Type 2 diabetes and prediabetes are epidemics because of excessive consumption of refined sugars and starches, and lack of physical activity. I can’t prove it; nevertheless that’s my impression after years of reading the nutrition science literature and thinking about it.
I could be wrong. I reserve the option to change my mind based on evidence as it becomes available. That’s one of the great things about science. Accurately identifying the cause of diabetes could provide strong clues about optimal prevention and treatment strategies.
Genetics undoubtedly plays a major role in diabetes, but the gene pool hasn’t changed much over the last several decades as type 2 diabetes rates have soared.
The problem in type 2 diabetes and prediabetes is that the body cannot handle ingested carbohydrates in the normal fashion. In a way, dietary carbohydrates (carbs) have become toxic instead of nourishing. This is a critical point, so let’s take time to understand it.
NORMAL DIGESTION AND CARBOHYDRATE HANDLING
The major components of food are proteins, fats, and carbohydrates. We digest food either to get energy, or to use individual components of food in growth, maintenance, or repair of our own body parts.
We need some sugar (also called glucose) in our bloodstream at all times to supply us with immediate energy. “Energy” refers not only to a sense of muscular strength and vitality, but also to fuel for our brain, heart, and other automatic systems. Our brains especially need a reliable supply of bloodstream glucose.
In a normal, healthy state, our blood contains very little sugar—about a teaspoon (5 ml) of glucose. (We have about one and a third gallons (5 liters) of blood circulating. A normal blood sugar of 100 mg/dl (5.56 mmol/l) equates to about a teaspoon of glucose in the bloodstream.)
Our bodies have elaborate natural mechanisms for keeping blood sugar normal. They work continuously, a combination of adding and removing sugar from the bloodstream to keep it in a healthy range (70 to 140 mg/dl, or 3.9 to 7.8 mmol/l). These homeostatic mechanisms are out of balance in people with diabetes and prediabetes.
By the way, glucose in the bloodstream is commonly referred to as “blood sugar,” even though there are many other types of sugar other than glucose. In the U.S., blood sugar is measured in units of milligrams per deciliter (mg/dl), but other places measure in millimoles per liter (mmol/l).
When blood sugar levels start to rise in response to food, the pancreas gland—its beta cells, specifically—secrete insulin into the bloodstream to keep sugar levels from rising too high. The insulin drives the excess sugar out of the blood, into our tissues. Once inside the tissues’ cells, the glucose will be used as an immediate energy source or stored for later use. Excessive sugar is stored either as body fat or as glycogen in liver and muscle.
When we digest fats, we see very little direct effect on blood sugar levels. That’s because fat contains almost no carbohydrates. In fact, when fats are eaten with high-carb foods, they tend to slow the rise and peak in blood sugar you would see if you had eaten the carbs alone.
Ingested protein can and does raise blood sugar, usually to a mild degree. As proteins are digested, our bodies can make sugar (glucose) out of the breakdown products. The healthy pancreas releases some insulin to keep the blood sugar from going too high.
In contrast to fats and proteins, carbohydrates in food cause significant—often dramatic—rises in blood sugar. Our pancreas, in turn, secretes higher amounts of insulin to prevent excessive elevation of blood glucose. Carbohydrates are easily digested and converted into blood sugar. The exception is fiber, which is indigestible and passes through us unchanged.
During the course of a day, the pancreas of a healthy person produces an average of 40 to 60 units of insulin. Half of that insulin is secreted in response to meals, the other half is steady state or “basal” insulin. The exact amount of insulin depends quite heavily on the amount and timing of carbohydrates eaten. Dietary protein has much less influence. A pancreas in a healthy person eating a very-low-carb diet will release substantially less than 50 units of insulin a day.
To summarize thus far: dietary carbs are the major source of blood sugar for most people eating “normally.” Carbs are, in turn, the main cause for insulin release by the pancreas, to keep blood sugar levels in a safe, healthy range.
Hang on, because we’re almost done with the basic science!
CARBOHYDRATE HANDLING IN DIABETES & PREDIABETES
Type 2 diabetics and prediabetics absorb carbohydrates and break them down into glucose just fine. Problem is, they can’t clear the glucose out of the bloodstream normally. So blood sugar levels are often in the elevated, poisonous range, leading to many of the complications of diabetes.
Remember that insulin’s primary function is to drive blood glucose out of the bloodstream, into our tissues, for use as immediate energy or stored energy (as fat or glycogen).
In diabetes and prediabetes, this function of insulin is impaired.
The tissues have lost some of their sensitivity to insulin’s action. This critical concept is called insulin resistance. Insulin still has some effect on the tissues, but not as much as it should. Different diabetics have different degrees of insulin resistance, and you can’t tell by just looking. (There are several other hormones involved in regulation of blood sugar.)
Did you know that people who work at garbage dumps, sewage treatment plants, and cattle feedlots get used to the noxious fumes after a while? They aren’t bothered by them as much as they were at first. Their noses are less sensitive to the fumes. You could call it fume resistance. In the same fashion, cells exposed to high insulin levels over time become resistant to insulin.
Insulin resistance occurs in most cases of type 2 diabetes and prediabetes. So what causes the insulin resistance? It’s debatable. In many cases it’s related to overweight, physical inactivity, and genetics. A high-carbohydrate diet may contribute. A few cases are caused by drugs. Some cases are a mystery.
To overcome the body tissue’s resistance to insulin’s effect, the pancreas beta cells pump even more insulin into the bloodstream, a condition called hyperinsulinemia. Some scientists believe high insulin levels alone cause some of the damage associated with diabetes. Whereas a healthy person without diabetes needs about 50 units of insulin a day, an obese non-diabetic needs about twice that to keep blood sugars in check. Eventually, in those who develop diabetes or prediabetes, the pancreas can’t keep up with the demand for more insulin to overcome insulin resistance. The pancreas beta cells get exhausted and start to “burn out.” That’s when blood sugars start to rise and diabetes and prediabetes are easily diagnosed. So, insulin resistance and high insulin production have been going on for years before diagnosis. By the time of diagnosis, 50% of beta cell function is lost.
EXTRA CREDIT FOR INQUISITIVE MINDS
You’ve learned that insulin’s main action is to lower blood sugar by transporting it into the cells of various tissues. But that’s not all insulin does. It also 1) impairs breakdown of glycogen into glucose, 2) stimulates glycogen formation, 3) inhibits formation of new glucose molecules by the body, 4) promotes storage of triglycerides in fat cells (i.e., lipogenesis, fat accumulation), 5) promotes formation of fatty acids (triglyceride building blocks) by the liver, 6) inhibits breakdown of stored triglycerides, and 7) supports body protein production.
In his fascinating book, Cheating Destiny: Living With Diabetes, America’s Biggest Epidemic, James Hirsch describes what happened to type 1 diabetics before insulin injections were available. Type 1 diabetics produce no insulin. Until Frederick Banting and Charles Best isolated and injected insulin in the 1920s, type 1 diabetes was a death sentence characterized not only by high blood sugars, but also extreme weight loss as muscle and fat tissue wasted away. The tissue wasting reflects insulin actions No. 4, 5, 6, and 7 above.
Banting and Best worked at the University of Toronto in Canada. Their “discovery” of insulin is one of the greatest medical achievements of all time.