Dietary strategies for preventing the onset of diabetes

The different natures of the two types of diabetes requires diverse dietary strategies in order to prevent their onset. For type 1 diabetes, while the exact causes are still being investigated, it is acknowledged that various environmental factors increase the risk of diabetes in genetically susceptible subjects. If these factors can be identified, there could be a good chance of decreasing the incidence of the disease.

It has been suggested that for type 1 diabetes an early exposure to cows' milk proteins may play a role in triggering the immune response that destroys pancreatic beta-cells.2 Observational studies have shown that breastfeeding is associated with a lower incidence of type 1 diabetes.3'4 It is hoped that the multicentre study, 'Trial to Reduce Type 1 Diabetes in the Genetically at Risk' (TRIGR) started in May 2002 will give a definite answer to this hypothesis. In this study, an offspring of someone with diabetes or first degree relative who possesses a high-risk genetic susceptibility to type 1 diabetes should be breastfed for at least 6 months of life. If the mother is unable to exclusively breastfeed, her child will then be randomly assigned to one of two groups. One group receives breastfeeding supplements of a special formula based on extensively hydrolysed cows' milk proteins; the other group receives a normal formula containing cows' milk with a small amount of hydrolysed proteins. In the hydrolysed cows' milk formula, the large molecular weight milk proteins are split into fragments too small to stimulate an immune response. The rationale here is that the immune response in young infants genetically predisposed to type 1 diabetes is less mature and therefore unable to handle large intact food proteins. This sets up an immune response which can ultimately lead to the autoimmune destruction of insulin-producing cells.

Other dietary factors being investigated include the active form of vitamin D,5 which is thought to help prevent the development of autoimmune diabetes and gluten since studies have shown that islet cell antibodies may disappear after a gluten-free diet in celiac patients.6'7 However, time is needed before an answer on the efficacy of these dietary intervention trials is known.

There are various risk factors for developing type 2 diabetes. One of the primary ones being obesity as defined by a body mass index of over 30 (Table 7.1). Other risk factors include increased age, a family history of diabetes, prior history of gestational diabetes, impaired glucose tolerance, physical inactivity andrace/ethnicity. For example, African Americans, Hispanic/Latino Americans, American Indians, some Asian Americans and Pacific Islanders are at particularly high risk of developing type 2 diabetes (Table 7.2). In recent years there has been an increase in type 2 diabetes related to changes in life style such as inactivity and diets rich in saturated fats. Approximately 80 per cent of people with type 2 diabetes are obese. Obesity is increasing both in the developed and in the developing countries. In the UK 20 per cent of the population is obese.8 There is a worldwide trend towards obesity among children, and in the UK about 15-20 per cent of the teenage population is obese.9

The association between abdominal obesity (waist circumference >102 cm in men, >88 cm in women10), high low-density lipoprotein (LDL) cholesterol, low high-density lipoprotein (HDL) cholesterol, hypertriglyceridaemia, high blood pressure, high fasting glucose (impaired glucose tolerance IGT > 110mg/dL and < 126mg/dL), and insulin resistance (known as metabolic syndrome) is highly predictive of type 2 diabetes and potential coronary disease. Recently, a large clinical trial, the 'Diabetes Prevention Program' (DPP),11 investigated whether diet and physical activity were more effective than metformin in preventing or delaying the onset of type 2 diabetes in subjects with impaired glucose tolerance and a family history of type 2 diabetes. The results of this study showed that the group that underwent lifestyle changes, intensive nutrition and exercise counselling (150 minutes a week) and behaviour modification lost 7 per cent of their body weight, with a 58 per cent reduction in the incidence of

Table 7.1 Body mass index and accepted criteria for defining body weight

<18.5

Underweight

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