Until mid-1970s people believed that equal portions of different carbohydrates generated the same blood sugar levels. Studies conducted by Phyllis A. Crapo, a Californian researcher from Stanford University, and his colleagues in 1976 have shown that carbohydrates having the same pure sugar/starch content did not necessarily have the same impact on blood sugar levels.
A carbohydrate’s potential to raise blood sugar levels and how it rates in comparison to other carbs should be taken into consideration when investigating the link between the level of carbohydrates and blood sugar levels. This is how the idea of a glycemic index and glycemic load came into being. What is the difference between them?
What is the GI?
The GI is the measurement of the ability of a food to raise blood glucose (sugar) lever after its consumption. How is the GI determined? By such factors as the used cooking method, presence of protein and fats – generally speaking nutrients- and the extent to which the food has been processed. Based on the measurements obtained, food has been divided into three main groups, of a low, medium and high GI.
The GI index runs from 0–100 and usually uses glucose, which has a GI of 100, as the reference. Slowly absorbed carbohydrates have a low GI rating (55 or below), and include most fruits and vegetables, some wholegrain cereals and bread. Low GI means that carbohydrates in the food consumed that break down slowly during digestion, release blood sugar gradually into the bloodstream, and keep blood sugar levels steady.
A medium GI (56-69) include pineapple, pinto beans or black beans. It means that the carbohydrates will break down moderately during digestion and release blood sugar moderately into the bloodstream.
A High GI (more than 70) includes white bread, backed potatoes, chips, crisps, pizza and all the highly processed fast-food.
High GI food means that carbohydrates that break down quickly during digestion release blood sugar rapidly into the bloodstream. This causes rapid fluctuations in blood sugar levels.
What is the GL?
However, it is said that glycemic load (GL) is a more predictable indicator of how food affects the level of blood sugar and insulin. This is because it takes into account the amount of carbohydrates in a food portion. Some food even though have a low GI have a large amount of carbohydrate what would lead to a high increase of sugar in the bloodstream and , consequently, high level of insulin.
Why are the GI and the GL (especially the latter!) so important in the PCOS diet plan and why we should be aware of them when preparing our meals?
Importance of the GL for PCOS women
During digestion glucose is realised into the bloodstream. As a result a hormone insulin is produced which main role is to transport glucose to muscle cells and our brain. A steady release of glucose during digestion is something our body can handle, however, our body’s regulatory system goes into overload.
The result of it is large amounts of insulin to be able to clear the glucose away into the body cells. High level of insulin makes us feel hungry. It increases our desire to eat more carbs (especially something sweet!) which are stored away in our fat cells. Frequent high level of insulin in our bloodstream results in weight gain and accumulation of fat tissue, especially around the waist.
Moreover, if it happens over a long period of time it can cause severe damage to our cells and lead to insulin resistance – our cells will become less sensitive to insulin. Research has shown that high insulin level, high GI food and insulin resistance are linked to Type 2 diabetics and can lead to heart disease, high blood pressure, high level of cholesterol, some types of cancer or premature ageing.
Because PCOS is a metabolic disorder caused by the lack of hormonal balance and often insulin resistance, it means that our bodies are having difficulties with transporting glucose from the bloodstream into cells. Eating food of high GI (sweets, cookies, white bread or rice) increases our blood sugar and insulin level what can result in intensifying the symptoms of PCOS.
Therefore, eating food that causes a slow and steady rise of insulin – so-called low GI food – is much more beneficial for PCOS women. The feeling of constant hunger can be delayed and calorie intake can be better controlled. Low GI and GL diet can improve the sensitivity of our cells to insulin.
How to calculate the GL?
So how does it work in practice? How do I know what I should eat and what to avoid. You can use the GI and GL tables that are available online . For instance, Glycaemic index (GI) and glycaemic load (GL) values determined in subjects with normal glucose tolerance (2008) or Glycaemic index and glycaemic load for 100+ foods (Harvard Medical School). You can also calculate the GL by yourself. Below we present a few examples that will help you to understand how the GL is calculated.
This is how we calculate GL values:
GL = GI x carbohydrate per portion by weight(g) / 100
We would like to know GL of cabbage. We know from the GI tables that the GI for cabbage is 10 which is low. The percentage of carbohydrate per portion by weigh is 5.8. If we multiply 10 by 5.8 and then divide by 100, we obtain the GL of 0.58 which is very low. Cabbage has both a low GI and a low GL and, therefore, eating it is very beneficial for PCOS women.
Cabbage (100) = 10 x 5.8g / 100 = 0.58
Should PCOS women eat then watermelon? It has a high GI (75) what means that our blood sugar will increase, however the amount of carbohydrates per portion is low (8g) what should not result in an increased need for insulin. Eating a portion of watermelon would not be as bad as we might have thought.
Watermelon (GL) (100g) = 75 x 8g /100 = 6 (low GL)
A different story is with bananas:
Banana (100g) = 72 x 22 g /100 = 15.84 (high GL)
The level of glucose after eating a banana is high (high GI = 72). Moreover, a banana has lots of carbohydrates (22g). Its consumption would quickly increase the level of glucose in the blood stream and consequently produce loads of insulin.
Therefore, it might be a good idea to replace bananas by berries, raspberries, strawberries or blackberries in your diet. They have a much lower GL.
What about vegetables? Do all vegetables have a log GL? The answer is ‘No’. However, the GL of some of them depend on their preparation method. For example, raw carrot has a low G but cooked carrot – a high GL. Potatoes, beetroots or corn have also high GL. I does not meant that you cannot ever eat them but rather that you should consume them with moderation.
To summarise the above principles of GI and GL we can identify the following combination of food:
- Low GI and low GL – yes, this is the type of food you should eat.
- Low GI ad high GL – this type of food eater in large quantities can significantly raise glucose in your blood if they are concentrated sources of carbohydrates
- High GI and low GL – contain small amount of carbohydrates per portion so they will not significantly affect the level of glucose . However, we should eat them together with other high GI or GL foods
- High GI and high GL – these need to be avoided and high increase of blood sugar and, consequently, insulin is guaranteed. They will make you fat!
The GI and GL indexes are very helpful when preparing your meals. However, we need to remember that not all low GL food is good for PCOS women. Even though diary products have low GI and GL values we should avoid them. In my next blog posts I will explain why.