Diabetes prevention: The Glucose Test

Diabetes is about to become a concern for millions of middle-aged Americans who never gave it much thought before.  The American Diabetes Association, backed by federal health authorities, recently called for routine screening of all Americans starting at age 45, using a simple, inexpensive test, in order to detect more cases of Type 2 diabetes earlier.  This form of diabetes, previously called non-insulin dependent or adult-onset diabetes, accounts for 90 to 95% of cases of diabetes.  Until now, the disease has generally been diagnosed when people develop symptoms, such as unusual thirst or frequent urination, or when people at high risk for the disease (such as those with a family history of it) are tested for it.  Now blood sugar testing may become as routine as blood pressure screening.

At the same June 1997 meeting, the Association issued new guidelines that lower the cutoff points between normal, borderline, and high (diabetic) levels of blood sugar (see chart at right).  That, combined with widespread screening, is expected to identify an additional 2 million Americans as diabetics.  It’s estimated that 14 to 16 million have diabetes, but half have not been diagnosed.  And the half that have been diagnosed typically have the disease for seven years before it is diagnosed.  Experts hope that early detection will identify cases when they are still mild.  It’s hoped that this way, before symptoms develop, people can take steps to minimize the subtle damage to organs and blood vessels caused by years of high blood sugar levels, and avoid later complications of diabetes, such as heart disease, hypertension, stroke, and diseases of the eyes, nerves, and kidneys, which often lead to premature death.

Diabetes is a breakdown in the body’s ability to utilize glucose (blood sugar) efficiently.  Glucose, the main sugar into which foods are digested, can be used by our cells only in the presence of the hormone insulin.  With Type 2 diabetes, the cells become resistant to the effects of insulin, and thus blood levels of glucose rise. (With Type 1, which is usually diagnosed in young people, the body virtually stops producing insulin.)  The incidence of Type 2 diabetes is on the rise, largely because the U.S. population is aging and getting heavier.

The new guidelines for the diabetes test

If you are 45 or over, you should be tested every three years.

You should be tested earlier and more frequently if you

• are obese (more than 20% above healthy body weight).  The obesity rate has risen    dramatically during the past two decades and now includes one-third of Americans

•  have a parent or sibling with diabetes.

•  are black, Hispanic, or Native American, or belong to another high-risk ethnic group.

•  gave birth to a baby weighing more than nine pounds, or developed gestational diabetes    during pregnancy.

•  have high blood pressure (140/90 or higher).

•  have an HDL (“good”) cholesterol level of 35 or below and/or a blood triglyceride level of 250    or higher.

The ADA recommends the fasting plasma  glucose test (no food for eight hours before) because it is simplest, cheapest (about $10), and most likely to be utilized on a regular basis.  The same vial of blood drawn for the test can also be used to measure cholesterol and for other standard blood work, if needed.

A result of 126mg/dl (milligrams of glucose in one-tenth liter of blood) or more, confirmed on a second day, means you have diabetes.  The former guidelines set the cutoff at 140.  Researchers now believe that serious problems linked to diabetes begin with test results in the mid-120s.

BLOOD SUGAR (mg/dl)            DIAGNOSIS

Less than 110                         Normal

110-125                                                                     Impaired fasting glucose

126 and above (twice)           Diabetes

If you are diagnosed with diabetes in its early stages, you’ll be advised to lose weight if you’re overweight, exercise more, improve your diet (choose the same low-fat, semi-vegetarian diet that is known to lower the risk of heart disease and cancer), and quit smoking if you smoke.  The goal of early detection is to avoid diabetes medications, or at least postpone or minimize their use, not merely to start drug therapy earlier.

If your result is between 110 and 125, you fall into a new category called “impaired fasting glucose,” a danger zone or borderline area.  This means that you should take the same steps as outlined above, since blood sugar levels tend to rise with age.  Here is where it may truly be possible to prevent diabetes.  (For more about diabetes prevention, see our November 1996 issue:  for specifics about a diabetes-prevention diet, see the article below).

Last words:  Unfortunately, there’s no clear evidence that earlier treatment with drugs will reduce the long-term complications of Type 2 diabetes (though it does for Type 1).  Next year the results of a major ongoing British study may provide this evidence.  In any case, if screening for diabetes serves as an additional incentive for people to make life-style changes (such as losing weight and exercising), that can only be beneficial.

Diabetes prevention:  the diet

Many people still believe that eating too much sugar causes diabetes.  This misconception arises because diabetes is diagnosed by measuring blood sugar (glucose).  But dietary sugar is only part of the picture.  According to two recent Harvard studies, a diet rich in certain high-carbohydrate foods-those low in fiber and with a high glycemic index (see box at right)-increases the risk of Type 2 diabetes, at least in those predisposed to it.

One study tracked 65,000 female nurses (age 40 to 65); the other followed 43,000 male health professionals.  Over the course of six years, a total of 1,438 developed diabetes.  Men and women whose diet had a high glycemic index and low fiber content more than doubled their chance of developing diabetes.  Foods that seemed to pose the greatest risk were white bread, white rice, potatoes, and sugary soft drinks.  In contrast, whole-grain breads and cereals (rich in fiber and with a lower glycemic index) appeared to reduce the risk of diabetes.  Fruits and vegetables didn’t seem to have an effect, good or bad.

The researchers suggested that excessive amounts of carbohydrate-rich foods with a high glycemic index put pressure on the pancreas to produce more of the hormone insulin, which stimulates the body’s cells to take in and store glucose.  Over time, the body may become resistant to insulin.  In such insulin resistant people, the cells become less and less sensitive to insulin.  This is characteristic of Type 2 diabetes.  Of course, not everyone on such a low-fiber, high-starch diet develops diabetes.  There seems to be a genetic predisposition to diabetes which may be exacerbated by this kind of diet.  Without these dietary factors, the men and women in these two studies might have developed diabetes later in life, or perhaps not at all.

Obesity is probably the leading risk factor for Type 2 diabetes.  Family history of the disease, advancing age, and lack of exercise are other important factors.

Magnesium for diabetes protection

The study also found that the mineral magnesium has a protective effect against diabetes.  A few studies have suggested that this mineral improves insulin sensitivity.  But since whole grains are rich in magnesium, it’s hard to say whether the proposed benefit is due to something else in the grain (notably its fiber) or the mineral.

Bottom line:  A diabetes-prevention diet, if there is one, is the same low-fat, high-fiber, semi-vegetarian diet that is known to lower the risk of heart disease and cancer.  The Harvard studies simply underline the importance of choosing whole-grain products, as opposed to highly refined, low-fiber grain products such as white bread, in order to help control blood sugar.  Such a diet helps in weight control.  It also provides the vitamins, minerals, and other nutrients you need to help prevent chronic diseases, including, perhaps, diabetes.

The glycemic index

The glycemic index indicates how fast a high-carbohydrate food is digested into glucose and how much it causes blood glucose to rise.  The index doesn’t depend merely on whether the carbohydrates are simple (sugars) or complex (starches).  Many factors come into play, including the amount of fiber and fat in the food, how refined the food is, how fast the food is digested, whether it was cooked, and what else is eaten with it.  Table sugar and honey have a high glycemic index (meaning they have a strong effect on blood sugar).  But so do raisins, corn, potatoes, carrots, white bread, instant rice, and most refined cereals.  Though sweet apples and peaches, as well as beans, grapefruit, and peanuts, have a low glycemic index.  Pasta gets a middle rating, as does oatmeal.  There is no reason to avoid foods with a high glycemic index-many are very nutritious.  Even people predisposed to diabetes, or with the disease, can eat these foods in moderation.

UC Berkeley Wellness Letter, October 1997