Blood Sugar, Energy and the Glycaemic Index
It was once thought that eating an equal amount of any kind of carbohydrate would have the same effect on blood glucose levels. It is now known that different carbohydrate-containing foods do in fact have different effects on blood glucose levels.
The Glycaemic Index (GI) is a ranking of foods based on their overall effect on blood glucose/sugar levels. Glucose, the quickest carbohydrate to be absorbed, is used as the standard reference (GI 100), and other foods are measured against this. Foods which are absorbed slowly have a low GI rating, whilst foods that are more quickly absorbed have a higher rating. The nearer a food’s rating to 100, the higher its glycaemic index.
Low GI foods may have a role in helping to prevent or reduce the risk of Type 2 diabetes by reducing the peaks in blood glucose that follow a meal. There may also be benefits for weight loss; low GI foods can help control appetite by helping people feel fuller for longer. Research ahs also shown that people who eat a low GI diet have a lower incidence of heart disease and improved levels of HSL cholesterol.
Determining the GI of a meal is not just about reading the GI number for carbohydrates from a chart. The addition of fat and protein also slows down the absorption of carbohydrate. This means that chocolate has a medium GI becuse of its fat content and crisps and chips will actually have a lower GI than potatoes cooked without fat. Milk and other dairy products also have a low GI because of their high protein and fat content. So, if people only ate low GI foods, their diet could be unbalanced and high in fat. This is why it is important not just to focus on GI, but also to think about the overall balance of the diet.
Examples of GI Ratings:
To help sustain even blood sugar levels and keep energy levels high throughout the day, choose plenty of low GI carbohydrate foods with some protein and fat in every meal.
Low GI Foods for Long-Term Energy
• All pulses e.g. lentils, chickpeas, soya beans, baked beans, kidney beans, butterbeans, borlotti beans etc, barley
• Apples, dried apricots, peaches, plums, cherries, grapefruit, pears
• Avocados, courgettes, spinach, peppers, onions, mushrooms, leafy greens, leeks, broad beans, green beans, sprouts, mange-tout, cauliflower, broccoli
• Natural yoghurt, milk, nuts
Medium GI Foods for Mid-term Energy
• Sweet potatoes, boiled potatoes, yams, raw carrots, sweetcorn, peas
• All types of wholewheat pasta, oats, porridge, oatmeal biscuits, noodles
• Whole-grain rye bread, pitta, buckwheat, bulgar wheat, brown rice.
• Grapes, oranges, kiwi, mangoes, beetroot, fresh dates, figs
High GI Foods for Short-term Immediate Energy
• Glucose, sugar, honey, pineapple, bananas, raisins, watermelon
• Baked potatoes, mashed potatoes, partsnips, cooked carrots, squash, swede
• Rye and wheat crispbreads, cream crackers, wholemeal bread, rice cakes, couscous
• Cornflakes, Bran Flakes, instant oats, popcorn, muffins, crumpets
• Orange juice, dried fruit
Example of a Low GI Eating Plan
Breakfast
Use an oat-based breakfast cereal and eat some fruit
SnacksFresh fruit
Low-fat yoghurt
Popcorn
Nuts, rye bread and fruit loaf (watch amounts if trying to lose weight)
Lunch
Add baked beans to a jacket potato
Try a lentil based soup
Add variety with different breads, e.g. pitta bread and bread made with a substantial amount of mixe grains and pumpernickel
Grilled chicken, salad, rice and peas
Evening Meal
Try basmati rice, sweet potato, buckwheat, bulgur wheat, pearl barley and noodles with your meal
Include more vegetables
Include more beans and pulses (dahl)
A Word About Glycaemic Load (GL)
A GI value tells you only how rapidly a particular carbohydrate turns into sugar. It doesn’t tell you how much carbohydrate is in a serving of a particular food. The Glycaemic Load (GL) is a ranking system for carbohydrate content in food portions based on their Glycaemic Index (GI) and the portion size. You need to know both figures to understand the effect of a food on blood sugar.
For example, the carbohydrate in a carrot has a high GI. However, there is not much of it, so the glycaemic load is relatively low. Calculating GL makes it easier to relate carbohydrate intake to its health effects.
How is GL Calculated?
Glycaemic Load for a single serving of food can be calculated as the quantity (in grams) of its carbohydrate content, multiplied by its GI, and divided by 100. For example, a 100g slice serving of watermelon with a GI of 72 and a carbohydrate content of 5g (it contains a lot of water) makes the calculation of 5 divided by 0.72 = 3.6, so the GL is 3.6. A food with a GI of 100 and a carbohydrate content of 10g has a GL of 10 (10 divided by 1 = 10), while a food with 100g carbohydrate and a GI of just 10 also has a GL of 10 (100 divided by 0.1 = 10).
Low GI = 55 or less, Medium GI = 56-69, High GI = 70 or more
Low GL = 10 or less, Medium GL = 11-19, High GL = 20 or more
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