Effectiveness of MNT (Medical Nutrition Therapy)
Clinical trials/outcome studies of MNT have reported decreases in HbA1c of ~1% in type 1 diabetes and 1-2% in type 2 diabetes, depending on the duration of diabetes. Meta-analysis of studies in nondiabetic, free-living subjects and expert committees report that MNT reduce LDL cholesterol by 15-25 mg/dl. After initiation of MNT, improvements were apparent in 3-6 months. Meta-analysis and expert committees also support a role for lifestyle modification in treating hypertension.
Goals of MNT for Prevention and Treatment of Diabetes
1. With Pre-Diabetes
To decrease the risk of diabetes and cardiovascular disease (CVD) by promoting healthy food choices and physical activity leading to moderate weight loss that is maintained.
2. With Diabetes
Achieve and maintain: Blood glucose levels in the normal range or as close to normal as is safely possible A lipid and lipoprotein profile that reduces the risk for vascular disease Blood pressure levels in the normal range or as close to normal as is safely possible.
To prevent, or at least slow, the rate of development of the chronic complications of diabetes by modifying nutrient intake and lifestyle.
To address individual nutrition needs, taking into account personal and cultural preferences and willingness to change.
To maintain the pleasure of eating by only limiting food choices when indicated by scientific evidence.
Nutrition Recommendations and Interventions for The Management of Diabetes (Secondary Prevention)
The nutrition has a direct relationship with obesity, and obesity has a correlation with insulin resistance. As the figure shown, disease risk increases with obesity class.
There are several types of foods including carbohydrate, dietary fat and cholesterol, protein, macronutrients, alcohol, micronutrients, and chromium other minerals and herbs. In this post we will discuss the management of these foods in diabetes.
Control of blood glucose in an effort to achieve normal or near-normal levels is a primary goal of diabetes management. Food and nutrition interventions that reduce postprandial blood glucose excursions are important in this regard, since dietary carbohydrate is the major determinant of postprandial glucose levels.
Monitoring carbohydrate, whether by carbohydrate counting, exchanges, or experienced-based estimation remains a key strategy in achieving glycemic control. In the figure below there are the glycemic index and glycemic load of common foods.
Low-carbohydrate diets might seem to be a logical approach to lowering postprandial glucose. However, foods that contain carbohydrate are important sources of energy, fiber, vitamins, and minerals and are important in dietary palatability. Therefore, these foods are important components fo the diet for individuals with diabetes.
Blood glucose concentration following a meal is primarily determined by the rate of appearance of glucose in the blood stream (digestion and absorption) and its clearance from the circulation. Insulin secretory response normally maintains blood glucose in a narrow range, but in individuals with diabetes, defects in insulin action, insulin secretion, or both impair regulation of postprandial glucose in response to dietary carbohydrate. Both the quantity and the type or source of carbohydrates found in foods influence postprandial glucose levels.
For carbohydrate, the amount and type of carbohydrate digested and absorbed determined the rate of appearance of glucose in blood stream. As noted in 2004 ADA statement, the average minimum carbohydrate requirement is about 130 g/day. However, several clinical trials found low-carbohydrate have no significant difference reduction in fasting glucose and A1C compared with other types of diet styles (e.g., low-fat).
In rationale, the amount of carbohydrate ingested is usually the primary determinant of postprandial response, but the type of carbohydrate also affects this response. The glycemic index of foods was developed to comare the postprandial responses to constant amount of different carbohydrate-containing foods. The glycemic index of a food is the increase above fasting in the blood glucose area over 2 h after ingestion of a constant amount of that food (usually a 50–g carbohydrate portion) divided by the response to a reference food (usually glucose or white bread). The glycemic loads of foods, meals, and diets are calculated by multiplying the glycemic index of constituent foods by the amounts of carbohydrate in each food and then totaling the values for all foods.
Relationship between Glycemic Index and Glycemic Load
The GI and GL of a food are related by the amount of available carbohydrates in a fixed serving of the food.
The glycemic load of a food is calculated by multiplying the absolute GI value by the grams of available carbohydrate in the serving, and then dividing by 100. Or:
GL = GI * Available Carbs (grams) / 100
Reversing the equation:
GI = GL *100 / Available Carbs (grams)
Note that Available Carbs is equal to the total carbohydrate content minus the fiber content.
For example, a 225 g (1 cup) serving of Bananas with a GI of 52 and a carbohydrate content of 45.5 g (51.4 g total carbohydrate – 5.9 g fiber) makes the calculation GL = 52 * 45.5 / 100 = 24, so the GL is 24.
For one serving of a food, a GL greater than 20 is considered high, a GL of 11-19 is considered medium, and a GL of 10 or less is considered low.
Several randomized clinical trials have reported that low-glycemic index diets reduce glycemia in diabetic subjects, but other clinical trials have not confirmed this effect. Nevertheless, a recent meta-analysis of low-glycemic index diet trials in diabetic subjects showed that such diets produced a 0.4% decrement in A1C when compared with high-glycemic index diets.
Fiber-containing foods such as legumes, fiber-rich cereals, fruits, vegetables, and whole grain products are encouraged in people with diabetes. Generally, to reach the fiber intake goals of 14 g/1,000 kcal is a first priority for people with diabetes.
Substantial evidence from clinical studies demonstrates that dietary sucrose does not increase glycemia more than isocaloric amounts of starch. Thus, intake of sucrose and sucrose-containing foods by people with diabetes does not need to be restricted because of concern about aggravating hyperglycemia. Sucrose can be substituted for other carbohydrate sources in the meal plan or, if added to the meal plan, adequately covered with insulin or another glucose-lowering medication.
In individuals with diabetes, fructose produces a lower postprandial glucose response when it replaces sucrose or starch in the diet; however, this benefit is tempered by concern that fructose may adversely affect plasma lipids. Thus, the ingestion of fructose is not recommended but there is, however, no reason to recommended that people with diabetes avoid naturally occuring fructose in fruits, vegetables, and other foods.
Dietary fat and cholesterol
The primary goal with respect to dietary fat in individuals with diabetes is to limit saturated fatty acids, trans fatty acids, and cholesterol intakes so as to reduce risk of CVD. Saturated and trans fatty acids are the principal dietary determinants of plasma LDL cholesterol. In nondiabetic individuals, reducing saturated and trans fatty acids and cholesterol intakes decreases plasma total and LDL cholesterol. Despite reducing saturated fatty acids may also reduce HDL cholesterol, the ratio of LDL cholesterol to HDL cholesterol is not adversely affected.
The target is to limit saturated fat acids to <7% of total energy, to minimize trans fatty acids intake, and to limit dietary cholesterol to <200 mg/day.
With the limit of ingestion of saturated fatty acids and trans fatty acids, some other foods such as monounsaturated fatty acids, polyunsaturated fatty acids, plant sterol, and stanol esters can lower plasma LDL.