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Carbohydrates and Health: Not that Simple…or that Complex Home > Welcome Newsweek readers > Carbohydrates and Health: Not that Simple…or that Complex

Carbohydrates and Health: Not that Simple…or that Complex

(This article was first printed in the December 2002 issue of the Harvard Heart Letter. For more information or to order, please go to http://www.health.harvard.edu/heart.)

Taking control of your blood sugar and insulin levels may pay off for your heart and overall health.

Picture a roller coaster, and you'll get an idea of what happens to sugar and insulin levels in your blood. The highs that follow meals and snacks turn to lows later on.

Whether your levels look more like a kiddie coaster with gentle ups and downs or a strap-'em-in, hang-on-tight ride with steep climbs and breathtaking drops can make a difference to your health. Routinely high blood sugar and insulin have been linked with a variety of chronic diseases.

Smoothing out your blood sugar and insulin levels help keep your heart in good shape. It can help control type 2 diabetes and possibly prevent it. It may even let you control or lose weight by helping you store less fat and by keeping you from getting hungry soon after a meal or snack. And, as described in The Fertility Diet, steadier blood sugar and insulin levels may improve fertility.

Taming this duo isn't that hard. Choosing foods that have a gentler impact on blood sugar and insulin levels can help. You can do this using the glycemic (glie-SEE-mick) index. This research tool, developed over 20 years ago, measures the ease with which your body turns carbohydrates into blood sugar.

The Problem with Bad Carbohydrates

When you eat a food with a high rating on the glycemic index, enzymes in your digestive system attack its carbohydrates and furiously snip off simple sugars such as glucose. These quickly slip into the bloodstream.

As blood sugar levels shoot up, cells in the pancreas churn out extra insulin. This hormone helps cells sponge up glucose. A surge of insulin also signals the body to store extra glucose as fat. Too much insulin may eventually drive blood sugar below the level your body needs to keep things running smoothly. This triggers responses that get your blood sugar levels back into the normal range. Hunger pangs are one of these.

When you eat carbohydrates that are low on the glycemic index, blood sugar and insulin levels climb more slowly and don't crest as high as they do with quickly digested carbohydrates. Both fall more slowly, too, making it less likely that blood sugar levels will drop below the hunger point.

Classifying Carbohydrates

Carbohydrates are the major component of breads, pastas, cereals, fruits, vegetables, and beans. They're also the major contributor to blood sugar.

That's because all carbohydrates are made of sugar. Some are made of one or two sugar molecules. Others, like the starches in potatoes, corn, and wheat, are a tangle of sugars strung together in long, branched chains.

For years, scientists divided carbohydrates into two main groups: simple ones like glucose (the form used by the body and found in many foods) and fructose (fruit sugar), and complex ones like starch and fiber. Most nutrition guidelines urge us to eat complex carbohydrates instead of simple ones.

Out with the Old…

No one had actually compared the effects of various carbohydrate-rich foods until a Canadian team started to do this systematically in the 1980s. The results shattered long-held assumptions that the body took longer to convert complex carbohydrates into blood sugar.

Nutrition scientist David Jenkins compared the blood sugar responses of foods and compared them to the response to an equal amount of glucose, a simple sugar. to make things simple, they gave glucose a score of 100. Foods that increased blood sugar more than glucose get scores on this glycemic index of greater than 100. Those with smaller effects got scores under 100.

Pure fructose, among the simplest of simple carbohydrates, barely registered on the scale, with a glycemic index value of 20 (meaning its impact was 20% of glucose). But cornflakes, carrots, and potatoes—complex carbohydrates by anyone's reckoning—raised blood sugar levels almost as much as glucose.

A later modification called the glycemic load measures how eating a normal portion of a particular food affects blood sugar. Watermelon, for example, has a fairly high glycemic index value of 72. But there's very little carbohydrate in a serving of watermelon, so its glycemic load is low.

…In with the New

Since that first effort, researchers have tested more and more foods for their glycemic index values. A list published in the July 2002 American Journal of Clinical Nutrition provides values for 750 foods. A searchable database maintained by the University of Sydney (www.glycemicindex.com) contains 1,600 entries. We've included the values for 100 common foods below.

FOOD

Glycemic index
(glucose = 100)

Serving size (grams)

Glycemic load per serving

BAKERY PRODUCTS AND BREADS      
Banana cake, made with sugar 47±8 80 18
Banana cake, made without sugar 55±10 80 16
Sponge cake, plain 46±6 63 17
Vanilla cake made from packet mix with vanilla frosting (Betty Crocker) 42±4 111 24
Apple, made with sugar 44±6 60 13
Apple, made without sugar 48±10 60 9
Waffles, Aunt Jemima (Quaker Oats) 76 35 10
Bagel, white, frozen 72 70 25
Baguette, white, plain 95±15 30 15
Coarse barley bread, 75-80% kernels, average 34±4 30 7
Hamburger bun 61 30 9
Kaiser roll 73 30 12
Pumpernickel bread 50±4 30 6
50% cracked wheat kernel bread 58 30 12
White wheat flour bread 70±0 30 10
Wonder™ bread, average 73±2 30 10
Whole wheat bread, average 71± 2 30 9
100% Whole Grain™ bread (Natural Ovens) 51±11 30 7
Pita bread, white 57 30 10
Corn tortilla 52 50 12
Wheat tortilla 30 50 8
BEVERAGES      
Coca Cola®, average 58±5 250 15
Fanta®, orange soft drink 68±6 250 23
Lucozade®, original (sparkling glucose drink) 95±10 250 40
Apple juice, unsweetened, average 40±1 250 12
Cranberry juice cocktail (Ocean Spray®) 68±3 250 24
Grapefruit juice, unsweetened 48 250 11
Orange juice, average 50±4 250 13
Tomato juice, canned 38±4 250 4
BREAKFAST CEREALS AND RELATED PRODUCTS      
All-Bran™, average 42±5 30 4
Coco Pops™, average 77 30 20
Cornflakes™, average 81±3 30 21
Cream of Wheat™ (Nabisco) 66 250 17
Cream of Wheat™, Instant (Nabisco) 74 250 22
Grapenuts™, average 71±4 30 15
Muesli, average 66±9 30 16
Oatmeal, average 58±4 250 13
Instant oatmeal, average 66±1 250 17
Puffed wheat, average 74±7 30 16
Raisin Bran™ (Kellogg's) 61±5 30 12
Special K™ (Kellogg's) 69±5 30 14
GRAINS      
Pearled barley, average 25±1 150 11
Sweet corn on the cob, average 53±4 150 17
Couscous, average 65±4 150 23
White rice, average 64±7 150 23
Quick cooking white basmati 60±5 150 23
Brown rice, average 55±5 150 18
Converted, white rice (Uncle Ben's®) 38 150 14
Whole wheat kernels, average 41±3 50 14
Bulgur, average 48±2 150 12
COOKIES AND CRACKERS      
Graham crackers 74 25 14
Vanilla wafers 77 25 14
Shortbread 64±8 25 10
Rice cakes, average 78±9 25 17
Rye crisps, average 64±2 25 11
Soda crackers 74 25 12
DAIRY PRODUCTS AND ALTERNATIVES      
Ice cream, regular 61±7 50 8
Ice cream, premium 37±3 50 4
Milk, full fat 27±4 250 3
Milk, skim 32±5 250 4
Reduced-fat yogurt with fruit, average 27±1 200 7
FRUITS      
Apple, average 38±2 120 6
Banana, ripe 51 120 13
Dates, dried 103±21 60 42
Grapefruit 25 120 3
Grapes, average 46±3 120 8
Orange, average 42±3 120 5
Peach, average 42±14 120 5
Peach, canned in light syrup 52 120 9
Pear, average 38±2 120 4
Pear, canned in pear juice 44 120 5
Prunes, pitted 29±4 60 10
Raisins 64±11 60 28
Watermelon 72±13 120 4
BEANS AND NUTS      
Baked beans, average 48±8 150 7
Blackeye peas, average 42±9 150 13
Black beans 30 150 7
Chickpeas, average 28±6 150 8
Chickpeas, canned in brine 42 150 9
Navy beans, average 38±6 150 12
Kidney beans, average 28±4 150 7
Lentils, average 29±1 150 5
Soy beans, average 18±3 150 1
Cashews, salted 22±5 50 3
Peanuts, average 14±8 50 1
PASTA and NOODLES      
Fettucini, average 40±8 180 18
Macaroni, average 47±2 180 23
Macaroni and Cheese (Kraft) 64 180 32
Spaghetti, white, boiled 5 min, average 38±3 180 18
Spaghetti, white, boiled 20 min, average 61±3 180 27
Spaghetti, wholemeal, boiled, average 37±5 180 16
SNACK FOODS      
Corn chips, plain, salted, average 63±10 50 17
Fruit Roll-Ups® 99±12 30 24
M & M's®, peanut 33±3 30 6
Microwave popcorn, plain, average 72±17 20 8
Potato chips, average 54±3 50 11
Pretzels, oven-baked 83±9 30 16
Snickers Bar® 55±14 60 19
VEGETABLES      
Green peas, average 48±5 80 3
Carrots, average 47±16 80 3
Parsnips 97±19 80 12
Baked russet potato, average 85±12 150 26
Boiled white potato, average 50±9 150 14
Instant mashed potato, average 85±3 150 17
Sweet potato, average 61±7 150 17
Yam, average 37±8 150 13
MISCELLANEOUS      
Hummus (chickpea salad dip) 6±4 30 0
Chicken nuggets, frozen, reheated in microwave oven 5 min 46±4 100 7
Pizza, plain baked dough, served with parmesan cheese and tomato sauce 80 100 22
Pizza, Super Supreme (Pizza Hut) 36±6 100 9
Honey, average 55±5 25 10

Using the Glycemic Index and Glycemic Load

As useful as these values are, there's no need to eat by the numbers. Instead, you can achieve the goal—slower, lower blood sugar and insulin responses—by following a few general principles:

  • Switch from refined to whole grains
  • Don't be afraid of pasta, especially whole grain blends
  • Eat more beans
  • Fruits and vegetables are your friends
  • Avoid sugared sodas and juices

If you find it helpful to use the glycemic index value and glycemic load, don't sweat the small differences. Here's a handy guide: Try to choose foods with glycemic index values under 55 (compared with glucose) and those with glycemic loads in the low teens or below. Foods with glycemic index values above 70 are better for the occasional snack or meal, not all the time.

Keep in mind that no matter how "good" a carbohydrate is, eating too much of it isn't. Quantity matters just as much as quality.

(This article was first printed in the December 2002 issue of the Harvard Heart Letter. For more information or to order, please go to http://www.health.harvard.edu/heart.)

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