|COMMON GLYCEMIC INDEX QUESTIONS
FOR AN UP-TO-DATE LIST OF EXACT GI VALUES CLICK HERE
What is the difference between glycemic index (GI) and glycemic load (GL)?
Your blood glucose rises and falls when you eat a meal containing carbs. How high it rises and how long it remains high depends on the quality of the carbs (the GI) and the quantity. Glycemic load or GL combines both the quality and quantity of carbohydrate in one ‘number’. It’s the best way to predict blood glucose values of different types and amounts of food. The formula is:
GL = (GI x the amount of carbohydrate) divided by 100.
Let’s take a single apple as an example. It has a GI of 40 and it contains 15 grams of carbohydrate.
What about a small baked potato? Its GI is 80 and it contains 15 g of carbohydrate.
So we can predict that our potato will have twice the metabolic effect of an apple. You can think of GL as the amount of carbohydrate in a food ‘adjusted’ for its glycemic potency.
Should I use GI or GL and does it really matter?
Although the GL concept has been useful in scientific research, it’s the GI that’s proven most helpful to people with diabetes. That’s because a diet with a low GL, unfortunately, can be a ‘mixed bag’, full of healthy low GI carbs in some cases, but low in carbs and full of the wrong sorts of fats such as meat and butter in others. If you choose healthy low GI foods—at least one at each meal—chances are you’ve eating a diet that not only keeps blood glucose ‘on an even keel’, but contains balanced amounts of carbohydrates, fats and proteins.
We suggest that you think of the GI as a tool allowing you to choose one food over another in the same food group—the best bread to choose, the best cereal etc.—and don’t get bogged down with figures. A low GI diet is about eating a wide variety of healthy foods that fuel our bodies best—on the whole these are the less processed and wholesome foods that will provide you with carbs in a slow release form. So what’s the take-home message?
Do I need to eat only low GI foods at every meal to see a benefit?
No you don’t, because the effect of a low GI food carries over to the next meal, reducing its glycemic impact. This applies to breakfast eaten after a low GI dinner the previous evening or to a lunch eaten after a low GI breakfast. This unexpected beneficial effect is called the “second meal effect”. But don’t take this too far, however. We recommend that you aim for at least one low GI food per meal.
While you will benefit from eating low GI carbs at each meal, this doesn’t have to be at the exclusion of all others. So enjoy baking your own bread or occasional treats. And if you combine high GI bakery products with protein foods and low GI carbs such as fruit or legumes, the overall GI value will be medium.
Why do many high-fibre foods still have a high GI value?
Dietary fibre is not one chemical constituent like fat and protein. It is composed of many different sorts of molecules and can be divided into soluble and insoluble types. Soluble fibre is often viscous (thick and jelly-like) in solution and remains viscous even in the small intestine. For this reason it makes it harder for enzymes to move around and digest the food. Foods with more soluble fibre, like apples, oats, and legumes, therefore have low GI values.
Insoluble fibre, on the other hand, is not viscous and doesn’t slow digestion unless it’s acting like a fence to inhibit access by enzymes (eg. the bran around intact kernels). When insoluble fibre is finely milled, the enzymes have free reign, allowing rapid digestion. Wholemeal bread and white bread have similar GI values. Brown pasta and brown rice have similar values to their white counterparts.
Can I download or can you email me a full list of all GI food values?
Sorry but we have no such list available for download or emailing purposes. Instead, we invite you to search out the foods you are interested in finding on our free GI Database (see the menu link on the left). There you will find a brief explanation on how best to conduct the search. Another option is to purchase our pocket book which is updated annually and contains the latest values at the time of publication: The New Glucose Revolution: Shopper’s Guide to GI Values.
Does the GI increase with serving size? If I eat twice as much, does the GI double?
The GI always remains the same, even if you double the amount of carbohydrate in your meal. This is because the GI is a relative ranking of foods containing the “same amount” of carbohydrate. But if you double the amount of food you eat, you should expect to see a higher blood glucose response – ie, your glucose levels will reach a higher peak and take longer to return to baseline compared with a normal serve.
If testing continued long enough, wouldn’t you expect the areas under the curve to become equal, even for very high and very low GI foods?
Many people make the assumption that since the amount of carbohydrate in the foods is the same, then the areas under the curve will finally be the same. This is not the case because the body is not only absorbing glucose from the gut into the bloodstream, it is also extracting glucose from the blood. Just as a gentle rain can be utilised better by the garden than a sudden deluge, the body can metabolise slowly digested food better than quickly digested carbohydrate. Fast-release carbohydrate causes “flooding” of the system and the body cannot extract the glucose from the blood fast enough. Just as water levels rise quickly after torrential rain, so do glucose levels in the blood. But the same amount of rain falling over a long period can be absorbed into the ground and water levels do not rise.
Why doesn’t the GI of beef, chicken, fish, tofu, eggs, nuts, seeds, avocadoes, many fruits (including berries) and vegetables, wine, beer and spirits appear on the GI database?
These foods contain no carbohydrate, or so little that their GI cannot be tested according to the standard methodology. Bear in mind that the GI is a measure of carbohydrate quality. Essentially, these types of foods, eaten alone, won’t have much effect on your blood glucose levels.
Some vegetables like pumpkin and parsnips appear to have a high GI. Does this mean a person with diabetes should avoid eating them?
Definitely not, because, unlike potatoes and cereal products, these vegetables are very low in carbohydrate. So, despite their high GI, their glycemic load (GI x carb per serve divided by 100) is low. Vegetables contain only small amounts of carbohydrate but loads of micronutrients and should be considered as “free foods”. Eat them all you like!
Can you tell me the GI of alcoholic beverages (beer, wine and spirits)?
Alcoholic beverages contain very little carbohydrate. In fact, most wines and spirits contain virtually none, although beer contains some (3 or 4 grams per 100 mL). A middy of beer (10 ounces) contains about 10 grams of carbohydrate compared with 36 grams in the same volume of soft drink. For this reason, a beer will raise glucose levels slightly. If you drink beer in large volumes (not a great idea) then you could expect it to have a more significant effect on blood glucose. As for enjoying an occasional drink, researchers from the University of Sydney found that a pre-dinner drink tends to produce a ‘priming’ effect, flicking the switch from internal to external sources of fuel and keeping blood-sugar levels low.
Why does some variability occur in the GI for the same food types? For example, Special K cereal shows values from 54 to 84.
The GI database confirms the reproducibility of GI results around the world. White and wholemeal bread, apples, cornflakes, breakfast cereals etc give the same results wherever/whoever tests them. Where there is variability, there are four possible explanations:
Why does pasta have a low GI?
Pasta has a low GI because of the physical entrapment of ungelatinised starch granules in a sponge-like network of protein (gluten) molecules in the pasta dough. Pasta is unique in this regard. As a result, pastas of any shape and size have a fairly low GI (30 to 60). Asian noodles such as hokkein, udon and rice vermicelli also have low to intermediate GI values.
Pasta should be cooked al dente (‘firm to the bite’). And this is the best way to eat pasta – it’s not meant to be soft. It should be slightly firm and offer some resistance when you are chewing it. Overcooking boosts the GI. Although most manufacturers specify a cooking time on the packet, don’t take their word for it. Start testing about 2-3 minutes before the indicated cooking time is up. But watch that glucose load. While al dente pasta is a low GI choice, eating too much will have a marked effect on your blood glucose. A cup of al dente pasta combined with plenty of mixed vegetables and herbs can turn into three cups of a pasta-based meal and fits easily into any adult’s daily diet.
Most breads and potatoes have a high GI. Does this mean I should never eat them?
Potatoes and bread, despite their high GI, can play a major role in a high carb/low fat diet, even if your goal is to reduce the overall GI. Only about half the carbohydrate needs to be exchanged from high to low GI to derive health benefits. Of course, some types of bread and potatoes have a lower GI and these should be preferred in order to lower the GI as much as possible.
The good news for potato lovers is that a potato salad made the day before, tossed with a vinaigrette dressing and kept in the fridge will have a much lower GI than potatoes served steaming hot from the pot. There are a couple of simple reasons for this. The cold storage increases the potatoes’ resistant starch content by more than a third and the acid in the vinaigrette whether you make it with lemon juice, lime juice or vinegar will slow stomach emptying.
What about flour? If I make my own bread (or dumplings, pancakes, muffins etc) which flours, if any, are low GI? What about sprouted grain breads?
To date there are no GI ratings for refined flour whether it’s made from wheat, soy or other grains. This is because The GI rating of a food must be tested physiologically that is in real people. So far we haven’t had volunteers willing to tuck into 50 gram portions of flour on three occasions! What we do know, however, is that bakery products such as scones, cakes, biscuits, donuts and pastries made from highly refined flour whether it’s white or wholemeal are quickly digested and absorbed.
What should you do with your own baking? Try to increase the soluble fibre content by partially substituting flour with oat bran, rice bran or rolled oats and increase the bulkiness of the product with dried fruit, nuts, muesli, All-Bran or unprocessed bran. Don’t think of it as a challenge. It’s an opportunity for some creative cooking.
Bread made from sprouted grains might well have a lower blood-glucose raising ability than bread made from normal flour. When grains begin to sprout, carbohydrates stored in the grain are used as the fuel source for the new shoot. Chances are that the more readily available carbs stored in the wheat grain will be used up first, thereby reducing the amount of carbs in the final product. Furthermore, if the whole kernel form of the wheat grain is retained in the finished product, it will have the desired effect of lowering the blood glucose level.
Some high fat foods have a low GI. Doesn’t this give a falsely favourable impression of that food?
Yes it does, especially if the fat is saturated fat. The GI value of potato chips or french fries is lower than baked potatoes. Large amounts of fat in foods tends to slow the rate of stomach emptying and therefore the rate at which foods are digested. Yet the saturated fat in these foods will contribute to a much increased risk of heart disease. It is important to look at the type of fat in foods rather than avoid it completely. Good fats are found in foods such as avocadoes, nuts and legumes while saturated fats are found in dairy products, cakes and biscuits. We’d all be better off if we left the cakes and biscuits for special occasions.
Why not just adopt a low carbohydrate diet (like the Atkins diet) to keep my blood glucose levels and weight down?
Recent studies show that low carb diets such as the Atkins diet produce faster rates of weight loss than conventional low fat diets. The probable mechanism is lower day-long insulin levels – allowing greater use of fat as the source of fuel – the same mechanism underlying the success of low GI diets. We believe that low carb diets are unnecessarily restrictive (bread, potato, rice, grains and most fruits are restricted) and may spell trouble in the long term if saturated fat takes the place of carbohydrate. Low GI diets strike a happy medium between low fat and low carb diets – you can have your carbs, but must choose them carefully.
Is there a GI plan for nursing mothers?
A low GI diet is ideal while you are breastfeeding. Breastfeeding requires a lot of energy and theoretically this additional energy comes from the body fat laid down during pregnancy. Of course in reality it doesn’t all get used up and most have to make a concerted effort to work off the baby weight. To do this though it is important that you don’t go on a low calorie diet or any sort of extreme measure such as the low carb diets popular in the press. Since breastfeeding tends to increase your appetite (the body’s way of ensuring you have the energy required to produce milk) this is good news as staying on such a diet would be a nightmare! This is what makes the low GI approach so successful – forget about trying to count calories or even your portions of food.
First and foremost focus on the sorts of foods you are eating. Low GI foods are the wholegrains, fresh fruit and vegetables and legumes. By eating these foods as the mainstay of your meals you can trust your appetite and eat to satisfaction while you are breastfeeding. Also get back to some exercise – even if it’s just a daily walk with the pram/carriage. You should then find that the weight slowly starts to shift – realistically give yourself at least that first six months to get back to your pre-pregnancy weight.
How relevant is the GI for athletes?
The GI can be a useful tool to help athletes select the right type of carbohydrates to consume both before and after exercise. Studies have consistently reported that a low GI pre-exercise meal results in a better maintenance of blood glucose concentrations during exercise and a higher rate of fat oxidation. This is likely to result in reduced muscle glycogen utilisation during prolonged exercise and possibly improve endurance performance. Eating high GI meals before exercise may result in plasma glucose concentrations peaking before the onset of exercise and then hypoglycemia occurring within the first 30 minutes of the exercise period. There is little data available on the effect of the GI of carbohydrates eaten before intermittent, power or strength related sports.
During recovery from exercise, muscle glycogen resynthesis is of high metabolic priority. The eating of high GI carbohydrates after exercise increases plasma glucose and insulin concentrations and this facilitates muscle glycogen resynthesis. If however, you are exercising for weight loss purposes or are involved in weight restricted sports, low GI carbohydrates after exercise may be more beneficial as the lower glucose and insulin concentrations will not suppress fat.
I have recently been diagnosed with celiac disease (gluten sensitivity). It’s extremely hard to find both low GI and wheat-free foods. Any suggestions?
This is not as hard as you may think! There are low GI gluten-free foods in four of the five food groups.
Fruit and Vegetables
Bread and Cereals
Legumes (pulses) including beans, chickpeas and lentils
Low fat dairy foods and calcium-enriched soy products
Is a low GI diet suitable for vegetarians?
The low GI diet is just as easy for a vegetarian to follow – in fact, teaching vegetarians to follow the low GI diet can be easier because most are eating many of the best low GI foods already. For the vegetarian, the same principles apply: substitute your plant protein sources for the meat. Eat more beans, lentils and other legumes – all among the lowest GI foods we have tested. Quorn is also a great meat substitute with no GI as it has almost no carbohydrate (2 g/100 g).
Some additional points:
Posted by: faithful | October 30, 2009
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