Dietary Fiber, Gut Bacteria and Type 2 Diabetes
There is a lot of discussion today about low-fiber diets and diseases caused by unfavorable colonization of bacteria in your gut as a result. It is now common to hear recommendations to eat a lot of fiber. For example, experts in nutrition suggest a diet containing 15 grams of dietary fiber for every 1000 calories consumed. This compares with the typical Western diet containing only 6 grams of fiber per 1000.
High fiber diets are supposedly good for diabetics. One of the recommendations by experts in diabetes is that a diet high in whole grains provides fiber, which helps keep the gut in good shape, improve “insulin sensitivity,” lower blood sugar levels and, reduce the amount of total calories your body absorbs from the food you eat.
I agree with the role of natural fiber in having complimentary bacteria in our guts. However, I disagree with the suggested role of gut bacteria to help with the so-called problem of “insulin resistance” and the argument that fiber helps reduce the amount of calories you absorb. Let me state my reasons.
It is said that a diet high in fiber reduces the marker for inflammation that supposedly leads to the development of insulin resistance. But assuming inflammation is the cause of insulin resistance, why is that people develop insulin resistance in only 3 out of 200 types of cell in the body (muscle fiber, liver cells and fat tissue)? Why don’t the other 197 types of cells develop insulin resistance? In fact, despite 80 years of research, there is no explanation of the actual mechanism of how “insulin resistance” occurs in any of the three sites or a test to measure the actual level of insulin resistance in total or at any one of these sites. Whether eating more dietary fiber for a period of weeks or months leads to a reduction in insulin resistance has never been proven.
It is argued that whole grain / high fiber diets result in a lower body weight due to the alteration of gut bacteria that consume more calories from the food you eat, allowing fewer calories to pass into the body. This has never been clearly demonstrated. In addition, it is argued that because fiber is bulkier than other nutrients, it causes the stomach to become more distended, which sends appetite-suppressing signals to the brain. A related argument is that soluble fiber slows down the passage of food through the digestive tract, which aids in the release of digestion-related satiety signals. Both of these arguments imply, without any evidence, that people stop eating based on fullness of their stomach, regardless of what they eat or how many meals they eat in a day. Anyone who has ever overeaten knows this is not true. Many times we feel fully satisfied without feeling fullness in the stomach and, many times we eat far beyond the sensation of fullness in the stomach.
In effect, I am suggesting that eating a high fiber diet neither helps your diabetes nor helps you lose weight.
The Real Story of Bacteria in the Gut
If you truly want to understand whether or not to eat a lot of grains to boost your fiber intake, you have to understand what role bacteria play in the gut.
First, there are actually two types of resident bacteria that help break down food in the large intestine (the colon). One type is Firmicutes, and a diet rich in fats and animal proteins helps their multiplication.
The other type is Bacteroidetes, which actually itself has two sub-species that flourish depending on one’s diet. A diet of mostly plant fibers favors one of them, while the presence of fat and protein favors the other.
Both types of bacteria glean their energy from the fermentation of undigested carbohydrate to produce fatty acids. These fatty acids are absorbed into the body and provide fuel for the body’s cells, or are stored in fat cells for later use. The fatty acid production, however, is higher when Firmicutes dominate the gut bacteria compared to when Bacteroidetes bacteria dominate, such as in a person who eats a lot of fats and animal protein. Such a diet can lead to weight gain, with the person wondering where the extra pounds came.
This might seem to lead us to believe that a diet high in plant fiber is better than a diet high in fats and animal protein. However, contrary to popular belief, not all whole grains are fiber “rich.” The amount of fiber varies from grain to grain, and some food products may actually have lentils or other foods added to boost their fiber content, so it is not the whole grains that are plant fiber rich. If you want a diet high in plant fiber, it is far better to eat legumes such as lentils and beans, plus fresh vegetables of any type. In short, the health benefits from the consumption of dietary fiber associated with whole grains is inaccurate.
The Link between Grains and Diabetes
Furthermore, eating whole grains sets the stage for high blood sugar and diabetes. Each molecule of complex carbohydrate in whole grain can contain up to 200,000 molecules of glucose that when absorbed into the body can lead to high blood sugar. This happens when excess glucose is not consumed immediately by body cells for energy, and the excess glucose leads to the formation of triglycerides, which break down into fatty acids for storage in your fat cells. Eventually, once your fat cells are full, there is nowhere for the fatty acids to go, and they remain in your bloodstream to be burned more easily by muscle cells for energy rather than glucose. This leaves glucose in your bloodstream, thus high blood sugar, prediabetes or diabetes.
This explains how grains are linked to obesity, and ultimately to diabetes. But it also explains why even thin people who eat a lot of grains can develop diabetes, as they, too, can fill all their fat cells, which may be smaller in quantity than fat people, but nevertheless can become equally filled to capacity.
This theory also explains why cultures in which grain is a major portion of their diet are now experiencing increasing incidences of obesity and diabetes. In the US, for example, Americans reduced their fat intake when measured as a portion of their total daily calories from 37% to 34% between 1996 and 2007, but they increased their carbohydrate portion from 44% to 49% with the result that they were eating more calories overall. The repercussions from this change of diet demonstrate the link between grains and diabetes. Between 1970 and 2006, the proportion of obese Americans grew from 14% to 32%. Meanwhile, the incidence of diabetes has also shot up sharply since 1970, with more than 1 in 4 people over age 65 who have diabetes and 1 in 3 Americans over age 20 who have prediabetes.
The upshot of my theory is that if you eliminate grains and grain-based products as much as possible from your diet, you can substantially lower blood sugar and prevent yourself from developing diabetes. I suggest that it is the carbohydrate from grains to avoid because grains are not an essential source of food for humans. Therefore, this dietary change should not adversely affect your sensations of hunger or satiation, before a meal or during a meal, respectively.