First of all, they are essential. For our body to function efficiently on a daily basis, we need to include Carbohydrates in our daily intake of foods. When we eat or drink, this provides fuel for our body in the form of Carbohydrates, Fats, Proteins and Alcohol with Carbohydrates being the body's preferred energy source. Glycaemic Index (GI) is a way to classify foods and drinks according to how quickly they raise blood sugar levels in our body
Digesting and absorbing carbohydrates
When we eat, the digestive system breaks down the Carbohydrates from the foods and drinks into simple sugars, mainly glucose. As a result, our Blood Sugar Levels rise and the body's natural reaction is to release a hormone called Insulin from the pancreas, which helps the glucose to migrate from the blood into the cells. This results in our blood sugars coming back down to a stable level. Once inside a cell, the glucose is 'burned' along with oxygen to produce energy. Our brain, muscles and nervous system all rely on glucose as their main fuel to make energy.
The body converts excess glucose from food into glycogen. Glycogen is a stored form of glucose within the muscle tissue and the liver. Its role is to supplement blood sugar levels if they drop between meals or during physical activity.
The glycaemic index (GI)
As noted, Carbohydrate based foods can be rated on a scale called the glycaemic index (GI). This scale ranks carbohydrates based on their effect on blood sugar levels over a period of time.
Carbohydrates that break down quickly during digestion have a higher glycaemic index (GI more than 70). These high GI carbohydrates, release their glucose into the blood quickly, giving us a burst of energy, but may also leave us feeling deflated after a period of time. Eating too many High GI Carbohydrate based foods may also lead to continual sugar cravings, swings in energy levels and moods and even the possibility of developing Type II Diabetes - this occurs when our body either stops being able to produce enough insulin to match the sugar in the blood stream, or the cells in our body become resistant to the insulin produced.
Carbohydrate based foods that break down slowly, such as oats, release glucose gradually into the bloodstream. They have low glycaemic indexes (GI less than 55). The blood glucose response is slower and flatter. Low GI foods prolong digestion due to their slow break down and may help with satiety (feeling full), sugar cravings and energy levels.
Factors that affect the GI of a food
Factors such as the size, texture, viscosity (internal friction or 'thickness') and ripeness of a food affect its GI. For instance, an unripe banana may have a GI of 30, while a ripe banana has a GI of 51. Both ripe and unripe bananas have a low GI.
Fat, protein, soluble fibre, fructose (a carbohydrate found in fruit) and lactose (the carbohydrate in milk) also generally lower a food's glycaemic response. Fat and acid foods (like vinegar, lemon juice or acidic fruit) slow the rate at which the stomach empties and slow the rate of digestion, resulting in a lower GI.
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