Are You at Risk for Diabetes?

Adapted with permission from Healthy Eating for Type 2 Diabetes, a special health report from Harvard Health Publishing.

Understanding diabetes

Diabetes is a metabolic disease that can lead to serious health complications if left untreated. Several factors, such as body weight, family history and race and ethnicity may increase your risk of diabetes. Diabetes can be effectively managed by exercising and eating a healthy diet.

What is diabetes?

Diabetes (medically known as diabetes mellitus) is a common, chronic disorder marked by elevated levels of blood glucose, or sugar. It occurs when your cells don’t respond appropriately to insulin (a hormone secreted by the pancreas), and when your pancreas can’t produce more insulin in response.

Diabetes usually can’t be cured. Left untreated—or poorly managed—it can lead to serious long-term complications, including kidney failure, amputation, and blindness. Moreover, having diabetes increases your risk for cardiovascular disease, including heart attack and stroke.

Your body and sugar

To understand diabetes, it’s helpful to understand the basics of how your body metabolizes (breaks down) sugar. Most of the cells in your body need sugar as a source of energy. When you eat carbohydrates, such as a bowl of pasta or some vegetables, your digestive system breaks the carbohydrates down into simple sugars such as glucose, which travel into and through your bloodstream to nourish and energize cells.

A key player in the breakdown of sugar is the pancreas, a fish-shaped gland behind your stomach and liver. The pancreas fills two roles.

  1. It produces enzymes that flow into the small intestine to help break down the nutrients in your food—proteins, carbohydrates, and fats—to provide sources of energy and building material for the body’s cells.
  2. It makes hormones that regulate the disposal of nutrients, including sugars.

Cells in the pancreas, called beta cells, release insulin in response to the rise in blood sugar levels after you’ve eaten a meal. By directing sugar into liver and muscle cells, insulin promotes nutrient storage and prevents blood sugar levels from rising excessively.

Insulin also increases the uptake of amino acids (the building blocks of proteins) and fatty acids (the building blocks of fats) into protein and fat stores, respectively. Insulin thus serves as one of the principal gatekeepers of metabolism, promoting energy storage and cell growth.

The liver converts glucose that is not needed immediately for energy into a storage molecule called glycogen. When blood glucose levels drop too low, insulin secretion falls and your pancreas releases the hormone glucagon, which prompts your liver to reconvert stored glycogen into glucose and release it into the bloodstream.

Usually insulin and glucagon levels fluctuate in a coordinated fashion to keep your blood glucose levels within a rather narrow range. This is important because certain organs, such as the brain and kidneys, depend on a consistent, steady supply of glucose. A normally functioning pancreas ensures a stable supply of nutrients for your body.

In healthy people, insulin prevents a large rise in blood sugar after eating. The normal blood sugar level before breakfast usually hovers between 70 and 110 milligrams per deciliter (mg/dL). Normal levels of sugar in the blood rarely exceed 180 mg/dL, even after a meal.

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How type 2 diabetes develops


The risk for developing diabetes follows a continuum. The higher your blood sugar level, the higher your chance of developing diabetes. Two conditions—impaired glucose tolerance and impaired fasting glucose—are used to define this high-risk category, also known as pre-diabetes.

If blood sugar levels are elevated in a person who has not eaten for at least eight hours, the condition is called impaired fasting glucose. If blood sugar levels are elevated after an oral glucose tolerance test, the condition is called impaired glucose tolerance.

An estimated 57 million Americans have some form of pre-diabetes and, therefore, are much more prone to developing diabetes. Like people with diabetes, those with pre-diabetes tend to be overweight, have high blood pressure and abnormal lipid levels, and have a higher risk for cardiovascular disease.


Diabetes results from a combination of abnormalities. First, cells of the body become less responsive to insulin, which in turn causes the body to secrete more insulin to maintain normal metabolism. The pancreas usually rallies to compensate for the resistance by pumping out more insulin.

For most people with insulin resistance—a condition where the body produces insulin but does not use it properly—blood sugar levels stay within a normal range. But for some, the insulin-producing cells eventually fail to keep up with the increased demand. Blood sugar levels rise, resulting in diabetes.

Essentially, the problem is one of supply and demand: the pancreas supplies too little insulin to keep up with the increased demand that occurs with insulin resistance. For this reason, people with diabetes can be treated with therapies that decrease insulin demand, including diet, exercise, and drugs; with medications that increase insulin supply, such as sulfonylureas or glinides; or with insulin itself.

Who gets type 2 diabetes?

Predominantly a disease of later life, type 2 diabetes generally develops after age 40, although the typical age of onset has become lower. A person’s blood sugar levels usually rise slowly and progressively over the years before they become high enough to be considered in the diabetic range.

Body weight: Although researchers have identified several genes that increase the risk of developing diabetes, the largest risk factors relate to lifestyle—particularly being overweight and failing to get enough exercise. Of the more than one million Americans who will develop diabetes this year, most are overweight or obese.

People are considered overweight if they have a body mass index, or BMI, of 25 or above. People with a BMI of 30 or above are considered obese. Obesity can be further divided into three classes:

  • Class I Obesity: BMI of 30 to 34.9
  • Class II Obesity: BMI of 35 to 39.9
  • Class III Obesity: BMI of 40 or above

Class III obesity is roughly equivalent to being at least 80 pounds overweight if you are a woman or at least 100 pounds overweight if you are a man.(See table below)

Body fat: The distribution of body fat also seems to be particularly important. People who tend to store fat in their abdominal area rather than their hips—so-called central obesity—are more likely to become diabetic.

More about Excess Body Fat

Fat is more than just a storage site for extra nutrients. Fat, or adipose, tissue also functions as an
endocrine organ, producing hormones that affect appetite and insulin action.

So far, scientists have found that fat cells produce the hormones leptin, resistin, and adiponectin. Leptin
is normally released after a meal and dampens appetite. Resistin and adiponect in both affect cells’
response to insulin. (Too much resistin may cause insulin resistance; too little adiponectin may do the
same.) Although the appetite regulation system is complex and scientists are still deciphering the roles of
individual hormones, it’s becoming clear that excess body fat disrupts the normal balance and functioning of
these hormones, thereby contributing to insulin resistance and setting the stage for diabetes.

The risk of added pounds is especially high when the excess weight is distributed around the abdomen—often
referred to as an “apple” shape—as opposed to around the hips, called the “pear” shape.

Environment: In most cases, environmental factors also play a major role in the development of diabetes, having as much influence, if not more, as an individual’s genes. For example, before the 20th century, diabetes was virtually unknown to Native Americans. But as hunting or farming gave way to a sedentary lifestyle, higher-fat diets, and obesity, diabetes became rampant.

People from many other cultures have had similar experiences after adopting “Western” habits. Thus, in people who are genetically susceptible, the influences of increasing obesity and a sedentary lifestyle unmask the tendency to develop diabetes.

Family history: In addition to people who are overweight or sedentary, people over age 65 or who have a family history of diabetes are at particularly high risk. However, a growing number of children and adolescents have been diagnosed with it. Typically, such children are obese and have a family history of the disease.

Race and ethnicity: Race and ethnicity also play a crucial role, probably because of a combination of genetic susceptibility and lifestyle factors: the disease is far more common, for example, among African Americans, Hispanics, Asian Americans, Pacific Islanders, and Native Americans than among whites.

Medication: Finally, some medications can increase insulin resistance or decrease insulin secretion. These include corticosteroids, used to treat inflammation; diuretics and beta-blockers, used to treat high blood pressure; or a class of drugs called atypical or second-generation antipsychotics, originally developed to treat schizophrenia. Hormone therapy for prostate cancer (which lowers testosterone levels) and HIV treatments (which redistribute body fat) can also precipitate diabetes in people who are susceptible.

Diabetes prevention and management

Scientific studies show that losing as little as 5% to 10% of your body weight can help manage diabetes. For example, a woman who is 5 feet 4 inches and weighs 165 pounds would need to lose just 8 to 16 pounds to see noticeable declines in her blood sugar, lowering her risk for diabetes. Healthy weight loss can be achieved through diet and exercise.


For people who have diabetes—or almost any other disease, for that matter—the benefits of exercise can’t be overstated. Exercise helps to:

  • control weight
  • lower blood pressure
  • lower harmful LDL cholesterol and triglycerides
  • raise healthy HDL cholesterol
  • strengthen muscles and bones
  • reduce anxiety, and
  • improve your general well-being

There are added benefits for people with diabetes: exercise lowers blood glucose levels and boosts your body’s sensitivity to insulin, countering insulin resistance.

A combination of aerobic and anaerobic exercise is the best way to lose weight.

Aerobic exercise

Aerobic exercise involves the repetitive use of large muscles—for example, by walking, bicycling, or swimming—so that your heart rate and breathing temporarily increase, bringing more oxygen to muscles. It can be either moderate or vigorous.

During moderate-intensity activities you should notice an increase in your heart rate, but you should still be able to talk comfortably. If you are breathing hard and fast and your heart rate rises substantially, you are probably doing vigorous-intensity activity. Many activities (such as bicycling or swimming) can be either moderate or vigorous intensity depending on your level of effort.

Levels of activity intensity
Moderate-intensity activities include:
  • walking fast
  • doing water aerobics
  • riding a bike on level ground or a few hills
  • playing doubles tennis
  • pushing a lawn mower
Vigorous-intensity activities include
  • jogging or running
  • swimming laps
  • riding a bike fast or on hills
  • playing singles tennis
  • playing basketball

Resistance/ strength training

Such exercise builds muscle by harnessing resistance—that is, an opposing force that muscles must strain against. Resistance can be supplied by your body weight, free weights such as dumbbells and weighted cuffs, elasticized bands, or specialized machines.

Before starting or changing a fitness routine, it is extremely important that you consult your doctor, especially if you are overweight or have a history of heart disease, peripheral vascular disease, or diabetic neuropathy.

Eating a healthy diet

In general, healthy eating for people with diabetes is similar to healthy eating for everyone else. The American Diabetes Association recommends eating a diet centered on fruits, vegetables, whole grains, legumes (peas and beans), and low-fat dairy products.

Contrary to popular belief, there’s no specific type of weight-loss diet—such as low-fat or low-carb—that’s best for people with diabetes. Rather than focusing too much on what you eat, concentrate more on how much you eat.

Another strategy is to eat fewer high-calorie foods—mainly those high in fat, sugar, or both, such as French fries, donuts, and ice cream. Many people have a hard time estimating the number of calories in most foods, so consult a calorie guidebook or online calorie reference to make sure you’re on track. You can also visit the HelpGuide Healthy Fast Food article for tips on making healthier meal choices when dining out.

Adapted with permission from Healthy Eating for Type 2 Diabetes, a special health report from Harvard Health Publishing.

Last updated or reviewed on February 23, 2023


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