The glycemic index is defined as a ratio of the incremental area under the blood glucose response curve (AUC) of a 50 g available carbohydrate portion of a test food to the same amount of available carbohydrate from a reference food (usually glucose/white bread) consumed by the same individual over a 2-hour period, expressed as a percentage. The GI system allocates each food a score between 0 and 100. The higher the number, the greater the speed at which sugar enters the bloodstream. A food with carbohydrates that break down quickly during digestion and release glucose rapidly into the bloodstream tends to have a high GI and raises blood sugar levels higher. These foods are suitable for energy recovery after exercise or for a person experiencing hypoglycemia. Foods with carbohydrates that break down more slowly, releasing glucose more gradually into the bloodstream, tend to have a low GI.
After a meal containing carbohydrates, plasma glucose rises, reaching a peak in about 15-45 minutes, depending on the rate of digestion and absorption. Plasma glucose returns to the fasting concentration within two to three hours. Plasma insulin concentration mirrors that of glucose, stimulating both glucose oxidation and glycogen storage.
In general, carbohydrate-containing foods rich in rapidly digestible starches (amylopectin) produce a high GI, whereas foods rich in slowly digestible starches (amylose), fructose, or containing substantial amounts of either insoluble fiber or fat produce a low glycemic response. The term glycemic response is used to describe the rise and fall of blood glucose levels and the duration over which it occurs.
High GI Foods: Maltose, glucose, potato, pumpkin, white rice, white bread, watermelon
Medium GI Foods: Brown rice, soft drink, pineapple, sucrose, papaya, honey, dates, ice cream
Low GI Foods: Chocolate, carrots, sweet potatoes, green banana, ripe banana, mango, broccoli, lettuce, barley, pizza
What is Low-GI Food: Low GI food produces less sugar and does not suddenly raise your blood sugar. Low GI foods are typically high in fiber and nutrients.
Benefits of Low GI Diet: High GI foods will suddenly increase our blood sugar levels. Our body takes extra insulin to bring down blood sugar levels. Extra insulin can cause type 2 diabetes. Low GI foods drive blood sugar levels more carefully by increasing insulin sensitivity and thereby reducing the risk of type 2 diabetes. Additional benefits include:
- Increasing HDL cholesterol and reducing LDL cholesterol
- Preventing cancer
- Reducing the risk of cardiovascular diseases
- Helping to reduce cholesterol and other fat levels
- Being slowly broken down for glucose utilization
Everyone can benefit by eating a balanced diet of protein and fat, and foods that have a lower GI index.
High and Low GI Foods:
| GI Classification | GI Range | Effect |
|---|---|---|
| Low | <55 | Slow increase in blood sugar |
| Medium | 55-69 | Moderate increase in blood sugar levels |
| High | >70 | Rapid increase in blood sugar levels |
Glycemic Index of Different Foods:
| Foods | High GI | Foods | Medium GI | Foods | Low GI |
|---|---|---|---|---|---|
| Maltose | 105 | Honey | 58 | Yoghurt | 33 |
| Glucose | 100 | Dates | 63 | Pear | 36 |
| Potato | 98 | Raisins | 64 | Apple | 40 |
| Oatmeal | 87 | Kiwifruit | 58 | Orange | 43 |
| Cornflake | 82 | Soft drink | 68 | Grapes | 43 |
| Pumpkin | 75 | Beetroots | 64 | Peas | 48 |
| White rice | 72 | Papaya | 56 | Mango | 51 |
| Watermelon | 72 | Orange juice | 57 | Tomato | 15 |
| White bread | 70 | Brown rice | 68 | Spinach | 15 |