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High glycemic foods contain easily digestible and absorptive carbohydrates that cause blood sugar levels to rise and then drop. Foods with a glycemic index (GI) rating of over 70 are considered highly glycemic. High carbohydrate foods such as white sugar, white flour and tropical fruits have high GI ratings. Diabetics should avoid a high glycemic diet since the sharp spikes and dips in blood sugar might aggravate their condition. Diet food companies such as South Beach Living™ promote their low glycemic foods as a means to weight loss.
All carbohydrates are not created equal, certain highly glycemic carbs cause rapid increases in glucose levels. These “sugar rushes” do not provide lasting energy, instead around two hours after consumption, blood sugar levels plummet, even below initial values. Foods with a better glycemic balance will slowly increase blood sugar levels to a much lower peak, and then return gradually to preprandial, or before the meal, levels.
The glycemic index ratings of foods indicate the reaction of normal healthy individuals to the different carbohydrates. To determine GI ratings, test subjects eat 50 grams of the food that is being rated. Their blood sugar levels are taken every fifteen minutes for two hours, and the glycemic index is derived from these results. By construction, glucose has a GI rating of 100. Foods with a GI rating under 55 are considered low, between 55 and 70 are medium, and above 70 are high glycemic foods.
Some notoriously high glycemic foods are French bread, watermelon and white rice. Many breakfast foods are highly glycemic such as bran and cornflake cereals, doughnuts and pancakes. The GI rating of some foods such as potatoes depends on their variety and preparation. An Irish boiled potato has a GI rating of around 60 whereas a Russet baked potato has a GI rating of over 100.
Both diabetics and people seeking to lose weight should avoid high glycemic foods, or at least consume them in moderation. Glycemic load—which is the GI rating, multiplied by the amount of carbohydrates in the food, divided by 100—can be a useful guide. By incorporating the notion of quantity, it is possible to predict the actual effect of a meal on blood sugar levels. A balanced glycemic load diet may allow for a small portion of a high glycemic food, as long as it is accompanied by another healthy food.