PAMF Health Blog

Be Well, Be Well Informed

Good Carbs, Bad Carbs: How to Choose

Posted on Dec 7, 2015

med diet

What are carbohydrates and how do they affect your health? Carbohydrates include starches like bread, pasta, rice, cereal and potatoes, as well as sugars such as milk, yogurt and cookies. During digestion, all carbohydrates are converted to sugar and released into the bloodstream, where they are either used for energy or stored as fat.

But not all carbs are created equal. Or more accurately, not all carbs have the same effect on blood sugar. The measure of the effect of carbs on blood sugar is called the glycemic index (GI).

High GI carbs like white bread, instant mashed potatoes and sugary beverages digest quickly, causing blood sugar levels to surge. “In the body, these blood sugar spikes cause the release of insulin, fat storage, mood swings and brain fog,” says Darcie Ellyne, M.S., R.D., CDE, a registered dietitian and certified diabetes educator at the Palo Alto Medical Foundation (PAMF). “Then blood sugar plummets, causing the release of the stress hormone cortisol, food cravings, fatigue and more brain fog.”

Good (low GI) carbs, on the other hand, like bran cereal, fresh fruit and vegetables, are digested slowly.  As a result, your blood glucose rises slowly than falls gradually over a longer period of time, which helps control appetite and delay hunger.

“Not only do we feel better when  blood sugar levels stay steady throughout the day, but a low GI diet also reduces your risk of diabetes, cardiovascular disease, breast and colon cancer, Alzheimer’s and obesity,” says Ellyne.

Ellyne answers these commonly asked questions about good and bad carbs:

How do I know which carbohydrates have a low or high glycemic index?

  • Processing – The more a food has been processed, the easier it is for the digestive enzymes to attack it quickly, and the higher the GI. To choose less processed foods, think about how that starch occurred in nature, and how much processing was required to get it to its current form.
  • Particle size – If your body has to do more of the work to break large food particles down, the GI is likely to be lower. For example, steel cut oats, which are covered by a layer of fiber, have a lower GI than long cook oatmeal, and long cook oatmeal has a lower GI than instant oatmeal.
  • Sugar Content – Consider both the type and amount of sugar contained in your food. Fructose has the lowest GI, then sucrose and then glucose.

What other factors affect glycemic index?

  • Food combination – Combining your carbohydrates with fat and protein slows down the rate of digestion and lowers the GI. So for a healthier snack that keeps you satisfied, have a wedge of cheese with your apple, or a spoonful of peanut butter on your toast.
  • Acid content – Adding acid to a food lowers the GI. This makes sourdough bread relatively low on the GI scale, and gives you another great reason (besides flavor), to add a dash of lemon or balsamic vinegar to foods.
  • Cooking time – The longer you cook a food, the higher the GI. Less cooking means the body has to work harder to digest the food, so keep your pasta al dente and serve your steamed broccoli as soon as it turns bright green and you can pierce it with a fork.
  • Physical entrapment – Whole grains have a fibrous coat that acts a physical barrier to slow down the digestion of the starch inside. White flour, on the other hand, has been processed and all the fiber has been removed. So instead of corn flakes, choose All Bran cereal, and instead of a bagel, choose pumpernickel bread.

What  general rules should I follow to lower the glycemic index in my diet?

  • Eat starches as they are in nature. Watch portions, especially of high GI starches like potatoes and white rice. Choose intact, minimally-processed grains and legumes.
  • Add an acidic fruit or condiment.
  • Include a lean protein in a meal or snack.
  • Include a healthy fat (olive or nut oils).
  • Include produce at every meal, and avoid juicing fruits and vegetables.

Glycemic food choices: More fun facts

  • Eggs and cheese are considered a protein. Fat and protein won’t increase blood sugar, but milk and regular (non-Greek) yogurt will. Greek yogurt generally has about half the carbs, and twice the protein of regular yogurt.
  • To choose lower GI fruits, keep in mind the general rule that tropical fruits (bananas, mangos, etc.), have a higher GI than non-tropical fruits (apples, oranges).
  • Pasta is a relatively low GI food – as long as you cook it al dente.
  • Potatoes – especially white potatoes – spike blood sugar more than eating straight sugar.

“Making food choices that lower GI and boost nutrition will not only keep you focused and productive throughout the day, but can help prevent diabetes and other diseases,” says Ellyne. “So get off the sugar roller coaster and enjoy smooth sailing all day long.”

Darcie Ellyne Blog photoDarcie Ellyne, M.S., R.D., CDE, is a registered dietitian and certified diabetes educator at the Palo Alto Medical Foundation.