us that we need to eat more because our blood glucose levels are falling quickly – as a result we crave more high-GL foods to satisfy the apparent hunger! What the brain doesn’t realize is that we ate a doughnut (or any high-GL food) only an hour ago! This turns into a vicious cycle as the rapid fall in blood glucose prompts us to crave more high-GL foods – which actually caused the problem in the first place!
High-GL foods eaten = blood glucose spike = blood insulin spike = blood glucose crash = craving for more high-GL foods = weight gain!
Fear not – this vicious cycle can easily be broken.
The carbohydrates in low-GL foods are broken down to glucose and absorbed more slowly, causing only a small rise in blood glucose levels and a corresponding small rise in blood insulin levels. As a result, glucose is moved into our muscle and liver cells at a slower pace and blood glucose levels are more stable. Eating low-GL foods every three to four hours helps keep our blood glucose levels steady – meaning no glucose and insulin spikes, no blood glucose crash and (you guessed it) NO CRAVINGS AND OVEREATING!
If we eat low-GL foods, we store less excess energy and blood glucose levels are kept stable, giving a slow-release, prolonged energy supply. This enables us to go about our activities with fewer cravings, feeling more balanced and of course ultimately storing less fat.
What Does High or Low GL Mean?
All foods that contain carbohydrate have an effect on our blood glucose levels – the more carbohydrate they contain, the bigger the effect. We can work out the effect they have in a laboratory setting by feeding people different foods and testing their blood to see how the glucose in the blood changes over time (we explain this properly in a minute). We can then give the food a number called its Glycaemic Index or GI (see page 15). Low-GI foods have a small but long-lasting effect on our blood glucose level whereas high-GI foods have a bigger but short-lasting effect.
The Technical Bit – How We Work Out the GI of a Food
GI is a scientifically proven method of categorizing foods according to how quickly the carbohydrates they contain are broken down and absorbed as glucose into the bloodstream. The Glycaemic Index or GI was created by comparing blood glucose levels of volunteers after eating different carbohydrate foods. Volunteers eat an amount of food that provides 50g of carbohydrate. Blood samples are taken from the volunteers at regular intervals over the next two hours to find out their blood glucose and insulin response to the test food. Each food is then given a number depending on how fast the body digested and absorbed the carbohydrate – the higher the number the faster the absorption. The number is called the food’s Glycaemic Index (GI).
55 and under is low Gl 55–70 is moderate Gl
So far, so good.
Every food tested has a GI number telling us how quickly it is absorbed when we eat an amount that contains 50g of carbohydrate. But this is where the major problem with GI crops up. Different foods contain very different amounts of carbohydrate.
For example, to reach the laboratory test level of 50g of carbohydrate you would need to eat about 75g of pasta, so a small portion, BUT you would need to eat a whopping 500g of parsnips to reach the 50g carb level, and how often would we do that outside the laboratory? We love parsnips but not that much! We would generally eat about 100g of parsnips at any one time. So the GI number isn’t based on realistic amounts of food that people usually eat in one sitting. The GI number you get for some foods like parsnips, watermelon and carrots, for example, is high, and if you just looked at the GI, these fine, nutritious foods would be deemed bad foods to be avoided! It’s clear that there are problems with basing a healthy-eating plan on the GI of foods.
The Problems with GI
• The way the GI of a food is worked out doesn’t always relate to the amount of food we actually eat at one sitting (remember the parsnips!).
• GI can be very confusing.
• If you base your diet on low-GI, some very healthy foods are excluded, such as carrots, watermelon, parsnips, pumpkin and broad beans to name a few. These foods contain little carbohydrate per portion and have a low GL.
GI gives us the first part of the story. It tells us that not all carbohydrates are equal; some are absorbed more quickly than others. But it doesn’t take into account how much carbohydrate a food contains. This is where the Glycaemic Load or GL comes in.
The GL Makes Sense of the GI
The GL goes a practical stage further. It takes the GI rating we’ve just outlined, but then very cleverly (thanks to Professor Walter Willett of Harvard Medical School who came up with the equation) takes into account the amount of carbohydrate in a portion of food we would normally eat. So now we know the effect a normal portion of food would have on our blood glucose levels, and that’s what gives us the GL rating:
• Foods with a high GI but with only a small amount of carbohydrate will generally have a low GL.
• Foods with a low or medium GI and a large amount of carbohydrate may have a high GL.
It’s so simple and, more importantly, relevant to what we actually eat!
Foods rated using the GL do still get a number:
10 and under is low GL 11–19 is moderate GL
If you did want to count your daily Glycaemic Load (GL) for the first few days in order to gain confidence that you are on the right track, you would be aiming to have a GL score of 80 or under on a low-GL day. A high-GL day would be 120 or over. If you are overweight and inactive it’s likely that your daily GL score is high and you are storing your excess energy as fat.
BUT don’t worry – although we do give some basic portion guidelines and GL references, you don’t have to count at all! Counting points, rigidly measuring and weighing foods is what turns us all off when it comes to diets. It’s the bit that makes diets boring, boring, boring – and besides, who has the time? Counting can also reinforce the obsessive behaviour around food that got quite a few of us here in the first place! Pay attention to what you’re eating and what your body is telling you. Once you’ve found your low-GL feet, it will all become second nature.
So What’s Right about GL?
The Glycaemic Load (GL) gives you the whole story:
• The GL allows you to understand with confidence how foods will affect your blood glucose levels.
• The GL is based on carbohydrates in the portion sizes we usually eat, rather than the amount needed in a laboratory setting to work out the GI.
• The GL means far more food choices.
• The GL makes practical sense of the GI science. It’s the final chapter in carbohydrate management and offers a real solution to weight loss.
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