Refined carbs, bad; whole carbs, good. Diabetes educators and nutritionists have repeated that saying for years. Low-carb advocates say they’re wrong, that almost all carbohydrates are bad. Who’s right? Are whole carbohydrates really good for us, and how whole do they have to be?
To answer this, we have to know more about carbohydrates and more about diabetes. In particular, we have to learn about insulin signaling. As we know, people with diabetes have trouble dealing with sugars and foods that break down into sugar. Some people can’t produce enough insulin, as in Type 1, LADA, often called Type 1.5, and MODY. For others, their insulin signaling systems are not working, which is usually called Type 2. This could mean that the beta cells are not receiving signals to produce insulin, or that the muscle cells and liver are not getting signals to cooperate with the insulin.
This failure of muscle and liver cells to cooperate is called insulin resistance (IR). We used to think that the beta cells wore themselves out trying to overcome IR. Then they would fall behind, start to die, or fail to produce, and you would be left with Type 2 diabetes.
But now it appears that beta cells are not “wearing out.” They are either being damaged, or they are not receiving the signals they need to grow and to start producing insulin.
Like all other cells in our body, beta cells only know what to do because chemical messengers, produced by other cells, tell them. There are thousands of these messengers, and many are still undiscovered. One key messenger is GLP-1 or glucagon-like peptide-1. As I explained last month — please reread that blog entry if you’ve forgotten — GLP-1 is produced by glands at the far end of the small intestine, in the distal ileum. These glands produce GLP-1 mainly when stimulated by the presence of carbohydrates.
The problem is that modern carbohydrates never reach the distal ileum. They are absorbed before they get there, so the gut glands don’t produce GLP-1. Without this messenger, beta cells don’t know to produce insulin. They also don’t reproduce as fast. GLP-1 also slows the rate at which glucose (and other nutrients) is absorbed from the gut, so without it, you will get big spikes in your blood glucose level as all the carbs come in at once.
GLP-1 is so valuable that a new class of expensive drugs, the incretin mimetics, are being prescribed to make up for it. The main ones are exenatide (brand name Byetta) and liraglutide (Victoza). They act like GLP-1, stimulating insulin production (but only in the presence of glucose), slowing glucose absorption, stimulating beta-cell reproduction, and keeping the liver from releasing glucose into the blood.
Good stuff. But there are side effects, considerable expense, and they’re still not as good as the real thing. What people with Type 2, and probably other types, can do is limit carbohydrate intake to mostly carbohydrates that will actually reach the distal ileum and stimulate GLP-1 (and related chemical messengers that we might not know about yet.)
What Carbs Can Stimulate the Distal Ileum?
So now that we know what we’re trying to do, what foods could do it? Are whole grains the answer? Our beloved nutritionist Amy Campbell said about whole grains in 2008: “Whole grains contain three layers: bran, endosperm, and germ… Refined grains (think white flour and white rice) have the bran and germ layers removed.”
It certainly sounds like whole grains would stay in the gut longer. But even whole-grain flours get into your bloodstream much faster than the old, natural roots, fruits, and leaves. They often get absorbed as fast as the refined ones. That’s because they’re ground up, so it’s easier for digestive juices to get to them, break them down, and absorb them.
As a result, the only really whole grains are probably those you eat right off the plant, or close to it, like corn on the cob or brown rice. Any grains that are ground into flour or blended into processed food likely won’t reach the distal ileum.
If grains and sugars don’t reach the distal ileum, don’t trigger GLP-1, and therefore can’t be well used by our bodies, what about vegetables and fruits? Well, big chunks of starch in the form of starchy vegetables (like carrots or squash), probably won’t reach the distal ileum either. Green vegetables, especially fibrous ones, like broccoli, kale, collard greens, and cabbage, are the vegetables most likely to make it to the distal ileum. (Although, see a big list of nonstarchy vegetables here .)
Likewise with fruits. Modern fruits like humongous commercial apples, pears, and peaches also get into the bloodstream far too fast to stimulate GLP-1. Berries are better (and I’m not talking about these quarter-pound strawberries you see now. Smaller ones are best.) You can see a big list of nonstarchy fruits here.
Bottom line — if you have Type 2 (and this probably applies to some people with other types), I think these slow-absorbing, high-fiber carbohydrates can be part of your diet, and might even be healing to your insulin-signaling system. But be aware that many foods that call themselves “whole” or “whole-grain” are not that whole. They’re just slightly less processed. The real whole grains are the ones you can see — the kernels of corn or rice, or oats. Note that these three grains are also gluten-free.
But even those “good” whole grains should be eaten in moderation. And please, don’t forget the plusses of vinegar, which appears to have some of the same benefits as GLP-1.
If you want an inspirational read, see my blog entry on the art of “Helping without Helping”.