By Harvard Medical International
Preventing diabetes from developing in the first place is better than treatment.
The world is in the grip of a diabetic epidemic. In the wealthy Gulf states, about 20% of the population is reckoned to have the disease. In the USA, about 21 million people are sufferers and many more have pre-diabetes. And all the indications suggest that the prevalence of diabetes will continue to soar in the years ahead.
Elevated blood glucose (sugar) levels define diabetes. A fasting blood sugar reading of 126 milligrams per deciliter (mg/dL) or higher is enough to diagnose the disease, and levels between 100 and 126 indicate pre-diabetes. But since diabetes is a leading cause of heart attack, stroke, kidney failure, visual loss, and memory loss, it's much more than a simple blood sugar problem. Treatment can help protect diabetics from many of the complications that cause disability and premature death. But preventing diabetes from developing in the first place is even better. And while treating the disease usually requires multiple medications, prevention can be accomplished without drugs. To be most effective, though, prevention requires multiple lifestyle modifications. Here is a rundown of the things that matter most and the little things that may help a bit more.
When it comes to preventing diabetes, weight control is the biggie. That's because excess body fat is the strongest single risk factor for diabetes. In a Harvard study of 27,270 male health professionals, for example, men who were even mildly overweight (body mass index, 25.4-27.1) were 2.9 times more likely to develop diabetes than the leanest men. And the more fat a man has, the higher his risk; in the Health Professionals Follow-up Study, the most obese men were 7.9 times more likely to become diabetic than their leanest peers. Any excess body fat increases risk, but abdominal fat is particularly culpable. In the Harvard study, waist circumference was a more powerful predictor of diabetes than body mass index; men with waists larger than 40 inches were at particular risk.
When new diabetic patients begin to control their disease, they usually focus first on nutrition.
Why is abdominal fat so harmful? One theory holds that abdominal fat cells produce hormones that actually counter the effects of insulin. Even without these substances, abdominal fat does not respond properly to insulin's actions. Instead, the fat cells release free fatty acids into the blood.
According to the concept of lipotoxicity, these fatty substances settle in the pancreas, damaging the beta cells and impairing insulin production. And there's more: The free fatty acids also find their way to the heart and liver, where they form deposits that lead to organ damage. Further, the liver converts excess free fatty acids into abnormally high levels of triglycerides. In fact, the combination of abdominal obesity, insulin resistance, and elevated triglycerides are major components of the metabolic syndrome, an important precursor of heart attacks and strokes.
If abdominal fat is such a big problem, can removing it by liposuction help? Unfortunately, it can't, because the fat that really counts is deep within the abdomen, surrounding the internal organs. Subcutaneous fat within a surgeon's reach is insulin-sensitive and metabolically similar to the fat around the hips, buttocks, and thighs. In the last analysis, weight loss is the only way to correct the visceral obesity that really matters.
Although weight loss is the most important way to prevent diabetes, it's also the most difficult to achieve. Fortunately, even a little bit can help. In the Diabetes Prevention Program, for example, each 2.2 pounds of weight lost reduced the risk of diabetes by 16%. Not coincidentally, exercise and diet are the keys to comprehensive prevention and to weight loss itself.
You don't have to be a physiologist to know that physical activity requires energy, much of which is supplied by glucose. Exercising muscles need more sugar, so the body makes exercising muscles more sensitive to insulin, allowing them to take in more glucose from the blood. Regular exercise also makes fat more responsive to insulin; research shows that exercise reduces the fat cells' production of a protein (RBP4) that contributes to insulin resistance. And exercise also reduces the liver's ability to turn its glycogen stores into glucose, which would otherwise pour into the bloodstream.
Since type 2 diabetes is characterized by insulin resistance, all these effects of exercise should help prevent the disease. And since exercise promotes weight loss, it should have extra benefits for people who are overweight.
Many studies from around the world reinforce the notion that exercise reduces the risk of diabetes. Three Harvard reports tell the tale. A study of 37,918 men found that the most physically active gents were 49% less likely to develop diabetes than the least active. An investigation of 21,271 male physicians reached similar conclusions; men who exercised at least once a week enjoyed a 29% lower risk of diabetes than sedentary men, even taking the effects of obesity into account. And among 70,102 female nurses, those who walked the most were 26% less likely to develop diabetes than nonwalkers, even after adjusting for body mass index.
Regular exercise can help prevent diabetes - and moderate exercise will do the job nicely. Walking for just 30 minutes a day is a great help. Exercise is every bit as important for people who already have diabetes; it will lower blood sugar levels and can reduce - or even eliminate - the need for medication. Above all, physical activity will reduce the death rate in diabetics just as it does in other people. Some examples: A 2003 study of 2,896 Americans linked walking for at least 2 hours a week to a 39% lower death rate; a Harvard study of 2,803 men associated walking with a 43% lower death rate; and a study of 3,708 Finnish diabetics linked moderate physical activity to a 39% reduction in the death rate.
Exercise does much more than lower blood sugar levels. Other benefits include better cholesterol levels, lower blood pressures, reduced body fat, and reduced stress. All this, and more, makes exercise one of the two pillars of diabetes prevention for everyone. The other pillar is diet.
When new diabetic patients begin to control their disease, they usually focus first on nutrition. It's equally as important as exercise for prevention, and two studies remind us that overall dietary patterns matter most. Researchers from Harvard and Finland identified two broad dietary patterns. The healthy "prudent" pattern featured fruits and vegetables, whole grains, fish, and poultry, while the "Western" (to use the phrase of the Harvard researchers), or "conservative" (the Finnish term), pattern was high in whole-fat dairy products, red meat, refined grains, and desserts. On both sides of the Atlantic, the prudent diet was associated with a lower likelihood of developing diabetes (16% in the Harvard study, 28% in the Finnish); the other diet was linked to increased risk (59% in the Harvard men, 49% in the Finns).
Patterns do matter most, but your diet is composed of foods, not trends. Here are some of the foods that can affect your risk of diabetes.
Sugars: Diabetics should avoid simple sugars and concentrated sweets. It's also good advice for healthy people who want to stay that way. Two examples are both from Harvard's Nurses' Health Study. One report linked the consumption of sugar-sweetened beverages to an increased likelihood of weight gain and type 2 diabetes; even one beverage a day nearly doubled a person's risk. The other study found that a diet with a large amount of rapidly absorbed carbohydrates increased the risk of developing diabetes by 59%.
Fibre: Not all carbohydrates are created equal. Dietary fiber is a "good carb" that reduces the risk of diabetes and improves metabolic, cardiovascular, and intestinal health. The human intestinal tract cannot digest and absorb this very special type of plant carbohydrate. Fiber has minimal caloric value, but it promotes a feeling of fullness. One type, soluble fiber, slows the absorption of food, delays stomach emptying, and lowers LDL ("bad") cholesterol. The other type, insoluble fiber, draws water into the colon, making the stool bulkier and easier to pass.
Studies from Framingham, Massachusetts, to Finland agree that eating large amounts of whole grains and cereal fiber protects against diabetes, ranging from about a one-third to two-thirds reduction of risk in various studies.
Dietary fat: Some diet gurus have grown fat by encouraging people to shun carbs and eat fat. It's a mistake for health and for weight control - and especially for diabetes, when it comes to saturated fat from red meat and whole-fat dairy foods. A multinational study linked a high consumption of animal fat to a high prevalence of diabetes. One Harvard study linked saturated fat to risk, another implicated red meat and processed meats, and a third found that low-fat dairy products appeared protective.
The Iowa Women's Health Study put it all together when it reported that substituting polyunsaturated fats from vegetable sources for saturated fat from animal sources appears to reduce the risk of diabetes. And the Nurses' Health Study linked polyunsaturated omega-3 fatty acids from fish to a reduced risk of heart disease and a lower death rate in women with diabetes.
Other factors: The dietary factors that have the greatest impact on the risk of developing diabetes are calories, carbs, fiber, and fat. Still, other things may help as well.
Surprisingly, perhaps, coffee leads the list. A 2005 review of 15 earlier studies reported that habitual coffee consumption is associated with substantial protection against type 2 diabetes; people who average six or more cups a day enjoyed a 35% lower risk. And four 2006 studies add to this impressive body of evidence.
Coffee may be a not-so-guilty pleasure, but does alcohol also break the "rule" that things that feel good must be bad for you? Perhaps - but only if the dose is right. A 2004 review of 32 earlier studies found that people who average one to three drinks a day are 33% to 56% less likely to develop diabetes than abstainers.
However, heavy drinking, more than three drinks a day, was linked to a 43% increase in the incidence of diabetes.
Although it may sound nutty to people who know that nuts have high calorie counts, a Harvard study reported that eating nuts and peanut butter appear to reduce the risk of diabetes. Similar benefits have been reported for fruits and vegetables, antioxidant-rich foods, vitamin D, calcium, and even cinnamon. Don't count on any of them to bail you out of a diabetes-prone lifestyle, but consider making all of them part of your program of diet and exercise.
Already notorious as the archrival of good health, smoking has added a notch on its belt of infamy, courtesy of a 2006 study. Researchers in Alabama evaluated the effect of tobacco exposure on the risk of developing glucose intolerance ("pre-diabetes") over a 15-year period. Both active smoking and exposure to secondhand smoke were strongly linked to risk; the people with the greatest exposure were the most likely to develop a resistance to insulin.
Wouldn't it be nice if there were a pill to prevent diabetes? Research says there is such a pill - two, in fact. Still, doctors are a long way from prescribing them.
Excess body fat is the strongest single risk factor for diabetes.
A study conducted by the Diabetes Prevention Study found that metformin (Glucophage, generics) could reduce the risk of diabetes by 31%. It's more good news about an excellent drug, but the same study found that a program of diet and exercise was nearly two times more effective (see below). More recently, a study with the promising acronym of DREAM reported that another diabetes medication, rosiglitazone (Avandia), reduced the risk of diabetes by 60%.
It's an impressive result, but more research is needed, particularly in view of the possible side effects of this class of drugs. The DREAM study also found that the excellent blood pressure drug ramipril (Altace) did not reduce the risk of diabetes. Still, ramipril and other ACE inhibitors have an important role in protecting the kidneys of diabetics, particularly those who have protein in their urine.
Does lifestyle prevention work?
You bet it does. Four randomized clinical trials show that it can work in a research setting, and a major observational study suggests that people can make it work on their own.
The Multiple Risk Factor Intervention Trial (MRFIT) evaluated 11,827 men with normal glucose metabolism. Half received special lifestyle counseling, the others, standard medical care. Among nonsmokers, the men who received information about diet and exercise were 18% less likely to develop diabetes than the men who got standard care. Unfortunately, lifestyle counseling did not protect smokers.
The Finnish Diabetes Prevention Study evaluated lifestyle interventions in 527 men and women who were obese and already had pre-diabetes. Diet and exercise reduced the risk of developing full-blown diabetes by 58%.
In the United States, the Diabetes Prevention Program studied 3,234 adults with pre-diabetes. Diet and exercise reduced the progression to diabetes by 58%. In comparison, treatment with metformin reduced risk by 31%. And if trials in Europe and the United States don't convince you, consider that a similar study of pre-diabetics in China found that diet and exercise could reduce the progression to diabetes by 46%.
It's clear that simple lifestyle changes can prevent diabetes in volunteers who receive education, motivation, and monitoring in a research trial. But does prevention work for people left to their own devices?
According to Harvard's Nurses' Health Study, the answer is an emphatic yes. Among 84,941 female nurses, the combination of a healthful diet, regular exercise, weight control, abstinence from tobacco, and moderate alcohol consumption was linked to a 91% reduction in the risk of diabetes - and it even reduced risk by 88% in women with a family history of the disease.
Nurses know a lot about health, and women tend to be more careful - and healthier! - than men. But with a little planning and diligence, you can do as well for yourself. And if diabetes does not top your worry list, remember that the same healthy lifestyle that cuts the risk of diabetes by 91% also cuts the risk of coronary artery disease by 83%.
This article is provided courtesy of Harvard Medical International. © 2007 President and Fellows of Harvard College.