As you can see, the Paleo Diet is extremely nutritious. The macronutrient breakdown for this sample 2,200-calorie diet is 33 percent protein, 25 percent carbohydrate, and 42 percent fat. Note that for every nutrient except vitamin D, the daily nutrient intake ranges from 1.5 to more than 10 times the governmentally suggested RDA. Even "healthful" vegetarian diets don"t reach these nutrient levels. The Paleo Diet is rich in antioxidant vitamins (A, C, and E), minerals (selenium), and plant phytochemicals, such as beta-carotene, which can help prevent the development of heart disease and cancer. In addition, the high levels of B vitamins (B6, B12, and folate) prevent elevated levels of blood h.o.m.ocysteine, a potent risk factor for atherosclerosis, and also have been a.s.sociated with a reduced risk of colon cancer and spina bifida, a neural tube birth defect.
Even though the fat content (42 percent of total calories) is slightly higher than that in the average American diet (31 percent of total calories), these are good fats-healthful, cholesterol-lowering monounsaturated and polyunsaturated fats. Actually, the monounsaturated fat intake is twice that of saturated fat. As I discussed earlier, the high levels of omega 3 fats also help protect against heart disease by their ability to thin the blood, prevent fatal heartbeat irregularities, and lower blood triglycerides.
Not only does the Paleo Diet provide you with an abundance of nutrients, it"s also extremely high in fiber. This, too, can lower blood cholesterol. It promotes normal bowel function and prevents constipation as well.
Finally, because extra salt and processed salty foods are not part of the Paleo Diet, the sodium (and chloride) content here is very low, while the pota.s.sium content is quite high. As we"ve discussed, this high-pota.s.sium/low-sodium balance helps prevent high blood pressure, kidney stones, asthma, osteoporosis, certain types of cancer, and other chronic diseases known to be a.s.sociated with high-salt diets.
The amount of vitamin D you"ll get on the Paleo Diet is negligible, because vitamin D is found only in trace quant.i.ties in all naturally occurring foods, except for fish liver oils. But we don"t need need to eat that much vitamin D-we can get all we need from the sun. (When we"re exposed to ultraviolet radiation from sunlight, our bodies synthesize vitamin D from the cholesterol in our skin.) Our Paleolithic ancestors spent much of their time outdoors, and they manufactured all the vitamin D they needed from the sun"s natural rays. Today, many of us get insufficient sunlight exposure to synthesize optimal levels of vitamin D. This is why milk, margarine, and other processed foods are fortified with vitamin D. We would all do well to incorporate some of the Stone Age lifestyle and make sure to get some daily sunshine. However, if your busy lifestyle doesn"t allow it, particularly during short winter days, I recommend that you take a vitamin D supplement (at least 2,000 I.U./day). to eat that much vitamin D-we can get all we need from the sun. (When we"re exposed to ultraviolet radiation from sunlight, our bodies synthesize vitamin D from the cholesterol in our skin.) Our Paleolithic ancestors spent much of their time outdoors, and they manufactured all the vitamin D they needed from the sun"s natural rays. Today, many of us get insufficient sunlight exposure to synthesize optimal levels of vitamin D. This is why milk, margarine, and other processed foods are fortified with vitamin D. We would all do well to incorporate some of the Stone Age lifestyle and make sure to get some daily sunshine. However, if your busy lifestyle doesn"t allow it, particularly during short winter days, I recommend that you take a vitamin D supplement (at least 2,000 I.U./day).
Perhaps the most important element of the Paleo Diet is its high protein intake-nearly four times higher than the RDA. As I"ve discussed, this high level of protein helps you lose weight by increasing your metabolism and reducing your appet.i.te. A 1999 clinical report in the International Journal of Obesity International Journal of Obesity by my friend Dr. Soren Toubro and colleagues from the Royal Veterinary and Agricultural University in Copenhagen, Denmark, has shown that when it comes to weight loss, high-protein, low-calorie diets are much more effective than low-calorie, high-carbohydrate diets. In the ensuing eleven years, hundreds of scientific papers have confirmed these seminal results. Also, high levels of low-fat protein lower your cholesterol, reduce triglycerides and increase good HDL cholesterol, and reduce your risk of high blood pressure, stroke, and certain forms of cancer. When accompanied by sufficient amounts of alkaline fruit and vegetables, high-protein diets do not promote osteoporosis. Instead, they protect you from it. by my friend Dr. Soren Toubro and colleagues from the Royal Veterinary and Agricultural University in Copenhagen, Denmark, has shown that when it comes to weight loss, high-protein, low-calorie diets are much more effective than low-calorie, high-carbohydrate diets. In the ensuing eleven years, hundreds of scientific papers have confirmed these seminal results. Also, high levels of low-fat protein lower your cholesterol, reduce triglycerides and increase good HDL cholesterol, and reduce your risk of high blood pressure, stroke, and certain forms of cancer. When accompanied by sufficient amounts of alkaline fruit and vegetables, high-protein diets do not promote osteoporosis. Instead, they protect you from it.
The Typical American Diet: A Nutritional Nightmare Now let"s take a look at this same 2,200 calorie diet for our sample twenty-five-year-old woman-but let"s replace most of the real foods (lean meats and fruits and vegetables) with processed foods, cereal grains, and dairy products. Remember, the U.S. Department of Agriculture (USDA) Food Pyramid encourages you to eat six to eleven servings of grains every day. The nutrient breakdown depicted below closely resembles that of the average American diet. This is the same diet that has produced a nation in which 68 percent of all American men over age twenty-five and 64 percent of women over age twenty-five are either overweight or obese.
For breakfast, our twenty-five-year-old woman eats a Danish pastry and two cups of cornflakes with 8 ounces of whole milk, topped off with a teaspoon of sugar, and drinks a cup of coffee with a tablespoon of cream and a teaspoon of sugar. Because of the large amounts of refined carbohydrates consumed for breakfast, her blood sugar level soon plummets and she is hungry again by midmorning, so she eats a glazed doughnut and drinks another cup of coffee with cream and sugar. By noon, she"s hungry again. She goes to the McDonald"s near her office and orders a Quarter Pounder, a small portion of French fries, and a 12-ounce cola drink. For dinner, she eats two slices of cheese pizza and a small iceberg lettuce salad with half a tomato, covered with two tablespoons of Thousand Island dressing. She washes it all down with 12 ounces of lemon-lime soda. Let"s examine the nutrient breakdown of this dietary disaster:
Nutrient Daily Intake RDA.
Calories 2,200.0.
100%.
Protein 62.0 (g) 57%.
Carbohydrate 309.0 (g) - Fat 83.0 (g) - Saturated fat 29.0 (g) - Monounsaturated fat 19.0 (g) - Polyunsaturated fat 10.0 (g) - Omega 3 fats 1.0 (g) - Water-soluble vitamins .
Thiamin (B1) 1.0 (mg) 95%.
Riboflavin (B2) 1.1 (mg) 87%.
Niacin (B3) 11.0 (mg) 73%.
Pyridoxine (B6) 0.3 (mg) 20%.
Cobalamin (B12) 1.8 (g) 88%.
Biotin 11.8 (g) 18%.
Folate 148.0 (g) 82%.
Pantothenic acid 1.8 (mg) 32%.
Vitamin C 30.0 (mg) 51%.
Fat-soluble vitamins .
Vitamin A 425.0 (RE).
53%.
Vitamin D 3.1 (g) 63%.
Vitamin E 2.7 (mg) 34%.
Vitamin K 52.0 (g) 80%.
Macro minerals .
Sodium 2,943.0 (mg) - .
Pota.s.sium 2,121.0 (mg) - .
Calcium 887.0 (mg) 111 %.
Phosphorus 918.0 (mg) 115%.
Magnesium 128.0 (mg) 46%.
Trace minerals .
Iron 10.2 (mg) 68%.
Zinc 3.9 (mg) 33%.
Copper 0.4 (mg) 19%.
Manganese 0.9 (mg) 28%.
Selenium 0.040 (mg) 73%.
Dietary fiber 8.0 (g) - Beta-carotene 87.0 (g) -
This diet typifies everything that"s wrong with the way most of us eat today-the modern, processed food-based diet. It violates all of the Seven Keys of the Paleo Diet-the ones we"re genetically programmed to follow. Except for calcium and phosphorus, every nutrient falls below the RDA. The protein intake on the standard American diet is a paltry 62 grams (57 percent of the RDA) compared to that of the Paleo Diet (a mighty 190 grams, or 379 percent of the RDA). Remember, protein is your ally in weight loss and good health. It lowers your cholesterol, improves your insulin sensitivity, speeds up your metabolism, satisfies your appet.i.te, and helps you lose weight.
Even though there is very little meat in the typical American diet of this woman, the saturated fat content (29 grams) is 38 percent higher than that of the Paleo Diet. Worse still is the mix of fats. Healthful, cholesterol-lowering polyunsaturated and monounsaturated fats total a meager 29 grams. (In contrast, they add up to 75 grams on the Paleo Diet.) There is only 1 gram of heart-healthy omega 3 fats for the whole day in the typical American diet compared to a bountiful 6.7 grams in the sample Paleo Diet meal. Is it any wonder that the cereal-based, processed food-laden American diet promotes heart disease?
Now take a look at vitamin B6 (20 percent of the RDA), vitamin B (20 percent of the RDA), vitamin B12 (88 percent of the RDA), and folate (82 percent of the RDA). This woman"s diet is deficient in all three of the vitamins that prevent toxic buildup of h.o.m.ocysteine, the substance that damages the arteries and further predisposes you to heart disease. Inadequate amounts of folate also increase the risk of colon cancer and the birth defect spina bifida. (88 percent of the RDA), and folate (82 percent of the RDA). This woman"s diet is deficient in all three of the vitamins that prevent toxic buildup of h.o.m.ocysteine, the substance that damages the arteries and further predisposes you to heart disease. Inadequate amounts of folate also increase the risk of colon cancer and the birth defect spina bifida.
It"s also worth noting that this sample American diet has three times more sodium-but four times less pota.s.sium-than the Paleo Diet. This mineral imbalance promotes or aggravates conditions and diseases due to acid-base imbalance, including high blood pressure, osteoporosis, kidney stones, asthma, stroke, and certain forms of cancer. The daily intake of magnesium is also quite low here (46 percent of the RDA). Numerous scientific studies have shown that having a low magnesium level puts you at risk for heart disease by elevating your blood pressure, increasing your cholesterol level, and predisposing your heart to irregular beats. A low intake of magnesium also promotes the formation of kidney stones.
A high intake of antioxidant vitamins and phytochemicals from fresh fruits and vegetables is one of the best dietary strategies you can adopt to reduce the risk of cancer and heart disease. Unfortunately, when cereals, dairy products, processed foods, and fatty meats displace fruits and vegetables, they automatically lower your intake of health-giving antioxidants and phytochemicals from fruits and veggies. There is no comparison between the RDA percentages of vitamin A (53 percent), vitamin C (51 percent), vitamin E (34 percent), and selenium (73 percent) in the example above and those in the Paleo Diet: vitamin A (858 percent), vitamin C (932 percent), vitamin E (331 percent), and selenium (267 percent). The Paleo Diet contains forty-one times more beta-carotene (a natural plant antioxidant) than the average American diet.
The average American diet is also deficient in zinc (33 percent of the RDA) and iron (68 percent of the RDA)-which, along with a low intake of vitamins A and C, can impair your immune system and open the door to colds and infections.
Because the average American diet is loaded with refined cereal grains (six servings in our example) and sugars (123 grams or about a quarter-pound in our example), it increases the blood sugar and insulin levels in many people. If insulin remains constantly elevated, it causes a condition known as hyperinsulinemia, which increases the risk of a collection of diseases called metabolic syndrome-type 2 diabetes, high blood pressure, high cholesterol, obesity, and harmful changes in blood chemistry. But refined cereals and sugars are not part of the Paleo Diet-which means that your dietary insulin level will be naturally low and you will automatically reduce your risk of metabolic syndrome diseases. Last but not least is fiber. The average American diet contains a measly 8 grams compared to 47 grams on the Paleo Diet.
Many nutritionists would say that the example diet is healthful because it contains large amounts of carbohydrate (55 percent of total calories) and a low total fat intake (34 percent of total calories). This is also the message that most Americans have heard loud and clear-that healthful diets should be high in carbohydrate and low in fat. Unfortunately, when it comes to actual practice, most high-carbohydrate, low-fat diets look pretty much like our example of the typical American diet-a nutritional nightmare that promotes obesity, heart disease, cancer, and a host of other chronic illnesses.
Why You Can"t Overeat on the Paleo Diet Most of the foods we crave-and that make us fat if we eat enough of them-contain some combination of sugar, starch, fat, and salt in a highly concentrated form. (If you think about it, sugar, starch, fat, and salt are pretty much the recipe for all all the foods people tend to overeat.) the foods people tend to overeat.) In nature, a sweet taste is almost always a.s.sociated with fruit. This is what drew our ancestors to strawberries, for instance-the desire for a "sweet." However, as a bonus, they got much more than the sweet taste-fiber, vitamins, minerals, phytochemicals, and other healthful substances that improved their chances of survival. Similarly, our Paleolithic ancestors sought foods with a salty taste. Salt is absolutely essential for your health-but you don"t need much of it. The trace amounts of salt found in fresh fruits, vegetables, and lean meats were just right for our ancient ancestors-who also got a hefty dose of pota.s.sium along with the sodium. Today, almost all processed foods are grossly overloaded with salt.
Real Food versus Fake Food Today, much of our food is also fake. What does this mean? It"s created, not natural, food. See for yourself. How about a snack of dry white flour? Of course not; by itself, flour is bland and tasteless-you"d choke on it. However, if you add water, yeast, salt, vegetable oil, and sugar and then bake the result, suddenly you"ve got white bread. If you take this same mixture, deep-fry it in hydrogenated fats, and then glaze it with sugar, it becomes tastier still-a glazed doughnut. Or you could add bananas and walnuts to the original dough, bake it, and coat it with sugar and margarine, and you"ve got banana nut bread with frosting.
If you want to feel more virtuous about the whole thing, you can subst.i.tute whole-wheat flour and honey and call it "health food." But the bottom line is that none of these highly palatable food mixtures even remotely resemble the foods that nourished all human beings until very recently. In Paleolithic times, starchy foods weren"t also salty also salty; now we have potato chips and corn chips. Sweet foods were never also fat. also fat. Now we have ice cream and chocolates. Fatty foods were almost never Now we have ice cream and chocolates. Fatty foods were almost never also starchy. also starchy. Now we have doughnuts that are not only fatty and starchy, but sugary as well. Now we have doughnuts that are not only fatty and starchy, but sugary as well.
It is extremely easy to overeat processed foods made with starch, fats, sugars, and salt. There is always room after dinner for pie, ice cream, or chocolates. But how about another stalk of celery or another broiled chicken breast? Many overweight people can easily polish off a quart of ice cream after a full dinner. How many could-or would-eat an additional quart of steamed broccoli? The point here is that it"s very difficult to overeat real foods-fruits, vegetables, and lean meats. Fruits and vegetables provide us with natural bulk and fiber to fill up our stomachs. Because they are low-glycemic, they also normalize our blood sugar and reduce our appet.i.tes. The protein in lean meats satisfies our hunger pangs rapidly and lets us know when we are full. Two skinless chicken b.r.e.a.s.t.s for dinner may be filling-and two more might be impossible. Can we say the same for pizza slices?
Fake foods distort our appet.i.tes, allowing us to eat more than we really need. The most insidious-doughnuts, corn chips, vanilla wafers, croissants, wheat crackers-have a terrible one-two punch: high fats plus high-glycemic carbohydrates.
Normally, purely high-fat foods allow our appet.i.tes to self-regulate. For example, you can only eat a certain amount of pure b.u.t.ter before your body says "Ugh" and you become full and stop eating. However, when a high-glycemic carbohydrate sneaks in along with fat, you can continue eating the fat long after you would normally be full. The carbohydrate makes the fat taste better than it would alone (particularly if some salt and sugar are added), so you eat more. But the high-glycemic carbohydrate also may fool your body into thinking that it"s still hungry.
When you eat a doughnut, for example, the high-glycemic carbohydrates cause your blood insulin level to shoot up. At the same time, your blood level of a hormone called "glucagon" tends to fall. These chemical changes cause a cascade of events that may result in impaired metabolism by limiting the body"s access to its two major metabolic fuels-fat and glucose. The other important result of these chemical changes is hypoglycemia-low blood sugar, which paradoxically stimulates your appet.i.te, making you feel hungry even though you"ve just eaten. These high-fat, high-glycemic carbohydrate foods perpetuate a vicious cycle of being hungry and eating and never being satisfied. They cause excessive rises in your blood sugar and insulin levels and promote rapid weight gain.
High-fructose corn syrup can make this bad situation even worse. Fructose powerfully promotes insulin resistance. It"s added to almost every processed food imaginable; we get most of it from soft drinks, sweets, and baked items. But it"s also an ingredient in most low-fat or nonfat salad dressings-foods many of us buy in an attempt to be more responsible, to count calories, and to limit as many unwholesome ingredients as possible. The best approach is to stay away from these foods. Stick with humanity"s original fare: fruits, vegetables, and lean meats.
What to Expect on the Paleo Diet The key to the Paleo Diet is to stay with this wonderful way of eating. I can guarantee that you will immediately feel better. Your energy level will increase; you won"t have to endure that late-afternoon tiredness or "blah" feeling. In the morning, you"ll wake up charged and ready to greet the new day. You"ll feel better with each pa.s.sing day, and as the weeks go by, you"ll notice that your clothes feel a bit loose. Your weight will gradually drop-week by week-until your normal, healthy body weight is restored. For some people, this may only take one or two months; for others, six months to a year; and for those with severe weight and health problems, a year or more. But the bottom line is that it will happen. it will happen.
Many people also experience clearing of their sinuses, less stiffness of their joints in the morning, and normalization of bowel function. Indigestion, heartburn, and acid stomach are reduced and may even vanish completely within a few weeks of adopting this diet.
People with high cholesterol and abnormal blood chemistry can expect to see improvements within two weeks of starting the diet. Blood triglyceride levels will drop within days, and the good HDL cholesterol will rise rapidly as well. In addition, for most people on the Paleo Diet, total blood cholesterol and LDL cholesterol drop within the first two weeks.
The Paleo Diet is particularly helpful for people with type 2 diabetes, cardiovascular disease, high blood pressure, kidney stones, asthma, acne, and osteoporosis. There is also a significant body of evidence suggesting that the Paleo Diet may be helpful in certain autoimmune diseases such as celiac disease, dermat.i.tis herpetiformis, rheumatoid arthritis, multiple sclerosis, and Sjogren"s syndrome. It even reduces your risk of many types of cancer.
So eat well, lose weight, and be healthy with the Paleo Diet.
3.
How Our Diet Went Wrong and What You Can Do about It The blink of an eye. That"s how long, in the grand scheme of human history, we have grown food and domesticated livestock. It"s been only 333 generations since this change-known as the "Agricultural Revolution"-happened, and yet we have almost completely lost track of the foods our ancient ancestors ate. The so-called new foods that agriculture gave us so completely displaced the old foods that most of us are unaware that these foods were ever new. Many people a.s.sume that cereals, dairy products, salted foods, legumes, domesticated meats, and refined sugars have always been part of our diet. Not true! We need to rediscover the foods that brought our Paleolithic ancestors vibrant health, lean bodies, and freedom from chronic disease. The foods that agreed nicely with their genetic blueprints are the same foods that agree nicely with our genetic blueprints.
But what are these foods? How can we possibly know what our Paleolithic ancestors ate? My research team and I have been asking these same questions for the past decade. I am happy to tell you that we have found answers to these questions by carefully piecing together information from four sources: * The fossil record* Contemporary hunter-gatherer diets * Chimpanzee diets * Chimpanzee diets* Nutrients in wild animals and plants The Paleolithic (Old Stone Age) era began some 2.5 million years ago in Africa when the first crude stone tools were developed. It ended about 10,000 years ago in the Middle East, with the first ancient farms. (Perhaps twenty different species of ancient humans lived in the Paleolithic era. However, for the purposes of this book, we"ll cover only the diets of our direct ancestors.) We can trace the evidence showing the dominance of lean meat in human diets from our origins 2.5 million years ago until the beginnings of agriculture 10,000 years ago.
Lean Meat Is Brain Food The notion that human beings were meant to be vegetarians runs contrary to every shred of evolutionary evidence from the fossil and anthropological record. We owe a huge debt to lean meat. In fact, scientific evidence overwhelmingly suggests that if our ancient ancestors had eaten a meatless diet, we wouldn"t be where we are today. I wouldn"t have become a scientist, you wouldn"t be reading this book, and we would all look a lot more like our nearest animal relative-the chimpanzee.
How can this be? Chimps are hairy, and they have a big gut. They swing from trees. Well, yes, but about 5 to 7 million years ago, so did our prehuman ancestors. The evidence is that the family tree forks-and humans moved into a category all their own. But genetically speaking, we are only about 1.7 percent different from the chimp.
Chimps are mostly vegetarians (although they do eat a few insects, bird eggs, and the occasional small animal), and they have the big, protruding belly characteristic of vegetarian animals (horses and cows, for example, have big bellies, too). Apes need large, active guts to extract the nutrients from their fiber-filled, plant-based diet.
About 2.5 million years ago, our ancestors began trading in their big guts for bigger brains-to the point where today our bellies are about 40 percent smaller than those of chimps and our brains are about three times larger. The turning point came when our ancestors figured out that eating animal food (meat and organs) gave them much more energy. Over the years, their bellies began to shrink-because they didn"t need the extra room to process all that roughage. All the energy formerly needed by the gut was diverted to the brain, which doubled and then tripled in size. Without nutrient-dense animal foods in the diet, the large brains that make us human never would have had the chance to develop. Meat and animal foods literally shaped our genome.
Interestingly, just before the same period when human brains began to expand, something new came on the scene: tools-crude stone weapons, and knives that our ancestors used to butcher animal carca.s.ses and later to hunt. We know this because of telltale cut marks that have been found on the bones of fossilized animals and from evidence (a cla.s.sic example is the 125,000-year-old spear crafted from a yew tree found embedded between the ribs of an extinct straight-tusked elephant in Germany) compiled at thousands of archaeological sites worldwide.
At first, humans were not terribly good hunters. They started out as scavengers who trailed behind predators such as lions and ate the leftovers remaining on abandoned carca.s.ses. The pickings were slim; ravenous lions don"t leave much behind, except for bones. But with their handy tools (stone anvils and hammers), our early ancestors could crack the skulls and bones and still find something to eat-brains and fatty marrow.
Marrow fat was the main concentrated energy source that enabled the early human gut to shrink, while the scavenged brains contained a specific type of omega 3 fat called "docosahexaenoic acid" (DHA), which allowed the brain to expand. Docosahexaenoic acid is the building block of our brain tissue.
Without a dietary source of DHA, the huge expansion of our brain capacity could never have happened. Without meat, marrow, and brains, our human ancestors never would have been able to walk out of tropical Africa and colonize the colder areas of the world. If these people had depended on finding plant foods in cold Europe, they would have starved. In a landmark series of studies, my colleague Mike Richards, at Oxford University, studied the bones of Paleolithic people who lived in England some 12,000 years ago. Their diet, Richards confirmed, was almost identical to that of top-level carnivores, such as wolves and bears.
Hunting Big Game Why would any sane person get close enough to poke a spear into a sharp-hoofed, kicking, and snorting 600-pound horse-much less a raging 5-ton mammoth? Why didn"t Paleolithic people play it safe, gathering berries and nuts and snaring rabbits, rodents, and small birds? Again, the wisdom of the old ways becomes clear.
The basic idea of foraging for food-whether you"re a human, a wolf, or even a house cat chasing a mouse-is simple. You"ve got to receive more energy from the food you capture than you use in trying to capture it. If you run around all day and use up 1,000 calories, but come home with only ten apples worth a grand total of 800 calories, you"re going to be very hungry. So when Paleolithic people went looking for food, they tried to get the most bang for the buck. The best way to do this, they found, was with a large animal. It takes a lot more energy to run down and capture 1,600 one-ounce mice than it does to kill a single deer weighing 100 pounds (1,600 ounces). But there"s a much more important reason why larger animals were preferred. It"s called "protein toxicity."
We can only tolerate a certain amount of protein at a time- about 200 to 300 grams a day. Too much protein makes us nauseated, causes diarrhea, and eventually can kill us. This is why our Paleolithic ancestors couldn"t just eat lean muscle meat. They needed to eat fat along with the lean meat, or they needed to supplement the lean meat with carbohydrates from plant foods. Early explorers and frontiersmen in North America knew this, too. They were painfully aware of the toxic effect of too much lean protein; they called the illness "rabbit starvation."
On average, large animals like deer and cows (or, for Paleolithic people, mammoths and wild horses) contain more fat and less protein than smaller animals like rabbits and squirrels. The squirrel"s body is 83 percent protein and 17 percent fat; the mule deer"s body is 40 percent protein and 60 percent fat. If you ate nothing but squirrel, you would rapidly exceed the body"s protein ceiling, and like those early pioneers, you"d end up with rabbit starvation. On the other hand, if you only had deer to eat, you"d be doing fine. You would not develop protein toxicity because you"d be protected by the deer"s higher fat content. This is why Paleolithic hunters risked their lives hunting larger animals.