Bone Chemistry Cannot Measure Ketogenic Metabolism

Around 13,000 years ago, people living in what is now North America were eating meat—lots of it.

Bone chemistry reveals the answer through stable isotope analysis, a technique that measures the ratio of carbon and nitrogen atoms in skeletal collagen and can show what proportion of someone's diet came from terrestrial animals versus plants. The logic seems airtight. High animal consumption means high fat intake. Means ketogenic metabolism, which means early Americans pioneered the keto diet until megafauna extinctions around 12,800 years ago forced them to eat more plants and carbohydrates.

But the argument contains an invisible seam—and once you see it, the whole apparatus becomes uncertain. The problem is not whether early Americans ate animals. They did. The problem is what we mean when we say "ketogenic diet."

That phrase does not exist in the archaeological record and cannot. Ketogenic status is a metabolic ratio—the percentage of calories derived from fat versus protein versus carbohydrate. Bone chemistry cannot measure percentages of calories. It can measure what was eaten but cannot measure how much energy came from each macronutrient, which depends on portion sizes, preparation methods. Individual variation in digestion that leave no trace.

Consider the Clovis people, the best-documented early American hunter-gatherers around 12,000 years ago. An isotope analysis tells us they ate a lot of megafauna but tells us nothing about whether a typical meal was primarily fat, whether they were starving or thriving, or whether they chose meat because it was abundant or because it was necessary. These are separate questions. We have collapsed them into one answer by borrowing a label from modern nutrition and pressing it backward onto data that cannot support it. What changes if the label disappears? Not the facts about what was eaten—those remain.

That distinction—between observable diet and inferred metabolism—shapes every inference that follows about adaptation, about extinction, about what early humans needed versus what they chose. And it matters, because in your own work, you are constantly mistaking measurement for understanding.