I've always said that carbs aren't bad in and of themselves. They're better in certain contexts and worse in others.

Are you CrossFitting five days a week? Training for the Olympics? Breastfeeding? These are contexts in which carbs are warranted, helpful, and even healthy.

Are you insulin-resistant and hyperinsulinemic? Are you a moderately active person with a few extra pounds? Are you diabetic, or nearly so? These are contexts in which a low carb intake would be warranted, helpful, and even healthy.

With my Carb Curve, I've tried to establish a basic framework that works for most people who come to this site looking to get healthy. I think I've mostly succeeded. 150 grams of carbohydrates from fruit, squashes, roots, and tubers is more than enough for the vast majority of people to feel sated, healthy, and energetic without leading to weight gain or exacerbating metabolic syndrome. Add more if you need it to fuel your training; remove some if you're particularly sedentary, diabetic, or looking to lose weight; try a carb refeed every few days of 200-300 grams if you're very low carb or ketogenic. Round that out with all the non-starchy vegetables you want and you're looking at a very diverse diet rich with phytonutrients, vitamins and minerals with lots of room for nutrient-dense meat and fat sources. Not bad, right? Pretty simple, and the results speak for themselves.

Despite that, there's an undercurrent that high-carb Primal and low-carb Primal are interchangeable. That macronutrient ratios don't matter regardless of health status or metabolic context, and that we evolved eating a diet rich in, if not based on, starchy tubers.

Today, I'm going to address some of the most common arguments for these claims. I'm not arguing against including starch in your diet, now. I'm arguing against this notion that inclusion of large amounts of starch is the defining characteristic of an ancestral diet.

Let's jump right in...

But Grok ate tubers, and lots of 'em!

This is a common refrain. And sure, wild tubers, AKA underground storage organs, have been around longer than we have. They're an important food source for many animals, including primates, so it's no wonder early humans utilized wild tubers. But before you rush out and buy potato futures, consider a few points:

Wild tubers are not Russet potatoes. They generally don't turn into creamy smooth starchy goodness when baked. They're tough, fibrous things that provide a fraction of the usable energy modern cultivars provide (PDF). Whereas your typical kilogram of potato offers over 1000 calories, a kilo of many wild tuber varieties hover at around 300 calories. Eating these would have provided a moderate dose of glucose - akin to, perhaps, butternut squash - plus a load of prebiotic fiber for the gut flora. In addition to fiber, wild tubers are extremely rich in minerals, with some varieties offering over 500 mg of calcium per 100 grams of tuber - so they're also more mineral-dense than the tubers most of us can buy at the store.

They were very likely fallback foods. Among the Hadza people of Tanzania, tubers are the least-preferred food source. If you could see the aftermath of a tuber feast, you'd understand why: piles and piles of chewed up fiber, spit out after sucking all the caloric glucose-rich starch from the tubers. It gets the job done, but it's not very pleasant or appetizing. Now, before you point to the fact that tubers were also the most-available food source, consider that the environment of the Hadza is not the environment of early man. The geography may be the same, but everything else has changed. Like most all other extant hunter-gatherers, they are the remaining members of people who have been driven off the best, most resource-rich lands into the margins, those scrubby relatively resource-poor lands. They've literally been marginalized. They eat lots of tubers because they are widely available and they eat less meat and honey because they aren't always available (even though they prefer the latter two). Before agriculture and the rise of the state, land was sparsely populated by humans and rich in game. Animals were simply more numerous and thus easier to come by. I'm not saying that our ancestors were carnivores - quite the contrary, in fact - but all else being equal hunter-gatherers on game-rich lands will have more opportunities to consume (the preferred) animals and less cause to fallback on fibrous tubers than hunter-gatherers on marginalized lands.

Specific genetic adaptations to tuber-based diets emerged only recently. Adaptations include detoxification of glycosides (potentially toxic substances found in tubers), enhancement of folate biosynthesis (tubers contain little folate, so people subsisting on tubers would need to develop ways to make enough of their own in-house), and improvements in starch metabolism. If we'd been eating a tuber-rich diet for our entire history as humans, why would these recent genetic adaptations even be necessary?

But we make salivary amylase!

Salivary amylase is like pancreatic amylase in that it digests starch into simple, absorbable sugars, only in your mouth. It helps prepare starch for further digestion, particularly the more you chew. Plus, your amylase-rich saliva gets swallowed and continues working on the starch throughout digestion. Compared to the fruit-eating and starch-eschewing chimpanzee with two copies, humans have between two and fifteen copies of the salivary amylase gene. Some have posited that this indicates a necessary role for starch in human nutrition. It sounds like a reasonable argument.

As I've mentioned before, though, having a high number of salivary amylase gene copies isn't universal. It depends on your background. If your ancestors ate a lot of starch, you're more likely to have more copies than the people whose ancestors did not eat as much. Beyond the first copies around 200 thousand years ago, researchers are still piecing together exactly when the extra copies of salivary amylase genes were added to (some segments of) the human genome, but judging from the emergence of other recent, tuber-specific adaptations (mentioned above), it wasn't too long ago for many of us.

And if you are one of the high-amylase individuals, remember why salivary amylase is ultimately there: to assist in the digestion (and thus assimilation) of dietary starch. It's not there to justify overconsumption of starchy tubers whose carbs you don't really need. High copies of salivary amylase genes are only helpful if you need the glucose to survive. If you need the calories, if you'll use the calories, then the salivary amylase will help you do it. But if you're a mostly sedentary modern computer-using human who works out moderately and drives to work, I wonder whether you truly need so much starch.

Which brings me to the next argument.

But people didn't start getting fat en masse until the advent of industrial foods; most starch-eating agriculturalists were actually pretty thin!

This is true. You can look at old pictures from the turn of the last century and you'll notice that most everyone is slim. If you could travel back through time and space to visit and view Mayan empire, the Indus valley civilizations, the Roman republic, the signing of the Magna Carta, the first farmers in the fertile crescent - you would bring back photos of mostly lean people as well. Lean, often perpetually exhausted and overworked people.

Agriculture introduced the concept of "labor." People living in agricultural societies had to work hard to survive. Rather than draw on the seemingly endless bounty of nature, agriculturalists imposed themselves on the land and struggled against the very laws of nature to force crops to grow. They worked long hours and performed tons of "reps." It's been estimated that medieval peasants, for example, had to consume up to twice as many calories as modern humans just to keep up with the demands of their daily labor. They certainly weren't fat on their high-calorie, high-carb diets because they were "earning" their carbs with loads of glucose-demanding physical work. If you're not doing the work of a medieval serf, you won't have the same tolerance of and need for starch.

I'm not suggesting hunter-gatherers didn't work or physically exert themselves, by the way. Hunter-gatherers worked, for sure, just not the kind of daily, miserable, physically-exhausting toil you'd do as a farmer. Maybe three to five hours a day. It wasn't day in, day out, either; a successful hunt was followed by days of relaxing, partying, and feasting. It was more fractal, varied, random, seasonal.

Thin doesn't always equal healthy, anyway. Remember: I stayed thin and "fit" on 750-1000 grams of carbs every day when I was running 100 miles a week. Doesn't mean it was a good idea or I wasn't hurting myself.

But the Kitavans ate a starch-based diet and were healthy!

I've touched on the Kitavans before, and I largely agree. They were healthy. Here's the thing, though: most people aren't raised in a pristine South Pacific island environment replete with sunshine (vitamin D), crystal clear waters, coconuts, biologically congruent sleep patterns, extended families and strong communities, and extended breastfeeding with a near absence of gluten-containing grains and processed seed oils (that last one could be said for the medieval serfs and other pre-industrial starch eaters, too!). They're very active and although they consume relatively low amounts of fat, what fat they do consume is derived from coconuts (saturated fats) and fish (omega-3s). Not to mention the epigenetic advantages of having parents and grandparents who lived this way. There's far more to the Kitavan way of life than all the tubers they eat.

If you hope to have the same results eating a potato-based diet, you better get all the lifestyle and other dietary factors right (plus figure out how to travel back in time to influence the way your parents and grandparents lived and ate!).

As an insular island people, the Kitavans may also have genetic component to their tolerance of a high-carb diet, similar to the proposed adaptations related to gluconeogenesis that allow Arctic natives to flourish on a very low carb diet nearly bereft of significant plant input. If you don't have those same island genetics, you may not have the same response to the Kitavan diet. Give it a shot, though; you could do a whole lot worse!

Anyway - those are the arguments I'm seeing. They're interesting but ultimately limited and short-sighted in my opinion. My goal is not to attack or dismiss them (or dietary starch), but rather to offer some nuances to consider before integrating them into the Primal framework.

What do you think, folks? What other arguments are out there? What have you experienced with starch?