Prediabetes:Time to Take Action

By Dace Trence, MD, FACE

From the Centers for Disease Control and Prevention (CDC), we know that the number of people diagnosed with diabetes mellitus has risen from 1.5 million in 1958 to 25.8 million Americans in 2011 -- about 8.3 percent of the U.S. population -- an increase that is of truly epidemic proportions. Certainly, some of this is due to changes in the blood sugar values physicians use for the diagnosis of diabetes, which now are significantly lower than in the past and come from studies that have looked at the association of sugar levels with the development of diabetes complications. But even accounting for the difference in criteria for diagnosing diabetes, the increase in the disease’s prevalence cannot be entirely explained.

The CDC additionally estimated in 2011 that 79 million adults aged 20 and older have prediabetes. Prediabetes is a condition in which blood glucose levels are higher than normal, but not high enough to be classified as diabetes. It is a state between normal blood sugars and frank diabetes sugars--but those with prediabetes have a high risk of developing diabetes. From the Diabetes Prevention Pilot Program (DPP)**, a study that looked at interventions thatcould decrease the likelihood of at-risk individuals developing the disease, 11 percent of those with prediabetes progressed to develop diabetes over three years! And although having prediabetes is very unlikely to lead to diabetes-related eye disease or kidney disease, there is a higher risk of developing vascular disease, i.e., heart attack and stroke.

The good news is that there are ways to decrease the risk of progressing from pre- to full diabetes. The DPP showed that decreasing weight and increasing physical activity can have a tremendous impact on individuals at risk. And the goal was not to target huge lifestyle changes. Losing about seven percent of weight and exercising for about 20-30 minutes a day was enough to decrease the progression from prediabetes to diabetes by almost 60 percent. Another group in the same study was asked to take metformin, an oral anti-diabetes drug. This medication also had a positive impact: it decreased the progression of prediabetes to diabetes by about 30 percent, some very impressive results. And this impact persists, as the groups initially studied continue to be followed, although the absolute numbers have changed. The incidence of diabetes during the 10-year average follow-up was reduced by 34 percent in those in the lifestyle changes group and 18 percent in those treated with metformin, compared with the group that had no intervention (the control group).

Other studies have also reported very positive results with weight and physical activity-targeted lifestyle changes. While the DPP was a U.S.-based study of over 3,000 individuals, a previous report from China called the Da Qing trial showed a very positive impact of lifestyle changes on decreasing the development of diabetes. In this study, 577 individuals with IGT (impaired glucose tolerance, defined as a blood sugar of over 140 but less than 200 after drinking a very sugary drink containing a specified number of carbohydrate grams) were assigned either dietary counseling, increased exercise, diet plus exercise, or general recommendations (control group).

The cumulative six-year incidence of new diabetes development was significantly lower in the diet group (44 percent), the exercise group (41 percent) and the diet-plus-exercise group (46 percent) than in the control group (67 percent).

In a Scandinavian study, the Finnish Diabetes Prevention Study, 522 overweight volunteers with IGT were assigned to usual care or diet plus exercise recommendations. The main dietary goals in the active intervention group were a low-fat diet (less than 30 percent energy as fat) with less than 10 percent saturated fatty acids and dietary fiber intake of more than 15 g/1000 kcal. Participants in this group also received instructions to increase exercise and were targeted for weight loss, which was accomplished to nearly five percent of their baseline weight. The cumulative incidence of diabetes was 23 percent in the control group and 11 percent in the active intervention group, i.e., a 58 percent reduction. Interestingly, diabetes risk reduction was directly proportional to the magnitude of lifestyle changes.

An additional clinical trial conducted in Japan examined lifestyle intervention for the prevention of diabetes while attempting to achieve and maintain ideal body weight. Men with IGT were randomly assigned to standard treatment (control group) or intensive intervention (active group). Participants in the control and active groups were advised to target staying at or slightly under a specific weight. Overall, body weight decreased by 0.88 pounds in the control group and by 4.8 pounds in the active intervention group. In the active group, the change was associated with a 67.4 percent reduction in the four-year incidence of diabetes. Diabetes risk and improved glucose tolerance were related to changes in body weight, suggesting once again that weight loss was influential in reducing diabetes risk.

But what about what one eats? Do you have to lose weight, or is there evidence that just changing your diet could decrease your risk of developing diabetes?

The answer is: changing diet itself can be effective!

As an example, a large nutrition-intervention trial for primary cardiovascular prevention in persons at high risk for cardiovascular disease showed that a non-calorie-restricted, traditional Mediterranean diet enriched with high-fat foods of vegetable origin decreased the incidence of diabetes after an average follow-up of four years. Diabetes rates were reduced by one-half for those eating a Mediterranean diet supplemented with virgin olive oil or mixed nuts, compared to those in a control group whose treatment consisted of advice on a low-fat diet.

Observational studies also strongly suggest that high intakes of fiber or fiber-rich, whole grain foods are independently associated with a reduced risk of diabetes. However, it is possible that high intake of fiber or whole grains may simply reflect a healthier lifestyle overall and not actually cause the reduced risk of diabetes. Fiber, particularly what is called insoluble fiber (cereals, legumes, nuts), plays an important role in controlling post-meal glucose andinsulin responses and satiety, which likely is due to its effect of slowing one’s stomach emptying and intestinal absorption.

Glycemic index (GI) indicates the glucose (blood sugar)-raising effect of a food in comparison with a standard (usually white bread), whereas glycemic load (GL) reflects both the glycemic index and carbohydrate content per serving, and both were associated with an increased risk of diabetes in a meta-analysis of observational studies (a combination of the results of several studies that address a set of related research hypotheses). Recent study results have shown that diets high in GI, GL and starch and low in fiber were associated with an increased diabetes risk . Low-GI diets were associated with improvements of blood sugar control and insulin sensitivity.

What about fat in the diet? Recent results suggest that a diet low in carbohydrate and high in protein, with a fat content of nearly 40 percent of energy, does not increase diabetes risk and may even lower it when vegetable sources of fat and protein were chosen instead of animal sources. Even more compelling are the results of The National Institutes of Health (NIH) National Heart, Lung, and Blood Institute’s (NHLBI) Women’s Health Initiative, where reducing fat in the diet from 37 percent in the usual diet group to 29 percent in the low-fat diet group was "ineffective" in reducing the incidence of diabetes in 48,835 postmenopausal women after intervention for six years. There is some suggestion that the type of fat eaten might be an important factor; monosaturated fats (olive oil, for example) are better than saturated fats (animal fats such as cream, cheese, butter, lard and fatty meats); and certain vegetable products (such as coconut oil, cottonseed oil, palm kernel oil, chocolate) for the possible prevention of diabetes.

Coffee and tea might also decrease diabetes risk. Drinking three to four cups of coffee daily was associated with a nearly 25 percent lower risk of diabetes in a huge diabetes study, with perhaps an even stronger association for decaffeinated coffee . Whether the effect can be attributed to caffeine is unclear. Potential roles for chlorogenic acid (a plant compound believed to decrease the absorption of dietary carbohydrates) or lignans (an estrogen-like chemical compound found in plants) contained in coffee deserve further investigation.

Moderate alcohol consumption also was associated with lower diabetes risk. The inverse association between alcohol consumption and diabetes risk was observed by researchers after adjusting several other lifestyle contributors. However, alcohol has its own health risks and, thus, moderation in intake is recommended.

Another study suggested that the relative risk of developing diabetes was reduced by 27 percent and 21 percent in women who ate nuts or consumed peanut butter five or more times per week, respectively, compared with those who rarely did. At odds with this report, recent findings from participants in the Physicians’ Health Study suggest no protective effect of nut consumption on diabetes risk in men.

So, the question becomes, what to do? To decrease your risk of diabetes, keep your weight down, get active, eat whole grain foods, maybe drink more coffee, use olive oil for cooking. And please pass that peanut butter sandwich this way.

**Editor’s Note: The Diabetes Prevention Pilot program is supported by the National Institutes of Health through the National Institute of Diabetes and Digestive and Kidney Diseases; the Office of Research on Minority Health; the National Institute of Child Health and Human Development; the National Institute on Aging; the Indian Health Service; the Centers for Disease Control and Prevention; the General Clinical Research Center Program, National Center for Research Resources; the American Diabetes Association; Bristol-Myers Squibb; and Parke-Davis.

Dr. Dace Trence is Director of the Diabetes Care Center and Professor of Medicine at the University of Washington Medical Center in Seattle. She is also the University of Washington Endocrine Fellowship Program Director and Director of Endocrine Days, a medical education program for endocrinologists practicing in the Pacific Northwest. She is on the American College of Endocrinology Board of Trustees and chairs the CME Committee and is also chair of the AACE Publications Committee.