5.1: The Doctor Looks at Blood Sugar

By the time carbohydrates from food reach the bloodstream, they’ve been broken down by digestion into single sugars, mostly glucose. Other single sugars are readily converted to glucose.

Glucose in the blood (blood-glucose) is kept within a normal range by the action of two hormones made in the pancreas: insulin and glucagon. After carbohydrates are ingested, blood-glucose rises, and insulin is secreted in response. Insulin promotes the entry of glucose into cells, thereby lowering the level of blood-glucose (see Fig. 5-1).

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Hormone: A chemical messenger secreted in one location, carried in the bloodstream, and having specific effects elsewhere. e.g., the pancreas secretes the hormone glucagon, which causes the release of glucose from the liver.

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When one hasn’t eaten for a few hours, blood-glucose falls, and the pancreas secretes glucagon in response. Glucagon triggers the release of glucose from liver glycogen (the body’s storage form of glucose). This raises blood-glucose (see Fig. 5-1).

Insulin and the Causes of Diabetes

The most common blood-glucose-related medical problem is diabetes mellitus, characterized by an abnormally high blood-glucose (see Fig. 5-2). Some of this glucose “spills over” into the urine, bringing water along with it. In 2020, it was estimated that in 2018, 34 million U.S. adults age 18 and older—11% of adults—had diabetes, including 7 million (1 in 5 diabetics) who didn’t know they had it (hadn’t been diagnosed).¹

Figure 5-1: Insulin and glucagon use liver glycogen to maintain blood glucose. When blood-glucose falls, glucagon releases glucose from liver glycogen. When blood-glucose rises, insulin promotes glycogen production and storage.

Diabetes, from the Greek, means passing through, referring to the fact that untreated diabetics urinate often. To this is added the term mellitus, derived from the word for honey—the urine of the untreated diabetic is sweet with sugar.

Unlike low blood sugar, which catches your immediate attention by symptoms like weakness and fainting, high blood sugar itself doesn’t make you feel bad. High blood-glucose causes glucose to stick to hemoglobin (Hb): glycosolated hemoglobin HbA1c. Thus, HbA1c levels (% of a person’s hemoglobin that is “sugared”) indicates how well blood-glucose has been controlled over the past 2-3 months (the lifetime of hemoglobin).

Diabetes is diagnosed when an abnormally high blood-glucose or HbA1c is found in a routine check-up, or if you’ve gone in because of a sudden increase in urination or thirst—or because you’ve developed more serious problems (e.g., kidney damage) from high blood-glucose.

Type 1 Diabetes

About 5-10% of diabetics have type 1 diabetes,¹ characterized by an inadequate or a total lack of insulin, due to destruction of the pancreatic cells that make insulin. It isn’t associated with obesity, and occurs most commonly among children and adults under 30 years of age. It’s controlled with insulin injections, diet, and exercise.

Before insulin was available as a drug, insulin-dependent diabetes was quite rapidly fatal. Type-1 diabetes is primarily an autoimmune disease that can be triggered by certain viruses. In autoimmune diseases, the body mistakenly sees a normal part of the body as foreign and destroys it via its immune system. In this case, the part seen as foreign is the cells in the pancreas that make insulin.

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Human insulin can be made by biotechnology. Before, the only insulin available for diabetics came from extracting animal pancreases.

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Type 2 Diabetes

Most diabetics (90-95%) have type 2 diabetes, and 89% of them are overweight or obese.1 Not all overweight people develop this disease, however, since a genetic susceptibility is involved. Type 2 diabetes is generally characterized by the resistance of cells to insulin action. The cells can’t adequately remove glucose from the blood, despite an adequate amount of insulin.

The risk of type 2 diabetes increases with age and the extent of overweight/obesity. In the U.S., about 17% of adults age 45-64 and about 27% of adults over age 64 have type 2 diabetes.¹

Type 2 diabetes is typically an adult disease, but as obesity has become more common in children and adolescents, so has type 2 diabetes in this age group.

Obesity brings out a genetic tendency to diabetes, just as alcohol consumption can bring out a genetic tendency to alcoholism, or a high-salt diet can bring out a genetic tendency to salt-sensitive high blood pressure. An interaction of environment and genetics is a common theme in disease. As obesity has increased, so has diabetes (see Fig. 1-1, 1-2).

Regular exercise, in addition to helping to control weight, increases a cell’s responsiveness to insulin. Type 2 diabetes often can be controlled with weight control, exercise, and diet. When overweight, even a small loss of weight is helpful. Various oral medications can be used, and sometimes insulin injections are needed as well.

Figure 5-2: Blood glucose levels are abnormally high in untreated diabetics.

One of the most severe effects of diabetes (both type 1 and type 2) is damage to blood vessels. Since all tissues are served by blood vessels, the consequences depend most on which vessels are affected and how severely they are affected.

There’s wide individual variation in how fast diabetes progresses—some diabetics develop severe symptoms rapidly, whereas others have only mild and non-progressing disease. But overall, adults with diabetes, compared with adults of the same age without diabetes, have a much higher death rate, including nearly double the death rate from heart disease or stroke. Diabetes is the leading cause of kidney failure, and a major cause of blindness, nerve damage, and amputations below the knee.

Whether the cause of diabetes is a lack of insulin or a resistance to the action of insulin, glucose doesn’t get into cells as it should, and glucose builds to abnormally high levels in the blood. A high blood-sugar is a result of diabetes, not its cause.

A diet high in carbohydrate doesn’t cause diabetes. In fact, the prescribed diet for diabetics is rich in whole grains and vegetables—foods rich in both fiber and starch, allowing the glucose to enter the bloodstream more slowly. The diet limits sugars, such as table sugar, corn syrup, honey, raw sugar, and foods high in such sugars. Large amounts of these sugars, rapidly consumed, cause a surge in blood-glucose levels. This can mean trouble for diabetics, with their impaired ability to deal with glucose.

Diabetes Prevention and Treatment

There isn’t yet a way to prevent type 1 diabetes (studies are underway). For type 2 diabetes, excess body fat, especially around the belly, increases the risk, so weight control by exercise and diet is important (see Chap. 3). For the overweight, losing weight is hard, and gaining weight is easy, so if one isn’t losing excess weight, the goal should be to not gain more.

Treatment for type 1 and type 2 diabetes focuses on keeping blood-glucose levels in check. Type 1 diabetics do this with insulin injections, diet, and exercise. Some type 2 diabetics can control blood-glucose with only diet and exercise, but many need oral medication, and some also need insulin injections. Weight control in the overweight is also a major focus in the treatment of type 2 diabetes.

Gestational Diabetes

Gestational diabetes occurs in some women during pregnancy; screening is a part of routine prenatal care in the U.S. If blood glucose is controlled by diet, exercise, and sometimes medication, there’s no harm to the mother or baby.

The risk factors and treatment are similar to type 2 diabetes. The diabetes usually goes away after pregnancy, but women with gestational diabetes have an increased risk of developing type 2 diabetes.

Are Carbohydrates Dangerous?

Large amounts of sugar cause problems for a diabetic, but what about the rest of us? Can sugar and other carbohydrates in excess be hazardous to one’s health? They can, but in the context that all nutrients, even water, can cause problems in large enough amounts.

True, these substances are needed by the body. Therefore, the body has mechanisms for using them, as well as mechanisms for dealing with excesses beyond need. But eventually, there comes a point at which the body’s mechanisms for use, and for protection against excess, are overwhelmed.

One of the primary questions when judging food safety is, what is the expected use of the food in relation to the rest of the diet? In the case of carbohydrates, the typical American intake is far less than that of many nations, some of which have diets which are 80% carbohydrate and more, but our diet is excessively high in sugar.

Figure 5-3: Recommended Diet ²

Another important thing to know about carbohydrates is that if we don’t consume any—a difficult trick, for there is some carbohydrate in the vast majority of foods—the body will make some. We can, for example, make glucose from protein.

Does this mean that we don’t really need to eat carbohydrate foods? No, it would be unhealthy for us. Whole grains, vegetables, and fruits—all carbohydrate-rich foods—provide us with an abundant source of vitamins, minerals, and fiber. And compared to protein-rich and fat-rich foods—usually animal foods—they provide us with an inexpensive source of calories.

We need a daily minimum of about 200 calories worth of carbohydrate (50 grams). Otherwise, the body must rely on the conversion of other nutrients to carbohydrates, and there can be an accelerated breakdown of body protein, and dehydration.

But this doesn’t mean that such a minimum is desirable. It’s recommended that 45-65% of our calories come from carbohydrate (900-1300 calories-worth in a 2,000-calorie diet) (see Fig. 5-3).

Is there any recommendation about the kind of carbohydrate? Yes, there is. The overconsumption of overly-refined carbohydrate foods (as well as calorie-dense foods high in fats) reduces our intake of vitamins, minerals, and fiber. That’s why nutritionists caution against consuming too much of our diet in the form of refined grains or sugar, and too little in the form of whole grains, vegetables, and fruits.

But this advice can easily be misinterpreted. Let’s consider one misinterpretation—the idea that relatively isolated sugars and starches are somehow harmful in themselves, rather than potentially harmful because they may displace other nutrients. This erroneous deduction leads some popular writers to describe isolated sugars and starches as “poisons.”

The reality is that a molecule of sucrose remains a molecule of sucrose, no matter what its source. “Refining” refers to what happens to the total food, rather than specific nutrients. So refined carbohydrate foods have substances removed, substances which might or might not have nutritive value. But the sugar or starch itself is likely to be unchanged in the food. In any event, before carbohydrates enter our bloodstream, digestion will have brought them all to the “refined” form of simple sugar.

Honey, maple syrup, corn syrup, white sugar, brown sugar, raw sugar, and white flour are all refined foods, separated—by a tree, a bee, or by a machine—from much that was in their original sources. To our cells, they are no more “toxic” than the same sugars and starch would be in apples, raisins, or wheat.

Hypoglycemia

Hypoglycemia is a condition of abnormally low blood glucose. Its symptoms are relieved by dietary sugar. The symptoms range from mild (e.g., dizziness, nervousness, hunger) to severe (e.g., convulsions, coma). The most common cause of severe hypoglycemia is excess insulin taken by a diabetic.

Some people experience mild hypoglycemia as a result of a temporary overproduction of insulin, paradoxically in response to a large amount of dietary carbohydrate. When taken on an empty stomach (e.g., skipping breakfast, and having a soft drink and pastry in mid-morning), the sudden carbohydrate intake causes a surge in blood glucose, in turn stimulating a surge in insulin secretion that can overshoot its mark.

This type of hypoglycemia is appropriately called reactive hypoglycemia. The symptoms are fairly mild, occur 2 to 4 hours after eating, and the advice is to ingest smaller “doses” of carbohydrate (e.g., an apple rather than a candy bar for a snack) in more frequent and well-spaced intervals.

Many people decide that they have hypoglycemia when they actually don’t. (A true diagnosis includes testing blood-sugar levels.) It’s a popular diagnosis because the symptoms are quite vague, and a diagnosis of “hypoglycemia” has been effective in promoting an array of worthless products, as well as the pet themes of some misguided health-practitioners and some authors of best-selling diet-and-health books.

Certain popular authors claim that low blood sugar afflicts a major part of our population, and see it as the cause of an endless array of symptoms. It’s one more example of an eternally popular and effective general tactic of creating a “non-disease,” and then selling its cure. Many who do this are truly sincere—but sincerity isn’t the same as scientific evidence.