There’s a chapter in Denise Minger’s book Death by Food Pyramid (full review coming soon) in which she explains one of the many reasons the grain-based Food Pyramid is such a disaster: there’s quite a lot of variability among humans in the ability to digest starch. Given the same load of starch, people who don’t digest it efficiently end up with far higher blood sugar (36 points higher on average in one study) than people who do digest it efficiently – and their blood sugar stays higher for hours.
The ability to efficiently digest starch is determined largely by genetics. As Minger explains:
In order to furnish the mouth with starch-digesting proteins, we all carry copies of a gene called AMY1, which encodes the salivary amylase enzyme. Indeed, amylase is a gem some plant-based diet advocates cite as evidence for a starchy diet being optimal for mankind. In his book The Starch Solution, McDougall discusses human amylase status as evidence that we are, as a species, genetic starchivores.
McDougall likes to point out that humans carry an average of six copies of the AMY1 gene, whereas our primate brethren carry an average of two. That would indicate that at some point after separating ourselves from chimps, we began eating more starch.
Fair enough. But then Minger writes this:
Just one problem. It’s not that simple. It turns out the number of AMY1 copies contained in our genes is not the same for everyone. And the amount of salivary amylase we produce is tightly correlated to the number of AMY1 copies we inherited. AMY1 copy number can range from one to fifteen, and amylase levels in saliva can range from barely detectable to 50 percent of the saliva’s total production. That’s a lot of variation.
Indeed it is.
Minger’s main point in the chapter is that people with fewer copies of the AMY1 gene are more likely to run into trouble with the high-carb, high-starch diet recommended by the USDA. They’re not genetically geared to handle it. And in fact, a recent study demonstrated that people who carry fewer copies of the AMY1 gene are more likely to be obese. Here are some quotes from an article about the study:
Researchers from Imperial College London, in collaboration with other international institutions, looked at the number of copies of the gene AMY1 present in the DNA of thousands of people from the UK, France, Sweden and Singapore. They found that people who carried a low number of copies of the salivary amylase gene were at greater risk of obesity.
The chance of being obese for people with less than four copies of the AMY1 gene was approximately eight times higher than in those with more than nine copies of this gene. The researchers estimated that with every additional copy of the salivary amylase gene there was approximately a 20 per cent decrease in the odds of becoming obese.
Given that modern diets are full of processed starch, it’s no surprise that people who don’t handle starch very well are more likely to become obese. But I think we need to look at the number of AMY1 genes from the other direction as well.
If you’ve been following the comments on my posts about the Perfect Health Diet and safe starches, you know some people still insist that nobody – absolutely nobody – would need any starch in the diet to avoid the health problems the Jaminets say some people develop on a strict very-low-carb diet: slow thyroid, cold hands and feet, low energy, etc. If anyone needs a bit of starch to avoid those problems, then by gosh, it must mean they’re sick. Or there’s some other problem with their diets – a missing nutrient or a food allergy — because it can’t possibly be that their diets are too low in starch to fit their genetics. Very-low-carb is the best diet for everyone, so those people must be doing it wrong.
People who experience problems on a strict low-carb diet probably are, in fact, missing a nutrient. But the nutrient they’re missing is a bit of starch to avoid a glucose deficiency. I don’t believe everyone needs a Perfect Health Diet intake of starch, but I believe some people certainly do. I believe that partly because of what Minger wrote about the number of AMY1 copies we carry.
Under evolutionary pressure, the traits that don’t provide a benefit tend to fall away. That’s why the vegan argument that humans obviously aren’t intended to eat meat since we don’t have fangs and claws is, frankly, ridiculous. Humans learned to hunt with weapons hundreds of thousands of years ago. Hunting with a spear or a bow and arrow provides a definite evolutionary advantage over hunting with your hands and teeth: you’re less likely to get yourself killed while trying to kill your dinner. Since claws and fangs weren’t necessary anymore, they fell to the side of the evolutionary road.
By the same token, if humans carry three times as many copies (on average) of the AMY1 gene as other primates, there’s an evolutionary reason for that. If some humans carry fifteen copies – more than seven times the number of copies other primates carry – there’s an evolutionary reason for that too. The reason would be that in some Paleolithic human societies, tubers and other starches were part of the diet for a long, long time. That doesn’t mean starches dominated the diet, but they were clearly part of the diet – somewhere in the range of 15% to 40% of calories depending on the location, according to the Jaminets. There’s no other evolutionary reason to carry those extra AMY1 genes.
So doesn’t it make sense that some people would feel lousy on a diet that doesn’t (despite being called “paleo”) actually mimic the diet their paleo ancestors consumed? Or more to the point, doesn’t it make sense that some people whose paleo ancestors regularly consumed tubers and other starchy plants might actually become healthier after adding small servings of safe starches back into their diets? And isn’t it a little silly to insist that they’re sick or carb-addicted if they do?