When one looks in the books and on the internet about a "paleolithic-style" or "evolutionary-based" diet, one will likely be confused at the end of it. Some will focus on what Kurt Harris calls "paleo re-enactment" - meaning we should be hunting wild boar, digging up roots, and honey is okay. (When I first told a friend of mine, who happens to be a gastroenterologist at Johns Hopkins, about my interest in paleolithic diets, she remarked, "The only guy I ever saw on a paleo diet was pooping leaves and blood." Take that as an object lesson, paleo re-enactors, don't forage unless you know what you are doing!). Some paleo folks will be (once again using Kurt Harris' term - he has a knack for them), "pc-paleo" - meaning low fat paleo. Loren Cordain and Boyd Eaton are scientists and paleolithic nutrition pioneers, and their first look at the research focused on the fact that animals in the wild tend to be leaner than our domesticated animals. Cordain's The Paleo Diet: Lose Weight and Get Healthy by Eating the Food You Were Designed to Eat and The Paleo Diet for Athletes: A Nutritional Formula for Peak Athletic Performance will both advocate a lower-fat approach. Notice both were published prior to 2007. And as this is where the research was headed at the time, the "paleo" diets studied in diabetics by Staffan Lindeberg and others were relatively low-fat and sometimes a little weird - not sure how many of us foraged for canola oil and mayonnaise. But there you go. That's where an IRB gets you, I guess.
What's so important about 2007? Well, that's when Good Calories, Bad Calories: Fats, Carbs, and the Controversial Science of Diet and Health (Vintage) came out. I think Taubes' work is incredible and amazing, and required reading for any health professional or nutritionist. However, I do believe he focuses a bit too much on the carbohydrate hypothesis as the cause of Western Disease. He does, however, do a heck of a lot to exonerate fat.
Since 2007 and "Good Calories, Bad Calories", there has been the advent of what many now call "primal" style paleo, exemplified best by Mark Sisson's excellent book, The Primal Blueprint: Reprogram your genes for effortless weight loss, vibrant health, and boundless energy. Like Stephan Guyenet, I do think Mark is a little too hard on the carbohydrates (starch has a lot in common with, but ultimately is very different from sugar. This could be its own post, but if you have the time, I highly recommend this youtube video of a lecture by Robert Lustig, a pediatrician and obesity expert. He has a rather strange idea of what a paleo diet is, but hey, doesn't everyone?).
Anyway, the "primal" folks love fat, real food, and allow for some "sensible indulgences" such as high fat dairy, dark chocolate and red wine. And it is rumored that even Loren Cordain is more pro-fat than he used to be. Anthropological reports from all over the world will show us that our ancestors favored the fatty cut of meat, anyway, leaving carcasses and the lean meat to rot, and savoring the glands, liver, brains, and marrow, all high in saturated fat (1)(2)(3). In fact, when our ancestors were forced to survive on lean meat alone, they endured a life-threatening condition called "rabbit starvation." These symptoms of fatigue, weakness, diarrhea, hunger, headache, and low blood pressure and heart rate come from a diet of too much protein, and can be ameliorated by substituting some of the protein with carbohydrates or fat.
I've been told most of my life that animal fat is bad for me. The scientific story why this is not true is explained in exhaustive detail in a number of different, excellent books (including GCBC, but also Eat Fat, Lose Fat: The Healthy Alternative to Trans Fats) I especially like Mary Enig, as it seems to me she is the researcher primarily responsible for finally getting the FDA to come down against the nutritional horror that is industrial trans fats.
There are two, final scientific arguments against saturated ("animal") fats, in this case palmitic acid, that are not addressed in full by any of the previous sources I've named above. One is that a high amount of free fatty acids (palmitic acid for the most part) in the blood causes insulin resistance. Any erudite fat-lover will say to this, yes, of course it does. Palmitic acid is released into the bloodstream by the metabolic action of our own livers every time we fast (overnight, for example) or lose weight. It has to be. Otherwise we would never burn our fat stores, and we can't store much glycogen. The release of palmitic acid signals our body that we might not have a lot of food around, and we better preserve our precious glucose stores (the glycogen) for our brain to use. Therefore our muscles become more insulin resistant, and we shift to burning fat as fuel rather than glucose (burning fat sounds good, right?) This mechanism is physiologic, and I would say has very little to do with the full body insulin resistance of diabetes. Stephan and Peter have their own, brilliant takes on the matter (more required reading in my mind - no one said learning about nutrition didn't take a lot of time).
But let's get down to brass tacks on the insulin resistance/palmitic acid debate. Remember, and this is key, that when we burn fat and lose weight, we release a flood of palmitic acid into the blood stream. Deadly, hard core saturated animal fat. Yes, our own livers are trying to do us in. So why is fat loss, really, the best treatment for diabetes? Why does bariatric surgery, with the resultant forced semi-starvation, fasting, and FAT LOSS often result in the immediate turnaround of diabetes (4)? (Let's see - maximum of 2 pounds of fat loss a week = 7200 calories of fat burned, more or less, which would equal 1029 calories of fat a day = 114 grams of saturated fat (more or less) a day supplied by our own rumps! (or, hopefully, our visceral belly fat)).
This physiologic insulin resistance in fasting can, in the short term, increase fasting glucose levels in diabetics, it's true, and Gary Taubes' explanation of muscle insulin resistance vs overall body insulin resistance is a good one. This finding led the American Diabetic Association to recommend high carbohydrate diets to diabetics for years, and, in the long term, that is a huge mistake.
Did you know that feasting on your own stores of animal fat can help heart disease too (5)?
All right, I think I've fairly addressed the insulin resistance. Now let's go to the last, best argument against fat. Lipotoxicity. Perhaps I shouldn't have waited until the end for this one, as it is rather biochemistry-heavy. We'll give it a whirl. I have the full text for this paper (6), but let's summarize with the abstract:
"Insulin resistance is one of the pathophysiological features of obesity and type 2 diabetes. Recent findings have linked insulin resistance to chronic low-grade inflammation in white adipose tissue. Excess storage of saturated fat in white adipose tissue due to a modern life style causes hypertrophy and hyperplasia of adipocytes, which exhibit attenuated insulin signaling due to their production and release of saturated fatty acids. These adipocytes recruit macrophages to white adipose tissue and, together with them, initiate a proinflammatory response. Proinflammatory factors and saturated fatty acids secreted into the bloodstream from white adipose tissue impair insulin signaling in non-adipose tissues, which causes whole-body insulin resistance."
Let's leave off the insulin resistance for a bit and go to the proinflammatory section. Basically, what this paper says is that if we stuff our fat cells full of fat and then release saturated fat, we get inflammation. We hate inflammation here at Evolutionary Psychiatry, and this paper seems to implicate saturated fat as a major cause in a huge part of our bodies, the white adipose tissue (much of our stored body fat). This inflammation is called "lipotoxicity."
Paleo-diet aficionados tend to agree that doing the following are anti-inflammatory in the diet: omega-3 fatty acids (and avoiding omega 6), avoiding grains (especially wheat) and casein, eating vegetables and fruits, and avoiding sugar (fructose) and processed food.
Using common sense and biochemistry, saturated fat is anti-inflammatory compared to either cooked monounsaturated or polyunsaturated fat, given that heat and air can make the vulnerable unsaturated bonds oxidize and become rancid, which everyone can agree is highly inflammatory and bad for you. (Cold, fresh virgin-pressed olive oil would escape the oxidation, I hope!)
But here we have some science telling us saturated fat is inflammatory. And I don't think we have a full handle on that. I think what makes the most sense is to speculate that lots of saturated fat is inflammatory when combined with lots of sugar (big thanks to Dr. BG for helping me clarify this in my own mind! *edit* But I've further refined my thinking on this matter since publishing this post - please see the comments! Thank you *end edit*) Burning fat is a signal to our bodies that there might not be a lot of food around. Eating carbohydrates signals summertime! Lots of tubers and fruit and foliage! We stumbled upon a beehive! Yippie! Store it up! There was never a situation in our evolutionary past when we combined the grotesque amount of sugar we consume year round on the western diet, combined with the all the fats. Dr. BG called this, metabolically speaking, putting our foot on the brakes and the gas at the same time. Not great for the transmission.
I think, overall, the most important anthropological lessons are these - hunter-gatherers are healthy and, excepting infant mortality and accidents, long-lived eating a wide variety of macronutrient ratios. The Kitavans are high carb, the Inuit and Tokelau and Masai high fat. Most other folks were likely somewhere in between. But they did not consume tons of sugar. Or industrial seed oils, or wheat.
Again and again I come to that point. Epidemiology and observation won't show us the truth, but it will show us what could possibly be true, and what cannot. Saturated fat alone does not cause heart disease or diabetes. Neither do starchy carbohydrates alone. Those facts are true unless the Kitavans and the Inuit are blessed with magical pancreases or livers or hearts. My guess is they have the same old hearts you and I have.
Hopefully, science, a holistic approach, and sense will tell us the rest.