Monday, September 01, 2014

What is a Carbohydrate

Last Updated Oct 2007


 

Success with the Zone Diet depends upon restricting the amount of carbohydrates consumed while maximizing the vitamins and minerals derived from them. Unfortunately, many people have trouble recognizing what a carbohydrate is because they think of carbohydrates as only pasta and sweets. In reality, fruits and vegetables are also carbohydrates. An easy way to remember this is that "carbohydrates grow in the ground, and don't move around." Pasta must be a carbohydrate, since it comes from wheat, which grows in the ground. Likewise, vegetables, such as broccoli grow in the ground, so they, too, must be carbohydrates. Finally, fruits, such as apples come from trees that grow in the ground, which makes them carbohydrates also. Although this may seem simplistic, the fact that fruits and vegetables are carbohydrates is a major revelation to many Americans.

INSULIN-STIMULATING CARBOHYDRATE CONTENT
Since the Zone Diet is about insulin control, you have to realize that not all carbohydrates affect insulin equally. Every complex carbohydrate must be broken down into simple sugars and will eventually enter the bloodstream as glucose, which in turn will have a stimulatory effect on insulin secretion. Fiber (both soluble and insoluble) cannot be broken down into simple sugars, and therefore it will have no impact on insulin. Taking this into account, I developed the concept of insulin-stimulating carbohydrate content for a food. Simply stated, this is the total amount of carbohydrate a food source contains minus its fiber content (which is usually included in determining the total amount of carbohydrates).

If a carbohydrate source (such as pasta) has very little fiber content, then virtually all of its listed carbohydrate content will be insulin-stimulating carbohydrate. On the other hand, if a carbohydrate source is rich in fiber (such as broccoli), then its insulin-stimulating carbohydrate content will be significantly reduced. This means that more volume of fiber-rich carbohydrate source must be consumed to have the same impact on insulin secretion as a much smaller volume of low-fiber content carbohydrate (see Table 1).

Table 1. Amounts of Insulin-Stimulating Carbohydrates in Various Food Volumes


 

 

Food

Volume

Total Carbs (g)

Fiber (g)

Insulin-stimulating carbs (g)

Pasta

1 cup

40

2

38

Apple

1 medium

20

4

16

Broccoli

1 cup

7

4

3


You can quickly see that you would have to eat a tremendous volume of broccoli (approximately 12 cups) to have the same impact on insulin as eating a relatively small amount of cooked pasta. This is why starches and grains are considered high-density carbohydrates, whereas fruits are medium-density carbohydrates, and vegetables are low-density carbohydrates. The Zone Diet relies heavily on low-density carbohydrates, so large volumes of food must be consumed in order to have an appreciable impact on insulin. This is also why high-density carbohydrates are used in moderation on the Zone Diet because very small volumes can stimulate excess insulin production.

ZONE BLOCKS OF CARBOHYDRATE

Zone Food Blocks are simply a way of putting various carbohydrates on an equal footing regarding their insulin-stimulating effect. I define a Zone Block of carbohydrate as a volume containing 9 grams of insulin-stimulating carbohydrate. So let's return to the above example, and determine the approximate amount of Zone Carbohydrate Food Blocks in each of the sources (see Table 2).

 

Table 2. Zone Food Block Calculations

Food

Volume

Insulin-stimulating carbs (g)

Approx. Zone carb. blocks

Pasta

1 cup

38

38/9 = 4

Apple

1 medium

16

16/9 = 2

Broccoli

1 cup

3

3/9 = 1/3

These numbers aren't too easy to remember, so I simplified them by normalizing the volume of the carbohydrate source required to make one Zone Carbohydrate Food Block. This is accomplished by dividing the volume of a carbohydrate source in Table 2 by the number of Zone Carbohydrate Food Blocks in that same source. Then you round that number to an approximate volume that you can easily remember, as shown in Table 3.


Table 3. Zone Carbohydrate Block Calculations Simplified

 


 

 

Food

Zone carb blocks in volume

Volume of Zone carb blocks

Pasta

1 cup has 4 Zone food blocks

1/4 cup

Apple

1 medium has 2 Zone food blocks

1/2 apple

Broccoli

1 cup has 1/3 Zone food block

3 cups


Now you have a way to compare carbohydrates directly with their ability to stimulate insulin secretion. A more complete listing of these Zone Food Blocks containing carbohydrates is found in the Zone Resources section of this web site.

The Concepts of Glycemic Index and Glycemic Load
One of the major nutrition breakthroughs was the development of the concept of the glycemic index. It was always thought that there were only simple and complex carbohydrates. The simple ones would enter the bloodstream rapidly, whereas the complex carbohydrates would be slowly broken down, thus providing sustained release over time. From this seemingly reasonable concept, came the nutritional "wisdom" that eventually led to the development of the USDA Food Pyramid.

Unfortunately, research began to rear its ugly head when investigators began to ask whether or not such simplistic thinking was justified. Lo and behold, it wasn't. Some simple carbohydrates, such as fructose, entered the bloodstream as glucose very slowly. On the other hand, some complex carbohydrates, such as potatoes, entered the bloodstream at a faster rate than table sugar. The explanation of this apparent paradox led to the development of the concept of the glycemic index.

The glycemic index is a measure of the entry rates of various carbohydrate sources into the bloodstream. The faster their rate of entry, the greater the effect on insulin secretion. There are three factors that affect the glycemic index of a particular carbohydrate. The first is the amount of fiber (and especially soluble fiber) a carbohydrate contains; the second is the amount of fat found in the carbohydrate source (the more fat consumed with the carbohydrate, the slower the rate of entry into the bloodstream); the third is the composition of the complex carbohydrate itself. The greater the amount of glucose it contains, the higher the glycemic index; whereas the more fructose a carbohydrate contains, the lower the glycemic index. This is because fructose cannot enter into the bloodstream without first being converted into glucose, a relatively slow process that takes place in the liver.

With time the glycemic index soon became the new fashionable guideline to determine which carbohydrates to eat. However, the glycemic index had significant experimental problems in dealing with low-density carbohydrates, such as vegetables.

The difficulties arose because determination of the glycemic index requires that a sufficient intake of carbohydrate (usually 50 grams) be consumed. But it is simply too difficult to consume this amount of carbohydrate from most vegetables at a sitting. For instance this would require consuming about 16 cups of steamed broccoli. As a result, nearly all the glycemic index work has been done with grains, starches, and some fruits, and virtually nothing is known about the glycemic index of low-density vegetables that are the backbone of the Zone Diet.

These difficulties have given rise to a more sophisticated understanding known as the glycemic load, which is far more important than the glycemic index in determining the insulin output of a meal. The glycemic load is the actual amount of insulin-stimulating carbohydrates consumed multiplied by its glycemic index. This reflects the reality that a small volume of high-glycemic carbohydrates has the same impact on insulin as a large volume of low-glycemic carbohydrates. Therefore, eating too many low-glycemic carbohydrates can have a major effect on increased insulin production. For example, black beans have a low-glycemic index because of their high fiber content. However, they are also very dense in carbohydrate content. As a result, eating too many black beans at a meal can have a very great stimulatory effect on insulin.

Ultimately, a healthy diet is obtained through insulin moderation, which can best be achieved by primarily consuming low-density carbohydrates that also have a low-glycemic index. That means eating a lot of vegetables. To illustrate this concept, Table 4 examines three distinct carbohydrate sources in the volumes which they are typically consumed. The glycemic load is the product of the number of grams of insulin-stimulating carbohydrate times the glycemic index for that carbohydrate. The lower the glycemic load number, the lower the insulin stimulation of that carbohydrate.

Table 4. Comparison of Different Glycemic Loads


 

 

Source

Typical volume (grams)

Glycemic index

Glycemic load

Pasta

1 cup

59

2242

Apple

1

54

864

Broccoli

1 cup

50*

150

*Estimated from the glycemic index of various boiled beans

Even though the glycemic index of each of these carbohydrates is about the same, 1 cup of pasta generates 20 times the insulin response as 1 cup of broccoli. And a single apple generates about 6 times the insulin response as the 1 cup of broccoli. It is clear that a glycemic load based on the serving size of carbohydrate is a much more valuable tool than using the glycemic index. Table 5 lists the various glycemic loads of a wide variety of carbohydrates. For vegetables that have never been tested for their glycemic index, I have used an estimate of 50 (although it could be considerably lower in reality) as I did in Table 4.

Table 5. Glycemic Loads of Various Tested Carbohydrates


 

 

Source

Typical volume

Grams

Glycemic index

Glycemic load

Fruits

Apple

1

18

54

864

Apple juice

8 oz.

29

57

1653

Apricot

1

4

81

324

Banana (med.)

1

32

79

2528

Cantaloupe

1 cup

15

65

975

Cherries

10

10

31

310

Grapefruit

1

10

36

360

Grapefruit juice

8 oz.

22

69

1518

Grapes

1 cup

15

66

990

Kiwi

1

8

74

592

Mango (medium)

1

33

80

2640

Orange (medium)

1

10

63

630

Orange juice

8 oz.

26

66

1716

Papaya (medium)

1

28

83

2324

Peach

1

7

40

280

Pear

1

21

54

1134

Plum

1

7

56

392

Raisins

1 cup

112

91

10192

Watermelon

1 cup

11

103

1133

Legumes

Black beans (boiled)

1 cup

41

43

1763

Black bean soup

1 cup

38

91

3458

Chickpeas (boiled)

1 cup

46

47

2162

Fava beans (boiled)

1 cup

34

113

3978

Kidney beans (boiled)

1 cup

40

39

1560

Kidney beans (canned)

1 cup

38

74

2812

Lentils (boiled)

1 cup

32

43

1376

Navy beans (boiled)

1 cup

38

54

2052

Pinto beans (canned)

1 cup

36

64

2304

Soy beans (boiled)

1 cup

20

26

520

Breads and pasta

Bagel, small

1

38

103

3914

Bread, dark rye

1 slice

18

109

1962

Bread, sourdough

1 slice

20

74

1480

Bread, white

1 slice

12

100

1200

Bread, whole-wheat

1 slice

13

99

1287

Croissant (medium)

1

27

96

2592

Hamburger bun

1

22

86

1892

Kaiser roll

1

34

104

3536

Linguine pasta (thin)

1 cup

56

79

4424

Macaroni

1 cup

52

64

3328

Pita bread

1

35

81

2835

Pizza

1 slice

28

86

2408

Spaghetti

1 cup

52

59

3086

Starches, grains and cereals

Barley (boiled)

1 cup

44

36

1584

Bulgur (cooked)

1 cup

31

69

2139

Cherrios

1 cup

23

106

2438

Couscous (cooked)

1 cup

42

93

3906

Corn, sweet (canned)

1 cup

30

79

2370

Corn Chex

1 cup

26

119

3094

Corn Flakes

1 cup

24

120

2880

Grapenuts

1 cup

108

96

10368

Oatmeal (slow-cooking)

1 cup

24

70

1680

Potato, red (boiled)

1

15

126

1890

Potato, white (boiled)

1

24

90

2160

Potato, white (mashed)

1 cup

40

100

4000

Rice cakes

3

23

117

2691

Rice Chex

1 cup

22

127

2794

Rice Krispies

1 cup

21

117

2457

Rice, white

1 cup

42

103

4326

Rice, brown

1 cup

37

79

2923

Dairy products

Milk (low-fat)

1 cup

11

43

473

Soy milk

1 cup

14

44

616

Frozen tofu

1 cup

42

164

6888

Yogurt (plain)

1 cup

17

20

340

Vegetables (cooked)

Artichoke hearts

1 cup

7

50*

350

Bok choy

1 cup