Glycaemic Goals : Be Clever With Carbs
Updated: Nov 5, 2019
Dietary carbohydrates ('carbs') have been demonised in the last decade following the popularity of high fat and high protein diets for weight loss. Fat itself endured decades of bad publicity. However, it seems to have been let off the hook in recent years due to the new belief that carbohydrates may be ‘worse than saturated fats’ for cardiovascular disease (CVD) risk. Indeed, there is some truth in this… But only if you over simplify the recent scientific findings, in the same way the fad diet and food industries did to fat all those years ago. CVD risks increase when saturated fats are substituted solely by refined, low fibre, high glycaemic carbohydrates. Often the same carbohydrates that were added to “low fat diet” foods and the most commonly consumed sources of carbohydrate in developed countries such as the UK. So, lets learn from the mistakes we made with fat and look at the facts in more detail this time aye.
Horses for Courses
There are no “bad” foods. Except for maybe trans fats, no-one likes those jabronis. However, there is such a thing as a bad time to eat certain types of foods and high glycaemic load carbohydrates fall into that category. Whilst you wouldn’t want to eat high glycaemic carbohydrates close to bed time or as a main source of fuel throughout the day. They can be particularly useful when eaten post exercise or first thing in the morning to restore liver glycogen (carbohydrate reserves). Moreover, they can be vital for performance in endurance sports and for acute recovery in-between multiple bouts of activity in a short period of time i.e. tennis tournament.
What is a High Glycaemic Index / Load Carbohydrate?
The three main groups of carbohydrate are sugars, starch and fibre. Sugars are often called fast release carbs because their simple structure enables them to be digested, absorbed and converted into readily available energy at a relatively fast rate. Comparatively, starches are commonly known as slow release carbs because they are digested, absorbed and converted into readily available energy at a more prolonged and sustained rate due to their complex structure.
"The glycaemic index is a rating of the potential blood glucose response onset by the particular food."
In truth, to accurately understand how the carbohydrate in your food is going to effect your energy levels, we must look at the food as a whole. Take an apple, apple juice and apple flavoured confectionery as an example. All contain the same simple carbohydrate, a sugar called fructose. However, the fructose in the apple juice is free in a solution. Fruit juices and other foods (e.g. syrup, honey, cane sugar) that contain "free sugars" such as this cause a sharp rise in your blood sugar levels. This is what’s known as a high blood glucose response. A high blood glucose response will also occur following the consumption of the apple flavoured confectionery or other foods (e.g. soft drinks, breakfast cereals, baked goods, sauces, jams) that have "free sugars" added to them. Alternatively, the fructose within the apple is contained within the cellular walls of the food. Dietary fibre constitutes to a great proportion of these cell walls. A high fibre content both enables the food to be digested at a slower rate and decreases the concentration of sugars found within a food. This in turn creates a more stable and sustained rise in your blood sugar levels or in other words, a lower blood glucose response. The glycaemic index is a rating of the potential blood glucose response onset by the particular food.
"Glycaemic load of a food = glycaemic index × available carbohydrate ÷ given amount of food."
Dietary fats also have the potential to lower blood glucose response because like fibre their presence within a food is likely to decrease the concentration of sugar. The same can also be said for foods that contain mainly the slow release complex carbohydrate, starch (e.g. bread, pasta, rice, potatoes and other tubers). However, when eaten in their average serving size many of these foods have a high blood glucose response. This is what’s known as a high glycaemic load. Glycaemic load of a food = glycaemic index × available carbohydrate ÷ given amount of food. Glycaemic load is the most accurate measurement for the blood glucose response of food.
So, by now you’re probably wondering why the glycaemic load of a food and its ability to raise the level of your blood sugar is important. The sugar in your blood (glucose) is used to provide the cells in your body with energy. It is also stored in your liver and muscles for later use. Excess will be converted and stored as body fat. A hormone called insulin is required for all these things to happen. Insulin is released by your pancreas into your blood to transport the sugars into your cells via receptors. Foods with a high glycaemic load cause rapid peaks and troughs in your energy levels. The troughs cause your body to crave more energy, usually in the form of sugars. This promotes an excess intake of energy dense foods. The excess sugars are stored as body fat and excess levels of insulin are released to remove the sugar from your blood. Overtime this excess insulin can cause the insulin receptors to become damaged. This is what’s known as insulin resistance and it is the precursor to type 2 diabetes and you guessed it... Type 2 diabetes is associated with comorbidities such as CVD.
The Take Away Message
To optimise insulin sensitivity and avoid insulin resistance consume a diet rich in high fibre foods (e.g fruits, vegetables and whole grains). For those of us that aren't high level athlete's looking to optimise performance, sugar dense foods offer little benefit and therefore should be eaten in moderation. As should all foods with a high glycaemic load.
Listing the glycaemic load of specific foods is beyond the scope of this short blog post. However, with a quick search you will discover many books and online databases that provide this service. Aston, et al (2010) CSV spreadsheets offer a particularly extensive list of UK, Spanish, Greek, German, Dutch, Danish and Czech foods.
Aston, L. M., Jackson, D., Monsheimer, S., Whybrow, S., Handjieva-Darlenska, T., Kreutzer, M., . . . Lindroos, A. K. (2010). Developing a methodology for assigning glycaemic index values to foods consumed across Europe. Obesity reviews : an official journal of the International Association for the Study of Obesity, (1):92-100. doi: 10.1111/j.1467-789X.2009.00690.
Augustin, L. S., Kendall, C. W., Jenkins, D. J., Willett, W. C., Astrup, A., Barclay, A. W., . . . Poli, A. (2015). Glycemic index, glycemic load and glycemic response: An International Scientific Consensus Summit from the International Carbohydrate Quality Consortium (ICQC). Nutrition, metabolism, and cardiovascular diseases : NMCD, (9):795-815. doi: 10.1016/j.numecd.2015.05.005.