Humans Are Starch Eaters

Here’s an inter­est­ing talk by Nathaniel Dominy, PhD, an Asso­ciate Pro­fes­sor of Anthro­pol­o­gy at Dart­mouth Uni­ver­si­ty. He explains the cen­tral role of diet in the amaz­ing world­wide suc­cess of the human species. If you can’t find enough to eat, you can’t do any of the oth­er things that you would need to do to help you and your chil­dren sur­vive.

He makes sev­er­al impor­tant points. One is that human beings are behav­ioral­ly “plas­tic.” He uses the term “plas­tic” in the sci­en­tif­ic sense, mean­ing that some­thing can take any shape. Our behav­ior is “plas­tic” because it can eas­i­ly be reshaped. As he point­ed out, human beings can adapt to many dif­fer­ent cli­mates because we have learned to make and wear clothes. We can also learn to eat lots of dif­fer­ent foods.

One type of food that is avail­able every­where except the Artic is starchy foods. All of the ener­gy in our diet comes from sun­light, which green plants use to make glu­cose out of car­bon diox­ide and water. Plants then store a lot of this glu­cose in the form of starch, often in their roots or tubers and in their seeds. Unfor­tu­nate­ly, starch is hard to digest. To digest it, we use amy­lase, an enzyme that con­verts the starch back to glu­cose.

Dominy sus­pects that our ances­tors’ abil­i­ty to rec­og­nize and use tuber-form­ing plants opened up a food source unknown to oth­er pri­mates. “It’s kind of a gold mine. All you have to do is dig it up.

Dominy points out that, when com­pared with oth­er pri­mates, human beings have extra copies of the gene for the starch-digest­ing enzyme amy­lase. As a result, we have a lot more amy­lase in our sali­va than goril­las or chim­panzees do. Peo­ple from soci­eties that depend heav­i­ly on starchy diets have sev­er­al more extra copies of the amy­lase gene and there­fore pro­duce a lot more amy­lase in their sali­va. In oth­er words, they have become genet­i­cal­ly more effi­cient at digest­ing starch­es. This kind of change can be seen in genet­i­cal­ly relat­ed pop­u­la­tions that have been adapt­ing to dif­fer­ent diets for only a few thou­sand years.

Although humans can and do eat prac­ti­cal­ly any­thing (we are behav­ioral­ly plas­tic), that doesn’t mean that we are well adapt­ed to a meat-based diet. As he puts it, “Anatom­i­cal­ly, we’re not adapt­ed to meat at all…. We sim­ply don’t have the adap­ta­tions that you would need to chew meat effi­cient­ly. Any­one can look at the teeth of their dog or cat and see what your teeth should look like if you’re going to eat meat. Our teeth don’t match.” Dominy con­cludes, “The fun­da­men­tal com­po­nent of the human diet is a mix of plant foods, with a large amount of starch com­ing from tubers and seeds.”

In this con­text, I’d point out that the adap­ta­tions to a meaty diet go far beyond the shape of the teeth. Even though dogs often eat a fat­ty, meaty diet, they gen­er­al­ly don’t get high cho­les­terol or ath­er­o­scle­ro­sis unless they also have a thy­roid dis­or­der that upsets their cho­les­terol metab­o­lism. In con­trast, human beings that eat a fat­ty, meaty diet are much more sus­cep­ti­ble than dogs are to high cho­les­terol and ath­er­o­scle­ro­sis. That explains why ath­er­o­scle­ro­sis is the lead­ing cause of death in the Unit­ed States but prac­ti­cal­ly nonex­is­tent in soci­eties where peo­ple eat a low-fat, plant-based diet.

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