Medical nutrition facts from Joslin Center

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Joslin_Diabetes_DeskbookThe week's excerpt answers the following questions

* Does using the " glycemic index " work?

* Is the type of carbohydrate important?

* Carbohydrate counting vs. the glycemic index and glycemic load

* How much carbohydrate do we really need?

* What percentage of consumed carbohydrates are converted to glucose?

* What is the caloric range for weight loss and recommended level for

weight maintenance?

* Does insulin may you fat?

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Food Types

Food types or nutrients can be divided into two categories, macronutrients

and micronutrients. To understand how to utilize these nutrients in a

medical nutritional treatment plan requires a basic understanding of the

nutritional roles of each. Macronutrients -- carbohydrate, protein and fat

-- will be covered in detail here; the micronutrients, vitamins and

minerals, will be discussed later.

As noted above, in 1994, the ADA revised its nutritional recommendations,

stating that there is no standard ADA or diabetic diet! A meal plan must be

individualized to each person's personal eating style and metabolic needs.

In fact, for many people with diabetes, the dietary guidelines are in

essence the same as those that would be recommended as a healthy nutritional

plan for most adults.

Carbohydrate

Carbohydrate is the major source of energy for the body's needs. It is the

major constituent of the " starchy " foods such as breads, cereals, grains,

and pasta. These polysaccharide carbohydrates are referred to as complex

carbohydrates, as compared with the refined or simple mono- and disaccharide

carbohydrates like sugar. Carbohydrate is also the main component of

" sugary " foods, such as cake, cookies, candy, table sugar, milk, fruits and

vegetables.

In the past, the recommendation for people with diabetes was to consume

primarily complex, or starchy, carbohydrates. The assumption was that these

sources of carbohydrate were more slowly absorbed, and thus were present at

a time that was more closely coordinated with either the second-phase

insulin secretion of a patient with type 2 diabetes or the regular insulin

action pattern for someone treated with exogenous insulin therapy.

Today, however, much more is known about carbohydrate. Research shows that

eating 50 grams of carbohydrate from a sugar, such as maple syrup, has the

same effect on blood glucose as eating an equivalent amount of carbohydrate

from a starch, such as bread. In fact, more than twenty research studies

show that when individuals choose a variety of foods containing either

starches or sugars in meals, if the total amount of carbohydrate is the

same, the glucose response will be essentially the same. A key education

point for patients first learning about diabetes meal planning is that

because foods containing either starches or sugars are digested into glucose

at approximately the same rate, it is important to control the total amount

(and not the type) of carbohydrate consumed. Of course, good nutrition

principles prevail, and the message regarding sweet foods should still be

one of moderation, as these foods are often high in fat and calories and

provide little nutritional value.

Glycemic Index

The concept of the " glycemic index " was developed by staff at the University

of Toronto and shows how certain food affects blood glucose levels. A more

precise definition of glycemic index (GI) is: a system of ranking foods

containing equal amounts of carbohydrate according to how much they raise

blood glucose in comparison with a reference food (50 grams of glucose or 50

grams of bread).

The glycemic index of a carbohydrate food is determined by assigning that

food a number from 0 to 100, where 100 means that 1 gm of carbohydrate from

this food raises the blood glucose to the same level as 1 gm of

carbohydrates from bread. In other words, foods with a lower GI have less of

an effect on blood glucose than do foods with a higher GI. Low GI foods are

ranked between 0 and 50; intermediate GI foods are ranked from 56 and 69,

and high GI foods are ranked 70 or higher. Some foods are surprisingly

fairly low on the glycemic index: the glycemic response of sucrose, for

example, resembles more closely that of rice or potatoes.

Fruits and milk (sugars) produce a much lower glycemic response than

starches. Even M & Ms, the chocolate-coated candy, have a lower glycemic index

than other, more healthful foods, including pasta.

To further complicate matters, many factors can affect the glycemic index of

a food, including how it is prepared and in what form it is eaten.

Furthermore, the glycemic index can be challenging for patients to apply to

their daily food choices because foods are compared with one another not in

usual portions but in equivalent amounts of carbohydrate. For example, a

pound and a half of carrots and one cup of pasta each contain 50 grams of

carbohydrate, and this amount is used to determine their GI even though it

is very unlikely that anyone would consume one and a half pounds of carrots

at one time.

Because of the difficulty of relating GI with portions size, some

researchers suggest using another approach, called the glycemic load (GL).

The GL combines the GI value and the carbohydrate content of an average

serving of a food or meal, and is calculated by multiplying the GI number of

a food by the number of grams of carbohydrate in a serving and then dividing

by 100. A GL of 10 or less is low; 11-19 is medium; and 20 or more is high.

The American Diabetes Association concludes in its evidence-based nutrition

recommendations that research does not support the glycemic index as a

primary method of meal planning for people with diabetes. Recent research

also casts doubt on the effectiveness of this approach as an effective

meal-planning tool; instead, the primary determinant of the postprandial

glucose response is the amount of carbohydrate consumed. Nevertheless,

several randomized clinical trials have shown that low GI diets do reduce

glycemia in people with diabetes. For people consuming a high GI diet,

changing to a low GI diet can improve postprandial hyperglycemia. Not all

carbohydrates have the same effects on blood glucose levels. Thus, while it

is not necessary to eliminate potatoes, it is important for people with

diabetes to choose a variety of carbohydrate foods each day and to

understand the differences among the various choices.

The glycemic index and glycemic load may be beneficial for people with

diabetes, and this view is in accord with Joslin's Nutrition Guideline, but

these tools should be used only as adjuncts to other meal planning methods,

such as carbohydrate counting. People adjusting their rapid-acting insulin

based on carbohydrate intake can actually develop their own glycemic index

by carefully counting carbohydrate grams and monitoring blood glucose levels

before and after meals. The use of self-monitoring of blood glucose (SMBG)

or continuous glucose monitoring (CGM), are key for individuals with

diabetes to determine their own postprandial response to foods.

Carbohydrate Content

How much carbohydrate do we really need? Before insulin was discovered in

1921, the diets recommended by Joslin physicians and others treating people

with diabetes were high in fat, high in protein, and low in carbohydrate.

This made sense to those physicians -- diabetes is a condition in which

patients cannot metabolize carbohydrate, so remove carbohydrate from the

diet! These diets were not unlike those advocated today in some commercial

diet plans for weight reduction like " South Beach " or the " Atkins " program.

Our understanding of the nutritional needs of people with diabetes has come

a long way since those early days. We know that about 100% of consumed

carbohydrates are converted to glucose and serve as the main source of

energy in our diet. Carbohydrate sources are bread, pasta, rice, cereals,

fruit, milk, table sugar and sweets.

An analysis of the current low-carbohydrate/high-protein diets advocated by

some reveals that the caloric range for weight loss is from 1000 to 1600

kcals. There is also a recommended calorie level for weight maintenance of

1800 kcals. Of course these diets work, they contain fewer calories! What is

not discussed in these diet plans is their ability to fit it into a healthy

lifestyle. Are they practical? Are there food limitations? Are they

providing enough vitamins and minerals that are known to aid in keeping good

health? What impact do these diets have on increasing the risk of coronary

artery disease?

The fact is that low-carbohydrate/high-protein diets cause ketosis,

electrolyte loss and dehydration. They may exacerbate kidney disease and

gout, and may cause calcium depletion. Because some of these commercial

plans promote the eating of highly saturated fat foods, they also may

contribute to coronary heart disease. While these diets may be a short-term

fix, they are not ideal for long-term health. In addition, people with

diabetes who also have kidney, liver or heart disease, or who are pregnant

or lactating should not follow a very low-carbohydrate/high-protein diet.

The ADA no longer recommends that a specific percentage of calories come

from carbohydrate; however, it does recognize in its nutrition

recommendations that, while the RDA for carbohydrate is 130 grams per day

and is an average minimum requirement, 1-year follow-up data from a

weight-loss trial showed that fasting glucose was lower in those following a

low carbohydrate diet compared with those following a low fat diet. The

source and distribution of carbohydrate calories among foods with differing

glycemic indices is secondary in concern to the total carbohydrate content.

Nevertheless, unrefined, unprocessed carbohydrate foods should be used

whenever possible. Joslin Diabetes Center's Clinical Nutrition Guideline for

Overweight and Obese Adults with Type 2 Diabetes, Prediabetes or at High

Risk for Developing Type 2 Diabetes recommends approximately 40% of calories

from carbohydrate, the total not to be less than 130 grams per day, in

accordance with the Recommended Dietary Allowance. This modest decrease in

carbohydrate may improve postprandial blood glucose levels and enhance

weight loss by utilizing stored fat for energy without causing ketosis or

dehydration.

Carbohydrate Metabolism

After digestion and absorption into the bloodstream, carbohydrate has three

key destinations, and insulin is important for all three to be reached.

Carbohydrate can be:

* used to provide for immediate energy needs

* stored as glycogen, primarily in liver and muscle, to serve as a

rapidly accessible energy supply (e.g., source of glucose for rebound

hyperglycemia or fuel for muscle undertaking sudden activity)

* converted to fat, an almost unlimited potential storage space that

can be used when glycogen stores are filled

Insulin must be present for glucose to take any of the three pathways

described above, including the storage of fat in adipose cells. As a result,

many patients think that insulin makes you fat. Of course, this is not true!

Insulin is non-caloric! However, insulin, when given to a person with

previously uncontrolled glucose levels, reduces calorie loss through

glycosuria, can temporarily promote edema, and, when not balanced properly

with food intake, can cause hypoglycemia, necessitating excess food

consumption. Proper insulin use, balanced in a physiologic manner with

carbohydrate intake, should not lead to excessive weight gain, although in

the short run some increase in weight may occur.

Copyright C 2010 by Joslin Diabetes Center. All rights reserved. Reprinted

with permission. Neither this book nor any part thereof may be reproduced or