The Lowdown on Glycemic Index
What is Glycemic Index?
Carbohydrates are a macronutrient found in many foods, including bread, pasta, rice, fruit, and vegetables. When we eat carbohydrates, they are broken down into glucose, which is used by the body as fuel. The speed at which carbohydrates are converted into glucose varies, depending on the type of carbohydrate, the processing of the food and our genetics (1).
Glycemic index is a ranking system that measures how quickly a carbohydrate-containing food raises blood sugar levels compared to pure glucose, which has a value of 100 (2).
High-GI foods, such as white bread, white rice, and sugary drinks are rapidly absorbed into the bloodstream and cause a rapid increase in blood sugar levels. Low-GI foods, such as whole grains, fruits, and vegetables, are more slowly absorbed into the bloodstream and cause a more gradual increase in blood sugar levels (3).
Why is Glycemic Index important?
The glycemic index is important for several reasons. First, high-GI foods can cause a rapid spike in blood sugar levels, which can lead to weight-loss resistance, insulin resistance, type 2 diabetes, and other metabolic disorders (4). By choosing low-GI foods, people can help regulate their blood sugar levels and reduce their risk of developing these issues.
Second, the glycemic index can be a useful tool for weight management. High-GI foods are often high in calories and can cause overeating, while low-GI foods are often high in fibre, which promotes satiety and can help with weight loss (5).
Third, the glycemic index can be an important consideration for athletes and other people who need to maintain stable blood sugar levels for optimal performance.
Low-GI foods provide sustained energy and can help maintain blood sugar levels during prolonged physical activity, while high-GI foods can cause a rapid drop in blood sugar levels and lead to fatigue and decreased performance (6).
How is Glycemic Index determined?
The glycemic index of a food is determined by feeding a group of people a standardised amount of the food and measuring their blood sugar levels over a two-hour period. The glycemic index value is then calculated by comparing the rise in blood sugar levels caused by the food to the rise in blood sugar levels caused by pure glucose, which has a value of 100 (7).
Factors that can affect glycemic index values include the type of carbohydrate, the processing of the food, the presence of fibre and other nutrients, and the individual's metabolic response to the food (8). As a result, glycemic index values may vary between individuals and may not always accurately reflect the impact of food on blood sugar levels.
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