Whether you have type 1 or type 2 diabetes, the food you eat is going to have a major impact on your blood glucose levels and therefore on your diabetes control and risk of related complications. In fact, what you eat is so important that the ADA refers to dietary management of diabetes as medical nutrition therapy (MNT).
Carbohydrates are your body’s primary source of glucose, and glucose is your cellular fuel. The body begins to convert carbohydrates almost entirely into glucose shortly after carb-containing foods are eaten, and insulin helps to “unlock” the cells to move the glucose from the bloodstream into the cells for energy. If you have insufficient insulin production or your body is resistant to insulin, consuming too many carbohydrates can cause blood glucose to rise unduly.
All foods that contain starches and/or sugars — including fruits, vegetables, milk, yogurt, breads, grains, beans, and pasta — contain carbs. Virtually the only whole foods that are carbohydrate-free are protein-rich meats, poultry, and finfish (when prepared without additional ingredients such as breading and marinades), and fats such as cooking oils and shortening.
To avoid all carb-containing foods is both impossible and unadvisable — your body needs the important micronutrients and phytochemicals contained in these foods. But you do need to learn the basics of assessing the quantity and quality of carbohydrates in your food, how your body reacts to them, and how to make smart carb choices based on this information.
Carbohydrates are categorized by their chemical structure. A monosaccharide, or simple sugar, is composed of a single saccharide (sugar) chain. Glucose, fructose (fruit sugar), and galactose are all simple sugars. Disaccharides are two simple sugars joined together, and include lactose (milk sugar), maltose (malt sugar), and sucrose (table sugar). Polysaccharides, or complex carbohydrates, are ten or more simple sugar chains joined. Glycogen, starches, and fiber are polysaccharides. (A fourth type of carbohydrate, oligosaccharides, is composed of three to ten sugar chains, but most of these are usually formed from the breakdown of polysaccharides.)
All carbohydrates are hydrolyzed, or broken down, into monosaccharides before they can be processed by the body. Amylase, a type of enzyme found in the saliva and secreted by the pancreas, helps to break down carbs into glucose during their journey through the small intestine. Once hydrolysis occurs, the resulting glucose is absorbed into the bloodstream. Any excess is converted to glycogen and stored in the liver, along with fructose and galactose.
Does it matter what kind of carbs you consume? At one time, nutritionists believed that people with diabetes should avoid simple sugars (monosaccharides and disaccharides) and eat foods containing complex carbohydrates instead, with the mistaken belief that simple sugars would raise glucose levels faster and more dramatically across the board. But it’s now known that gram for gram, complex carbohydrates found in breads, cereals, potatoes, vegetables, and other foods raise the blood sugar approximately the same amount as do simple sugars like honey, fructose, or table sugar.
However, there may be a difference in how rapidly certain foods raise blood sugar levels. The glycemic index, or GI, is a measure of how quickly the carbs in certain foods are transformed into blood glucose. Foods with a low GI (e.g., beans, multigrain bread) raise glucose levels at a slower and steadier rate than a high-GI food (e.g., rice, potatoes).
Carbohydrates and the glucose they generate are an energy source — the dietary fuel of the human body. Insulin produced by the pancreas enables our cells to burn this carb-generated glucose. This is why determining the amount of carbohydrates in a meal is so important for blood sugar control.
People with type 1 diabetes, and some with type 2 diabetes, have to inject enough insulin to accommodate, or “cover,” all the carbohydrates they eat. And many people with type 2 diabetes have the added task of having to adjust their diets to lose excess weight, as well. Concepts like carbohydrate counting and dietary exchanges enable people with diabetes to manage their blood sugar levels effectively.
It’s also important to understand that carbohydrates don’t work in isolation. Other nutrient components of the food you eat also can affect carb absorption. High-fat and high-protein foods can delay carb absorption. And although fiber is considered a carbohydrate, high-fiber foods also slow the absorption of glucose since they slow the passage of food through the digestive tract.
Fiber, or roughage, is composed from plants’ cell wall material. Whole grains, legumes (dried beans and peas), nuts, and vegetables are all good sources of dietary fiber. Fiber is considered a carbohydrate, but since we cannot digest the majority of fiber, it does not effectively contribute to a rise in blood glucose levels. In fact, dietary fiber is an important nutritional tool in normalizing blood glucose levels because it slows digestion and therefore the absorption of accompanying nutrients.
When viscous (water-soluble) fiber absorbs water in the gastrointestinal tract, it turns to a gel-like substance that helps to normalize blood glucose and insulin levels by slowing the passage of food through the intestines. The delay in nutrient absorption means a slower and more stable rise in blood glucose levels.
Because it absorbs the excess intestinal bile acids that help to form cholesterol, soluble fiber helps lower blood cholesterol levels, another important consideration in people with diabetes who are at risk for cardiovascular disease.
Another benefit is that viscous fiber improves satiety, or the feeling of fullness you get when eating a fiber-rich meal. It delays stomach emptying, and in those people with type 2 diabetes who are also overweight, satiety can be a useful tool for weight loss.
A diet high in low-glycemic whole-grain cereal fiber has been found to have a beneficial effect in controlling postprandial (after-meal) blood glucose levels and reducing serum cholesterol levels in people with type 2 diabetes. And some studies have shown a glucose- and lipid-lowering benefit with fiber intake of up to 50 grams daily. The ADA recommends a daily fiber intake of at least 14 g per 1,000 calories. Talk to your doctor and dietitian about what level of fiber in your diet is right for you.
Fiber intake has also been associated with a reduction in diabetes risk in a number of studies. One of these, the six-year Nurses’ Health Study involving more than 65,000 participants, found that women on a low-fiber diet heavy in processed, sugary foods were 2.5 times more likely to develop type 2 diabetes than those who ate at least 25 grams of fiber daily.
The no-sugar myth is probably one of the biggest misconceptions about diabetes. The reality is that it isn’t sugar specifically that raises blood glucose levels — it’s any food containing carbohydrates, including honey, fruit, milk, and vegetables, to name a few. So whether it’s a spoonful of sugar, a bagel, or a banana, it will cause blood sugar levels to rise. However, some foods may cause a faster or more pronounced blood sugar spike.
So sugar isn’t, in itself, completely off-limits in a diabetes meal plan. However, moderation in sugar intake is important. The reason some people with diabetes prefer to use sugar substitutes such as artificial sweeteners or sugar alcohols is because they contain few or no carbohydrates or calories.
A sugar alcohol is, quite simply, a monosaccharide that has been chemically transformed into its alcohol form. There are a number of naturally occurring sugar alcohols (also called polyols), including sorbitol, mannitol, xylitol, lactitol, maltitol, isomalt, erythritol, and hydrogenated starch hydrolysates. Because they are not completely absorbed in the gastrointestinal tract, they don’t cause much of a rise in blood glucose levels, which is why people with diabetes may find them desirable. Polyols are frequently used as sweeteners and bulking agents in processed foods marketed as sugar-free.
Some people find that sugar alcohols have a laxative effect, causing diarrhea and/or gas. The U.S. Food and Drug Administration requires that foods containing significant amounts of sorbitol or mannitol (those products where daily consumption may result in over 50 grams of sorbitol or 20 grams of mannitol) must be labeled with the statement: “Excess consumption may have a laxative effect.”
When calculating carbohydrates in foods that contain sugar alcohols, you should subtract half of the sugar alcohol grams (located on the nutrition label) from the total carbohydrate count.
As opposed to naturally derived sugar alcohols, artificial sweeteners include the following synthetically manufactured sugar substitutes:
Some artificial sweeteners are available in special blends that combine the sweetener with sugar. These are marketed for use in baking and cooking to add texture and color. When using a sweetener blend, be sure to check the nutrition facts label carefully for the total carbohydrate count per serving.
Stevia is a dietary supplement derived from the herb Stevia rebaudiana, a wild shrub that is grown in South America and the Pacific Rim. Although used extensively as a sweetener for food products throughout South America and Asia, stevia is not approved for use in the United States, Canada, or the European Union. The FDA initially banned the import of the herb in 1991, following a study that raised questions about its toxicity as a food additive, but subsequently allowed it to be sold as a dietary supplement. However, the FDA has refused to add it to its GRAS list, citing a lack of substantial, controlled data on the safety of the herb.
Because stevia does not affect blood glucose levels, it is often touted as a sweetener alternative for people with diabetes. The extract of the herb (called steviosides) is said to be 200 to 300 times sweeter than table sugar and is used in cooking and baking outside the United States. Extracts are available in powder, tablet, liquid, and capsule form. Stevia is also available in a green herbal powder formula that is less intense than the extract. Both types of stevia are available in health food stores, marketed as dietary supplements.
If you’re considering using stevia, talk with your doctor and dietitian before incorporating it into your food plan. A dietitian familiar with the herb can also provide information on sugar-to-stevia conversion for cooking.
Ideal calorie intake is based on your activity level, gender, age, and other factors. Many people with type 2 diabetes also face weight-loss challenges; since reducing calorie intake is one component of an effective weight-reduction program, it is an important consideration in dietary management of diabetes.
The U.S. Department of Agriculture provides guidelines for daily calorie intake “Dietary Guidelines for Americans” provides guidelines for estimated amounts of daily calorie intake based on gender, age, and activity levels. These “Dietary Guidelines for Americans” can be found at www.cnpp.usda.gov/dietaryguidelines.
If you are overweight and have type 2 diabetes, keep in mind that even modest weight loss can decrease insulin resistance and improve control. But calorie reduction alone rarely leads to long-term weight control. The ADA suggests a comprehensive approach of reduced calories (500 to 1,000 fewer than the USDA guidelines listed for weight maintenance), regular exercise, reduced fat intake (no more than 30 percent of daily calories from fat), and diabetes and weight management education for long-term success. In their 2008 Clinical Nutrition Recommendations, the ADA also recognized the utility of low-carbohydrate diets in weight loss.
The nutrient balance in the food your calories come from is also important. The ADA suggests that 15 to 20 percent of your caloric intake should be protein, while no more than 7 percent of total calories should come from saturated fat.
Fat insulates the body and supplies energy when no carbohydrate sources are available. It also enables the body to absorb and process the fat-soluble vitamins A, D, E, and K. However, too much saturated fat and cholesterol can increase the risk of atherosclerosis and other cardiovascular complications from diabetes.
Fats are confusing to many people when they first start learning the ropes about dietary management of diabetes. The off-target message that all fat is bad has entrenched itself in popular dietary culture; fat-free food production is now a multimillion-dollar industry. While some fats are bad for you in excess, others can actually help improve your cholesterol profile. Here are the basics on dietary fats:
Less than 7 percent of daily calories should come from saturated fats, and trans-fat intake should be limited as much as possible. Cholesterol intake should be less than 200 milligrams per day. The ADA also recommends two or more servings of fish weekly for the cardioprotective benefits of omega-3 fatty acids.
Fat substitutes are food additives derived from protein, carbohydrates, or chemically modified fat. They are designed to replace the texture, moisture-retention, and bulk of fat in food while contributing a lower amount of calories. The main pitfall of reduced-fat and fat-free foods is that some people interpret the label as meaning calorie-free and overindulge. However, when prudently used, reduced-fat products can be a useful component of a weight-loss plan. Further studies are needed to determine the long-term impact of fat substitutes on overall calorie intake and nutrient absorption. Some fat substitutes, such as olestra (Olean), may inhibit the absorption of fat-soluble vitamins A, D, E, and K. The FDA has mandated that products made with olestra be fortified with these vitamins to overcome the deficit.
Proteins are chains of amino acids responsible for cell growth and maintenance and are found in virtually every part of the body. Protein in foods from animal sources (meat, poultry, fish, and dairy) is called complete protein because it contains essential amino acids necessary for building and maintaining cells. Plant-based foods such as grains, beans, fruit, and vegetables contain incomplete proteins, with only partial groups of these amino acids. However, different incomplete plant-based proteins can be combined to form complete proteins in the diet. If you are a vegetarian or vegan and have diabetes, a dietitian with experience in vegetarian menu planning can advise you on appropriate protein consumption.
People with diabetes should have 15 to 20 percent of total calories from protein, as is recommended for the general population. Anyone with impaired kidney function, or nephropathy, should avoid a high protein diet because damaged kidneys cannot filter protein efficiently from the bloodstream. If you have kidney problems, talk to your doctor and dietitian about an appropriate level of protein for your diet.
In moderate amounts, dietary sodium or sodium chloride (salt) is not harmful. In fact, the mineral helps to maintain a healthy electrolyte balance and works in tandem with potassium to regulate blood acid/base balance, heart function, nerve impulses, and muscle contractions.
However, people with high blood pressure need to be cautious about having too much sodium in their daily diet. The Dietary Approaches to Stop Hypertension or DASH diet study found that limiting dietary sodium is associated with a substantial reduction in blood pressure in adults with hypertension. For people with diabetes and hypertension, the ADA recommends a reduction in sodium intake to 2,300 milligrams, equivalent to a teaspoon of sodium chloride, or table salt. The average American, however, consumes over twice that much. Watch out for added sodium in condiments and packaged and canned foods.
Some people with diabetes and hypertension may benefit from an even bigger cut in dietary salt. A study published in the New England Journal of Medicine examined sodium intake in the Dietary Approaches to Stop Hypertension (DASH) diet and found that reducing sodium intake to 1,560 milligrams and 960 milligrams daily reduces blood pressure significantly when it is part of a comprehensive DASH diet — a dietary approach low in saturated fat and cholesterol and rich in fiber, protein, calcium, magnesium, and potassium. However, other studies have shown that adherence to the DASH diet among hypertensive patients is not high. Keeping meals interesting and introducing spices and new flavors is key to maintaining a low-sodium eating approach.