Medical Nutrition Therapy

Medical nutrition therapy (MNT) is an important component of diabetes self-management. MNT has been shown to decrease A1C by approximately 2% among people with newly diagnosed type 2 diabetes[1] and by 1% among people with newly diagnosed type 1 diabetes.[2] Although many patients still believe that there is a “diabetic diet,” healthy nutrition recommendations for the general public are also appropriate for people with diabetes.

The goals of medical nutrition therapy for all people with diabetes are: 1) to attain and maintain optimal metabolic outcomes; including blood glucose and A1C level, LDL and HDL cholesterol and triglyceride levels, blood pressure and body weight; 2) to prevent and treat all diabetes complications; 3) to improve health through healthy food choices; and 4) to address individual nutritional needs, taking into account personal preferences, cultural preferences, lifestyle, and willingness to change.[3]

For all people with diabetes, carbohydrates should comprise 45% to 65% of daily caloric intake. Both the amount and source of carbohydrate affect glycemic levels. Because of the strength of the association between amount of carbohydrate and glycemic levels, most approaches to meal planning focus primarily on amount. However, approaches that incorporate glycemic index may offer additional benefit on glycemic control over and above what can be achieved by using approaches that focus solely on carbohydrate amount. In spite of the increased popularity of the high-protein and low-carbohydrate diet, this approach is not recommended, as the long-term consequences on plasma LDL are not known.[3]

MNT and type 1 diabetes

In terms of medical nutrition therapy for type 1 diabetes, the most important goal is to integrate insulin therapy into the patient’s normal dietary routine and preferences. Because carbohydrate content in a meal is the major determinant of insulin requirements, most meal planning techniques focus primarily on carbohydrates. Premeal insulin dose should be adjusted to accommodate for carbohydrate content of a given meal. If insulin dose is fixed, then it is important that carbohydrate content be kept constant from day to day. However, insulin analogs offer patients a greater amount of flexibility in meal timing.[4]

There are a number of different approaches to diabetes meal planning.[4] The exchange list is a system that categorizes foods based on their nutritional properties. Because the exchange list system is difficult to learn, many patients prefer the carbohydrate counting method. This method is based on the assumptions that all carbohydrates (regardless of type) have a comparable effect on blood glucose levels and that carbohydrates have the greatest effect on blood glucose levels. People who use this method can count carbohydrate grams, carbohydrate choices (where each choice is 15 g of carbohydrates), or can use a carbohydrate/insulin ratio (appropriate only for patients using a pump or for patients using a flexible regimen with a long-acting basal insulin combined with variable amounts of rapid-acting insulin at meals). Training in appropriate adjustment of insulin to match carbohydrate intake has been shown to significantly improve A1C.[5]

Insulin use may be associated with weight gain, so weight gain prevention is also an important part of MNT for people with type 1 diabetes and insulin-treated people with type 2 diabetes.[6] Physical activity is an ideal way to promote weight-gain prevention. Because physical activity promotes glucose uptake, either a decrease in insulin dose or an increase in carbohydrate intake is necessary.[6] Because of weight gain concerns with insulin use, decreased insulin dose is the recommended way of addressing glycemic changes associated with planned physical activity. Unplanned activity requires an increase in carbohydrate intake to prevent hypoglycemia[6]; 10 g to 15 g of carbohydrate per hour are required for moderate-intensity activity.

MNT and type 2 diabetes

Weight loss is a critical part of type 2 diabetes treatment. Type 2 diabetes is highly comorbid with obesity,[7] and weight reduction has been associated with decreased insulin resistance,[8] improved glycemic control,[9] and an improvement in cardiovascular risk profile.[10] Specific recommendations for people with type 2 diabetes include reducing total energy intake in order to decrease overweight and improve insulin resistance and glycemic control, as even modest weight loss can improve insulin sensitivity in the short term.[6] Because people with type 2 diabetes have an increased risk of cardiovascular disease, diets low in saturated fats, cholesterol, and sodium may also be a part of nutrition recommendations for this group.[6] For people who are also obese, structured educational programs that include reduced fat and energy intake, regular physical activity, and regular participant contact are an effective way to promote long-term weight loss.[6] Teaching people with type 2 diabetes how to make appropriate food choices, encouraging physical activity, and monitoring of blood glucose levels also are important components of type 2 diabetes MNT.[11]

References

1. UKPDS Group. UK Prospective Diabetes Study 7. Response of fasting plasma glucose to diet therapy in newly diagnosed type II diabetic patients. Metabolism. 1990;39:905-912.
2. Kulkarni K, Castle G, Gregory R, et al. Nutrition Practice Guidelines for Type 1 Diabetes Mellitus positively affect dietitian practices and patient outcomes. The Diabetes Care and Education Dietetic Practice Group. J Am Diet Assoc. 1998;62-70.
3. American Diabetes Association. Standards in medical care-2006. Diabetes Care. 2006;29(suppl 1):S4-S42.
4. Hill JBC, Beaser RS. Medical nutrition therapy. In: Beaser RS and the staff of the Joslin Diabetes Center, eds. Joslin’s Diabetes Deskbook: A Guide for Primary Care Providers. Boston, MA: Joslin Diabetes Center; 2001:63-99.
5. DAFNE Study Group. Training in flexible, intensive insulin management to enable dietary freedom in people with Type 1 diabetes: dose adjustment for normal eating (DAFNE) randomized controlled trial. BMJ. 2002;325:746-751.
6. American Diabetes Association. Nutrition principles and recommendations in diabetes. Diabetes Care. 2004;27(suppl 1):S36-S46.
7. Hillier TA, Pedula KL. Characteristics of an adult population with newly diagnosed type 2 diabetes: the relation of obesity and age of onset. Diabetes Care. 2001;24:1522-1527.
8. Williams KV, Kelly DE. Metabolic consequences of weight loss on glucose metabolism and insulin action in type 2 diabetes. Diabetes Obes Met. 2000;2:121-129.
9. Kelly DE. Effects of weight loss on glucose homeostasis in NIDDM. Diabetes Rev. 1995;3:366-377.
10. Dunn AL, Marcus BH, Kampert JB, Garcia ME, Kohl HW III, Blair SN. Reduction in cardiovascular disease risk factors: 6-month results from Project Active. Prev Med. 1997;26:883-892.
11. Franz MJ, Warshaw H, Daly AE, Green-Pastors J, Arnold MS, Bantle J. Evolution of diabetes medical nutrition therapy. Postgrad Med. 2003;79:30-35.