Why do Americans become overweight and diseased on a high-carbohydrate diet while the carbohydrate-loving Kuna and Kitavans remain exceptionally free of chronic disease? Dr. Lindeberg proposes an answer- grains.
Dr. Lindeberg's hypothesis is that grains cause leptin resistance, which as we saw in the last post, has the potential to precipitate the metabolic syndrome and its various consorts. It's an attractive idea. The Kitavans (who he has studied personally), Kuna, and other cultures in Melanesia, Malaysia, Africa, the Arctic and South America, do not suffer from the diseases of civilization. These are all cultures that consume little or no grain, despite some having starchy diets. The Kitavans have low circulating leptin and remain lean and disease-free despite a high intake of carbohydrate.
Dr. Lindeberg says that grain-based cultures almost universally suffer from varying degrees of our illnesses, although his references to support that statement are unsatisfying. He did provide a reference showing that stroke occurs in affluent grain-based societies (whereas it seems not to in Kitavans), but I would really have liked to see a side-by-side comparison of cultures with similar lifestyles and differing grain intakes.
One thing that's certain is humans have not been eating grains for very long. Before the invention of agriculture in the fertile crescent, grains were a minor and seasonal crop for a small number of groups. Something we have been eating for a long time however is starchy tubers, bulbs and roots. Hunter-gatherers didn't generally go after wild grass seeds (grains) because they weren't a concentrated enough food source in most places. If you collect grass seeds all day, you might end up with a mouthful, after which you have to soak, grind, and cook them before chowing down. Dig up a few camas bulbs however, and you've got yourself a meal in 5 minutes.
The distinction between different sources of starch may lie in a class of molecules called lectins. Lectins were originally defined by their ability to aggregate red blood cells (erythrocytes). They do this by binding to the natural coating of carbohydrate on the cells' surface. A more current definition of a lectin is a molecule that specifically binds carbohydrate. Lectins are found throughout all kingdoms of life, and they serve a variety of useful functions. Many plants use lectins as a defense against hungry animals. Thus, an animal that is not adapted to the lectins in the plant it's eating may suffer damage or death.
Grains and legumes (beans, soy, peas, peanuts) are rich in some particularly nasty lectins. Especially wheat. Some can degrade the intestinal lining. Some have the ability to pass through the intestinal lining and show up in the bloodstream. Once in the bloodstream, they may bind all sorts of carbohydrate-containing proteins in the body, including the insulin receptor. They could theoretically bind the leptin receptor, which also contains carbohydrate (= it's glycosylated), potentially desensitizing it. This remains to be tested, and to my knowledge is pure speculation at this point. What is not so speculative is that once you're leptin-resistant, you become obese and insulin resistant, and at that point you are intolerant to any type of carbohydrate. This may explain the efficacy of carbohydrate restriction in weight loss and improving general health.
Another thing I have to mention about lectins is they can be broken down by certain food processing techniques. Remember all those old-fashioned things our grandparents used to do to grains and beans before eating them, like soaking beans overnight, sourdough-fermenting bread dough and nixtamalizing corn? All those things we've abandoned in favor of modern convenience foods? You guessed it, those reduce lectins dramatically, along with a long list of other toxins like phytic acid and protease inhibitors. Modern yeast-leavened breads, pastries, crackers, corn and soy products are no longer prepared according to these methods, and their lectin levels are typically much higher. One thing to keep in mind is that these processes reduce but generally do not eliminate lectins and other toxins.
The thing I really like about Dr. Lindeberg's idea is it explains a lot of what is happening in the world around us. The Kitavans eat yams, sweet potatoes, taro and tapioca as their staples. Incidentally, the long-lived Okinawans also eat sweet potatoes as a staple. The Kuna eat mostly plantains, yucca and kidney beans. These are three exceptionally healthy populations with a very low intake of grains. What happens when you feed these same people wheat? The Kuna have a well-documented rise in blood pressure, diabetes and cardiovascular disease mortality when they move to an urban, westernized setting. Okinawans became obese and unhealthy when American food was introduced. Wherever white flour and sugar go, the diseases of civilization follow. Weston Price documented this in the dental and skeletal health of 14 different cultures throughout the world.
It also explains what's going on under our very noses. Like I mentioned earlier, modern processed food is rich in lectins because it hasn't been treated by soaking, sprouting or bacterial fermentation. Soy has one of the highest lectin activities of any food, unless it's traditionally fermented into miso, tempeh, tamari or natto. As we've begun relying more and more on industrial food, our health has taken a major turn for the worse. Obesity is soaring in the US and diabetes is close on its heels.
I think it's very likely that grains are one of the major culprits in the diseases of civilization. This could be due to lectins causing leptin resistance. It's a fantastic hypothesis that could explain the health problems we see in modern grain-based societies.