Nutritional Priorities: Type 2
The overall aim of nutritional therapy in type 2 diabetes is to promote a healthy, balanced diet with particular consideration for the dietary factors that affect glycaemic control and cardiovascular health. It is recommended that dietary advice should be provided by a healthcare professional with the appropriate expertise and competencies in nutrition and behaviour change, but all members of the MDT should be knowledgeable about diet and diabetes and help to support individuals with their dietary goals.
Diet for diabetes
There is no special diet for diabetes. The principles of healthy eating which apply to the general population are recommended. The eatwell plate model illustrates the proportion of the different food groups that should be included in the diet in order to maintain health. Foods marketed towards people with diabetes are generally not recommended. They provide no benefit over standard products, are typically more expensive, can still elevate blood glucose levels and can also have a laxative effect. The recommendations for alcohol intake are also no different for those with type 2 diabetes as the general population (i.e. no more than 2-3 units per day for females, 3-4 units per day for males and at least 2 alcohol free days per week). Special consideration should be given to those who take insulin or insulin secretagogues due to an increased risk of hypoglycaemia following alcohol intake. It may be necessary to take additional carbohydrate before, during or after alcohol or to alter insulin doses in order to protect against hypoglycaemia.
One of the risk factors for developing type 2 diabetes is being overweight or obese. As a result, a high proportion of people with type 2 diabetes are overweight or obese at diagnosis with a degree of insulin resistance. Weight management is therefore one of the nutritional priorities in type 2 diabetes. Weight loss is associated with many positive health outcomes, including reduced insulin resistance, hyperglycaemia and blood lipids. Decreasing energy intake and increasing expenditure should be the main focus of any weight management plan. Any degree of weight loss for those who are overweight or obese is positive and can lead to improvements in health outcomes. However, a 5-10% weight loss is considered an appropriate, achievable starting point for most individuals whose body mass index (BMI) is above 25kg/m2 . Giving consideration to the effect of medication on body weight is also important in order to help the individual choose achievable goals. For example, it is estimated that sulfonylureas and insulin are associated with weight gain of up to 6.5kg, with GLP-1 agonists resulting in weight loss of up to 4kg. Working with individuals to set realistic targets for weight management is likely to improve motivation and encourage long term improvements in lifestyle choices.
There is evidence to suggest that different approaches to weight loss can be effective, including low fat, Mediterranean, low carbohydrate, very low calorie diets (VLCD) plus national or local slimming groups. The overall aim of any weight loss strategy should be a reduction in energy intake whilst maintaining sufficient intake of nutrients to maintain health. The use of commercial slimming groups may be appropriate for some individuals as they provide regular contact and peer support, which can be motivating factors. Weight Watchers, Slimming World and Rosemary Conley are examples of national slimming groups, with many areas running their own local versions. Very low calorie diets (VLCD), defined as providing 800kcal per day, have been proven to be effective in the short term for weight loss, however they are difficult to adhere to long term and are associated with a higher rate of weight regain compared with low fat diets. It is also recommended that VLCDs should only be followed short term (<12 weeks) and with expert supervision. The most effective method for weight loss will depend on many factors, including local provision, individual preferences, co-morbidities, ability and motivation.
Blood glucose management
Limiting hyperglycaemia is an important objective for people with type 2 diabetes which is greatly affected by diet. Depending on medication that is used, the prevention of hypoglycaemia may also be a necessary consideration. From a dietary perspective, the amount (portion size) of carbohydrate ingested has the greatest impact on blood glucose levels compared to the other macronutrients. Having an awareness of which foods contain carbohydrate and an understanding of portion sizes can help someone with diabetes understand the effect of food on their blood glucose level. There have been many different low carbohydrate diets that have become popular over the years, including the Atkins and Dukan diets. The underlying principle of these diets is that a reduction in the amount of carbohydrate ingested can help to prevent hyperglycaemia. However, it has been suggested that low carbohydrate diets could lead to suboptimal intakes of water soluble vitamins and fibre and therefore the nutritional adequacy of such diets could be questioned.
There are two types of carbohydrate – sugars and starches. Both cause blood glucose levels to increase. Examples of starchy food include bread, rice, pasta, potatoes and yam. Sugars can be found in fruit and fruit juice (fructose), milk and milk products (lactose) plus added sugars in cakes, biscuits, chocolate, etc. It is often stated that people with diabetes should have a sugar free diet. However, this would actually mean cutting out foods from the diet that are beneficial to health (e.g. fruit, dairy). The type of carbohydrate found in most fruit, milk and yoghurts causes blood glucose levels to rise slowly. Some starchy foods (e.g. white bread) can cause a rapid elevation of blood glucose level. The rate at which carbohydrates are digested and absorbed into the blood stream is known as the glycaemic index (GI). A high glycaemic index food will cause a rapid increase in blood glucose level compared with a low glycaemic index food. Although consideration of the GI of foods can give added benefit to help control blood glucose levels, the portion size of carbohydrate ingested in one sitting is the most important factor that influences blood glucose level.
Cardiovascular disease (CVD) is twice as common in people with diabetes compared with the general population and accounts for 52% of deaths among people with type 2 diabetes. Diet can have a major effect on CVD risk factors including cholesterol, blood lipids, blood pressure and hyperglycaemia. In order to minimise CVD risk factors, the following dietary advice is recommended:
- reduce weight if overweight or obese (BMI >25kg/m2)
- reduce intake of saturated fat and trans fat and choose monounsaturated fat sources (e.g. choose low fat dairy, oily fish, nuts)
- choose high fibre options of carbohydrate foods
- limit salt intake to less than 6g per day
To summarise, the aim of nutritional intervention in type 2 diabetes should be to limit hyper and hypoglycaemia and improve cardiovascular risk factors, namely blood pressure and lipids. These aims can be achieved through having a healthy, balanced diet which includes adequate portions from each of the food groups. Special emphasis should be given to carbohydrate portion sizes, high fibre choices, the avoidance of added salt or frequent consumption of high salt foods and a limited intake of saturated fat. Aiming for weight loss if overweight or obese through a reduction of energy intake and an increase in energy expenditure is also a priority. Support and dietary advice should be provided by a suitably qualified professional, which would ideally involve referral to a structured group education program involving a dietitian or referral to a dietetic service for one to one advice and support.
^ NICE (2010) Type 2 diabetes: The management of type 2 diabetes, Clinical guideline 87.
^ Franz, M. J., Warshaw, H., Daly, A.E., Green-Pastors, J., Arnold, M.S., & Bantle, J. (2003), Evolution of diabetes medical nutritional therapy, Postgrad Med J, 79:30–35
^ NICE (2011) Preventing type 2 diabetes: population and community level interventions, public health guidance 35
^ Diabetes UK (2011) Evidence-based nutrition guidelines for the prevention and management of diabetes.
^ UK Prospective Diabetes Study (UKPDS) Group (1998), Intensive blood-glucose control with sulphonylureas or insulin compared with conventional treatment and risk of complications in patients with type 2 diabetes (UKPDS 33), Lancet, 352: 837–853.
^ Phung, O.J., Scholle, J.M., Talwar, M. & Coleman, C.I. (2010), Effect of Noninsulin Antidiabetic Drugs Added to Metformin Therapy on Glycemic Control, Weight Gain, and Hypoglycemia in Type 2 Diabetes, JAMA, April 14, Vol 303, No. 14, pp 1410-1418.
^ Hankey, C.R. (2010) Management of obesity Weight-loss interventions in the treatment of obesity – Symposium on “Dietary management of disease”, Proceedings of the nutrition society, 69:34-38
^ Castaneda-Gonzalez, L.M., Gascon, M.B., & Cruz, A.J. (2011) Effects of low carbohydrate diets on weight and glycaemic control among type 2 diabetes individuals: a systemic review of RCT greater than 12 weeks. Nutricion Hospitalaria, 26, 1270-1276.
^ Diabetes UK (2012), Diabetes in the UK 2012 – Key statistics on diabetes.