Glycemic Load and Glucose Control
Glycemic load and glycemic index are two buzz phrases that you may have heard in magazines, diet columns and TV shows. These terms may sound technical and rather confusing to understand, however, it is rather simple. So you want to know what is the difference between glycemic load and index? However, first we need to understand what glycemic index is.
The first thing you will have to understand is what “glycemic index” actually means. Glycemic index (GI) is the effect of glucose (sugar) content of food on the body’s blood sugar concentration. Simply, the higher the sugar content of a piece of food, the bigger the effect on the body’s blood sugar concentration. GI has three different levels;
- Low (good): A GI lower than 55.
- Medium (OK): A GI between 55-70
- High (bad): A GI over 70.
It is not just plain sugars that effect GI, any foods that contain carbohydrates and starches will increase GI. For example; a chicken breast would have a lower GI than raspberry jam for instance.
Carbohydrates are long chains of sugars, which can very in length and type of sugar. Preliminary digestion of carbohydrates begins in the mouth, which is why if you suck on a piece of bread long enough it will begin to taste sweet. However, the main carbohydrate metabolism occurs in the duodenum of the small intestine under enzymatic control.
Once these carbohydrates are in the duodenum they are broken into smaller chains of either single glucose molecules or two sugar chain (as seen right). Glucose is then absorbed from the small intestine through, transporter proteins called SGLUT-1 and into the body’s blood supply. Once sugars are in the body’s blood supply, sugars are transported to the liver where they are then sent around the body to be used by cells, stored in the liver or transformed into fats and stored as adipose tissue (fat tissue). Sugars are very common and found in pretty much every food, but there are different types of sugars that are unique to different foods.
- Glucose; the simplest of all sugars, found in all foods.
- Fructose; found primarily in fruits.
- Galactose; found primarily in milk.
- Lactose; a combination of galactose and glucose, chained together. Found in milk and makes up 2-8% of milk products.
- Maltose; two glucose molecules attached together. Found in beers, cereals and pastas.
Glycemic load (GL) is the estimated impact of the total carbohydrate makeup of your food item. This is calculated by using the following formula.
- (GI score) x (carbohydrates in grams) /100=GL
One GL unit represents 1g of sugar that will be deposited into your blood system once the food is consumed. A food that has a GL score of over 20 is considered to be high. GL can vary from breed, the food’s origin and how the food is prepared. For example there are many different types of potatoes; King Edward, New, Russet, Yukon Gold, Russian Banana and many more. There are also many ways to prepare potatoes, they can be fried, boiled, baked, mashed, or putting them in a stew…. When it comes to the potato, covering the potato in fat reduces the glycemic load as the total grams of carbohydrates available decreases. GL decreases as the amount of carbohydrates available to be absorbed into the body decreases. Mashing potatoes has a higher GL than fried potatoes because you break down the cells inside the potato in the mashing process and expose more readily absorbed carbohydrates compared to plainly boiling the potato instead. Like GI, GL has a scale;
- Low (good); GL score lower than 10
- Med (OK); GL score between 11-20
- High (bad); Gl score over 20
It is possible for a food to have a high GI score but a low GL score. Watermelon is the most popular example because it has a high GI but a very low GL. This is because when a food has high GI score it contains sugars that are easily absorbed, which causes a spike and then a large dip in the body’s blood sugar (this what can make you feel tired after a big meal or sugary treats). Watermelon is a paradox in way, where you will get the spike and dip in blood sugar, however this is so small that you would not even notice it. What gives watermelon such a low GL score is that the water content is much larger than the sugar content and you end up ingesting more water than sugar (plus other good bits like anti-oxidants and vitamins).
Monitoring GI and GL for Health
GI can be a useful tool when you are trying to loose weight or trying to maintain a healthy weight. High GI diets have shown to promote weight gain and over secretion of insulin, which can lead to a decrease in insulin sensitivity (which is a risk factor for type 2 diabetes) when exposed to long periods of high blood sugar. Foods with a high glycemic load have shown to increase the risk of heart disease as well.
Furthermore, consuming foods with a high glycemic load increase the chances of succumbing to the post meal slump as the body over corrects itself to deal with high blood sugar concentration, which makes you crave sugary and fatty foods. For a non-diabetics blood sugar concentration should be between 3.9 and 5.5 mmol/L (70 to 100 mg/dL).
However, there are some downsides to following a low GI diet. Foods that do have a high glycemic index are foods like fruits which would need to be limited to someone who was on a low GI diet. GI is just an estimate of how the food item is going to effect the general population, however you may be the exception and certain foods may effect you more or less than other people. To properly use this system people should be concentrating on GL rather than GI. However, using GL may be too tricky to use as you will need to know the GI score, the carbohydrate content of the foodstuff, and you will have to use the formula above to calculate the GL.
That may have seemed a little confusing towards the end but people do use this to great effect. People with diabetes use a similar scheme to count carbohydrates to estimate how much sugar they are going to ingest so they can pre-inject to avoid highs or lows in their blood sugar. There is a website you can use to check the GI and the GL of the foods you consume. In this post I have figures from the University of Sidney. The list is rather extensive and useful so you should go and check it out and plan your low GL meals for next week.
If you have any comments of questions regarding GI and GL please feel free to leave a comment below.
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Griffith, J., Ma, Y., Chasan-Taber, L., Olendzki, B., Chiriboga, D., Stanek, E., Merriam, P. and Ockene, I. (2008). Association between dietary glycemic index, glycemic load, and high-sensitivity C-reactive protein. Nutrition, 24(5), pp.401-406.
Ludwig, D., Majzoub, J., Al-Zahrani, A., Dallal, G., Blanco, I. and Roberts, S. (1999). High Glycemic Index Foods, Overeating, and Obesity. PEDIATRICS, 103(3), pp.e26-e26.