Читать книгу The 7-Day GL Diet: Glycaemic Loading for Easy Weight Loss - Nigel Denby - Страница 6
ОглавлениеChapter 1 GI AND GL MADE SIMPLE
The first thing you probably want to know about this diet is: ‘Does it work?’
Well, from my experience as a dietician working with patients in my own clinics, I can tell you yes, it most certainly does. Every day I see more and more people who previously thought they were stuck in a ‘diet trap’ telling me that the GL diet is finally getting them back in the driving seat where their weight is concerned. They are looking at life with renewed optimism and excitement as a world of possibilities and freedom opens up to them with every positive step they take towards their weight-loss goals.
Slow Carbs not No Carbs
Before we start looking at GI and GL and the differences in more detail, we need to go back a little further so you can see how our understanding of carbohydrate management has evolved.
A few years ago I was actively and publicly criticizing the ‘high-protein, low-carb’ diet phenomenon that was sweeping the world. We knew people were losing weight, but as a responsible dietician I could never sit comfortably with the idea of cutting out a whole food group from our diet.
What we can say about high-protein, low-carb diets today is this: in controlled weight-loss studies, they perform no better than any other weight-loss programme in the long term, and worryingly we remain unsure about how safe these diets are in terms of heart health and long-term kidney function.
So, let’s get one thing straight: this is not a no-carb diet. The principle behind the GL diet is SLOW CARBS, and there’s a big difference in terms of success and long-term health.
Although research into the Glycaemic Index (GI) has been carried out progressively over the last 20 or so years in Australia (University of Sydney) and Canada (University of Toronto), and more recently in the United States by Harvard Medical School, * the GI only really began to hit the headlines a couple of years ago as a possible, healthier successor to low-carb diets.
How Can the GI Help Weight Control?
Foods that contain carbohydrates have an effect on our blood glucose (or blood sugars). This effect is measured as the ‘glycaemic response’. A food that will make our blood glucose level rise quickly is classed as high glycaemic, whereas a food that has little or no impact on our blood glucose is low glycaemic.
When we eat high-glycaemic carbohydrates we get a rapid rise in blood glucose or a ‘spike’. This is bad news for the body and prompts our pancreas to produce insulin, the most powerful hormone in the body, so not to be underestimated. Insulin comes rushing in to flush the glucose from our bloodstream as a safety mechanism and carries it to our liver and muscles, where it is stored as energy for later use. Healthy blood glucose is quite finely balanced – when blood glucose goes too low or too high it can detrimentally affect most of the organs in the body. If this situation becomes the norm it can have quite serious long-term health implications. The muscles and liver fill up very quickly, especially if we are not doing a lot of exercise to use up this ‘stored energy’ – by ‘a lot’ we mean the sort of training you might do to run a marathon. When the muscles and liver are full and can’t store any more glucose, the only thing insulin can do is transfer the excess to other body tissues, where this excess energy is stored as FAT. Yes, those awful wobbly bits!
Once insulin has done its job and dispersed the glucose from our blood, the ‘spike’ in blood glucose falls rapidly. This is a vicious cycle as the rapid fall prompts us to crave more high-glycaemic foods – which actually caused the problem in the first place!
If we eat low-glycaemic foods, we store less excess energy and blood glucose levels are kept stable. This gives a slow-release, prolonged energy supply, enabling us to go about our activities with fewer cravings, feeling more balanced and ultimately storing less fat.
That’s the basis of all low-glycaemic diets. But why low GL (Glycaemic Load) rather than low GI (Glycaemic Index)?
So What’s Wrong with GI?
In principle nothing, except …
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.
GI can be very confusing.
If you base your diet on low-GI foods, some very healthy foods are excluded, such as carrots, watermelon, parsnips, pumpkin and broad beans to name a few.
GI gives us the first part of the story. It tells us that not all carbohydrates are equal. But that’s a bit like knowing that you spend more money than you earn each month – it doesn’t actually help you manage your money and get back in the black!
What’s So Right about GL?
The Glycaemic Load (GL) gives you the whole story:
GL allows you to understand with confidence how foods will affect your body.
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.
GL means far more food choices.
GL makes practical sense of the GI science. It’s the final chapter in carbohydrate management and offers a real solution to long-term weight control.
The Technical Bit – How We Work out the GI and GL of a Food
Note: if you don’t want to know about the science – and you don’t need to in order to follow the GL diet – then skip to Chapter 2.
GI – the First Part of the Story
To work out the GI of a food, scientists take whatever amount of a food is needed to give you 50g of carbohydrate. Now, with a food like bread that isn’t a problem because two slices of bread give us about 50g of carbohydrate. The bread is then fed to human volunteers and blood samples are taken from them at regular intervals to see how much glucose has been released into their bloodstream. The result of these tests is a GI number between 1 and 100.
Foods are classed as:
55 or less = low Gl
56–69 = moderate GI
70 plus = high Gl
So far, so good.
But let’s look at another food. Take carrots and use the same procedure. To get 50g of carbohydrate from carrots you would need to consume about one-and-a-half pounds (0.7kg). That’s a normal portion for a donkey maybe, but a bit excessive for the likes of us humans in one sitting. The volunteers (poor things) are fed the carrots, and the same blood tests and calculations are carried out as with the bread. The result is that carrots get a GI of about 75, making them high GI, which is why many GI diet books advise you not to eat them! Carrots are, in fact, a very healthy and low-‘GL’ food based on an average portion, so we can all thankfully continue to enjoy them as part of a balanced diet.
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 carrots (around 100g) would have on our blood glucose levels, and that’s what gives us the GL rating.
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 = low GL
11–19 = medium GL
20 plus = high GL
If you did want to count your GLs for the first few days to gain confidence that you are on the right track, you would be aiming to have 80GL or under on a low-GL day. A high-GL day would be 120GL or over.
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 and 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?
All you need to do is read through the rest of the book, start loving healthy, low-GL foods, losing weight and, best of all, be able to keep it off forever as the GL diet becomes a way of life.
As serial dieters we are all searching for our own elusive ‘diet freedom’. The GL finally brings this within everyone’s grasp without deprivation or hunger.
For us, this GL plan is the ultimate permanent weight-loss solution because:
It works – you’ll see results in just seven days.
It’s easy to follow.
It’s based on sound, sensible science.
It suits both men and women.
There’s no counting points.
There’s no endless weighing and measuring.
There’s no hunger or feeling deprived.
There’s no humiliation or guilt.
It’s a healthy diet you’ll want to adopt for life, not just for Christmas …
Oh … and it’s safe!
* The Harvard Medical School has carried out the longest running studies into human nutrition, stretching back over 20 years, and these are still continuing today.
