of reindeer. Deer, like cattle and sheep, are called ruminants because they digest food through a circular process of chewing, digesting (in a part of the stomach called the rumen), regurgitating, chewing again, and repeating.

If you’ve ever wondered where the word “ruminate” comes from, now you know. Good luck trying to forget.

2. The original Gatorade

Many a young man has taken a sip of a flat, warm beer and said to himself, “Ugh! That tastes like buffalo piss!” And of course nobody would ever drink such a thing on purpose, right?

Some did.

The Comanche were the most deadly and feared fighting force of the early 19th century on America’s Great Plains. On a long hunt in hot, dry weather, they would sometimes ride for a day or two between water sources. The risk of dehydration, and loss of electrolytes, would’ve been considerable.

The solution, according to Empire of the Summer Moon, a history of the Comanche, was found inside the bison they hunted. As soon as the magnificent mammal bit the prairie, they scrambled for its juicy innards. “Children would … squirt the salty bile from the gallbladder onto the liver and eat it on the spot, warm and dripping blood,” author Sam Gwynne writes.

All fluids were appreciated, including “warm curdled milk from the stomach of a suckling calf.” That warm beer doesn’t look so bad now, does it?

(Are You Drinking Too Much Water? Here's how to tell.)

3. Man ham

All in all, the Comanche were so good at what they did that they were typically healthy and robust. But that’s not why a rival tribe, the Tonkawa, were known to eat the Comanche warriors they killed in combat. They were after more than lean protein.

Today we think of cannibalism in terms of the Donner party—something desperate people do during desperate times. But archaeologists and historians have found lots of evidence of cannibalism throughout human history, including the remains of 11 juveniles who were butchered and eaten 800,000 years ago at a cave in Spain. Our close cousins, the Neanderthals, were also known to have feasted on their own.

The open question is why. Did they enjoy the taste of hominid flesh? Was there a nutritional advantage to Soylent Green over, say, chyme? Were they simply desperate? Or was there a ritualistic or magical element that had little to do with appetite?

For the Tonkawa, it was the latter. The goal was to absorb the mojo of their badass enemies. That’s according to an eyewitness report of dead-guy goulash from Noah Smithwick, one of the rare palefaces to live and travel with Indian tribes in the 1800s: “Having fleeced off the flesh of the dead Comanche, they borrowed a big wash kettle … into which they put the Comanche meat, together with a lot of corn and potatoes – the most revolting mess my eyes ever rested on.”

4. Heads and tails

Fat is an essential nutrient. No matter how much protein you have in your diet, you’ll starve to death without fat. Of course that’s not an issue for a modern, meat-eating guy. An 8-ounce sirloin steak provides 20 grams of fat, and that’s one of the leanest cuts.

(What's Your Beef? The cut of the cow can make a difference.)

But there was no such thing as marbled beef in the Stone Age. Wild animals don’t store fat the way domesticated ones do. Ancient hunters had to get their fat where the animals kept it: in their brains, around their internal organs, in their tails, and even in their gonads. Yes, we’re talking about the original nut butter.

Australian aborigines came up with an ingenious way to extract all the fat they could out of a kangaroo. When they managed to kill one—which wouldn’t be easy with a bow and arrow—they would open up the belly and cook the liver on the spot. They’d also empty the stomach and intestines of undigested food (no chyme for them!), close up the cavity, and carry the animal back to camp for everyone to share.

Now comes the clever part: They roasted the animal on its back, letting all the juices from organ and cellular fat, mixed with blood, accumulate in the abdominal cavity. Those juices were the first course at the feast. One researcher noted that it “tastes like a rich beef broth.”

5. Paleo ale

Some paleo-diet advocates are adamantly anti-alcohol, reasoning that cavemen wouldn’t have had any grains to brew, or any way to systematically ferment fruit for wine. They have a point. The few remaining hunter-gatherer tribes don’t typically make beer or wine (with one exception, as we’ll see), so it’s logical to assume their ancient counterparts didn’t either.

But that doesn’t mean our ancestors didn’t get soused any chance they got.

Related: This Is Your Body on Booze

Researchers at the Foundation for Applied Molecular Evolution in Gainesville, Florida, recently calculated that the ability to metabolize alcohol goes back 10 million years, which is 5 million years before humans and apes became distinctly different species. To put that in even more perspective, humans adapted to eating meat as a regular part of the diet just 1.5 million years ago.

Our taste for alcohol would have started with the innocent discovery that overripe fruit, in the right circumstances, will give you a nice little buzz. It starts when wind-blown yeast spores land on fruit. The fruit’s sugars ferment and turn into alcohol at concentrations up to 4.5 percent, similar to beer. Call it the world’s first buzzfeed.

We can only guess when our ancestors figured out how to turn grains into beer. All we know is that it happened long before they invented writing, which gives us a sense of their priorities. And once they started writing, they wrote about booze. The Old Testament tells us that Noah planted a vineyard soon after he got off the boat (he certainly would’ve had plenty of fertilizer to help it along), and early pagan religions included wine gods in their pantheons. One gets the impression that most people were constantly drunk from the earliest days of civilization until coffee came into its own during the Renaissance.

But that brings up a chicken and egg question: Did civilization lead inexorably to alcohol? Or did alcohol lead to civilization? Some researchers have proposed that the first cultivated grains weren’t used to make bread. It was beer they were after, and that may help explain the shift from hunting and gathering to planting and harvesting.

That’s the thesis of Uncorking the Past, a history of alcohol and civilization by University of Pennsylvania archaeologist Patrick McGovern, Ph.D., who found traces of a Chinese drink made from rice, honey, and fruit that dates back 9,000 years.

We’ll never know which came first, the pizza or the beer. But it didn’t seem to take our ancestors long to figure out that life is better with both.

6. Bone on the range

Bone marrow was another important source of fat for ancient hunters, and is still consumed in remote villages as well as elegant restaurants. But while marrow today is typically slow-cooked into stews and broths, back then it was enjoyed at the site of a kill, like Paleo Pixie Stix.

The technology to crack open big bones and suck them dry developed in tandem with our ancestors’ taste for meat. This is also the time when the brains of our ancient ancestors more than doubled in size. Make of that what you will.

By the time humans were smarter than the average bear, they became increasingly proficient at killing said bears, along with lots of other animals whose carcasses were too big to schlep long distances. So they developed a routine. They would immediately eat the parts that were most perishable, like the brain. Then they went to the parts that were too big to carry, like the marrow in the bones. Finally, they would carve out the muscle, and carry it by slinging it over their shoulders.

Archaeologists call this a “meat shirt.” We call it cardio.

7. Hemo therapy

We’ve mentioned blood a few times, but would be remiss if we didn’t point out just how important a source of nutrition it is to tribes during recorded history, and almost certainly would’ve been in ancient times. Take the Maasai of East Africa, whose lifestyle dates back 10,000 years, when the cattle they now herd were first domesticated. Their diet is based on milk, meat, and blood. (Yes, we know the Paleo diet is anti-dairy, but we’d like to see one of its advocates try to explain to a Maasai warrior why he shouldn’t drink milk.)

The Maasai, like the Comanche, face the problem of long treks from one water source to the next. Unlike the Comanche, they bring their relief with them, making a kind of primitive protein shake with milk and blood from their cattle, who function as ambulatory vending machines. Milk is an obviously good source of protein, and blood is too. Bovine blood is relatively high in leucine, the amino acid with the most powerful muscle-building qualities.

8. Sweet surrender

We could go on for days recounting the many, many ways that the diets of Stone Age people, or their modern equivalents, are different from what Paleo authors and advocates recommend. Some of the traditional diets directly contradict hard and fast Paleo rules, like the idea that no one should drink milk. The Maasai drink more than even the Dairy Council would recommend, and others wouldn’t hesitate to take it straight from the udder of a cow killed on the hunt.

Then there are the many, many things that our ancestors, as well as more contemporary hunter-gatherers, were known to eat that most of would find disgusting: salty body fluids like blood and urine, half-digested stomach contents, fatty deposits from testicles, their next-door neighbors…And we haven’t even mentioned how many bugs they ate. (Which actually aren’t bad when fried up with garlic and a little salt, although you could say that about pretty much anything.)

Here’s one more way reality trumps theory:

The Paleo diet is adamantly anti-sugar. And that’s fine. Avoiding sugar helps you cut back on calories, not to mention dental cavities. But it’s not a rule that any actual caveman, or modern hunter-gatherer, would’ve followed. When anthropologists study the diets of the few remaining primitive tribes, one staple shows up over and over again: honey. Which is, basically, pure sugar. They eat as much as they can find, as often as they can find it. The Ache of Paraguay get up to 40 percent of their daily calories from honey in the early summer, when it’s most plentiful. The Maasai even make an alcoholic beverage out of it.

That takes us to the most important point of all:

It’s great to limit your diet to whole, healthy foods. It’s great to seek out the foods that make you look and feel better, and avoid those you tend to overeat, or that make you feel worse. Every lean, fit person has to make those choices.

All we ask is that you don’t claim you eat this way because it’s the only way humans are supposed to eat, or that it’s based on what people used to eat before they settled down to open microbreweries. Cavemen ate anything they came across, and then went back for seconds. Ruminate on that.

Lou Schuler is an award-winning journalist and contributing editor to Men’s Health. John Williams, Ph.D., is an archaeologist based in Denver.

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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