The Science Behind the Slow-Carb Diet
All the details on the slow-carb diet and whether or not you can lose weight while on the plan
You've eaten your weight in grapefruit, counted your share of fat grams (then eaten as many as possible on the keto diet), and sworn off bread, pasta, and every other carbohydrate—all in an effort to lose weight. Now, you can finally breathe easier: The next big thing in weight loss isn't low-fat, low-flavor, or low-carb. It's the slow-carb diet, aka low-glycemic index diet, and if you haven't already heard of it, you will. Research is beginning to confirm what popular diet plans like The South Beach Diet have been preaching for years: Eating a "slow-carb" diet composed mostly of foods with a low glycemic index may help you balance blood-sugar levels and eat less while still feeling full.
What is the slow-carb diet?
In the simplest of terms, a low-glycemic slow-carb diet is generally high in "good" carbohydrates (like vegetables and whole grains) and low in "bad" ones (like chocolate chip cookies). Lean proteins and healthy fats round out the rest.
"It's the middle ground between diets that are packed with protein, which promise satiety, and those loaded with fiber, which are the most nutritious," explains Walter Willett, M.D., chairman of the department of nutrition at the Harvard School of Public Health. But that's not the whole story. Glycemic-index diet plans are some of the most complicated ever to hit the bookstore shelves. Some allow carrots, some don't. Some say bananas are okay, others say they're not. What most experts do agree on about the slow-carb diet, however, is that following one may not do any harm and can even confer health benefits beyond basic weight loss.
Before you try the slow-carb diet, here's what you need to know.
Why does the glycemic index of food matter?
The glycemic index (GI) is a system of ranking carbohydrates based on how much they raise blood-glucose levels. It was originally developed for diabetics, but its usefulness has grown with our understanding of the impact blood-sugar levels have on hunger. (BTW, here are 10 subtle signs of diabetes women need to know about.) It's now the concept that has inspired the sl0w-carb diet.
According to Christine Pelkman, Ph.D., an assistant professor of nutrition at SUNY Buffalo, the theory goes: You eat a carbohydrate. The rise in blood sugar triggers a boost in insulin production. Insulin reduces your blood sugar, which leaves you feeling irritable and lethargic. "Falling blood-sugar levels can cause you to get hungrier faster," says Pelkman. (Related: This Is Your Body on Sugar)
How to balance your blood sugar levels on a slow-carb diet
There are lots of things you can do to keep your blood-sugar levels balanced. Daily exercise helps, and so do regularly spaced snacks and meals, but your food choices are key. That's where low-GI slow-carb diet foods come in. Foods with a GI lower than 55 raise blood sugar slightly, while those in the 55 to 70 range raise it a little higher; carbohydrates with a GI of more than 70 send it soaring. Low-GI foods have a more moderate effect on blood-sugar levels, primarily because they slow digestion—that's why some low-GI plans call themselves "slow carb." (Related: This Study On Carbs Might Make You Rethink Your Keto Diet Aspirations)
A number of studies show that a low-GI meal can be more satisfying than a high-GI meal and can help control overeating; some experts speculate that this effect may lead to weight loss. Research also shows that eating a low-GI diet may help prevent insulin resistance, which is a likely culprit in the development of diabetes. "Furthermore, since insulin resistance leads to excess weight gain around the waist, a known risk factor for cardiovascular disease, a diet based on low-GI foods may also be protective of your heart," says David Katz, M.D., director of the Yale Prevention Research Center.
How to make a slow-carb diet work for you
Rigidly following a low-glycemic index slow-carb diet plan isn't easy. For one thing, it's difficult to know what to eat unless you carry an extensive list like ours around with you. Just try picking out a breakfast cereal: All-Bran has a low GI (38) while Bran Flakes has a high one (74). And, oddly, sugar has a lower GI (61) than whole wheat bread or potatoes. "You can't throw out all of your nutrition know-how because of the index," says Thomas Wolever, M.D., Ph.D., a GI researcher and professor of nutrition at the University of Toronto. "Chocolate cake may have a lower GI than wheat bread, but this doesn't mean it's better for you. You have to take into account that the cake also has more fat, sugar, and calories and less fiber."
Complicating things even further is that GI rankings compare foods based on a set amount of carbohydrates (usually 50 grams), which doesn't always correlate to normal portion sizes. And when you start combining foods, their effect on your blood-sugar levels changes. But before you give in to your doughnut desires, relax.
Here's how to reap the most benefits of a low-GI slow-carb diet.
- Replace as many as possible high-GI foods in your diet with healthy lower-GI alternatives.
- Add or substitute at least one healthy low-GI food at each meal. Include protein and fat whenever you eat a high-GI food.
- Choose low-GI whole grains over refined as often as possible.
- Reduce the blood-sugar impact of any food by pairing it with one that has a lower glycemic index. For example, smother waffles (high-GI) with blueberries (low-GI).
- Control portions. Big meals—no matter what they contain—always stimulate a higher blood-glucose response than smaller ones, says Dr. Katz.
Slow-Carb Foods & Meals to Try
Instead of: Instant oatmeal
- Try: Old-fashioned oatmeal (One of these time-saving overnight oat hacks can help cut down on prep!)
- Why: The chewiness of old-fashioned oatmeal is largely due to the high percentage of hard, compact starch granules, as well as fiber. These granules are more complicated to break down, and they slow the digestive process. In contrast, much of the starch in instant oatmeal has been presoftened during processing, so it's digested more quickly.
Instead of: Turkey sandwich on whole wheat; baked chips
- Try: Turkey on 100 percent stone-ground whole wheat with lettuce, tomato, avocado; cup of tomato soup
- Why: Stone-ground whole wheat is coarser, which makes it slightly more difficult to digest (that's a good thing). The avocado provides fat and the tomato soup is acidic. Fat and acid both slow digestion by delaying the rate at which food leaves your stomach.
Instead of: Pretzels
- Try: Apple slices with peanut butter
- Why: The apples provide fiber and the peanut butter adds fat, both of which slow digestion.
Instead of: Veggie stir-fry with instant white rice
- Try: Chicken or tofu stir-fry with vegetables over basmati rice
- Why: Like instant oatmeal, instant white rice gets digested very quickly because processing has softened much of the starch granules. Basmati rice is a better choice because the starch granules are more compact. The protein from the chicken or tofu helps slow digestion.
Instead of: Rice pudding
- Try: Low-fat frozen yogurt with strawberries
- Why: Strawberries add fiber and acid, which slow digestion.
Low Glycemic Index Foods with a GI < 55
Food | Serving Size | Glycemic Index
Apple | 1 medium | 38
Artichokes, Jerusalem | 1/2 cup | 0
Avocado | 1/4 cup | 0
Baked beans | 2/3 cup | 38
Banana | 1 medium | 52
Barley, pearled | 1 cup, cooked | 25
Beans, kidney | 2/3 cup, cooked | 23
Black-eyed peas, canned | 2/3 cup cooked | 42
Bread, 100% whole grain | 1-ounce slice | 51
Broccoli, raw | 1 cup | 0
Bulgur | 3/4 cup, cooked | 48
Carrots | 1 medium, raw | 47
Cashews, salted | 1.75 ounce | 22
Cauliflower, raw | 3/4 cup | 0
Celery | 2 stalks | 0
Cereal, All-Bran | 1/2 cup | 30
Cherries, fresh | 18 | 22
Chickpeas, canned | 2/3 cup | 42
Chocolate cake, with frosting, from a mix | one 4-ounce slice | 38
Chocolate pudding, instant, with whole milk | 1/2 cup | 47
Cucumber, raw | 3/4 cup | 0
Grapes, green, fresh | 3/4 cup | 46
Grapefruit | 1/2 medium | 25
Grapefruit juice, unsweetened | 1 cup | 48
Ice cream, light, vanilla | 1/2 cup | 50
Lentils, brown | 3/4 cup, cooked | 29
Lentils, green | 3/4 cup, cooked | 30
Lettuce | 4 leaves | 0
Lima beans, baby, frozen | 3/4 cup | 32
M&M's, peanut | 15 pieces | 33
Mango | 4 ounces | 51
Maple syrup | 1 tablespoon | 54
Oatmeal | 1 cup | 49
Orange | 1 medium | 42
Orange juice, unsweetened | 1 cup | 53
Pasta, capellini | 6 ounces, cooked | 45
Pasta, fettuccine | 1 1/2 cups, cooked | 45
Pasta, linguine | 1 1/2 cups, cooked | 52
Pasta, ravioli, meat-filled | 6.5 ounces, cooked | 39
Pasta, spaghetti | 1 1/2 cups, cooked | 38
Pasta, tortellini, cheese-filled | 6.5 ounces, cooked | 50
Pasta, whole wheat spaghetti | 1 1/2 cups, cooked | 32
Peach, fresh | 1 large | 42
Peas, green, frozen | 1/2 cup, cooked | 48
Potato chips, plain, salted | 2 ounces | 54
Rice, brown | 1 cup, cooked | 50
Rice, converted, white | 1 cup, cooked | 38
Soup, canned, lentil | 9 ounces | 44
Strawberry jam | 1 1/2 tablespoons | 51
Sweet potato | 5 ounces, cooked | 44
Tomato juice, canned, no sugar | 1 cup | 38
Tomato soup | 1 cup | 38
Yam | 1 cooked | 37
Yogurt, low-fat, with fruit and sugar | 1 cup | 33
Medium Glycemic Index Foods with GI 55 - 70
Food | Serving Size | Glycemic Index
Basmati rice | 1 cup, cooked | 58
Beets, canned | 1/2 cup| 64
Bread, light rye | 1-ounce slice| 68
Bread, pita, white | 1 ounce | 57
Bread, rye | 1-ounce slice | 58
Bread, white | 1-ounce slice | 70
Cereal, muesli, Swiss formula | 1 ounce | 56
Cereal, Raisin Bran | 1/2 cup | 61
Corn | 1/2 cup, cooked | 60
Couscous | 3/4 cup, cooked | 65
Croissant | 1 medium | 67
Hamburger bun | 1.5 ounces | 61
Honey | 1 tablespoon | 55
Muffin, blueberry | 1 small | 59
Muffin, bran | 1 small | 60
Oatmeal cookies | 4 small | 55
Oatmeal, instant | 1 cup | 66
Pancakes, made from mix | two 4-inch | 67
Pizza, cheese | 1 slice | 60
Potatoes, new | 1 cup | 62
Raisins | 1/2 cup | 64
Rice, white, long-grain | 1 cup, cooked | 61
Soup, black bean | 1 cup | 64
Soup, pea, canned | 1 cup | 66
Taco shells, baked | 2 | 68
Tortilla chips, plain, salted | 1.75 ounces | 63
High Glycemic Index Foods with GI > 70
Food | Serving Size | Glycemic Index
Bread, French baguette | 1 ounce | 95
Cereal, Bran Flakes | 1/2 cup | 74
Cereal, Corn Flakes | 1 cup | 92
Cereal, Grape-Nuts | 1/4 cup | 75
Cereal, Total | 3/4 cup | 76
Doughnut, cake-type | 1.75 ounces | 76
English muffin | 1 ounce | 77
French fries, frozen, heated | 30 fries | 75
Gatorade, orange-flavored | 1 cup | 89
Popcorn, plain, cooked in microwave | 1 1/2 cups | 72
Potato, baked | 1 medium | 85
Potatoes, mashed | 1 cup | 73
Pretzels | 1 ounce | 83
Puffed rice cakes, white | 3 cakes | 82
Rice, instant, white | 3/4 cup, cooked | 87
Scone, plain | 1 ounce | 92
Stuffing, bread | 1 ounce | 74
Waffles, Aunt Jemima | one 4-inch | 76
Watermelon, fresh | 4 ounces | 72