About low GI diets
How low GI diets work
GI stands for glycemic index, which is a way of measuring the rise in blood glucose (or 'blood sugar') after eating specific foods. It only applies to carbohydrates. For instance, a 500-calorie steak will not affect blood sugar levels significantly but a 500-calorie baked potato will. (For a more detailed explanation, see below.) Low GI diets are based on the principle that eating too much of the kind of food that makes your blood sugar rise fast and high is an important cause of overweight. (This is also the science upon which low carb diets such as the Atkins Diet are based).
Which diets are low GI
Weight-loss diets based on the GI principle are not new. The Montignac method, which dates back to the 1980s, is probably the earliest popular low GI diet and represented a radical change from the low calorie/low fat diets which were in fashion at the time.
In the late 1990s, low carb diets took centre stage, led by the Atkins Diet. Low carb diets, like low GI diets, are based on the blood sugar control principle. The low carb movement re-stimulated interest the relationship between blood sugar, insulin and the explosion of obesity that we see today in the Western world. Meanwhile, the inventors of the glycemic index, David Jenkins and Thomas Wolever of the University of Toronto, had been continuing the work they started in the 1970s/80s. Having developed the index primarily as a tool to help diabetics manage their blood sugar levels, they had begun to see its potential as a weight loss tool. A new wave of low GI diets was a logical follow-on, particularly for those who saw the Atkins Diet as too restrictive. (The Atkins Diet in fact only restricts 'bad' carbohydrates - 'good' carbs are positively encouraged up to the limit of the individual's tolerance to them. This last point is extremely important but is generally overlooked).
There are many variations of the low GI diet around today, including The Glucose Revolution Life Plan, The Good Carb Diet Plan, Good Carbs Bad Carbs and Nutrisystem Nourish. Most well-known are probably the GI Diet by Rick Gallop and the South Beach Diet by Dr A Agatston.
Carbohydrates allowed on low GI diets
Low GI (and to a great extent low carb) eating means a return to the type of carbohydrate foods that our great-grandparents ate - the 'good' carbs - plenty of whole grains such as barley and oats, dried peas and beans, root vegetables and whole fruits. Our great-grandparents didn't have the processed foods made from highly refined white flour, sugar and other processed grains that have become our staple foods today. They were also more physically active than we are, with few labour-saving devices in the home, no cars to take them everywhere instead of walking and no highly automated industrial and agricultural production methods. In consequence, our great-grandparents were able to keep their blood sugar levels in a steady state, much in the way that nature intended.
Why low GI is a healthy way to eat
However, the position is different for most of us today. Our diet has changed significantly since the time of our great-grandparents. We eat large quantities of refined flour and sugar every day - foods our blood sugar control mechanisms were not designed to handle. These foods make our blood sugar rise very high very quickly. It is the job of insulin to get our blood sugar levels back within the correct range, by organising the transport of this excess sugar out of our bloodstream and into storage. Unfortunately for us, if we do not use up the stored energy, we get fat. For many of us, the constant outpouring of insulin also leads to the eventual exhaustion of our insulin-secreting organ, the pancreas. If this happens, we become diabetic. Constantly high insulin/blood sugar levels can also have other serious consequences, such as heart disease and complications commonly suffered by diabetics such as blindness, kidney failure and amputations.
Other users of the glycemic index
Diabetics are generally recommended to select foods that rank low to moderate on the glycemic index as a way to help them balance their blood glucose levels. Athletes are also familiar with the glycemic index and use it to select foods which optimise their energy reserves.
Low carb dieters focus more on the total amount of carbohydrate rather than the relative speed with which the carbohydrate-containing food is absorbed. They do nevertheless take the GI effect into account, for instance, when choosing between a selection of foods with a similar carb content.
Are low GI diets better than low carb?
As yet there are few clinical studies showing how effective low GI diets might be from a purely weight loss point of view, whereas there is plenty of evidence supporting low carb diets in this respect. In all probability the issue boils down to the individual's tolerance to carbs - if your tolerance is not very high, then you are unlikely to lose weight simply by eating low GI foods. If this is the case, you would need to ensure that the low GI foods you eat are also very low in total carbs. One way to do this is to follow a low GI diet which also takes into account the glycemic load (see below for more detail). At this point the difference between a low GI diet and a low carb diet becomes very small. If on the other hand you have a reasonably high tolerance to carbs, then you would probably do well on a low GI diet - or equally, a quality low carb plan such as the Atkins Diet which encourages intake of 'good' carbs up to your individual level of tolerance.
That said, there is no doubt that eating the low GI (and low carb) way means eating less refined carbohydrates such as sugar and white flour (the 'bad' carbs) and more vegetables, whole fruits, fibre, whole grains, pulses, nuts and seeds (the 'good' carbs). Few would argue that this can be anything but beneficial for most people's long term health.
Similarities between low GI and low carb diets
Although the 'rules' may look different, the foods eaten on a low GI diet are very similar to those eaten on a low or controlled carb diet such as the Atkins Diet. Both approaches involve the avoidance of carbohydrate-dense highly processed foods. Both approaches encourage lots of healthy salads and vegetables (although the Atkins Diet is often misquoted as not allowing vegetables and fruits). The scientific reasoning behind these seemingly different diets is not contradictory. They are all based on the principle that many people cannot eat significant quantities of carbohydrate foods, particularly refined ones, without risking constant overproduction of insulin and its consequences.
In fact, it is not unusual for people who have succeeded on a low carb diet such as Atkins to 'move' to a low GI plan once they have reached the less strict 'lifetime maintenance' phase of the diet. (Whether this is really a move to a different diet or whether they are two slightly different routes towards eating the same things at this stage is a point for debate).
Both low carb and low GI diets are primarily concerned with controlling the type of carbohydrate foods eaten. They do not usually require calorie counting, or if they do, this is of secondary importance. Because some foods (sticky buns, pastries and sugar candy for instance) are so high in carbs and so high on the GI scale, these foods are likely to be prohibited by both low carb and low GI diets (as opposed to being permitted in small portions as they might be on a low calorie diet.)
Although low carb dieters are primarily focused on the total carb content of a food, GI rankings do nevertheless have some relevance for them. Low carbers may refer to the GI ranking to help them choose between a selection of foods with a similar carb content. The Atkins Diet also introduces the concept of 'glycemic load' (see below for more detail). This involves multiplying the glycemic index of the food by the carbohydrate content of the amount to be consumed. This gives a more meaningful picture of what the overall effect will be of eating that particular portion of food. For instance, if you rely on the GI alone, you may be put off eating carrots because they are surprisingly high on the glycemic scale. Looking instead at the 'glycemic load', it is obvious that carrots are still a good choice in terms of the effect the quantity you are likely to eat will have on your blood sugar.
Both low GI and low carb diets represent a return to whole, nutritious foods and a turning away from heavily processed foods such as mass produced breads, cakes, biscuits, mixes and sauces, ready meals, snacks, 'fast foods', fizzy drinks etc. These foods usually contain artificial colourings, flavourings and preservatives - the chemicals that we commonly refer to as 'E numbers' - in quantity. Both low GI and low carb diets are founded on eating healthily (as opposed to 'eat whatever you like as long as it is low in calories or fat-free'). They are both based on the premise that we would be much healthier if we went back to eating natural, whole foods the way Nature intended.
Differences between low GI and low carb diets
Low GI dieters do not count carbs, but choose their carbohydrate foods and menus based solely on the GI ranking of the food or meal. In contrast, low carb dieters count carbohydrates and, although they may also make food or meal choices according to the GI of a particular food or meal, the total carb count is of more importance to them.
Low GI diets generally include starchy vegetables (potatoes, parsnips, carrots etc), fruits, pulses and wholegrains from the outset. Many low carb diets however prohibit these 'good' carbs in their initial phase. The good carbs are then gradually added back into the diet according to the individual's ability to tolerate them. (Unfortunately some people do not have a very high carb tolerance - which is why low GI diets may not be restrictive enough for such people to lose weight on them. By the same token, some of the low carb plans are not low enough in carbs for some people either. This is one reason why the four phases of the Atkins Diet work so well - the dieter starts at the lowest level and works gradually up to the highest level he or she can tolerate without putting on weight.)
Both low GI and low carb diets are concerned to a certain degree with fats. However, low GI diets tend to promote the avoidance of fat, saturated fat in particular, whilst low carb diets, and most notably, the Atkins Diet, do not. (What is not often recognised is that the Atkins and other low carb diets have always paid attention to fat - but they distinguish between 'good' and 'bad fats'. For instance, olive oil and fish oils and certain saturated fats are 'good' fats, while trans fats (hydrogenated oils) are 'bad' fats. Unfortunately, saturated fat got the blame for the wrongdoings of trans fats years ago, before it was recognised that there was more than just one type of saturated fat. This fact is now becoming more widely recognised.)
One important difference between low GI and low carb diets is that low GI diets are currently more widely accepted in the medical world. This is because low GI diets are more closely aligned to the healthy eating guidelines promoted by most Western governments than low carb diets. (Official healthy eating advice still follows the principles that around 60 per cent of daily calories should come from carbohydrates and that the only healthy diet is a low fat one. Some clinicians, Dr Atkins included, have been saying for the past thirty years that these two principles are wrong, and recent clinical studies have consistently been proving them right. But mainstream medical acceptance of these new ideas is slow, mainly because of the need for many years of evidence-based research to support changes in government health policy. So in the meantime, all 'new' diets are measured against the existing, and many would say, outdated guidelines. For this reason, GI diets are more likely to be seen as acceptable by doctors, nutritionists and dieticians, whilst low carb diets, despite plenty of compelling scientific evidence, are very often not.)
Following a low GI Diet
A low GI diet can approximately be achieved by following the typical 'healthy eating' diet promoted by government health departments but choosing carbohydrates which fall towards the lower end of the GI scale. In other words, substituting foods such as sugar, cakes, biscuits, white bread and rice, sweets, starchy vegetables, sugary drinks and fruit juice with sugar-free whole grains, whole fruits, pulses, nuts and seeds and non-starchy vegetables.
Another way to look at it is that everything allowed on a low carb diet is permitted on a low GI Diet* - because foods that are low in carbs cannot have much of a glycemic effect. So the low GI dieter can for instance use recipes developed originally with low carbers in mind. (However, it does not necessarily work the other way round - many GI diet recipes are fine for low carbers, but some of them may contain a higher level of carbs than the individual can tolerate, if he/she is very carb-sensitive.)
* Some GI diets are more restrictive of fats than low carb diets generally are. Certain GI diets reflect a high fat content in a food by placing the food in the high GI column, or giving it a red rather than a green traffic light. This does not mean the food is actually high GI - it just means that that particular food is discouraged on that particular diet for other reasons.
What is the glycemic index
The glycemic index is a measurement of how much blood glucose increases after eating a specific food. It only applies to carbohydrate foods. Carbohydrates often used to be categorised as either simple (eg fruit sugars and table sugars) or complex (breads, pasta, grains). This was on the basis that simple carbohydrates tended to be absorbed faster than complex carbohydrates. Such simple classification is now considered to be fairly meaningless and the glycemic index is an attempt to provide a more accurate method.
Glucose is the reference food for the glycemic index, with its value arbitrarily set at 100. All other foods have to be tested (in humans) before they can be given a ranking in the glycemic index. (Not all foods have been tested so far). Volunteers eat a portion of the food which has been calculated to supply 50 g of carbohydrates and their blood sugar response is measured. On another occasion, the same volunteers are given the equivalent amount of glucose. A comparison of the two outcomes, averaged over a number of volunteers, allows the glycemic index of the food to be determined. For instance, a food causing half of the blood sugar rise of glucose is given a GI of 50.
Unfortunately the glycemic index is not a perfect method of classification, either. Many factors can influence the effect on the blood sugar of particular foods (not least because foods with different indexes may be eaten simultaneously). Take kidney beans, for example. They have a low GI of 27 - they are notoriously hard to digest. But baked potatoes have a GI of 93 - higher than that of almost all other foods, including ice cream (61), sweet potatoes (54), and white bread (70). Chocolate/candy bars on the other hand tend to have a relatively low GI, presumably because their fat content slows their digestion. Factors affecting the GI of a food include:
- Biochemical structure of the carbohydrate - for example, amylopectin is more readily absorbed than amylose
- Intestinal absorption
- Food particle size - smaller particles are absorbed faster
- Cooking and preparation - both mechanical and thermal processing break the food into smaller particles thus facilitating absorption
- Content and timing of the previous meal
- Accompanying foods that include fat, fibre, or protein - fat and protein decrease the speed with which the stomach empties, thus decreasing the rate of carbohydrate absorption.
The glycemic index of a food can also vary with crop varieties, growing conditions, geographic location, genetic strain, ripeness, acidity and fibre, protein and fat content. For this reason, glycemic index values for non-branded foods in reference tables can only be approximate. (Incidentally these factors also affect the accuracy of carbohydrate values).
Not all foods have been tested yet, but the list of GI and GL rankings on the Mendosa.com site is one of the most comprehensive. Note that GI lists don't include carbohydrate foods which contain very small amounts of carbohydrate, as these are unmeasurable by the methods currently used. It is difficult to get test volunteers to eat enough of a very low carb food to achieve the 50 grams worth of carbs which is the standard test portion! Such foods are often simply listed by GI diet authors as 'free foods' (but diabetics and those counting carbs still need to take account of these in their daily allowance.) These foods include salad vegetables and other non-starchy vegetables such as cauliflower, broccoli, tomatoes, onions, green/French beans, cabbage, eggplant/aubergine, mushrooms, courgettes/zucchini. Other foods which may not be listed for similar reasons are avocados, raspberries, strawberries, pecans, milk, cream cheese, hard cheese, ricotta, plain yoghurt and artificial sweeteners.
What is glycemic load (GL)
Some feel that the glycemic index is not the right way to assess the insulin-related effects of food. This is because it measures blood sugar response per gram of carbohydrate contained in a food, not per gram of the food. This can leads to some misleading results. For example, a parsnip has a glycemic index of 98, almost as high as pure sugar. But this ranking fails to take into account the large amount of parsnips you would have to eat to produce such a blood sugar response.
This problem is resolved with the concept of glycemic load. The GL is calculated by multiplying the GI ranking of the food by the amount of carbohydrate in the portion to be consumed, then dividing by 100. In other words, it measures the glucose/insulin response per gram of food rather than per gram of carbohydrate in that food. On this basis, the glycemic load of a parsnip is 10, while glucose has a relative load of 100 - a more meaningful result.
Low GI recipes
Looking for low GI recipes to help make your low GI diet easier and more enjoyable? Check out the Low Carb / Low GI Cookbook. All the recipes in it are made from healthy ingredients which are low in carbs. This means that they are all automatically suitable for low GI diets as well as low carb diets.
The Low Carb / Low GI Cookbook comes with free bonuses which you are sure to find useful - including a 38-page guide to everything you need to know about low carb, low GI and low GL diets, the differences between them and how to follow them; and a 22-page set of GI & GL Handy Reference Tables, specially designed to make your GI diet easy.