Macronutrients and type 1 diabetes

The ideal macronutrient composition for optimum glycaemic control is yet to be defined. Carbohydrate causes the majority of variation in glycaemia however it is known that protein and fat also play a significant role.

Carbohydrate

Carbohydrates are an important source of energy. The term carbohydrate encompasses both starches and sugars. Guidance from the Department of Health in 1991 recommended that we should consume 50% of our daily energy requirements from carbohydrate.[1] In June 2014 the Scientific Advisory Committee on Nutrition (SACN) released a draft report suggesting that we should continue to advocate this, with people choosing wholegrain varieties where possible (SACN, 2014). [2] The majority of this should come from the starchy form and only a small portion from sugary sources. The brain requires 130g carbohydrate per day but the reference nutrient intake is 260g per day, to allow for daily physical demands.[1]

Diabetes UK found that consuming over 50% of daily energy from carbohydrates was not appropriate for everyone. In 2011, their nutritional guidelines were revised to state that there is not an ideal percentage of energy which should come from carbohydrate for optimal blood-glucose control. [3]

Prior to the discovery of insulin in 1922, dietary restriction was the only treatment available for Type 1 diabetes mellitus with intakes of less than 10% energy from carbohydrate advocated. In the 1940s and 50s the suggested percentage energy from carbohydrate had risen to 25-30% and exchange lists came into use. Eventually in the 1980s restrictions were lifted with the initiation of carbohydrate counting programmes such as DAFNE. The use of low carbohydrate diets for the treatment of diabetes mellitus is a controversial topic. The term “low carbohydrate diet” is subjective with differing quantities of carbohydrate being proposed, ranging from 20g to 130g per day. There is no firm evidence to suggest that low carbohydrate diets improve glycaemic control or reduce the risk of diabetic complications in people with Type 1 diabetes.

The amount and type of carbohydrate consumed will have varying effects on blood glucose levels. Theory suggests that 10g of carbohydrate can increase blood glucose levels by 2-3mmol/l in people with Type 1 Diabetes. An increased carbohydrate load will slow gastric emptying and blood glucose levels will rise later than expected. A carbohydrate load of over 100g tends to lead to greater error in estimation of carbohydrate value leading to erratic blood glucose levels.

The Glycaemic Index (GI) is a list of foods numbered from 1-100 depending on how quickly they affect blood glucose levels. Lower GI foods such as basmati rice, sweet potato and granary bread digest and convert to glucose more slowly resulting increased blood glucose levels later than expected. The risk of hypoglycaemia soon after eating these types of foods is high due to rapid acting insulin onset time being faster than the breakdown of these foods to glucose. If consuming over 50-60g of carbohydrate at any one time or eating a low GI meal, individuals on Continuous Subcutaneous Insulin Infusion (CSII) are recommended to use an extended/square wave bolus or a multiwave/dualwave bolus with a 50:50 or 70:30 split over 2 hours. Those on multiple daily injections (MDI) could split their dose, taking some upfront and the remainder 1-1 ½ hours later.

When individuals with diabetes experience hypoglycaemia they rely solely on the release of stored glucose. Injected insulin cannot be removed in the way that endogenous insulin production is reduced in the non-diabetic population. To counteract the relative insulin excess may take hours and therefore the use of 15 - 20g rapid acting carbohydrate is essential. Examples include 120ml Lucozade, 5 jelly babies, 150ml full sugar cola, 4-5 dextrose tablets. Symptoms such as hunger or fear of hypoglycaemia may lead to over consumption of appropriate and inappropriate treatment. This is likely to lead to high blood glucose levels which are combated with additional insulin doses possibly resulting in further hypoglycaemia and creating a vicious circle.

Fat

Fats fulfill a wide range of functions including, providing fuel for cells and essential fatty acids and carrying fat soluble vitamins. Current guidelines recommend that we consume no more than 35% of our daily energy from fat. [1] Fatty foods have no direct effect on blood glucose levels; yet their indirect effect can be quite significant. Excessive consumption of any nutrient can lead to weight gain; however, containing 9kcal per gram, fats are the most concentrated source of energy in the diet. The prevention of obesity in individuals with Type 1 diabetes is imperative. Obesity has several adverse effects on blood pressure, lipid profile and insulin resistance. Individuals with diabetes have an increased risk of cardiovascular disease therefore encouraging the consumption of a healthy diet is vital in the management of this patient group. Encouraging the replacement of saturated fats with mono-unsaturated fats is recommended. Saturated fats have been shown to increase LDL cholesterol levels and the development of atherosclerosis. They can be found in animal products and baked goods such as pies and pastries. Alternatives such as olive oil and rapeseed oil should be encouraged, as well as choosing leaner cuts of meat and avoiding cooking methods such as frying. [4]

Recent studies have suggested that dietary fat may contribute to delayed increases in blood glucose levels. This is because the presence of fat will slow the rate of gastric emptying. Individuals may be at risk of hypoglycaemia shortly after a high fat meal. The onset time of rapid acting insulin is likely to be faster than the digestion and absorption carbohydrate taken as part of a high fat meal. To combat this, it is suggested that those who are on MDI should either give insulin after this type of meal or split their dose (50% upfront and 50% 1-1 ½ hours later). Those using CSII should use an extended/ square wave or multi/dual wave bolus. [5] For the above reason, the use of high fat foods such as chocolate and milk are inappropriate treatments for hypoglycaemia.

Protein

Protein is essential for muscle growth and repair. The current recommendation for the dietary intake of protein is 15% of total daily energy. The dietary reference value for healthy individuals is currently 0.75g/kg of ideal body weight; however this can vary according to specific states such as infection, renal disease, pregnancy and lactation. [1]

It has been suggested that long-term high protein intakes can have a detrimental effect on renal function; however recent studies have refuted this and reported that it is only the case where renal impairment is already present. With that in mind, The National Kidney Foundation state that around 30% of people with Type 1 diabetes and 10-40% of those with Type 2 will eventually suffer from some form of renal disease. [6]

When consumed protein is broken down into amino acids. The presence of these amino acids will stimulate the release of insulin to help transport them to muscle cells. Glucagon is also released to counteract insulin and ensure blood glucose levels remain stable. In individuals with diabetes only glucagon is released. Glucagon will stimulate the liver to breakdown glycogen which appears in the blood as glucose; it will also act to convert amino acids into glucose in a process called gluconeogenesis. This process takes longer than carbohydrate metabolism and therefore will cause a delayed rise in post prandial blood glucose. [7]This can be difficult to manage when on MDI as rapid acting meal time insulin has around four hour duration of action. It is likely the blood glucose level will rise after this. Patients using continuous subcutaneous insulin infusion (CSII) can combat this by using an extended/square wave bolus for high protein meals.

Fat and Protein Counting

Many studies have been carried out to determine the effects of protein and fat and whether we should be advising our patients to also count these food groups when calculating insulin doses. A popular method titled “The Warsaw Method” was developed by Ewa Pankowska in 2012. It uses both carbohydrate units (CU) and fat/protein units (FPU). [1] FPU equals 100kcal from protein and fat. A multiwave or dual wave bolus would be used by giving insulin upfront for CU and extending the insulin required for the FPU. The time extended for will depend on the number of FPU. For example 1 FPU = 3 hours, 2FPU = 4 hours, 3 FPU = 5hours, 3+ FPU = 8hours.[8]

In theory it is very challenging for individuals to count all 3 food groups and therefore a more simple starting point could be to extend insulin doses by 1 hour per 10g of fat and/or count protein on a ½ : 10g ratio (for meals containing more than 50g of protein).

Final Thoughts

Achieving optimum glycaemic control is challenging for all individuals with Type 1 diabetes. Accurate carbohydrate counting is key, however, in reality it is more of an art than a science. Bolus doses need to be continuously fine-tuned, taking into account individual factors such as nutritional composition of meals/ snacks, current glycemic control, lifestyle and activity.

Counting carbohydrate is demanding enough on its own. The introduction of fat and protein counting must be carefully considered on an individual patient basis. In practice many people guess the carbohydrate content of their meals and snacks therefore we have to ask ourselves is counting fat and protein a help or a hindrance? Ultimately methods used to control diabetes should be selected by the individual after informed discussions.

References

  1. ^ Department of Health (1991) Dietary reference values for food energy and nutrients for the United Kingdom. London: HMSO Publications.

  2. ^ Scientific Advisory Committee on Nutrition (SACN) (2014) Draft Carbohydrates and Health Report. Available at: https://www.gov.uk/government/uploads/system/uploads/attachment_data/file/339771/Draft_SACN_Carbohydrates_and_Health_report_consultation.pdf (Accessed 07/09/2014).

  3. ^ Diabetes UK (2011) Evidence-based nutrition guidelines for the prevention and management of diabetes. London: Diabetes UK.

  4. ^ Thomas and Bishop (2007) The Manual of Dietetic Practice. 4th Edition. Oxford: Blackwell Publishing.

  5. ^ Walsh, J. and Roberts, R. (2000) Pumping insulin: everything you need for success with an insulin pump. 3rd edn. San Diego: Torrey Pines Press.

  6. ^ National Kidney Foundation (2013) Available at: http://www.kidney.org/atoz/content/diabetes.cfm (accessed 12/08/2014)

  7. ^ Hughes, R. (2007) Type 1 Diabetes in Children, adolescents and young adults, 3rd edition, London: Class publishing

  8. ^ Pankowska, E., Błazik, M. and Groele L. (2012) Does the fat-protein meal increase postprandial glucose level in type 1 diabetes patients on insulin pump: the conclusion of a randomized study. Diabetes Technology and Therapeutics, 14 (1) pp, 16-22.

Comments

Nobody has commented on this article

Commenting is only available for registered Diapedia users. Please log in or register first.