Diabetes

Diabetes mellitus is a chronic disease caused by too much sugar (glucose) in the blood. Blood sugar levels rise when there is not enough insulin in the blood or the insulin that is in the blood does not work properly. Insulin is an important hormone secreted by the beta cells of the islets of Langerhans in the pancreas. It regulates blood sugar levels by, for example, promoting the uptake of glucose into the cells. When things go wrong, high levels of glucose in the blood can cause damage to the nerves and blood vessels. Without treatment diabetes can lead to long-term health problems including kidney failure, gangrene, sensory loss, ulceration, blindness, cardiovascular disease and stroke.

Type 1 and Type 2 diabetes

There are two main types of diabetes. Type 1 (insulin-dependent diabetes) occurs when the body produces little or no insulin. People who have type 1 diabetes must check the levels of glucose in their blood regularly and will need treatment for the rest of their lives. Type 1 diabetes is sometimes called juvenile-onset diabetes because it tends to develop before the age of 40, often in the teenage years. The peak age for diagnosis in the UK is between 10 and 14 years but is becoming younger with a steep rise in the under fives (Williams and Pickup, 2004). Symptoms include a frequent urge to urinate, extreme thirst and hunger, weight loss, fatigue, irritability and nausea. The cause of type 1 diabetes is poorly understood, but some evidence suggests it involves a combination of genetic factors and environmental triggers. Type 1 diabetes is usually treated with regular injections of insulin to regulate blood sugar levels.

Over 80%
of people with type 2 diabetes are overweight

NHS Direct, 2005

Type 2 diabetes occurs either when the body does not produce enough insulin or when it cannot use the insulin produced. This type of diabetes is linked with obesity. Over 80 per cent of people with type 2 diabetes are overweight (NHS Direct, 2005). Type 2 diabetes occurs mostly in people over the age of 40, but is now increasingly affecting people at a much younger age. Symptoms include tiredness, irritability, nausea, hunger, weight loss, recurrent skin infections, blurred vision, tingling sensations in the hands and feet and dry, itchy skin. Not all symptoms occur and those that do might be subtle and may go unnoticed for years. Blood sugar levels in type 2 diabetes can be controlled by lifestyle changes including regular exercise coupled to diet control and weight loss. Type 2 diabetes accounts for over 80 per cent of all cases of diabetes seen. While rising obesity levels have contributed to the increase in the incidence of type 2 diabetes, the increase in obesity does not explain the threefold increase in the number of cases of type 1 diabetes seen over the last 30 years. This is the most common form of the disease in children; over 90 per cent of children under the age of 16 with diabetes have type 1.

Gestational diabetes

A third type of diabetes, gestational diabetes, develops in some women during pregnancy but usually disappears after giving birth.

Diabetes affects over one million people in the UK but there may be as many as a million others who have the disease but do not know it yet. The WHO describes the global rise in diabetes as epidemic (WHO, 2006a). In 1985 an estimated 30 million people worldwide had diabetes; a decade later this figure had increased to 135 million and by 2000 an estimated 171 million people had diabetes. It is predicted that at least 366 million people will have diabetes by 2030 (WHO, 2006a). The increase in diabetes is attributed to a range of factors including population growth, ageing, unhealthy diets that are high in saturated fat and cholesterol, obesity and lack of physical exercise.

Diabetes has become one of the major causes of premature illness and death in many, but not all, countries. Indeed, diabetes occurs much more in some parts of the world, principally in developed countries. Diabetes tends to occur more in cultures consuming diets high in animal fats and less in cultures consuming diets high in complex carbohydrates. As carbohydrate intake increases and saturated animal fat intake decreases from country to country, the number of deaths from type 2 diabetes plummets from 20.4 to 2.9 people per 100,000 (Campbell and Campbell, 2005).

In England and Wales, the rates of diabetes fell markedly between 1940 and 1950. This is because during the Second World War, and in the period following it, people tended to eat less fat and sugar and more plant foods, and therefore more fibre, antioxidants, complex carbohydrates, vitamins and minerals (Trowell, 1974). All available land was used; many people grew their own vegetables and vegetable patches were cultivated all over the country. Gardens, flowerbeds and parks were dug up and planted with vegetables; even the moat around the Tower of London (drained in 1843) was used for growing vegetables. Then as rationing came to an end and people moved away from whole grains towards a more processed diet, rates of diabetes increased again (Trowell, 1974). The conclusion must be that a high-carbohydrate, low-fat plant-based diet offers some protection against type 2 diabetes.

The risk factors for type 2 diabetes (obesity, poor diet and lack of exercise) are well-documented and there are many steps people can take to limit their chances of developing type 2 diabetes. One obvious step is to reduce the amount of saturated fat in the diet, this means cutting down on meat and dairy and increasing the intake of fruit, vegetables, whole grains, pulses, nuts and seeds. Large, population-based studies in China, Canada, USA and several European countries suggest that even moderate reduction in weight and half an hour of walking each day reduces the risk of diabetes considerably (WHO, 2006a).

A study of the relationship between diet and chronic disease in a cohort of 34,192 California Seventh-day Adventists revealed that the vegetarian Adventists were much healthier than their meat-eating counterparts: the meat-eaters were twice as likely as the vegetarians to suffer from diabetes (Fraser, 1999). This study also revealed that obesity increased as meat consumption increased; the difference between vegetarian and non-vegetarian men and women was 6.4kg and 5.5kg respectively (Fraser, 1999).

The importance of high-fibre diets in diabetes has been studied extensively since the 1970s by James Anderson, Professor of Medicine at the University of Kentucky. Anderson used a high-fibre, high-carbohydrate low-fat diet to treat 25 type 1 and 25 type 2 diabetics (Anderson, 1986). The experimental diet consisted mostly of whole plant foods (although it did contain a small amount of meat). After three weeks, Anderson measured blood sugar levels, weight and cholesterol levels and calculated their medication requirements. The results were astounding. Remember in type 1 diabetes no insulin is produced so it seems unlikely that a change in diet would help. However, Anderson’s patients required 40 per cent less insulin medication than they had needed before the trial. In addition to this, their cholesterol levels dropped by an average of 30 per cent too. This is just as important in lowering the risk factors for secondary outcomes of diabetes such as heart disease and stroke. Type 2 diabetes is generally more treatable and the results among the type 2 patients were even more impressive: 24 out of the 25 participants consuming the high-fibre, low-fat diet were able to stop taking their insulin medication completely! These benefits were not of a temporary nature, indeed they were sustained over time in a group of 14 diabetic men continuing on the high-carbohydrate, high-fibre diet for four years (Story et al., 1985). The evidence is overwhelming: a high-carbohydrate, high-fibre diet provides effective, positive and safe treatment for diabetes and lowers the associated risk for coronary artery disease (Anderson et al., 1990). Of course it should be noted that this is not a special diet for diabetics; most people would benefit from increasing their fibre intake while reducing the amount of fat they consume.

In 2000 an extensive study of children from 40 different countries confirmed a link between diet and incidence of type 1 diabetes (Muntoni et al., 2000). The study set out to examine the relationship between dietary energy from major food groups and incidence of type 1 diabetes. The total energy intake was not associated with type 1 diabetes incidence. However, energy from animal sources (meat and dairy foods) was associated and energy from plant sources was inversely associated with diabetes. This means that the more meat and milk in the diet, the higher the incidence of diabetes and the more plant-based food in the diet, the lower the incidence.

Type 1 diabetes is an autoimmune disease where the immune system’s ‘soldiers’, known as T-cells, destroy the body’s own insulin-producing beta cells in the pancreas. This type of response is thought to involve a genetic predisposition (diabetes in the family) coupled to an environmental trigger. The trigger may be a virus or some component of food. In the early 1990s a Canadian research group suggested that cow’s milk proteins might be an important environmental trigger providing specific peptides that share antigenic epitopes with host cell proteins (Martin et al., 1991). This means that the proteins in cow’s milk look the same as proteins in our own bodies; these similarities can confuse our immune system and initiate an inappropriate (autoimmune) response that can lead to diabetes.

The milk protein casein is similar in shape to the insulin-producing cells in the pancreas. Because the body may perceive casein as a foreign invader and attack it, it may also start to attack the pancreas cells having confused them for casein, again leading to diabetes (Cavallo et al., 1996). Some studies have suggested that bovine serum albumin (BSA) is the milk protein responsible. In a study of 142 children with type 1 diabetes, all the diabetic patients had higher serum concentrations of anti-BSA antibodies compared to 79 healthy children (Karjalainen et al., 1992). These antibodies may react with proteins on the surface of the beta cells of the pancreas and so interfere with insulin production.  

Other studies suggest it is the cow’s insulin present in formula milk that increases the risk of type 1 diabetes in infants (Vaarala et al., 1999). Research shows that some infants may be more vulnerable to type 1 diabetes later in life if exposed to cow’s milk formula while very young. A Finnish study of children (with at least one close relative with type 1 diabetes) examined whether early exposure to insulin in cow’s milk formula increased the risk of type 1 diabetes. Results showed that infants given cow’s milk formula at three-months-old had immune systems which reacted far more strongly to cow’s insulin (Paronen et al., 2000). This raises concerns that exposure to cow’s insulin plays a role in the autoimmune process leading to type 1 diabetes.

A review of the clinical evidence suggests that the incidence of type 1 diabetes is related to the early consumption of cow’s milk; children with type 1 diabetes are more likely to have been breast fed for less than three months and to have been exposed to cow’s milk protein before four months of age (Gerstein et al., 1994). The avoidance of cow’s milk during the first few months of life may reduce the risk of type 1 diabetes. Infants who cannot breast feed from their mothers may benefit more from taking a plant-based formula such as soya-based formula rather than one based on cow’s milk. Other studies support the finding that both early and adolescent exposure to cow’s milk may be a trigger for type 1 diabetes (Kimpimaki et al., 2001; Thorsdottir and Ramel, 2003).

Taken together, the evidence suggests that avoiding milk and milk products may offer protection from diabetes (types 1 and 2).