1. What makes blood glucose go up and down?
With respect to the major nutrients in foods and beverages, carbohydrates have the most profound effect on blood glucose and insulin levels, however, protein and fats also have an effect.
But as most people with diabetes know – particularly those who monitor their blood glucose levels regularly – it’s not just the foods and beverages we eat that affect our blood glucose levels. For example, blood glucose levels are often highest in the morning after an overnight fast, and after exercising, our insulin requirements typically decrease. The reasons why are relatively complex, and require a little knowledge of the way our bodies work.
Let’s start with the pancreas. It’s a small tadpole-shaped organ located in the abdomen, tucked behind the stomach. It secretes digestive juices into our gut, which digest the proteins, fats and carbohydrates from foods and drinks into their components (amino acids, fatty acids and sugars, respectively) so that they can be absorbed into our bodies through our intestines. In addition, it releases (secretes) hormones into our blood stream that regulate blood glucose levels. The hormone insulin is secreted by beta-cells, and glucagon is secreted by α-cells that are clumped together in little islands (islets of Langerhans) in the pancreas.
Most insulin is secreted by the pancreas after a meal containing carbohydrate, but it is also released in small amounts in-between meals at what’s known as the basal rate. Interestingly, our brain and nervous system uses about 80 per cent of the glucose utilised by our whole body, but glucose uptake by our brain and nervous system is not regulated by insulin. Also, while insulin stimulates glucose uptake by our muscles, they have other glucose receptors that do not require insulin to work.
Insulin lowers blood glucose levels partly by suppressing the release of glucose from the liver, by increasing glycogen (a kind of starch) synthesis and storage, and by inhibiting glycogen breakdown and the formation of glucose from other sources such as glycerol (from fat), lactate (from the metabolism of fuels like glucose and fructose by the liver and muscles) and amino acids (from proteins) by the process known as gluconeogenesis. It also enhances the uptake of glucose and some amino acids by our muscles and increases protein synthesis. In fat cells, it stimulates the synthesis of fatty acids from other fuels (e.g. glucose and fructose), and prevents the breakdown of fats into fatty acids.
Glucagon is secreted by the pancreas when blood glucose levels start to go below optimal levels, such as after an overnight fast, or during periods of increased energy expenditure (e.g., when exercising), to sufficiently induce a rapid, yet transient, rise in blood glucose. Glucagon raises blood glucose levels by having essentially the opposite effects of insulin by promoting the production (gluconeogenesis) and release (glycogenolysis) of glucose from glycogen stores in the liver and muscles. In fat cells, glucagon causes the breakdown of fats into free fatty acids which are released into the circulation to provide another source of fuel for our bodies.
So, while the foods and drinks we consume have a significant effect on blood glucose levels, they are not the only factors that make our blood glucose go up and down.
2. 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 carbohydrates (the GI) and the quantity (the serve size). 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.
GL = 40 x 15/100 = 6 g
What about a small baked potato?
Its GI is 80 and it contains 15 g of carbohydrate.
GL = 80 x 15/100 = 12 g
We can predict from this 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.
3. 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.
4. Why do many high-fibre foods still have a high GI value?
Many people think that if a food is rich in fibre it will automatically be low GI, but that’s not the case at all. To begin with, there’s not just one type of dietary fibre – there are many different kinds and is typically divided into two main categories: soluble fibre and insoluble fibre. In addition, processing makes a big difference to fibre’s digestibility.
Soluble fibre is the one with the reputation for helping to reduce blood cholesterol levels and modulate blood glucose levels – but whether it does so or not depends in part on the amount of food processing and of course how much of it you eat.
It is often thick and jelly-like (viscous) in solution (water) and remains viscous even in the small intestine. What it means is that soluble fibre thickens the mixture of food entering the digestive tract and therefore slows down the time it takes for the fibre to pass through the stomach and small intestine. Essentially soluble fibre makes it hard for the digestive enzymes to move around and do their job, which is why foods with more soluble fibre have low GI values.
Soluble fibres include gums (e.g. agar), fructans (e.g. inulin), mucilages (e.g. psyllium) and pectins and they are found in fruits, vegetables, legumes (beans, peas and lentils) and some cereal grains (oats and barley).
Insoluble fibre is the one that’s often described as “roughage” and is renowned for keeping us regular on the inside.
It is found in all wholegrain cereals and products made from them that retain the outer layer bran (nature’s packaging) of the grain (corn, oats, quinoa, rice, spelt, wheat), and in vegetables, nuts and seeds.
Insoluble fibre is not viscous and doesn’t slow digestion of a food unless it’s acting rather like a fence, delaying access of digestive enzymes to the starch. However, when it is finely milled, the enzymes have free reign, allowing rapid digestion. This explains why high-fibre cereals like Bran Flakes that look so healthy and are full of fibre, actually have a high GI. They are digested in a flash because the production process makes the starch very accessible. It’s the same with most ready-to-eat breakfast cereals you’ll find in the supermarket.
5. 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 at the top of the page). 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 Low GI Diet: Shopper’s Guide to GI Values.
6. 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 – i.e. your glucose levels will reach a higher peak and take longer to return to baseline compared with a smaller serve.
7. Can I follow a Low GI Diet while pregnant?
It is important to eat a healthy diet while pregnant and a low GI diet is ideal. Unlike many other types of diets, following a low GI eating plan is NOT restrictive, does not cut out major food groups and is a healthy way of eating before, during and after pregnancy. It benefits the whole family. For more information on the benefits of a low GI diet in pregnancy, including meal plans and recipes, visit www.bumptobabydiet.com
8. 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.
9. 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 assume 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.
10. Why doesn’t the GI of beef, chicken, fish, tofu, eggs, nuts, seeds, avocadoes, many fruits (including berries) and vegetables 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.
11. Some vegetables 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 do not contain a lot of carbohydrate. So, despite their high GI, their glycemic load (GI x carb per serve divided by 100) is medium. These vegetables contain loads of micronutrients and can be consumed as part of a healthy balanced meal.
12. 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 (2 or 3 grams per 100 mL). A middy of beer (10 ounces) contains about 6 grams of carbohydrate compared with 25-30 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-glucose levels low.
13. 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.
14. Most breads and potatoes have a high GI. Does this mean I should never eat them?
Potatoes and bread, despite their typically high GI, can play a major role in a higher carb/lower 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.
15. 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! 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.
16. 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 predominantly 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 help contribute to an increased risk of heart disease. It is important to look at the type of fat in foods rather than avoid it completely. Good fats (mono and polyunsaturated) are found in foods such as seafood, avocadoes, nuts, seeds and legumes while saturated fats are found in dairy products, fatty meats, cakes and biscuits. We’d all be better off if we saved the cakes and biscuits for special occasions.
17. 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.
>>>See the following article on GI News which discusses low carb diets in detail.
18. 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 consequently improved endurance performance. Eating high GI meals before exercise may result in plasma glucose concentrations peaking before the onset of exercise and then hypoglycaemia 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.
19. 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
- Temperate climate fruits – apples, pears, citrus (oranges, grapefruit) and stone fruits (peaches, plums, apricots) – all have low GI values. Tropical fruits – pineapple, paw paw, papaya, rockmelon and watermelon tend to have higher GI values, but their glycemic load (GL) is low because they are low in carbohydrate.
- Leafy green and salad vegetables have so little carbohydrate that we can’t test their GI. Even in generous serving sizes they will have no effect on your blood glucose levels. Higher carb starchy vegetables include sweet corn (which is actually a cereal grain), potato, sweet potato, taro and yam, so watch the portion sizes with these. Most potatoes tested to date have a high GI, so if you are a big potato eater, try to replace some with lower GI starchy alternatives such as sweet corn, yam or legumes. Pumpkin, carrots, peas, parsnips and beetroot contain some carbohydrate, but a normal serving size contains so little that it won’t raise your blood glucose levels significantly.
Bread and Cereals
- Opt for breads made from chickpea or legume based flours. For example chapattis made with besan (chickpea flour) have a low GI. If you make your own bread, try adding buckwheat kernels, rice bran and psyllium husks to lower the GI. Most gluten-free breads seem to be better toasted than used to make sandwiches.
- Breakfast cereals containing pysllium husks are likely to have a lower GI – you could also add a teaspoon or two of pysllium to you usual cereal. To date there are just a few gluten-free breakfast cereals on our database that have a low GI. If you do have a higher GI gluten-free cereal, combine it with lots of fruit and low fat yoghurt or low fat milk, to lower the GI.
- Noodles are a great stand-by for quick meals, a good source of carbohydrate, provide some protein, B vitamins and minerals and will help to keep blood glucose levels on an even keel. There are several low GI gluten-free options available fresh and dried: buckwheat (soba) noodles; cellophane noodles, also known as Lungkow bean thread noodles or green bean vermicelli, are made from mung bean flour; rice noodles made from ground or pounded rice flour, are available fresh and dried.
- Gluten-free pastas based on rice and corn (maize) tend to have moderate to high GI values so opt for pastas made from legumes or soy. As for wholegrains, try buckwheat, quinoa, low GI varieties of rice such as basmati and sweet corn. Currently there are no published values for amaranth, sorghum, and tef. Millet has a high GI.
- Minimise refined flour products and starches irrespective of their fat and sugar content such as crispy puffed breakfast cereals, crackers, biscuits, rolls, most breads and cakes or snack foods. Limit high GI snacks such as corn and potato chips, rice cakes, corn thins and rice crackers.
Legumes (pulses) including beans, chickpeas and lentils
When you add legumes to meals and snacks, you reduce the overall GI of your diet because your body digests them slowly. So make the most of beans, chickpeas, lentils, and whole and split dried peas.
Although nuts are high in fat (averaging around 50 per cent), it is largely unsaturated, so they make a healthy substitute for foods such as biscuits, cakes, pastries, potato chips and chocolate. They also contain relatively little carbohydrate, so most do not have a GI value. Peanuts (actually a legume) and cashews have very low GI values.
Low fat dairy foods and calcium-enriched soy products
Low fat milk, yoghurt and ice-cream or soy alternatives provide sustained energy, boosting your calcium intake but not your saturated fat intake. Check the labels of yoghurts, icecream and soymilks as many contain wheat-based thickeners. If lactose intolerance is a problem, reach for live cultured yoghurts and lactose-hydrolysed milks. Even ice-cream can be enjoyed if you ingest a few drops of lactase enzyme first.
20. Why does some variability occur in the GI for the same food types?
The GI database confirms the reproducibility of GI results around the world. White and wholemeal bread, apples, breakfast cereals etc. give the same results wherever/whoever tests them. Where there is variability, there are four possible explanations:
1. When measuring the GI of foods, some GI testing groups do not comply with the International Standard (ISO 26642:2010) Determination of the glycaemic index (GI).
2. Some GI testing groups are not as experienced/accurate as SUGiRS measuring the GI of foods. They use venous blood which gives more variability than capillary blood. If we test a product over and over again at SUGiRS, we get the same result +/- 5%. That’s as good as nutrient data such as protein, fat, fibre etc.
3. The variability among different types of potatoes, rices, and oats is real. They contain different types of starch (amylose, amylopectin) and that affects the degree of starch gelatinisation. When it comes to sugars like fructose, the concentration of the solution makes a difference to the rate of gastric emptying and therefore the glycemic response. A more dilute solution, say 25 grams fructose in 500 mL water will have a higher GI than 25 grams fructose in 250 mL. But fructose has a very low GI whichever way you consume it.
4. Sometimes the manufacturer may change the formulation of their product by reducing the fat content for example. Reducing the fat can increase the GI. If manufacturers make significant changes (greater than 1.5 per cent) to the formulation, or they source ingredients from different suppliers, they may have their products retested.
21. Why do fermented foods have a low GI?
One reason many fermented foods are beneficial to health is the production of organic acids such as lactic acid, acetic acid (the same acid as in vinegar), etc. These are by-products of the fermentation process when the bacteria/yeast metabolise the carbohydrates (sugars and starches) in the food or drink. These organic acids not only add distinctive flavours to the food or drink, they also lower the pH, making it difficult for harmful microorganisms to grow. In our stomachs, they slow down a food’s rate of emptying into the intestine, which in turn slows the rate of digestion and absorption of the food’s carbohydrates into the blood stream, lowering the overall GI.
In traditional breads (e.g. sourdoughs), the slow fermentation not only produces the organic acids that create that unique flavour, but also the slow rise of the dough due to the production of gases (e.g., carbon dioxide). This helps the bread develop the bubbly and chewy texture characteristic of a quality bread. The gluten (protein in wheat) matrix slowly develops and traps the bubbles of gas, which is why traditional sourdough breads have a low GI (54), even when they are made of refined white flour.
Yoghurt and fermented milk drinks like kefir, lassi, leben, and Yakult all have a low GI. There are several reasons why.
- Unique proteins in milk increase insulin production which accelerates the removal of glucose from the bloodstream.
- Milk sugar (lactose) has a lower GI (46) than sucrose (65) because the enzyme lactase works more slowly.
- Finally, the lactic acid produced by the fermentation of the lactose by various strains of bacteria like of Lactobacillus delbrueckii subsp. bulgaricus and Streptococcus thermophiles slows stomach emptying and therefore the rate that food is digested and absorbed.
While milk itself is low GI (20–34), the GI values of natural yoghurts (the fermented version of milk) are even lower, ranging from 10–19, depending on whether full cream or skim milk is used. Even sweetened yogurts have a GI in the 30s and 40s.
22. How do I go low GI?
Think of going low GI as adding a filter to your regular healthy eating pattern.
- It only applies to the carb-rich fruit, vegetables, legumes and grains you like to eat
- It’s flexible and can be tailored to suit a range of “diets” from high carb to low; paleo to vegetarian/vegan; gluten-free or low FODMAP to sugar quitters or Weight Watchers.
Here’s our 2-step approach going low GI.
Step 1: Swap it: Replace the high GI foods in your diet with low GI ones. You can find out more about how to do this here.
Step 2: Don’t overload: Choosing low GI is not a free pass to pile your plate. Keep those carb-rich portions moderate so the glycemic load is moderate too. What’s moderate? It’s about a quarter of your dinner plate (inner rim) or 2–3 small lower GI potatoes such as baby Carisma or Nicola, ½ cup diced orange fleshed sweet potato or corn kernels or baked beans and ⅓ cup cooked basmati or other lower GI rice or pasta.
23. Can I trust food labels that claim a food is low GI?
Claims about the GI of foods were incorporated into the Australian and New Zealand Food Standards Code in 2013 and came into full effect in January 2015. Under this legislation, in order to make a generic low GI claim, food must have been tested to Australian Standard 4694-2007 and also meet the requirements of Food Standards Australia and New Zealand Nutrient Profiling scoring criterion. The GI value must also be included mon the food’s nutrition information panel so that the claim can be verified.
Consumers in Australia or New Zealand who have concerns about GI label claims should contact FSANZ and/or the ACCC (Australian Competition and Consumer Commission).
24. I have type 2 diabetes. How much carbohydrate should I aim for each day?
This depends on many things including your body size, age, gender, plus how active you are, your food preferences, food culture and family background. And on the amount and type of diabetes medication you are taking.
In the past 20 years, diabetes organisations around the world have recommended that people with diabetes aim to consume 45–60 per cent of their energy intake from carbs. However, ongoing research suggests that there’s quite a range of eating patterns that can help people with diabetes manage their blood glucose levels in the short to medium term.
Ongoing research however, has shown that a variety of eating patterns, including lower-carbohydrate, higher-protein and Mediterranean-style diets, can all be effective in decreasing HbA1c in people with diabetes by 0.12 to 0.47 pertentage points if they are followed for 6 to 18 months. However, we don’t really know what happens after that. Most studies that are long term (that is, more than 2 years) show that people slowly but surely go back to eating what they used to eat.
For most people diabetes is a lifelong condition. What matters is that from the outset you adopt a healthy eating pattern that you enjoy, that helps you manage your diabetes and that you can live with for the rest of your days. Food after all is one of life’s great pleasures to enjoy with family and friends.
The best thing to do is talk over your options with your diabetes dietitian, as within wide limits there is a great deal of flexibility in the macronutrient proportions that are considered healthy.
25. I have read that very low carb diets make it easier to manage blood glucose. Are there any problems with them?
By very low we assume you mean the kick-start phase of diets such as Atkins which provide less than 50 grams of carbohydrate a day. A CSIRO study published in 2015 found that both higher carbohydrate (around 220 grams carbohydrate per day) and lower carbohydrate (around 75 grams carbohydrate per day) diets produced improvements in diabetes management, but this wasn’t any old “low-carb” diet – it was high in dietary fibre and unsaturated fats.
Remember, without enough carbohydrate in your diet you may experience in the short term:
- Muscle fatigue, causing even gentle exercise to be an exceptional effort
- Insufficient fibre intake and therefore constipation
- Headaches and tiredness due to low blood glucose levels
- Bad breath due to the breakdown products of fat (ketones), and
- Negative mood (e.g., grumpiness).
A real concern with very low carbohydrate diets is the potential for adverse cardiovascular outcomes. High saturated fat intake is usually part and parcel of nearly all very low carb diets. Even a single meal high in saturated fat can have an adverse effect on blood vessels by inhibiting vasodilation, the normal increase in the diameter of blood vessels that occurs after a meal. A short-term and long-term effect of most low carb diets includes an increase in LDL cholesterol. Compounding this, there may be a low intake of micronutrients that are protective against disease. For this reason, a vitamin and mineral supplement is an essential accompaniment to most low carb diets.
To ensure that blood glucose levels can be maintained between meals, your body draws on the glucose stored in the liver; that form of glucose is called glycogen. Supplies of glycogen are strictly limited and must be replenished from meal to meal. If your diet is low in carbohydrate, your glycogen stores will be low and easily depleted.
26. I have heard that a person’s glucose tolerance may vary from day to day by as much as two-fold. How come? Is the GI still relevant?
Why a person’s glucose tolerance varies is not clear, but we can point to varying pancreatic beta-cell responsiveness and insulin sensitivity, both factors that are beyond anyone’s control. The beta cells just work better on some days than on others. This variability among and within people must be managed carefully to detect true differences in the glycemic potential of the carbohydrates in different foods. This variability is actually less in people with diabetes, than in those without.
A person with diabetes however can be confident that a high GI food (GI value of 70 or more) will produce a significantly higher glycemic response than a low GI food (GI value of 55 or less) 95 per cent of the time. Just as the height of high tide and low tide varies from day to day and place to place, we still know that high tide will be higher than low tide on any one day at any one place. It’s not the absolute level, but the difference, that’s important.
That’s why GI testing has such a strict protocol. Ten subjects are used, each of whom is given the reference food (glucose) on three separate days. Each time, the overall fluctuation in their blood glucose is determined by measuring it eight times over a period of two hours. The findings from those three days of testing are averaged to find each person’s usual response to the reference food, glucose. Next, his or her glycemic response to the test food is measured once, using the same two-hour testing protocol. Then each person’s response to the test food is expressed as a percentage of their average response to the reference food. Finally, the relative responses of all ten subjects to the test food are averaged. This is the published GI value. The GI value of bread (70) means that the overall fluctuation in blood glucose after eating an exchange of white bread will be about 70 per cent of the effect of pure glucose (GI value of 100).
By taking the average of ten subjects, each of whom has undergone this painstaking process, we are simultaneously compensating for both within-subject and between-subject variability. If we were to test white bread over and over again using this protocol, we’d get the same result: a GI of 70.
27. What about the GI of mixed meals and the effect of extra protein and fat in the food?
The GI was introduced back in 1981 to rate the glycemic character of the carbohydrate in individual foods like bread, breakfast cereal, rice, pasta, apples etc. The purpose was to exchange one carbohydrate source with another in your meals and snacks (e.g. replacing a high GI breakfast cereal like corn flakes with a low one like natural muesli). The decision behind the cut-offs for rating high GI (70 or higher) and low GI (55 or less) foods, was based on the spread of GI values among the single foods that had been GI tested.
Increasingly we are asked about the GI of mixed meals and the effect of extra protein and fat in the food on GI and blood glucose response. Eaten alone, protein and fat have little effect on blood glucose levels, but that’s not to say they don’t affect your blood glucose response when they are combined with a carbohydrate-rich food. Protein will stimulate additional insulin secretion, resulting in lower blood glucose levels. Protein and fat both tend to delay stomach emptying, thereby slowing the rate at which carbohydrate can be digested and absorbed. So, a high fat meal will have a lower glycemic effect than a low fat meal even if they both contain the same amount and type of carbohydrate.
We believe there’s a real need to define the difference between a low GI diet and/or meal and a low GI food. Because a low GI food is defined as 55 or less, everyone has made the reasonable assumption that a whole diet that averages 55 or less is a low GI diet. In fact, the average Australian and American diets already have a GI of around 55–60 because we eat fruits and dairy foods which are naturally low GI. So, to reduce the risk of chronic disease, we believe we need to aim lower and suggest that 45 is a better cut-off point for a low GI diet.
Why 45? Well, we know from numerous observational cohort studies around the world that the daily average GI of the diet of people in the lowest quintile (20% of the population) is about 40–50. Similarly, in a meta-analysis in Diabetes Care of 15 experimental studies investigating the role of low GI diets in managing diabetes, the daily average GI was 45. Since this average GI has been proven to have significant health benefits in people with existing diabetes and in reducing the risk of chronic diseases like heart disease and diabetes, and importantly, people can and do achieve it in real life, we believe a GI of 45 or less is what we all need to be aiming for.”
28. I am vegetarian. Can you give me some tips on which low GI plant foods provide protein and how much?
Building your diet around plant foods such as wholegrains, legumes, fruits and vegetables, nuts and seeds can give you all the nutrients including protein you need for long-term health and wellbeing.
Beans, peas and lentils
½ cup (150 g) baked beans in tomato sauce (GI 49) provides an average of 7 g protein
½ cup (130 g) canned, drained cannellini beans (GI 31) provides an average of 8 g protein
⅔ cup (125 g) cooked red lentils (GI 26) provides an average of 12 g protein
1 cup (180 g) cooked split peas (GI 25) provides an average of 12 g protein
1 cup (170 g) cooked soy beans (GI 18) provides around 23 g protein
100 g (3½ oz) tofu provides around 10 g protein (GI not relevant as tofu contain no carbohydrate)
1 cup (250 ml) light soy milk (GI 44) provides around 7 g protein
Grains and grain foods
¾ cup (30 g) Kellogg Special K original (GI 56) provides around 6 g protein
¾ cup (45 g) Kellogg All-Bran (GI 44) provides around 7 g protein
¼ cup (30 g) uncooked traditional rolled oats (GI 57) provides around 3 g protein
1 slice (35 g) Tip Top 9-grain Original bread (GI 53) provides around 4 g protein
1 slice (40 g) Burgen Soy-Lin bread (GI 52) provides around 6g protein
1 cup (170 g) cooked brown rice (GI 59–86, so check the tables and choose a low GI one) provides around 5 g protein
1 cup (170 g) cooked basmati rice (GI 58) provides around 4 g protein
1 cup (180 g) cooked pasta (GI 35–54) provides around 6–7 g protein
1 cup (180 g) cooked fresh rice noodles (GI 40) provides around 2–3 g protein
1 cup (180 g) cooked soba/buckwheat noodles (GI 46) provides around 7 g protein
1 cup (190 g) cooked pearl barley (GI 25) provides around 4–5 g protein
½ cup (90 g) cooked quinoa (GI 53) provides around 4.5 g protein
Nuts and seeds
A small handful (30g/1oz) of most nuts or seeds will deliver around 5 g protein (GI not relevant as most nuts and seeds contain almost no carbohydrate, they are rich in good fats)
Stock your pantry with legumes, wholegrains (such as grainy breads, muesli, quinoa, amaranth, brown rice, pearl barley and rolled oats), nuts (particularly almonds, Brazil nuts, cashews and peanuts), and seeds (sesame seeds, tahini paste, and pumpkin seeds). They are also good sources of iron and zinc typically sourced from protein-rich foods.
29. What is the Insulin Index
When we consume carb-rich foods, our bodies convert their sugars and starches to glucose, but it converts them at very different rates. Some foods break down quickly during digestion, and the glucose in the bloodstream increases rapidly; others break down slowly, and the glucose is released gradually into the blood. And, of course, there are moderates.
The glycemic index or GI is a numerical ranking that provides a good indication of how fast the body is going to digest, absorb, and metabolise carb foods that have been tested following the international standard.
But the GI is only part of the story. It can only measure carb-containing foods and it’s not always proportional to the insulin response to a food. When our blood glucose levels rise, our pancreas releases insulin (a hormone) that drives the glucose out of our bloodstream and into our body’s cells where our body can use it as an immediate source of energy or store it as glycogen.
Enter the food insulin index or FII which scientists at the University of Sydney have been researching for almost 20 years. “The FII looks at how much insulin the body normally releases in response to a whole food or meal (its carbohydrate and the quantity and quality of its protein and fat). Some foods need more insulin to help utilise them, while other foods need much less. Choosing foods with a lower FII can help reduce your overall insulin demand on your pancreas or insulin requirements,” says dietitian and diabetes educator Dr Kirstie Bell.
Despite all their best efforts, some people with type 2 diabetes have trouble managing their blood glucose. In a recent study in the American Journal of Clinical Nutrition, University of Sydney researchers found that the FII may be an additional tool for people with type 2 diabetes to help them reduce postprandial hyperinsulinemia and improve insulin resistance and beta cell function. Here are some tips to help people with diabetes achieve that:
- Balance meals with some carbs, lean protein and plenty of salad or vegetables as all foods stimulate some insulin response.
- Opt for lower FII carbohydrates such as pasta and noodles over higher FII ones such as white rice and regular cous cous when it comes to putting starchy carbohydrates on the dinner plate.
- Choose higher fibre, less processed breads and cereals, such as dense grainy bread and traditional porridge oats.
- Snack on fruit and non-starchy vegetables as they are low FII and packed with vitamins and minerals.
- Pick lean cuts of red meat, chicken or fish and team them with lots of non-starchy veg and/or salad. Processed meats like bacon and sausages may have a lower FII, but their high saturated fat content makes them a much less healthy choice.
30. Many of the studies you write about in your newsletter, GI News, talk about “insulin resistance” and “insulin sensitivity”. Can you explain these terms in a really simple way?
Insulin is a hormone that plays several critical roles in our health and wellbeing. It’s been called the master hormone because it regulates so many things, including our blood glucose levels. When we eat carbohydrate-rich foods like bread, breakfast cereals, pasta, rice or noodles, or starchy vegetables like potatoes and fruit, our body converts them into a glucose (a sugar) that is absorbed from the intestine and becomes the main fuel that circulates in our blood. When glucose levels in the blood rise after a meal, the beta cells in the pancreas move insulin out into the bloodstream to drive the glucose into the cells so it can be put to work either as an immediate source of energy or converted to glycogen (a stored energy source), or to fat.
You are what’s called ‘insulin sensitive’ – a good thing – if you require relatively little insulin to process your BGLs (blood glucose levels).
On the other hand, if your body needs to secrete a lot of insulin into the blood, you have “insulin resistance”. We sometimes describe it as your body being “partially deaf”, to insulin. Think of it like this: just as we may shout to make a deaf person hear, the body needs to make more insulin to drive glucose where it’s supposed to go. So, moving glucose from the blood into cells necessitates the release of large amounts of insulin.
How can you optimise your insulin sensitivity and decrease insulin levels over the whole day? A healthy low GI diet plus physical activity are the most powerful ways to do this, as numerous studies have shown. The Diogenes study looked at the effects of diets with different protein content and glycemic index on prevention of weight re-gain in overweight adults and found that an “increase in dietary protein and a reduction in GI content over a 6-month ad libitum dietary intervention was related to a lower drop-out rate and produced favourable effects on glycemic control and insulin sensitivity in overweight/obese subjects after an initial body-weight loss.”