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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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