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Harvard Commentaries
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Food for Thought Food for Thought

Carbohydrates -- Good or Bad for You?

July 09, 2013

By Jacqueline Minichiello, M.S.
Brigham and Women's Hospital

Over the years, carbohydrates have gotten a bad reputation. Diets such as Atkins and South Beach promote easy, rapid weight loss that can be very attractive to someone trying to lose weight.

By restricting the amounts of carbohydrate that you eat, these diets claim that you can turn your body into a fat-burning machine. When you limit carbohydrates, however, you deprive your body of a main source of fuel — and many essential nutrients that you need to stay healthy.

What are carbohydrates?

Carbohydrates are foods that get converted into glucose, or sugar, in our bodies during digestion. Glucose is a main source of fuel for our body. It is especially important for the brain, which cannot easily use other fuel sources (such as fat or protein) for energy.

There are two kinds of carbohydrates:

  • Simple carbohydrates include sugars found in foods such as table sugar, honey, dairy products, fruit and fruit juice.


  • Complex carbohydrates are starches — long chains of glucose molecules — which include grain products, such as bread, crackers, pasta and rice. Some vegetables — corn, peas, white and sweet potatoes, and butternut and winter squash — are high in starch. Complex carbohydrates can be broken down further into refined and whole grain carbohydrates.

Are all carbohydrates created equal?

All carbohydrates turn into glucose and raise our blood sugar. But some do it faster than others. Controlling blood glucose is important for weight management as well as diabetes control.

Fiber is important for your digestive health as well as regulating blood glucose. Foods with fiber — such as broccoli, beans, and apples with the skin, 100% whole-wheat bread — take longer to be digested. This means that glucose is released into the bloodstream slowly.

Refined carbohydrates, such as white rice and white pasta, have had their fiber and nutrients removed. Whole grains, such as brown rice and whole-wheat pasta, have not. Therefore, the glucose from refined carbohydrates can get into the bloodstream faster than the glucose from whole grains.

Fruits also contain fiber. The sugar from a piece of fruit does not affect blood glucose the same way fruit juice would.

Which nutrients am I missing if I cut out whole grains and fruit from my diet?

The nutrients found in whole grains include essential fatty acids, the B vitamins, folate, vitamin E, zinc and magnesium. Whole grains also have fiber. Fruit and starchy vegetables contain many vitamins and minerals, as well as phytonutrients. Phytonutrients are plant compounds that help prevent disease in humans. Phytonutrients include carotenoids and flavonoids.

What does my body use for fuel if I am not getting enough carbohydrates?

If you are not getting enough carbohydrates from your diet, then your body must use fat and protein for energy. This is why the carbohydrate-restricted diets claim they are great for weight loss. However, neither protein nor fat is an efficient source of energy.

  • Fat digestion – Fat does not completely digest when it is used as an energy source. Byproducts called ketones are formed. Ketones are mildly acidic. They can build up in the blood and make it more acidic. Over time this may be harmful to the body.


  • Protein digestion – Protein's main job is to be a building block, not an energy source. Using protein for energy can compromise the building of muscles and other cells.

Which carbohydrates should I eat?

  • Skip the fruit juice and go straight to the fruit. Eat a variety of fruits and vegetables daily.


  • Limit the amount of refined sugars, such as high-fructose corn syrup, corn syrup, agave, honey and white and brown sugar. These are often found in cakes, cookies and donuts. These lack nutrients and are high in calories.


  • Choose whole grains, such as brown rice, oats, whole-wheat pasta and whole-wheat bread. To ensure that you are buying a whole-grain product, check the ingredient list. Look for the words "100% whole grain." If you see whole wheat or whole grain listed as the first ingredient, then the product probably is mostly whole grain, but also has refined grains. The label won't tell you how much, so pick products with the words 100% whole grain in the ingredient list. Don't rely on the front of the package or color of the food!

What about portion size?

It's important to include carbohydrates in your diet. But to avoid weight gain, pay attention to portion size. Try to limit the amount of carbohydrates, such as potatoes, peas, butternut squash, rice or pasta, to a quarter of your plate (about 1 cup). Be mindful of carbohydrate snacks, such as chips, cookies, crackers and donuts.

What are some different whole grains to try?

Here are some suggestions:

  • Amaranth – Serve as a warm porridge in the morning or mix with vegetables.
  • Barley (hulled) – Use in soup instead of rice or pasta.
  • Brown rice – Use in place of white rice in recipes.
  • Quinoa – Mix with vegetables to make a salad or stir-fry.
  • Wheat berries – Mix with vegetables to make a salad.

The Bottom Line

Carbohydrates are a major source of fuel and nutrients for our bodies. They should be part of a healthy diet, even when the goal is to lose weight. When adding carbohydrates, pay attention to portion size, choose whole fruits and make it a whole grain!

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Jacqueline Minichiello, M.S., is a dietetic intern at Brigham and Women's Hospital. She graduated with a B.S. in Psychobiology from Binghamton University and an M.S. in Biochemical and Molecular Nutrition from Tufts University. She completed her D.P.D. program at Simmons College.

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