Glycemic-Index Diet Overview

Scorecard

Overall
Weight Loss Short-term
Weight Loss Long-term
Easy to Follow
Nutrition
Safety
For Diabetes
For Heart Health

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Pros & Cons

  • You shape your diet
  • You won’t be hungry
  • No guidance on foods other than carbs
  • Got to do homework

Do's & Don'ts

Don’t: Eat highly refined carbs like white bread See more Do's & Don'ts

Overview

Type:

Balanced.

Resembles these U.S. News-rated diets:

Zone Diet, Nutrisystem, South Beach Diet

The aim:

Weight loss, better blood-sugar control, heart health.

The claim:

You’ll lose (or maintain) weight while cutting your risk of heart disease and type 2 diabetes.

The theory:

Eating “good” carbs—bran cereal and many fruits and veggies, like apples and carrots, for example—controls appetite and delays hunger, promoting weight loss. “Bad” carbs, like white bread and instant mashed potatoes, are quickly digested and released into the bloodstream, spiking blood sugar and making you hungry sooner. The glycemic index (GI) is a measure of a carb’s effect on blood sugar. Good carbs are lower on the glycemic index. They are digested slowly, so you feel fuller longer, and your blood sugar and metabolism don’t go out of whack.

How does the Glycemic-Index Diet work?

It looks simple—all you need to know is where different carbs fall on the 0-100 GI index. You fill up on low-GI carbs (55 and under), eat smaller amounts of medium-GI carbs (56 to 69), and mostly nibble on high-GI carbs (70 and up). Lists of carbs in each category are available online, or you can mine a database from the University of Sydney, which operates a GI-testing laboratory. Other than the bother of having to refer to the lists for foods whose GI index you don’t know or have forgotten, there’s no fussy weighing or measuring. But you’ll have to devise your menus yourself. The GI index only ranks foods containing carbs, so meat, fish, and poultry, for instance, don’t have GI numbers. You’re on your own in deciding how much your diet should include.

Many experts say the GI approach is misleading (some junk food is low-GI) and can’t predict with consistency how a specific food—or combination of foods—will affect blood-sugar levels. They also question whether a large carb-induced spike in blood sugar matters.

But if you want to try the GI diet and need help getting started, the University of Sydney recommends a “this-for-that approach”—subbing in a low- or medium-GI carb for a high-GI one at each meal. At breakfast, go for cereals made with oats, barley, or bran; at lunch, eat your sandwich on whole-grain bread; and at dinner, toss up a salad instead of baking a potato.

Additional guidance is available from diet programs based on GI principles, such as Nutrisystem, and books like Sugar Busters and the The New Glucose Revolution. Sample GI meal plans and cookbooks can be tracked down without much difficulty.

Will you lose weight?

GI diets demonstrate short-term weight loss but not much more than other diets show. And the claim that eating low-GI carbs is the key to weight loss is still controversial. An advisory committee to the government’s 2010 Dietary Guidelines even concluded that evidence overwhelmingly shows that diets based on the glycemic index do no better at weight loss than those that aren’t, nor are they better at keeping off pounds already lost.

In 2009, the independent, nonprofit Cochrane Collaboration reviewed six small, randomized controlled trials of low-GI diets tested over periods from several months to a year. Overall, low-GI dieters fared a little better than comparison dieters, losing an average of about 2 more pounds.

Here’s a closer look at a few of the trials Cochrane analyzed:

  • In a 2006 study published in the Archives of Internal Medicine, 129 overweight or obese adults were assigned to one of four diets: high-carb/high-GI, high-carb/low-GI, high-protein/high-GI, and high-protein/low-GI. All diets provided between 1,400 to 1,900 calories a day, with reduced fat and moderate fiber. At 12 weeks, the low-GI groups had lost an average of 10 and 11 pounds while high-GI groups had lost 8 and 12 pounds. The differences in weight loss among the groups wasn’t considered meaningful.
  • A study of 45 overweight women, published in the American Journal of Clinical Nutrition in 2004, assigned to either a low- or high-GI diet found a slight weight-loss edge for low-GI dieters after 10 weeks, but the findings weren’t considered trustworthy.
  • An even smaller study, published in 2005 in the American Journal of Clinical Nutrition, tracked 23 obese young adults for one year, one group on a low-GI diet and the others on a low-fat diet. The low-GI dieters lost 8 percent of their initial body weight compared with 6 percent for the low-fat group, but the difference wasn’t statistically meaningful. (Still, even losing 5 percent of your current weight can help stave off some diseases.)

Here’s a look at some studies Cochrane didn’t review:

  • A study published in the New England Journal of Medicine in 2010 examined weight-loss maintenance of 773 overweight adults on high- and low-GI diets. After 26 weeks, the low-GI dieters had regained 2 pounds less on average than their high-GI counterparts had.
  • Another study, published in 2010 in Nutrition, Metabolism, and Cardiovascular Diseases, compared low-GI and low-fat regimens in 202 overweight and obese adults, about half of whom had metabolic syndrome, which increases the risk of heart disease and is considered an early sign of type 2 diabetes. After three months, the low-GI group had lost an average of 10½ pounds, the low-fat group 8. After a year, however, both groups had lost about 9 pounds.
  • A study published in 2007 in the American Journal of Clinical Nutrition assigned 203 normal to overweight Brazilian women to either a low- or high-GI diet. After 18 months, low-GI dieters had lost an average of 1 pound compared with half a pound for the high-GI dieters.
  • Three additional small trials that pitted low-GI diets against either high-GI or control diets also found no notable differences in weight loss after periods of up to a year.
  • A study published in the Journal of the American Medical Association in 2012 found that a diet based on healthy carbohydrates, rather than a low-fat or low-carb plan, offers the best chance of keeping weight off without bringing unwanted side effects. Study participants following a low-glycemic-index diet also saw improved cholesterol levels and other markers that indicate a lower risk of developing heart disease and diabetes. The research suggests a low-GI diet burns more calories per day than a low-fat diet, and is typically easier to stick to than a low-carb diet.

Does it have cardiovascular benefits?

Unknown. Some research suggests low-GI diets may reduce “bad” LDL cholesterol and triglycerides (which can contribute to blocked arteries), while increasing “good” HDL cholesterol (which helps prevent clogged arteries). But a 2008 Cochrane Collaboration review of 21 trials concluded that the only support for these claims comes from short studies of poor quality.

Can it prevent or control diabetes?

The jury is still out, but it’s unlikely.

Prevention: Being overweight is one of the biggest risk factors for type 2 diabetes. If this approach helps you shed pounds and keep them off, you’ll stand a better chance of avoiding the chronic disease. Although some studies seem to suggest a low-GI diet may help protect against type 2 diabetes, an advisory committee to the 2010 Dietary Guidelines found little convincing evidence. And many experts aren’t sure the diet helps thwart insulin resistance, a hallmark of type 2 diabetes; the body doesn’t respond as it should to the hormone insulin, which is supposed to help ferry glucose into cells for energy.

Control: The approach was originally developed to help diabetics control their condition, but whether it can do that is debatable.

One 2009 analysis by the Cochrane Collaboration concluded low-GI diets may have a beneficial effect on hemoglobin A1C levels—a measure of blood sugar over time—in both type 1 and 2 diabetics. They decreased hemoglobin A1C levels appreciably—by .5 percentage points, according to data from 11 short studies involving 402 participants.

Still, some studies haven’t found low-GI diets have an edge. One, published in the American Journal of Clinical Nutrition in 2008, assigned 162 type 2 diabetics to three diets, two of which were high- and low-GI approaches. Researchers found no marked difference among the groups in A1C levels after a year. Another, published in Nutrition in 2008, showed similar drops after a year in A1C in type 2 diabetics on a low-GI diet or a diet based on recommendations from the American Diabetes Association.

Many experts suggest diabetics count carbs throughout the day to keep blood-sugar levels in check. Adding the glycemic index to the mix may help some whose blood-sugar levels could use a little “fine tuning,” says the ADA.

Are there health risks?

No indications of serious short-term risks or side effects have surfaced.

However, a food’s GI ranking doesn’t always reflect how nutritious it is—foods can be laden with calories, sugar, and saturated fat but still have a low GI. A Snickers bar, for example, is considered low-GI. A diet heavy on sugary and fatty foods will jeopardize your weight-loss efforts and your health, too.

While the index also doesn’t offer guidance on fat and protein sources, that’s no reason to go on a bacon binge. Lean meat (chicken breast) and healthy poly- and monounsaturated fats (olive oil) can help keep cholesterol levels in check.

How well does it conform to accepted dietary guidelines?

Fat. It’s possible to stay within the government’s recommendation that no more than 20 to 35 percent of calories come from fat—if you make sensible choices.

Protein. Lots of low-GI carbs are also high-protein—like quinoa, beans, and lentils—but meat doesn’t have carbs, so you’ll have to decide what and how much you eat to stay within the recommended 10 to 35 percent of daily calories from protein.

Carbohydrates. You’ll have no trouble meeting the government’s recommendation that 45 to 65 percent of your day’s calories come from carbs.

Salt. The majority of Americans eat too much salt. The recommended daily maximum is 2,300 milligrams, but if you’re 51 or older or African-American, or have hypertension, diabetes, or chronic kidney disease, that limit is 1,500 mg. A sample low-GI menu—taken from The Low GI Diet Revolution, one of many guides to adopting the approach—came in just under 2,300 mg. If you’re diligent about reading labels on packaged or canned products for sodium content, it’s possible stay under 1,500 mg.

Other key nutrients. The 2010 Dietary Guidelines call these “nutrients of concern” because many Americans get too little of one or more of them:

  • Fiber. Getting the recommended daily amount—22 to 34 grams for adults—helps you feel full and promotes good digestion. Lots of fruits, veggies, whole grains, and beans are high-fiber, low-GI foods, so including a variety of them should get you to your target. The sample GI menu mentioned previously provided 27 g.
  • Potassium. A sufficient amount of this important nutrient, according to the 2010 Dietary Guidelines, counters salt’s ability to raise blood pressure, decreases bone loss, and reduces the risk of developing kidney stones. It’s not that easy to get the recommended daily 4,700 mg. from food. (Bananas are high in potassium, yet you’d have to eat 11 a day.) Most Americans take in far too little, and it’s even harder to meet the recommendation on a reduced-calorie diet. Adding yogurt, beans, lentils, and orange juice to your menu can help—they’re all low-GI and pack up to 600 mg. of potassium. Unfortunately, you don’t have the luxury of reaching for a baked potato, which has more than 700 mg. of potassium but is high-GI. It may be difficult to meet your potassium benchmark.
  • Calcium. It’s essential not only to build and maintain bones but to make blood vessels and muscles function properly. Many Americans don’t get enough. Women and anyone older than 50 should try especially hard to meet the government’s recommendation of 1,000 mg. to 1,300 mg. At about 744 mg., the sample low-GI diet came up short, although your actual intake will vary based on your meal plan. To meet the target, choose low-fat dairy products and calcium-fortified juices and cereals.
  • Vitamin B-12. Adults should shoot for 2.4 micrograms of this nutrient, which is critical for proper cell metabolism. The sample menu didn’t meet the government’s recommendation, but yogurt and fortified cereals can help.
  • Vitamin D. Adults who don’t get enough sunlight need to meet the government’s 15 microgram recommendation with food or a supplement to lower the risk of bone fractures. The sample diet provided enough. If you’re concerned about skimping, get plenty of low-fat dairy and vitamin D-fortified cereals.

Supplement recommended? N/A

How easy is it to follow?

Moderately difficult.

Following the University of Sydney’s suggestions, a low-GI approach can be as simple as swapping the baked potato that usually accompanies your steak for a medley of zucchini, yellow squash, and baby carrots.

But you won’t find a GI ranking for every food—researchers will never be able to test them all—so who knows if that exact box of crackers is low-GI? And a low GI ranking isn’t all that determines the effect of a particular food item on your body. How the food is prepared, or if it's a fruit or veggie how ripe it is, are just two of many wild cards. Good luck coming up with a close estimate of the effect your entire dinner (or of a particular recipe for cornbread) has on your blood-sugar levels. Moreover, perfectly healthy foods might be high-GI and unhealthy ones low-GI. It adds up to a lot of confusion.

The index also isn’t helpful with non-carb foods. Without guidance, many dieters, especially those aiming to lose weight, would have a tough time designing a plan that reduces calories enough to deliver weight loss.

You can avoid some of this uncertainty with one of the many diet programs or books on the market that provide shopping lists and meal plans. Or just take the University of Sydney’s advice.

Convenience:

There aren’t many rules—cook if you want, or just dine out. But without the structure of an actual program, you’ll have to figure out how much, what, and when to eat on your own.

Recipes. The Internet is rife with low-GI recipes. For extra inspiration, one of the many low-GI cookbooks on the market might help.

Eating out. Shouldn’t be a problem once you have a handle on what’s low and high in the GI world.

Alcohol. Drinking alcohol in excess, particularly beer, can raise blood-sugar levels. Moderation is your best bet—that’s one drink a day for women, two a day for men. (A drink is considered 12 ounces of beer, 5 ounces of wine, or 1½ ounces of liquor.)

Time-savers. You’re stuck with all the work if you choose to follow a general GI approach. Some books or guides might make the process simpler.

Extras. None.

Fullness:

Nutrition experts emphasize the importance of satiety, the satisfied feeling that you’ve had enough. Because low-GI foods—especially beans, produce, and whole grains—are thought to take longer to digest, you’ll likely keep hunger pangs at bay.

Taste:

You’re preparing the food—if it doesn’t taste good, you know who to blame.

How much does it cost?

It’s hard to say. Whole-grain products, fruits, and vegetables—which should be filling your cart if you’re doing it right—are generally more expensive than are highly processed foods like white bread, sugary cereals, and sweets.

Does the diet allow for restrictions and preferences?

Anyone can follow this approach—choose your preference for more information.

Very doable. Most of your staples—vegetables, pasta, and beans—are low-GI foods.

Doable. Many fruits and veggies are low-GI. Bread made from chickpea flour and buckwheat noodles are good gluten-free options. The University of Sydney has more suggestions on its website.

It’s up to you to track sodium. But with some extra attention paid to reading labels on anything canned or processed, you should be able to do it.

Yes, you can make sure your diet is kosher.

Yes, you can make your diet conform.

What is the role of exercise?

The GI approach deals only with ranking carbs. But that doesn’t mean you shouldn’t exercise.

No matter the diet, the more you move, the quicker you’ll see the pounds come off—and reduce the risk of certain chronic diseases. Adults are generally encouraged to get at least 2½ hours of moderate-intensity activity (like brisk walking) each week, along with a couple days of muscle-strengthening activities. The Centers for Disease Control and Prevention offers tips to get you started.


Last updated by Kurtis Hiatt | December 12, 2013

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