No, we don't know how much protein "cavemen" ate
How hard it is to read a scientific study? Should you bother to learn? I recently commented on a blog post on that subject.
Reading a study to figure out what to tell other people what to do is hard. Almost all the people who plant a pubmed reference in front of you to tell you to eat magic macronutrient XYZ or to avoid food X forever lest you perish from cancer are unqualified to pontificate on the subject. That includes many people with fancy titles. The people really qualified to talk about these things are not going to be pontificating. Nutrition science is too young for such surety.
But there is a much lower bar to be able to look up a reference and say whether or not it actually even possibly supports what the author who reference it was saying. That's fairly easy a lot of the time, since apparently many news outlets don't seem to care to fact check. I took a science journalism class in college and was taught a very meticulous and accurate way of writing that I don't see very often. A perfect and wonderfully topical example cropped up recently. The headline reads "Uh-Oh, Paleo: Cavemen Ate Less Meat Than Previously Thought." Surprisingly, the Fox News title, while stupid, is not completely inaccurate: "Secrets of the Caveman Diet." I get the feeling they are more interested in the SEO value of the paleo diet than ancient diets.
It took me more time than I would have liked to find the actual paper because they don't even link to the abstract. It turns out this paper is open-access, so anyone can read it, and that makes not linking to it even more suspicious. Well, I understand why. Just do a ctrl-f for "paleolithic." Don't bother with "caveman" because that's not even a technical or meaningful term. When I did that my computer made that annoying noise that I keep forgetting to disable that means it didn't find that word at all. Well, let's just try "paleo." Aha, something...but it's in the references...it's a paper in the journal " Biogeochemical approaches to paleodietary analysis." I could Google "paleodietary" and realize that the term encompasses all archeologically-studied diets from any time period, but without even reading anything, I've gained a lot of skepticism for the conclusions of news articles. The Fox News article is crafty and does say "first farmers" but makes a tenuous connection to the paleolithic.
I can then read the abstract and the discussion, the least science-y parts of the paper, which have several standouts anyone who is reading this blog post can probably pick up. Oh look at this sentence "This larger value goes some way to resolving the conundrum of interpretations of very high animal protein intake in isotopic studies of prehistoric farmers." Wait, so this whole thing was comparing to prehistoric farmers and not hunter-gatherers? Another minus point to the news articles. If you are a good reader, you can also figure out that the reason they did this study is that stable isotope analyses was based on animal data and they wanted some human data to compare that to.
If you want, you can delve further by reading a bit about that method. Considering how many of my readers are procrastinating computer coders with the next tab over open to their GitHub account or some API, I think a lot of them can handle this. The Fox News article, just like my science journalism teacher taught, describes this method.
To see how much meat ancient people ate, archeologists rely on the fact that protein is the only macronutrient that contains nitrogen. Different foods have different ratios of heavy and light nitrogen isotopes, or atoms of the same element with a different number of neutrons. So in a given ecosystem, scientists can reconstruct ancient diets by measuring the fraction of heavy-to-light nitrogen isotopes in fossilized bones.
But the body also preferentially stores heavier isotopes of nitrogen, so scientists calculate an offset to adjust for that tendency when determining what a person actually ate. Historically, the offset was derived from studies in which animals were fed diets with different protein amounts. [7 Perfect Survival Foods]
Using that offset, many studies estimate that between 60 and 80 percent of the prehistoric human diet came from proteins, with most of that from animal sources.
I'll just Google "isotopes diet." If you've taken a basic college level class in geology or archeology you probably know to Google "stable isotopes diet." The first results are a free and fairly readable paper and a blog post by a physical anthropology professor, John Hawks. Neither of these is easy to read, but if you can read .php or .ru files or are just a good reader, you can probably figure out the basics of the method. Fox News starts to get it right. But that last sentence is flat-out wrong. Isotope analysis is a way to determine trophic level of the protein in the diet, so where the protein might have come from in the local ecosystem. It is simply not capable of telling you what percentage of the total diet was protein.
There are more complexities to the method I could go into, such as potential inaccuracies of the method, but that's the overall gist of it. I'd note that I've also seen this method butchered in books popular with paleo dieters, claiming that because some skeletons from the paleolithic indicate they got most of their protein on the same trophic level as arctic foxes that their diet was like that of an arctic fox. That's the kind of thing this study is relevant to- whether or not we can extrapolate animal data to humans accurately in stable isotope analysis of diet. That's probably not as good for sexy headlines or SEO though, is it? The reality is that if we applied this we'd find paleolithic humans ate many different diets, with plant protein increasing with sedentism and with certain local ecologies. But in the wild plant proteins are not easy to come by. Most of them are not digestible by humans and many that are, such as certain wild legumes, are seasonal. And in the end, both of those articles fail to make the issue relevant in any comprehensible way, the blisstree taking nonsensical potshots at the paleo diet:
Many contemporary paleo diet gurus advocate a diet that’s 50 percent or more animal products (though contrary to what some people think, this doesn’t just mean chowing down on bacon and burgers — paleo dieters stress the importance of eating lean meat, fish and eggs that come from grass-fed livestock). This is based on the conventional wisdom that paleolithic humans ate a diet of between 60% and 80% protein, mostly from animal sources.
First, I don't know where I can get grass-fed fish but it sounds cool and if you know any sources, email me. Second of all, since when are animal products just protein? The ones I eat have plenty of fat. Maybe there is a parallel universe where I eat a 60% protein diet and have already wasted away from rabbit starvation, but in this universe I don't know anyone who eats an 80% protein paleo diet. Most people naturally gravitate away from absurd protein intakes because it's unappetizing and makes you feel bad, though lately I've found many people persist on diets that are exactly that for years and even decades. I don't like feeling bad or eating bad food, so I've never had that long-term problem.
We don't know what percentage of a paleolithic hunter-gatherer's diet was protein, we don't know that for "caveman" or for early farmers. It's just not knowable right now and probably never will be. We do know that for modern humans, there seems to be a physiology ceiling for protein intake which John Speth addresses quite readably in his excellent, though bizarrely expensive (worth getting on interlibrary loan) book, which requires humans not eat like an arctic fox, but be innovative and seek out either fat or carbohydrate in order to avoid potential costs of high protein intake. But that ceiling is controversial.
So there, those two news articles are essentially debunked and we didn't even have to discuss various nitrogen isotopes or anything really truly technical. In the end, we realize that the study in question doesn't tell us how those in the past really ate or what we should eat now. It's just a little piece of a large completely unsolvable puzzle. To even be able to realize that gives you immense power not to be deceived.