The glycemic impact diet is used by some to lose weight and by others to control diabetes and boost health. It's meant to take the way your food is metabolized and digested into account instead of just counting calories for the foods you eat. Foods low on the glycemic index, or GI, cause your blood sugar to rise more slowly than high GI foods. When your blood sugar rises, this sparks release of insulin, your fat storage hormone. The theory is that preventing blood sugar spikes means your body produces less insulin and is apt to store less fat. Regulating blood sugar levels also is an important factor in controlling diabetes.
History
The glycemic index was introduced in the 1980s and contained a listing of 62 foods. The "American Journal of Clinical Nutrition" published the most comprehensive list of glycemic index of foods in July 2002, with 750 listed. As of 2010, the University of Sydney, Australia, maintains a searchable database with some 1,600 entries.
Function
The glycemic index is a science-based method for determining how the carbohydrates in foods affect your blood sugar levels, says Meri Raffetto in "The Glycemic Index Diet for Dummies." You use the index to select your foods rather than following a specific meal plan, excluding foods or following other typical diet rules. For example, the GI diet does not require you to count calories or reduce portions, advise the experts at the Mayo Clinic.
Features
You choose foods that prevent rapid increases in your blood sugar level when using a GI diet to lose weight or manage diabetes, according to the Mayo Clinic. However, it is not a low-carb diet. Instead, the aim is to pick carbohydrates that keep your blood sugar balanced. It's meant to regulate your blood sugar throughout the day, which can reduce risk for insulin resistance or reduce your need for diabetes medication. Foods low on the GI produce the smallest fluctuations in blood glucose and insulin levels, according to the University of Sydney. Low GI foods have a value of less than 55, medium GI foods are ranked from 56 to 69 and high GI foods have a value of 70 or more, notes Raffetto.
Theories/Speculation
Scientific evidence that supports using the GI diet for weight loss and health is controversial and uncertain, according to the Mayo Clinic. Detractors say you can achieve the same health benefits touted by supporters by exercising enough and maintaining a healthy weight. Proponents say high blood sugar levels are linked to health problems including obesity, diabetes and heart disease and that using a low GI diet helps you select foods that bring about weight loss and help prevent chronic diseases.
Considerations
The GI diet has some drawbacks that can make it difficult to use, according to the Mayo Clinic. The glycemic index lists single foods but not combinations of foods likely to be in a recipe that can have varying impacts on your blood sugar. It also does not take variables like how food is prepared or portion size into account, as it is calculated for only a specific weight of food, most often 50 grams. It also does not take nutrient value into account, thus some foods with low GI ratings have lots of calories, saturated fat or sugar. For example, some candy bars have a GI of 41 but are not healthy to eat, according to Harvard School of Public Health.
Types
Low GI foods include high-fiber veggies and fruits, beans and legumes. Medium foods include oatmeal, 100 percent fruit juices and whole-grain breads and pastas. High GI foods include baked potatoes, white-flour pasta and couscous. Harvard notes that processing can affect a food's GI. Grain that is ground finely is digested more rapidly than grain that is ground coarsely, thus has a higher GI rating. Foods with high fat and acid contents tend to be low on the GI scale because these factors slow digestion.
