Odds are you’ve heard the idea that not all carbs are created equal. That’s both true and not true. On one level, your body doesn’t care where the carbohydrates in your food come from, because all carbs provide usable energy for your body — and especially your brain, which is a carb hog. That doesn’t mean that all carbs, or the foods that contain them, are equal in quality.
Let’s take “fast” vs. “slow” carbs. In other words, how fast or slow the sugars in a carbohydrate are digested and absorbed. Allow me to get technical for a moment. All carbohydrates are made up of chains of sugars, more formally known as saccharides. Disaccharides like sucrose (table sugar) are made up of two sugar units and are generally digested and absorbed faster than polysaccharides, which may be made up of hundreds of sugar units. It takes longer for our digestive system to break apart those long chains. Keep in mind that naturally occurring sugars in plant-based foods (fruit, vegetables, grains, pulses) and dairy foods are not the same as sugar added to foods.
One common measure of fast vs. slow carbs is the glycemic index (GI), which ranks carbohydrates on a scale from zero to 100 based on how eating 50 grams of the carbohydrate in a specific food affects blood sugar. High-GI foods are rapidly digested and absorbed, so they may cause a fast, sharp rise in blood sugar. Foods with a low GI take longer to digest and absorb, so your blood sugar rises more slowly.
Both the type of carbohydrate and the presence (or absence) of fiber in a particular food affects its GI. For example, table sugar, honey, corn syrup, maple syrup, brown sugar and molasses contain easily digested disaccharides and no fiber, so they are fast carbs. Products made from white flour also tend to be fast carbs, because the flour has been stripped of the fiber that would otherwise help slow digestion. Fruit juice keeps the natural sugar but loses the fiber, so it’s a fast carb, too.
Examples of slow carbs are whole grains, vegetables, legumes and fruits. These intact plant foods contain their natural fiber, which slows down digestion. Many are also water-rich, which reduces the amount of carb per serving. These factors come into play when you look at glycemic load, which accounts for a food’s GI and the normal amount consumed. For example, carrots have a GI of 35, but a typical serving of carrots has a glycemic load of only 6. Watermelon has a GI of 80, but one serving has a glycemic load of five. These foods also contain an abundance of vitamins, minerals, antioxidants and phytochemicals, further adding to their quality.
Does this mean you should avoid fast carbs altogether? No. A small glass of orange juice with breakfast offers nutrients and pleasure. A flavorful pasta dish with veggies and chicken or seafood offers lots of nutrition, even when using white pasta. Keep in mind that how you cook carb-rich foods and what you eat with them also affects how fast or slow they are. Pasta cooked al dente has a lower glycemic index than pasta cooked until it’s mushy. Cooked potatoes have a lower glycemic index if they are chilled before eating. Eating balanced meals and snacks that include carbohydrates, protein and healthy fats lowers the meal’s overall glycemic load and is probably going to help you feel more nourished and satisfied overall. And that’s what’s really important.