This site is intended for health professionals only

Dietary treatment and prevention of type 2 diabetes

Norma McGough
BSc SRD
State Registered Dietitian

Diabetes mellitus is a condition in which the amount of glucose in the blood is too high because the body cannot use it properly. Glucose comes from the digestion of starchy foods such as bread and potatoes, and from sugar and foods that contain sugars. Glucose is also produced by the liver and passes into the bloodstream. Insulin, a hormone produced by the pancreatic b-cells, helps the glucose to enter the cells, where it is used as fuel by the body. The main symptoms of untreated diabetes are increased thirst, passing large amounts of urine, extreme tiredness, weight loss, genital itching and blurred vision. The main aims of treatment are to achieve near normal blood glucose levels, which helps to improve wellbeing and protect against long-term damage to the eyes, kidneys and nerves, while adopting a healthy lifestyle to protect the heart and major arteries.

Diabetes in the UK
There are 1.4m people currently diagnosed with diabetes in the UK. Out of this number more than one million adults are diagnosed with type 2 diabetes.(1) At least 80% of people with type 2 diabetes are overweight. Weight management is a crucial aspect in the prevention of type 2 diabetes and the management of diabetes in general.(2)
 
Types of diabetes
Type 1 diabetes develops when there is a severe lack of insulin in the body because most or all of the cells that make insulin have been destroyed. This type of diabetes usually appears before the age of 40. The cause is not known, although viruses may play a part. It is treated by insulin injections and diet control.
With type 2 diabetes the body can still make some insulin, although not enough for its needs, or the insulin that the body does make is not used properly. This type of diabetes usually appears in people over the age of 40. It is common among the elderly and overweight. It is treated by diet alone, diet and tablets, or sometimes by diet and insulin injections. Approximately 75-90% of people with diabetes have type 2 diabetes.

Risk factors for type 2 diabetes
Risk factors for type 2 diabetes include increasing age (with people between 40 and 75 being most at risk)(3); family history; being overweight (particularly with abdominal obesity); being of Asian or African-Caribbean origin; and women who have given birth to a large baby. The emerging public health problem of childhood obesity, both in developed and developing countries, is also leading to a rise in type 2 diabetes in children, particularly in association with other risk factors, such as ethnic group and family history.(4)

Insulin resistance
Insulin resistance is a reduced sensitivity of body tissues to the action of insulin. When cells do not respond to normal levels of insulin, glucose builds up in the blood, resulting in hyperglycaemia. To overcome this resistance and to maintain normal blood glucose levels, the pancreas secretes more insulin. However, excess insulin secretion can exhaust b-cell function, leading to further deterioration in both b-cell function and insulin sensitivity. When this occurs in people with insulin resistance, glucose homeostasis breaks down and type 2 diabetes occurs.(5) Although some people with insulin resistance develop diabetes, others do not.
 
Prevention of type 2 diabetes
There is clear evidence of the role of obesity as a risk factor for developing type 2 diabetes. In fact it is the most important underlying yet preventable risk factor for type 2 diabetes. Weight management and physical activity are both crucial aspects in the prevention of type 2 diabetes. The results of the Helsinki Study(6) and the Diabetes Prevention Programme(7) (a multicentre trial from the United States), both published last year, provide us with evidence of significant reductions in the onset of type 2 diabetes (58% and 71% respectively), when there is intervention with weight management and exercise programmes in people at risk. Weight reduction alone has been shown to reduce the risk factors associated with type 2 diabetes.

Weight management in diabetes care

Obesity is recognised as a leading cause of insulin resistance, and so weight management is crucial in controlling blood glucose levels in people with diabetes.(8) All aspects of diabetes management (blood glucose control, blood pressure control and blood lipid levels control) are improved by weight management. Weight management will also reduce the risk of heart disease and stroke and lower blood pressure. In addition, losing weight improves mobility and reduces tiredness and joint damage.
People with diabetes who are overweight or obese have a wide range of symptoms and complications. In general, more symptoms can be related to BMI (body mass index) than can be related to blood glucose. Weight management is associated with a reduction in secondary heart disease and increased life expectancy. In fact, modest weight loss (5-10%) is associated with increased survival in people with type 2 diabetes who are overweight. A weight loss of 10kg leads to a reduction of risk from diabetes-related death by more than 30%.(9) However, it is important to bear in mind that not all obese people develop type 2 diabetes, nor are all people with diabetes obese.

Dietary guidelines for people with diabetes
Diabetes UK, formerly the British Diabetic Association, made the first UK position statement on diet in diabetes care in the 1980s.(10) Previous advice had focused on carbohydrate intake and sugar restriction. The new recommendations promoted a diet in line with healthy eating recommendations for the general population and compatible with dietary advice for people at high cardiovascular risk. Further review, 10 years later, resulted in an update that reinforced the high-carbohydrate, low-fat diet.(11) More recent recommendations from other parts of the world have updated these recommendations.(12,13)

The ADA Guidelines
Last year, a technical review and position statement on medical nutrition therapy in diabetes care was published.(13) This is a comprehensive, evidence-based set of recommendations from the American Diabetes Association on medical nutrition therapy in diabetes care. Each recommendation is graded from A to C, according to the level of scientific evidence available, with A having the best available supporting evidence. The recommendations address lifestyle approaches for diabetes prevention and make a distinction between treating and managing diabetes and the complications of diabetes.
The recommendations set out the goals of nutrition therapy in diabetes care and also include goals for specific situations such as: young people with type 1 diabetes; young people with type 2 diabetes; pregnant and lactating women; and those at risk of diabetes. The first section includes nutrition recommendations for type 1 and type 2 diabetes - intake of carbohydrate, sweeteners, protein, fat, micronutrients and alcohol, energy balance and obesity, and special considerations. The second section reviews nutrition recommendations for special populations - children and adolescents, pregnant and lactating women, and older adults. The third section focuses on nutrition recommendations for acute complications - hypoglycaemia and acute illness - and associated conditions - hypertension, dyslipidaemia, nephropathy and catabolic illness. Finally, lifestyle recommendations for the prevention or delay of diabetes are also included.

Energy requirements
There is no change from the recommendations made by the ADA in 1994 on calorie distribution. There is still flexibility between the proportion of energy from carbohydrate and monounsaturated fat, accounting for 60-70% of total energy, and dependent on individual management goals, in particular energy intake, rather than a rigid prescription of calories from fat and carbohydrate. In the USA, and in most European countries, the average intake of protein is in excess of the recommended intake, and for those people with type 1 diabetes, especially those with hypertension, intakes of protein should not exceed 20% total energy because of the increased risk of nephropathy.
 
Fats
Reduced energy intake and modest weight loss improve insulin resistance in people with type 2 diabetes who are overweight. Weight management is therefore an important goal for this target group. One recommendation is that reduced fat diets, if maintained in the long term, can contribute to modest weight loss and improvement in dyslipidaemia. Cutting down on saturated fats and trans fats (found in fatty foods, like pastry, fried foods and cheese) and recommending use of low-fat versions of food in replacement for the full-fat varieties can reduce fat and calorie intake. In general, monounsaturated fat (olive and rapeseed oils) and fish should be chosen in preference to foods high in saturated fat, to help lower cardiovascular risk factors.

Carbohydrates
A consistent intake of carbohydrate is recommended for those individuals on fixed daily insulin regimens. Foods containing carbohydrates, such as wholegrains, fruits and vegetables, are recommended. In addition, there is "A level" evidence that sugar and sugary foods do not need to be restricted by people with diabetes, as sugar does not increase glycaemia to a greater extent than the same amounts of starch. In persons with type 2 diabetes, ingestion of a variety of starches or sugar, both acutely and for up to six weeks, produced no significant difference in glycaemic response if the amount of carbohydrate was similar. Therefore, the total amount of carbohydrate in meals and snacks is more important than the source or type of carbohydrate.(13) Although fibre should be encouraged, there is less emphasis on the benefits of cereal fibre other than for general gut health and satiety.

Supplements
The precise effects of antioxidant nutrients with regard to being potential cardioprotective factors are still uncertain. Routine supplementation of the diet with antioxidants is not advised because of the uncertainty related to long-term efficacy and safety.(13)
 
Physical activity
Regular daily physical activity is of benefit to people with diabetes, regardless of body weight. Physical activity aids weight control, improves insulin sensitivity and lipid levels, and reduces cardiovascular risk factors. Regular physical activity is also associated with a reduced risk of developing type 2 diabetes in overweight individuals. Therefore the promotion of regular physical activity should be included in any lifestyle advice. As a guide, substantial health benefits can be gained by accumulating at least 30 minutes of physical activity at a moderate intensity during most days of the week.(14,15) Activity includes both structured exercise, such as an aerobics class or gym session, and daily tasks such as walking to work, housework and gardening.

Summary
Most people diagnosed with diabetes will receive dietary advice from the primary care team, and in particular from practice and district nurses. It is vital that all members of the team who are involved in providing dietary advice give consistent, up-to-date information tailored to the individual with diabetes. Advising patients to eat a healthy balanced diet, to keep their weight at a reasonable level and to do regular physical activity, along with ongoing support and monitoring, is an approach that is likely to succeed.

Advice for patients with type 2 diabetes

  • Advise to eat regular meals based on carbohydrate foods, such as bread, pasta, chapatis, potatoes, rice and cereals.
  • Advise to cut down on fat intake, particularly saturated (animal) fats, which are linked to heart disease. Advise to use monounsaturated fats (eg, olive oil and rapeseed oil), to use less butter, margarine, cheese and fatty meats, and to choose low-fat dairy products in place of full-fat versions.
  • Advise to grill, steam or oven bake instead of frying or cooking with oil or other fats.
  • Advise to eat more fruit and vegetables - to aim for at least five portions a day.
  • Advise to use less salt, because a high intake of salt can be associated with high blood pressure. Advise to flavour food with herbs and spices instead of salt.
  • Advise to drink alcohol in moderation only - two units of alcohol per day for women and three units per day for men. Alcohol should not be consumed on an empty stomach, as alcohol can induce hypoglycaemia.

Key points

  • Diabetes mellitus affects some 3% of the UK population, and the prevalence is predicted to double by 2025
  • Type 2 diabetes results in long-term health complications such as cardiovascular disease
  • Weight management and physical activity can reduce the risk of type 2 diabetes and its associated complications
  • There is a need for consistent, evidence-based dietary advice in the management of people with diabetes

References

  1. Amos AF, et al. The rising global burden of diabetes and its complications: estimates and projections to the year 2010. Diabet Med 1997;14 Suppl 5:S1-85.
  2. Tuomilehto J. Primary prevention of non-insulin dependent diabetes mellitus: a dream or reality? In: Alberti KGMM, Mazze RS, editors. Current trends in non-insulin dependent diabetes mellitus. Amsterdam: Elsevier Science; 1989.
  3. Diabetes UK. Available from URL: http://www.diabetes.org.uk/diabetes/get.htm
  4. Ehtisham S, et al. Type 2 diabetes mellitus in UK children - an emerging problem. Diabetes Med 2000;17:867-71.
  5. Marks V. Insulin resistance in relation to diabetes. Nutr Pract 2002;3(2):1-4.
  6. Tuomilehto J, et al. Prevention of type 2 diabetes mellitus by changes in lifestyle among subjects with impaired glucose tolerance. N Engl J Med 2001;344:1343-50.
  7. Diabetes Prevention Program Research Group. Information on the website of US National Institute of Diabetes and Digestive and Kidney Diseases; 2001. Available from URL: http://www.preventdiabetes.com
  8. Krotkiewski M, et al. Impact of obesity on metabolism in men and women. Importance of regional adipose tissue distribution. J Clin Invest 1983;72:1150-62.
  9. Lean MEJ, et al. Obesity, weight loss and prognosis in type 2 diabetes. Diabetes Med 1990;7:228-33.
  10. Nutrition Subcommittee of the BDA's Medical Advisory Committee. Dietary recommendations for diabetics for the 1980s. A policy statement. Hum Nutr Appl Nutr 1982;36:378-94.
  11. Nutrition Subcommittee of the BDA's Professional Advisory Committee. Dietary recommendations for people with diabetes: an update for the 1990s. Diabet Med 1992;9:189-202.
  12. The Diabetes and Nutrition Study Group of the European Association for the Study of Diabetes. Recommendations for the nutritional management of patients with diabetes mellitus. Eur J Clin Nutr 2000;54:353-5.
  13. Evidence-based nutrition principles and recommendations for the treatment and prevention of diabetes and related complications from the ADA. Diabetes Care 2002;25:202-12. Available from URL: http://care.diabetesjournals.org/ cgi/content/full/25/1/202
  14. Department of Health. Obesity: reversing the increasing problem of obesity in England: a report from the Nutrition and Physical Activity Task Forces. London: HMSO;1995.
  15. Department of Health. More people, more active, more often. Physical activity in England. London: HMSO; 1995.

Resources
Diabetes UK
10 Parkway London NW1 7AA
T:020 7424 1000
F:020 7424 1001
E:info@diabetes.org.uk
W:www.diabetes.org.uk

British Nutrition Foundation
High Holborn House
52-54 High Holborn
London WC1V 6RQ
W:www.nutrition.org.uk