I've read that while fats slow down the body's response to high GI foods, the body still sees the same level of glucose response from the food, just over a considerably longer period of time (which is perhaps not accounted for when doing GI testing). Is this true?
No, this isn’t true. Fats do slow down digestion and reduce overall blood glucose levels, even if we continued testing beyond 2 hours. But you need the same amount of insulin, possibly more because excess fat intake makes you insulin resistant. The bottom line: choose a diet of 25–35% energy from fats. Good fats of course. We published a paper in 2004 on it in the American Society for Nutritional Sciences entitled: ‘The degree of fat saturation does not alter glycemic, insulinsemic or satiety responses to a starchy staple in healthy men’.
What about a glossary? I'm familiar with glycemic index, glycemic load, and a few other ‘normal’ GI terms, but when I start reading terms like ‘glycemic response’ or ‘glycemic impact’ I begin to wonder whether I know anything at all.
We try where possible to turn the science into everyday language, but sometimes terms are quite specific so a glossary is a great idea. We’ll start with the ‘GI terms’ you raise and keep building the glossary over the next few issues. When it’s completed, we’ll post it on the website as a ready reference.
Glucose When you eat carbohydrate foods such as bread, cereals and fruit, your body converts them to glucose (a monosaccharide sugar that’s present in most animal and plant tissues) during digestion. It is this glucose that is absorbed from the intestine and becomes the fuel that circulates in the bloodstream. As the level of blood glucose rises after you have eaten a meal, your pancreas gets the message to release insulin which then drives the glucose out of the blood and into the cells. Once inside the cells it is channelled into several pathways simultaneously – to be used as an immediate source of energy, converted into glycogen (a storage form of glucose) or into fat.
Blood glucose (blood sugar) is the amount of glucose in the blood stream. If you haven’t eaten in the past few hours (and you don’t have diabetes), your blood glucose level normally falls within the range of 3.5–6 mmol/L. If you eat, this will rise, but rarely above 10 mmol/L. The extent of the rise will vary depending on your glucose tolerance (your own physiological response) and the type of food you have just eaten. Although blood glucose levels will fluctuate over the course of the day, they will normally remain with this fairly narrow range. Keeping levels within the normal range is important for your health whether you have diabetes or not.
The test that measures your average blood glucose level over the past 2–3 months has a variety of names. It’s mostly described as HbA1c (hemoglobin A1c or glycated hemoglobin). It indicates the percentage of hemoglobin (the part of the red blood cell that carries oxygen to the cells and sometimes joins with glucose in the bloodstream) that is ‘glycated’. Glycated means has a glucose molecule riding on its back. This is proportional to the amount of glucose in the blood. The higher the level of HbA1c, the greater the risk of developing diabetic complications. People with diabetes should aim to keep their HbA1c at or less than 7%.
Glucagon Between meals your blood glucose levels will start to fall. As this happens, the pancreas releases the hormone glucagon into the blood. This hormone promotes the conversion of glycogen stored in the liver and muscles to glucose and raises your blood glucose level to keep it within the normal range.
Glycemia is the concentration of glucose in the blood. Hence the adjective, glycemic.
Glycemic Index (GI) Different carbohydrate foods can behave quite differently in your body. Some break down quickly during digestion and release glucose rapidly into the bloodstream; others break down gradually as you digest them and slowly trickle glucose into the blood stream. The glycemic index or GI, a relative ranking on a scale of 0 to 100, is how we describe this difference. After testing hundreds of carbohydrate foods around the world, scientists have found that foods with a low GI will have less effect on your blood glucose than foods with a high GI. High GI foods tend to cause spikes in your glucose levels whereas low GI foods tend to cause gentle rises. To make a fair comparison, all foods are compared with a reference food and tested following an internationally standardised method.
Glycemic Load (GL) How high your blood glucose actually rises and how long it remains high when you eat a meal containing carbohydrate depends on both the quality of the carbohydrate (its GI) and the quantity of carbohydrate in the meal. Researchers at Harvard University came up with a term to describe this: glycemic load. It is calculated by multiplying the GI of a food by the available carbohydrate content (carbohydrate minus fibre) in the serving (expressed in grams), divided by 100.
GL = GI/100 x available carbs per serving.
Glycemic potential A food or meal’s predicted blood glucose raising effect.
Glycemic response or glycemic impact describes the change or pattern of change in blood glucose after consuming a food or meal. Glucose responses can be fast or slow, short or prolonged. It is primarily determined by the food’s carbohydrate content. Other factors include how much food you eat, how much the food is processed and even how the food is prepared (for example, pasta that is cooked al dente has a slower glycemic response than pasta that is overcooked).
Glycogen is the name given to the glucose stores in the body. It can be readily broken down into glucose to maintain a normal blood glucose concentration. In an adult male, approximately two-thirds of the body’s glycogen is found in the muscles and one-third in the liver. The total stores of glycogen in the body are relatively small however, and will be exhausted in about 24 hours during fasting or starvation.
Hypoglycemia (also called an insulin reaction) occurs when a person’s blood glucose falls below normal levels – usually less than 4 mmol/L. People with diabetes know all about it. Hypoglycaemia is treated by consuming a carb-rich food such as a glucose tablet. It may also be treated with an injection of glucagon if the person is unconscious or unable to swallow. If you don’t have diabetes, but you have vague health problems ranging from tiredness to depression and think you may have hypoglycemia or someone tells you that you probably have ‘low blood sugar’, see your doctor and get a proper diagnosis. Hypoglycemia is far less common that once was thought in people who do not have diabetes.
Impaired glucose tolerance is sometimes called pre-diabetes or impaired fasting glucose. It is a condition in which blood glucose levels are higher than normal, but are not high enough for a diagnosis of diabetes. People with impaired glucose tolerance are at increased risk of developing diabetes, heart disease and stroke.
Insulin is a hormone produced by the pancreas that helps the body use glucose for energy. Although the body needs glucose, it doesn’t want it all in one hit, so it pumps out insulin to drive the glucose out of the blood and into the tissues. The pancreas should automatically produce the right amount of insulin to move glucose into the cells. People with type 2 diabetes do not always produce enough insulin. People with type 1 diabetes produce no insulin at all. When the body cannot make enough insulin, it has to be taken by injection or through use of an insulin pump. It can’t be taken by mouth because it will be broken down by the body’s digestive juices.
Insulin is not only involved in regulating blood glucose levels, it also plays a key part in determining whether we burn fat or carbohydrate to meet our energy needs – it switches muscle cells from fat burning to carb burning. For this reason lowering insulin levels is one of the secrets to life-long health.
Insulinemia simply means the presence of insulin in the blood; hyperinsulinemia is excessive amounts of insulin in the blood.
Insulin resistance When insulin levels are chronically raised, the cells that usually respond to insulin become resistant to its signals. The body then responds by secreting more and more insulin, a neverending vicious cycle that spells trouble on many fronts. Insulin resistance is at the root of diabetes, many forms of heart disease, and polycystic ovarian syndrome (PCOS).
Insulin sensitivity If you are insulin sensitive, your muscle and liver cells take up glucose rapidly without the need for a lot of insulin. Exercise keeps you insulin sensitive: so does a moderately high carbohydrate intake.
I have heard that the GI of sugar is 67 – is this true? Are NutraSweet or Splenda considered as being low GI?
In our online database, regular table sugar is listed under the scientific name ‘sucrose’, not as ‘sugar’. But point taken and we’ll see what we can do to get it cross referenced to make it easier to use the database. Sucrose has been tested on a number of occasions and has an average GI of 68. You can add a teaspoon of sugar to your tea or coffee without upsetting your blood glucose levels. For lower GI sweeteners, try a pure floral honey, 100% pure maple syrup, apple juice, grape nectar, or Sweet Cactus Farms agave nectar, or fructose sweeteners such as such as Sweetaddin® or Fruisana®.
Dietitian Alan Barclay of the GI Group says: ‘If you are trying to lose weight or reduce your insulin or oral hypoglycemic medications, alternative sweeteners can be handy. There are numerous brands, but essentially just two main types:
- nutritive sweeteners
- non-nutritive sweeteners
Non-nutritive sweeteners (such as Equal®, Splenda®, NutraSweet® or saccharin) are all much sweeter than table sugar and have essentially no effect on your blood glucose levels because most are used in such small quantities and are either not absorbed into or metabolised by the body. Because they are only used in minute amounts, the number of kilojoules they provide is insignificant. The best non-nutritive sweeteners to cook with are Splenda®, saccharin and Neotame®, and to a lesser extent Equal Spoonful®. This is because the non-nutritive sweeteners made of protein molecules often break down when heated for long periods and lose their sweetness.’
Why is there no information about stevia?
Stevia (Stevia rebaudiana), native to South America, first came to the attention of the Western world in the 1800s, but remained relatively obscure until it was used as an alternative sweetener in the UK during the Second World War. It’s not widely available. The leaves of this semi-tropical herb of the aster family are around 30 times sweeter than cane sugar but with no kilojoules (calories). As a herb, they can be used fresh or dried. In the dried form less than 2 tablespoons of crushed leaves can replace a cup of sugar, although it's hard to be specific as actual sweetness can vary. Stevioside, its extract, is 250–300 times sweeter than sucrose and is not approved for use as a food in Australia but is listed as a 'therapeutic good' with the Therapeutic Goods Administration. You can buy the herb, stevia leaf powder, online from specialty spice merchants such as Herbies Spices (www.herbies.com.au). Herbie (Ian Hemphill) has a couple of hints for using stevia. He says: ‘use sparingly as there is a bitter aftertaste if too much is added to food. Because stevia does not have the same properties of sugar, it is not suitable as a sugar substitute when baking.’
I read that people just trying to lose weight or eat more healthily should use GL, but people with insulin resistance (like me) should use GI. Is this true?
Our advice is to stick with the GI in all but a few instances. When you choose low GI carbs you’re invariably getting a healthy diet with an appropriate quantity and quality of carbohydrate. Portion size still counts, though. And this is where low GI foods are star performers – the foods with the lowest GI values also have the best fill-up factor. If you listen to your true appetite, you are far less likely to overeat when you are choosing low GI foods.
GL doesn’t distinguish between foods that are low carb or slow carb. Going with GL could mean you’re eating an unhealthy diet, low in carbs and full of the wrong sorts of foods. So the take home message is to use GI to identify the best carbohydrate choices and take care with portion size to limit the overall GL of your diet.