Glycemic index rates carbohydrate-containing foods on how they affect the body's blood sugar (glucose) levels after eating them. A food's glycemic index (GI) is ranked against a glucose solution, set at the top level of 100. Foods with a higher glycemic index produce a greater increase in blood glucose levels than low GI foods.
That said, figuring the body's response sounds simpler than it really is. So be wary of products marketed using glycemic index. Glycemic index is calculated for a specific amount of food, usually 50 grams of total carbohydrate minus the fiber. Many factors affect glycemic index for a single food, including its ripeness, its variety, how it's prepared or processed, the type of sugar and starch, how much fat and fiber it contains, and how long it takes to digest.
In general, nonstarchy vegetables, most fruits, legumes (dry beans), and milk tend to have a low glycemic index. For example, 1h cup of kidney beans has a glycemic index of 52; a medium apple, 38. White bread (from refined flour), crackers, and cornflakes are high-GI foods. The glycemic index of a medium baked potato (no skin) is 85, considered high. Yet this rule of thumb doesn't always hold true. Foods like watermelon and carrots also have a high glycemic index.
To clarify two common misperceptions: (1) The GI doesn't measure how fast blood glucose levels rise. Regardless of the carbohydrate source, blood glucose levels peak at about the same time. (2) The body's insulin response to a specific food isn't directly related to its GI value or its carbohydrate content.
The glycemic index of a single food isn't reliable for helping most healthy consumers make food choices. Why? First, the food is usually eaten with other foods; glycemic index doesn't measure what happens with mixed foods. A high-GI food eaten with a low-GI food may give a moderate GI response. Second, the amount eaten may be more or less than the amount for calculating glycemic response; to address that issue, glycemic loads for standard portions have been determined. And third, the GI of a food can vary from one person to another. A person's individual response may vary from day to day, too.
That said, glycemic index is being used in research related to type 2 diabetes, heart disease, and obesity-with potential for more use in the future. Currently no evidence shows that eliminating foods with a higher glycemic index, such as baked potatoes or cornflakes, promotes weight loss or helps with appetite control. And these foods may offer nutrient and phytonutrient benefits.
For people with diabetes, glycemic index can be useful as one tool to manage blood sugar levels, along with blood glucose monitoring and monitoring total grams of carbohydrate. That should be guided by a registered dietitian or other health professional. Refer to "Diabetes: A Growing Health Concern" in chapter 22.
The Dietary Guidelines advise: Reduce the incidence ofdental caries by practicing good oral hygiene and consuming sugar- and starch-containing foods and beverages less frequently.
Just what causes cavities—and how can you protect your teeth? For years, we've connected tooth decay to eating sugary foods. But whether or not you get cavities depends on many factors—and certainly not diet alone! Heredity, as well as the makeup and flow of saliva, are factors. Although part of the equation, sugar itself isn't the culprit as once thought.
The cavity-producing process starts when bacteria in your mouth mix with carbohydrates—both sugars and starches—to make acids. Bacteria are found in dental plaque, an invisible film that forms in your mouth and clings to the surfaces of your teeth and along your gum line.
Acids, produced by oral bacteria, can eat away tooth enamel, causing tooth decay, also known as dental caries. Every time you eat sugars and starches, acids begin to bathe your teeth. The cavity-producing action continues for 20 minutes or more after you eat something starchy or sugary.
These two "equations" offer a quick summary of the action that takes place in your mouth when bacteria in plaque mix with carbohydrate in food:
plaque + carbohydrate = acid acid + tooth enamel = potential tooth decay
Hard candy offers no more threat to your teeth than pasta does. Surprised? Any food that contains carbohydrate—pasta, bread, rice, chips, fruit, even milk, as well as cake, cookies, and candy—can "feed" the bacteria in plaque.
Table sugar, or sucrose, isn't the only sugar that plays a role in oral health, either. Any sugar—whether it's added or naturally occurring—has the potential to promote cavities. Fructose in fruit and lactose in milk, for example, also cause bacteria to produce plaque acids. So too, fruit juice-sweetened cookies have the same cavity potential as cookies made with table sugar.
Among young children, baby-bottle tooth decay is caused when teeth or gums are exposed to milk, breast milk, formula, fruit juice, or another sweet drink for extended periods of time. This happens most often when babies fall asleep sucking on a bottle or fall asleep frequently while breast-feeding. For more on baby-bottle tooth decay, refer to chapter 15, "Caring for Baby Teeth."
Do some foods promote cavities more than others? There's no definitive list that ranks the cavity-forming potential of food. However, two factors that make a difference include how often you eat (or how often carbohydrate comes in contact with your teeth) and how long it stays on your teeth.
Frequency. The more often you eat carbohydrate foods, especially between meals, the more likely acid attacks teeth. Sucking hard candy or cough drops, nibbling chips, or slowly sipping a sweetened drink nourishes bacteria and bathes teeth with plaque acids for a while. The action continues for 20 minutes or longer after you finish each candy, nibble each chip, or drink each sip of regular soft drink or juice.
Type of Food. Because some foods stick to your teeth, plaque acids continue their action long after you stop eating or drinking. The word "sticky" may conjure up thoughts of caramels. Yet caramels dissolve and leave your mouth faster than bread or chips that stick between your teeth or in the pits of your molars. It may take hours for the food particles to finally leave
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