Glycaemic Index (GI)

The glycaemic index (GI) is a measure of how quickly the carbohydrates in a particular food enter the blood stream after it is eaten. The GI concept can be extended from single foods to meals or even the entire eating pattern of an individual or group. The glycaemic load (GL) accounts for the amount of carbohydrate as well as its GI (GL= GI x grams of carbohydrate).

Foods are classified as low, medium or high GI according to a somewhat arbitrary scale:

  • GI = 100 for pure glucose. All other foods are compared to this standard.
  • GI over 70 is HIGH
  • GI 55 – 70 is INTERMEDIATE
  • GI less than 55 is LOW

These measurements are all done using a single serve of a single food containing a standard quantity of carbohydrate in a small group of subjects. Results can vary wildly between laboratories. Whole plant foods vary according to season, variety and ripeness. Results vary between subjects and on different occasions for the same subject. Despite these limitations, foods can be classified according to their GI and the concept has been shown to have useful applications.

A great many health benefits are claimed for low GI diets. Most of them not well supported by research. The health benefits of low GI diets may be restricted to particular groups of subjects – in particular, those who are obese and/or diabetic. An individual who is lean, active and has a low fat diet, all of which improve the capacity of the body to deal with carbohydrates, may not benefit greatly from replacing whole high GI carbohydrates with whole low GI carbohydrates.

When using GI to assist in food choices it is important to consider the energy density of the food item. An item such a carrot has a high GI but is so low in calories that a GI serve is a much larger quantity of carrots than you are likely to eat in one sitting. A small quantity of carrots will not have much impact on your low GI diet.

The higher [animal] protein, low GI diet is gaining popularity among Australian health professionals. It may compare favourably with the typical Australian diet and a diet rich in sugars and other highly refined carbohydrates. We would welcome research directly comparing the higher protein diet with a low fat whole foods plant-based diet.

Beware of highly processed foods and low carbohydrate/ high fat foods which misuse the GI health claim for marketing. The overall nutritional value of foods should be considered first, and the GI only used to assist in selecting between similar items. A whole foods plant-based diet has a lower GI than the typical Australian diet.

Medical conditions that may be improved with a low GI diet include:

  • Type 2 diabetes, type 1 diabetes and pre-diabetes (impaired glucose tolerance)
  • High triglyceride levels (and the associated low HDL levels)

Reducing the overall GI of your diet is not difficult. You can find a few healthy very low GI foods that you enjoy and use more of them in your meals and cooking.

Examples of very low GI whole plant foods:

  • Lentils and beans
  • Oats and barley
  • Apples and pears

The physical form of whole plant foods influences GI. Chopping, grinding and blending foods tends to make the GI higher. For example, quick oats have a slightly higher GI than ordinary rolled oats. Some foods have a lower GI because they are lumpy and claggy. For example pasta has a lower GI than flour.

Knowledge of GI values can also be used to replace foods with similar items of lower GI. The following are some examples of low GI food exchanges:

                                                HIGH                          LOW

Breakfast cereal                    (breakfast cereals)         rolled oats
Bread                                    wholemeal bread          generally heavier more grainy breads
Potato                                   potato                          sweet potato
Rice                                       medium grain               long grain
Fruit                                       watermelon                  apple


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Type 1 Diabetes

Type 1 diabetes is characterised by the destruction of the insulin producing beta cells in the pancreas. Therefore someone with type 1 diabetes will always require an external source of insulin (unless medical technology can create new insulin producing cells and protect them from the same fate as the original cells).

Most often, type 1 diabetes is an autoimmune disease in which the immune system mistakenly targets proteins displayed on the beta cells. Many people carry immune system genes that make them susceptible to this autoimmune disease but most do not develop type 1 diabetes. Who gets it depends on exposure to environmental factors and a bit of bad luck. The consumption of cow’s milk has a strong association with type 1 diabetes. A proposed mechanism is that “foreign” cow’s milk proteins provoke the production of antibodies that are also a close match for a beta cell protein, and indeed there is a 17 amino acid sequence that is found in both. There is also a strong association between autoimmune diseases in general and eating a rich Western diet versus a plant based diet. Whilst there is nothing gained by ruminating over what caused type 1 diabetes in individuals who already have it, it is important to consider how the disease might be prevented, particularly in siblings and children who may share the same genetic risks as these individuals.

Most people eating the high fat, protein rich Western diet will develop atherosclerosis which may manifest as heart disease, stroke and peripheral vascular disease. Diabetics are at even greater risk than the general population, particularly if the diabetes is not well controlled. In the past, well-meaning health professionals have advised diabetics to eat less carbohydrates and more fats and animal products, further increasing heart risk. These high fat, high protein diets also promote kidney disease and weight gain.

The same low fat plant-based diet that improves insulin sensitivity in type 2 diabetes can reduce insulin needs in type 1 diabetes.

A low fat high carbohydrate plant-based diet may make it easier to balance food intake with insulin needs. Carbohydrate content makes up most of the calories and the energy density of different starchy foods in their cooked, hydrated state is similar. Therefore the size of the meal will be a reasonable guide to its carbohydrate content. The PCRM plate and the McDougall starch-based plate are both mixes of vegetables and high starch grains, legumes and root vegetables. The low energy density of these foods means portions can be generous and between meal snacks can be included without causing weight gain.

The glycaemic index (GI) can be used to further refine the choice of carbohydrates. Low GI choices may help stabilise blood glucose levels. Use the GI to choose between different whole plant foods and avoid processed foods that use GI for marketing.


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Dietary Transition for Diabetes

Warning – changing to a whole foods plant based diet may work too well and too quickly. Your current medications, particularly insulin, may become too strong for you, causing hypoglycaemia. This includes other classes of drugs including sulfonylureas but not metformin. We recommend that you consult your doctor before making major dietary changes. See disclaimer. It is helpful if you can get your doctor on board with what you are doing – perhaps you could share some educational material such as Dr Neal Barnard’s PCRM diabetes resources for physicians.

The next thing to consider is how quickly to make the transition. When no medical conditions are present, an abrupt overnight transition to a 100% whole foods plant based diet often works well. There is a definite demarcation between the old and the new, no indecision over food choices, and the benefits such as losing weight or feeling more energetic are immediate. This approach may be suitable for someone with “diet controlled” diabetes on no medications. Those on tablets may need to stop them as they make the transition but this decision should only be made in consultation with your doctor. Type 2 diabetics treated with insulin will have rapid changes in their insulin requirements and are not advised to change their diets overnight unless under daily medical supervision.

A gradual transition over several weeks, with frequent glucometer reading and close medical supervision is the preferred option for anyone on insulin. Taking a more gradual approach gives you time to try out new recipes, discover quick and easy options, and restock your kitchen. This way you won’t be left not knowing what to eat on day one of your new eating plan. This website is supportive for all degrees of “plant strong” eating but we do recommend that you give a totally plant based, no oil diet a fair trial of at least 3 weeks. The full benefits are often not apparent until you are nearly 100% whole foods plant based.

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Treating diabetes with a high carbohydrate plant-based diet

It may seem counterintuitive to treat diabetes with a high carbohydrate diet, but consider the following points:

  • Diabetics have elevated blood sugar levels even on low carbohydrate diets.
  • There is least diabetes in cultures where the most carbohydrate is eaten, such as rural Asia.
  • Some of the most successful dietary intervention programs for diabetes are those that use a high carbohydrate mostly vegan diet.

The epidemiology provides evidence that high carbohydrate diets are less likely to result in diabetes. There is least diabetes in the regions of the world where people eat a mostly plant based diet consisting of minimally processed starchy foods and vegetables. These type of diets are not only high in carbohydrates but also low in fat, high in fibre and have a low energy density. But foremost, they are based on whole plant foods, and as such we should not expect any reconstructed processed foods of similar composition to have the same effect. The China study observed that there was more diabetes in regions with quite modest departures from this eating pattern.

Observational studies such as the Seventh Day Adventist study contradict the notion the higher protein intakes control obesity and prevent diabetes. The meat eaters were heavier and had more diabetes than the vegetarians while the vegans were the leanest and had the least diabetes. It is likely that meat has diabetes promoting properties beyond its fat content, energy density and lack of fibre. Conversely, whole plant foods have metabolic effects that are not fully explained by their nutrient composition.

It is not surprising that the same nutrition that prevent the diabetes can also be used to treat diabetes. Dr Neal Barnard has decades of experience in treating diabetes with a low fat plant-based diet. His published studies on dietary intervention in diabetes have shown remarkable results with this approach. Some individuals were cured of diabetes, with blood measurements returning to the non-diabetic state and staying there. Please listen to presentations by Dr Neal Barnard through the links in the Diabetes Resources if you want more information.

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Diabetes Physiology

In order to understand diabetes one needs to consider the normal physiological role of insulin and glucose in the transport of carbohydrate around the body. Nerve cells in the brain, spinal cord and elsewhere always take as much glucose from the blood as they need. Carbohydrates are the real brain food. Other tissues, particularly muscle cells and fat cells, only take glucose from the blood when directed to, by the hormone insulin. Insulin can be likened to a key that fits into a lock and opens the door for glucose to enter the cell. The lock is the insulin receptor which straddles the surface membrane of the cell and the door is the set of proteins which actively transport glucose into the cell. This door also has a security chain to keep out additional glucose when the house is full, the house being the cell in this analogy. As a cell become fully loaded with energy from both glucose and fats it becomes increasing resistant to insulin, and ever higher concentrations of insulin are required to coax it to take in that extra little bit of glucose.

Muscle is a metabolically active tissue and typically makes up half of our body weight, making it the number one player in glucose/insulin metabolism and diabetes. It is fairly well accepted that the build-up of fat globules (intramyocellular lipid) within the muscle cells is the main factor that causes them to become resistant to insulin. The fat you eat is not only the fat you wear but also the fat that clogs your muscle cells. To put this in terms of the insulin lock and key analogy, fat in the muscle cell is the gum that stops the insulin key from fitting into the lock. There are two ways that we can ungum our muscle cells: exercise and a low fat plant-based diet. Exercise simply burns off the muscle stores of both fat and glucose. A low fat, plant-based diet prevents the muscle cells from becoming overladen with fat.

There are factors outside the cell that can make the insulin receptor more resistant to insulin. Perhaps they could be keyhole covers in the lock and key analogy. These include, saturated fat, stress hormones and inflammatory mediators. The saturated fat comes from a diet rich in meat, dairy, eggs and processed foods. The stress hormone cortisone is increased by both physical and psychological stressors. Dietary fats, animal protein and several inflammatory substances in meat cause an acute rise in blood levels of cytokines and other inflammatory mediators. Abdominal fat produces its own inflammatory mediators. A low fat plant-based diet minimises saturated fat intake and reduces inflammation.

Let us consider what happens if we keep shovelling fats and other concentrated calories into our bodies beyond our needs. The whole system becomes overloaded with glucose and oils and the cells all over the body become insulin resistant. Insulin resistance is what cells are meant to do when they don’t need any more glucose – it’s a normal response, which protects cells from becoming overloaded with energy substrates, while leaving more glucose available for the cells that do need it. With insulin resistance happening all over the body, there is nowhere for the glucose in the blood to go, and glucose levels spiral out of control despite maximum production of insulin – this scenario is type 2 diabetes.

Some people have fat cells that are willing to just keep taking in glucose and fats and getting bigger and bigger to morbidly obese levels, and this may hold back diabetes, but most of us have fat cells that take the more sensible approach of saying no more by becoming insulin resistant. Obesity was not a useful survival trait for hunter-gatherers – nor any other species for that matter.

Low carbohydrate diets are a quick fix for diabetes. The underlying problem of insulin resistance is dealt with by simply cutting off the main supply line for blood glucose, dietary carbohydrate. Unfortunately low carbohydrate diets are high in fat, animal protein, and usually of high energy density. They maintain the body in a permanent state of energy overload and insulin resistance. They also increase the risk of the number one killer in diabetes – heart disease.

Type 2 diabetes can eventually become irreversible. The insulin producing cells of the pancreas initially work very hard to make as much insulin as they can, often many times the normal amount. Eventually these cells can become damaged, producing less insulin, and as a result blood glucose levels rise and diabetes gets worse. Even at this late stage, a whole foods plant based diet will improve insulin sensitivity.

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There is perhaps no medical condition that responds so well to a whole foods plant-based diet than type 2 diabetes. It is a nutritional disorder caused by the high fat, protein rich Western diet. Take away the cause and the disease will get better. Early diabetes and pre-diabetes can be completely cured. There are also benefits in eating a plant-based diet for people with type 1 diabetes.

Diabetes is not a genetic disease. Your genes are your predisposition not your destiny. Diabetes incidence in China has gone from from less than 1% (in 1980) to 12% (in 2010) in one generation as they increasingly adopt a Western diet. A similar pattern was seen in Japan – diabetes incidence increased as the traditional staple of rice was replaced by meat, oils and processed foods. Genes and rice are not the problem.

The current medical treatment for diabetes targets blood glucose, blood pressure, cholesterol and other biomarkers with an ever increasing number of pharmaceuticals. This approach largely fails to deal with the cause of the disease – a high protein, high fat diet deficient in whole plant foods. The underlying diabetes physiology is largely unaltered because the dietary patterns that caused the disease have not been changed. Under this approach the severity of diabetes becomes gradually worse over the years. The most effective treatment for diabetes is a high carbohydrate plant-based diet. Low carbohydrate diets are always high in fat (see Energy Pie) and while they may result in lower blood glucose levels in the short term, they only serve to maintain the diabetic state in the long term. Whole foods plant-based nutrition is an effective solution for diabetes and obesity, and the low energy density of these foods means that there is no need for small portions and food rationing.More on Diabetes Physiology

Low GI (glycaemic index) diets are promoted by many Australian health professionals. Unfortunately the low GI concept in Australia often translates into higher consumption of meat and other animal products as people cut back on all carbohydrates, including those complex carbohydrates which have only ever been associated with better health. We recommend that if you use the GI concept, you make sure you select from a range of complex carbohydrates, i.e. whole foods – fruits, vegetables (including starchy vegetables), whole grains and legumes. Beware of highly processed food and high fat foods which use the low GI health claim for marketing.More on GI


It’s Heart disease that is responsible for much of the early death and disability in diabetes, not spiralling blood sugar levels. Dr Barnard says that “diabetes makes everything else worse” and this includes Alzheimer’s disease and heart disease. The nutrition that we use for diabetes must be the same nutrition that we use to prevent and manage heart disease – a low fat mostly vegan diet. The current trend towards higher (animal) protein diets for diabetes in Australia, even if it were effective, is not compatible with long term heart health.More on Heart Health


A word of warning before you start – this approach may work very quickly. If you are on insulin or other medications for diabetes and high blood pressure you should consult your doctor before you make the transition to a whole foods plant based diet.More on Transition

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Page last updated 29 July 2015


When vegan is not enough. Nina and Randa have been vegan all their lives. Listen to their story when they went travelling and began eating a more high-fat, heavily processed vegan diet. Both of them broke out in severe acne. When roaccutane was the only other option, they adopted a very low-fat McDougall starch-based diet and their acne began to improve within days. See Success Stories below for the written story to accompany video.

Although acne is not a life threatening or serious disease in a physical sense, it can still cause considerable personal distress and lead to social isolation and depression. It used to be considered as a condition associated with hormonal changes during teenage years but this may be changing, with many continuing to suffer from acne through their twenties and beyond. Severe acne, if left untreated, can result in permanent scarring.

While medications have their place in the treatment of acne, most acne can be managed by lifestyle changes which treat the cause of the disease – and diet is the most important of these. Many dermatologists and endocrinologists, as well as some sectors of the food industry downplay the link between diet and acne. One study that was often quoted to support the myth that diet has no effect on acne was a study of teenagers which compared the effect of adding a chocolate bar to the usual diet versus a confectionery bar – of course with such minimal change to the overall diet, there was no difference in acne.

The process of acne works something like this: it begins with the excess production of skin oil (sebum) and an overgrowth of the cells that line the ducts that carry this oil to the skin surface. The ducts become blocked and oil collects under the skin and becomes infected with skin bacteria. The mixture of oil and bacteria is highly inflammatory and produces the characteristic red lumps and pustules of acne.

It has often been said that acne is caused by hormones rather than diet. While it is true that acne is the result of excessive levels of androgens (those hormones with testosterone-like effects) and IGF-1 (insulin-like growth factor), it is the rich Western diet that causes these hormones to become elevated to unnatural levels. The effects of diet further accentuate the natural increase in androgens during adolescence and the higher androgen levels of young adults. Elevated androgen levels are also a feature of polycystic ovary syndrome (PCOS), a diet-related condition that many now consider to be a metabolic disease like type 2 diabetes.

The hormone IGF-1 (insulin-like growth factor) plays a key role in acne. There is a complex interaction between IGF-1, insulin and the reproductive hormones that results in increased androgen hormone activity throughout the body. IGF-1 is a growth hormone which stimulates cell proliferation and inhibits the death of cells that are no longer needed. Dietary factors that raise IGF-1 levels are thought to stimulate cancer growth as well as acne. The proteins in cow’s milk are a potent stimulus for the liver to produce more IGF-1. The growth promoting hormonal effects of milk are not unexpected as it is really ‘baby cow growth fluid’. Several large observational studies have found an association between dairy consumption and acne. This is, of course, disputed by the dairy industry. More recently there was a published report of several cases of severe teenage acne associated with whey protein supplements.

Cow’s milk also delivers estrogen hormones directly. Cows are now milked during pregnancy when estrogen levels are high, resulting in significant estrogen levels in the milk which gives consumers an unintended hormone supplement.

Animal protein-rich diets, even without dairy foods, cause elevated IGF-1 levels. And although calorie restricted diets or intermittent fasting have been found to lower IGF-1 levels, a vegan diet is associated with the lowest IGF-1 levels. Plant proteins don’t appear to elevate IGF-1 in the same way that animal proteins do. However high intakes of concentrated soy protein do seem to raise IGF-1 and it is possible that other vegan protein supplements may have a similar effect. Protein supplements are unnecessary and those with acne may benefit by avoiding them.

The hormone insulin also plays a role in acne as well as PCOS and of course, diabetes (type 2). High fat, calorie rich diets, particularly those high in meat, lead to the development of insulin resistance. The resistance to insulin is largely the result of fat-laden muscle cells no longer removing glucose from the blood in response to insulin. The body responds by producing even more insulin and this in turn leads to elevated androgen levels. There is some research suggesting that a low GI (glycaemic index) diet improves acne, presumably through reduced insulin levels.

It may seem intuitive that eating less carbohydrates might reduce insulin levels but this is not the case – a diet based more on fats and/or meat leads to increased insulin resistance. Diabetes research demonstrates that the most effective diet for reducing insulin resistance is a low fat, whole foods plant-based diet (Barnard et al 2009) .

Inflammation plays a role in many diseases including acne. It is the excessive inflammatory response to the trapped oil and bacteria that is responsible for the features of acne. The effectiveness of long term antibiotics for acne is thought to be due, in part, to their anti-inflammatory actions rather than their anti-microbial actions. Animal products, vegetable oils and processed foods promote inflammation throughout the body by multiple mechanisms. Whole plant foods – vegetables, fruits, whole grains and legumes – not only lack these pro-inflammatory effects but contain many phytochemicals that have potent anti-inflammatory effects. While some of these may be due to non-specific free radical scavenging effects, others act directly on some of the key cellular mediators of inflammation such as NFkb. A truly high intake of whole plant foods will alleviate acne and for those with fair skin, replace it with a healthy orange glow.

Sometimes a vegan diet is not enough to control acne. Fat-rich, calorie dense nut products and vegetable oils have become a common feature of modern vegan diets, while whole grains and vegetables have been in retreat. This is particularly true when eating out. The video under Success Stories below is a good illustration of how a rich vegan diet caused severe acne in two young vegan women and how they cured it by adherence to a low fat, whole foods, plant-based diet.



  • McDougall Message: Acne & Your Diet – In this video, Dr. John McDougall debunks the original study that suggested that diet had no effect on acne and then explains how dairy foods cause acne.
  • Skim Milk and Acne – This video looks at three Harvard studies that found a link between dairy consumption and acne in adolescent boys and girls. As with all videos, you will find links to the original studies under ‘Sources Cited’.
  • National Dairy Council on Acne and Milk  – This video discusses the observed association between milk consumption and acne published in the Journal of the American Academy of Dermatology. It then considers the natural hormones in milk and how these might cause acne. The presenter also raises the issue of drinking milk from pregnant cows.
  • The Acne-Promoting Effects of Milk – This short video discusses a publication on the insulin increasing effects of cow’s milk and the absence of acne in non-milk drinking societies. It is stated that the hormone signalling system of mammalian milk is exclusively designed for early infancy, and that the “chronic abuse” of this signalling system may be the cause of acne and many more serious chronic diseases.

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Page created 10 January 2013
Last updated 5 April 2017