The Glycaemic Secret
What is the Glycaemic Secret?
It’s likely you’ve heard of the glycaemic index and terms like ‘high GI’ and ‘low GI’ but possibly been left wondering what do they really mean and how can you best use them to support your own weight loss goals?
Understanding and applying the principles of the glycaemic index (or GI for short) and, just as importantly, the glycaemic load (or GL) is key to maintaining healthy blood sugar and insulin levels which, in turn, supports a healthy weight and energy.
So what is the difference between GI and GL?
Glycaemic Index - GI
The glycaemic index (GI) rates carbohydrates according to how quickly they raise blood sugar levels over a period of time – usually two hours. The GI compares foods that have the same amount of carbohydrate, gram for gram, and are compared against glucose or white bread as a reference food - which is given a GI score of 100.
This means food with a glycaemic index of 95 raises blood sugar (and insulin!) almost as much as pure glucose, but a food with a glycaemic index of 20 doesn't raise blood sugar much at all. Let me explain:
- Carbohydrates that break down quickly during digestion have a higher glycaemic index (GI more than 70). These high GI carbohydrates release their glucose into the blood quickly - a good example of which is a baked potato.
- Carbohydrates that break down slowly release glucose gradually into the bloodstream - a good example of which is oats. They have low glycaemic indexes (GI less than 55). The blood glucose response is slower and flatter. Low GI foods prolong digestion due to their slow break down and may help with satiety (feeling full).
GI generally reflects the quality of the carbohydrate and thus we recommend focussing on more low and intermediate GI foods, and limiting high GI foods.
- Low GI foods are foods with a GI of 55 or less
- Intermediate GI foods are foods with a GI between 56 and 69
- High GI foods are foods with a GI of 70 or more
For a full list of foods and their GI rating click here.
Factors that affect the GI of a food
Factors such as the size, texture, viscosity (thickness) and ripeness of a food affect its GI. For instance, an unripe banana may have a GI of 30, while a ripe banana has a GI of 51. Both ripe and unripe bananas have a low GI.
Fat, protein, and soluble fibre also generally lower a food’s glycaemic response. Fat and acid foods (like vinegar, lemon juice or acidic fruit) slow the rate at which the stomach empties and slow the rate of digestion, resulting in a lower GI.
Other factors present in food, such as phytates (used to store phosphorous in plants) in wholegrain breads and cereals, may also delay a food’s absorption and thus lower the GI.
Cooking and processing can also affect the GI – food that is broken down into fine or smaller particles will be more easily absorbed and so has a higher GI. Foods that have been cooked and allowed to cool (potatoes, for example) can have a lower GI when eaten cold than when cooked.
High GI foods are influenced by low GI foods
Generally, eating low GI foods and high GI foods at the same time has the effect of ‘averaging’ the GI. This is important, as most foods are eaten as part of a meal and this affects the GI value of foods. I don’t recommend this as a meal but for the sake of an example - eating cornflakes (a higher GI food) with milk (a lower GI food) will reduce the effect on blood sugar levels.
To give you a real life example of how this works, let’s look at sugar. Glucose has an average GI of 100 which means, if you consume straight sugar, your blood sugar levels go through the roof (and so does your insulin). If, however, you added 15-20 grams of fibre the GI comes down to anywhere between 57-85 (still bad, but better). If you consume glucose with protein and fat you reduce the GI down to 56.
I’m not saying ‘let them eat sugar’ but this is why we say to have a handful of nuts/seeds when you have a piece of fruit!
What do the numbers mean?
It's important to keep in mind, though, that the glycaemic index does not take portion size into account. The actual amount any food raises blood sugar has to do both with how glycaemic it is, and how much of it you eat. The glycaemic load attempts to combine these concepts, and some diets are using the glycaemic load for this reason.
Glycaemic Load - GL
The glycaemic load (GL) is a concept that builds on GI, as it takes into account both the GI of the food and the amount of carbohydrate in a portion. GL is based on the idea that a high GI food consumed in small quantities would give the same effect on blood glucose levels as larger quantities of a low GI food.
A food’s glycaemic load is determined by multiplying its GI by the amount of carbohydrate the food contains in each serve and dividing by 100.
The GL of a typical apple is 6
Similar to the glycaemic index, the glycaemic load of a food can be classified as low, medium, or high:
- Low: 10 or less
- Medium: 11-19
- High: 20 or more
For optimal health, aim to keep your daily glycaemic load under 100.
How does GI and GL relate to weight loss?
In summary, opting for low GI/GL options ensure you keep your blood sugar levels stable, which also keeps your insulin levels down (remember insulin switches off fat-burning!). Choosing low GI/GL foods means less sugar cravings, more energy, and better fat burning!
The simplest way to use the GL is to choose foods with the lowest GI within a food group or category, and to be mindful of your serving size. The diagram below is a helpful reference when doling out your portions and it is ideal to aim for this at every meal.