Carbs are not automatically bad, but eating too much of certain heavily-processed and refined carbohydrate-rich foods can lead to unwanted weight gain. That's because starchy or sugary foods are high in calories.
A Little Carbohydrate Chemistry
Let's back up a moment, and start with a carbohydrate lesson. Your body needs carbs for energy. They're one of the macronutrients that your body requires as part of a healthy balanced diet. There are two different types of carbohydrates: simple sugars and complex carbohydrates.
Simple carbohydrates, or simple sugars, are small molecules, and they include glucose, table sugar, fruit sugar and milk sugar. Candy, soft drinks and many fruits are high in simple sugars. Complex carbohydrates are larger molecules. The most common dietary complex carbohydrate is starch, and it's found in foods like bread, pasta, potatoes and rice.
So what makes a carbohydrate bad or good? Carbohydrate-rich foods that are high in fiber are good for you, especially when they're also nutrient-dense. Potatoes with the skins intact are a good source of nutrients and fiber. When you prepare them properly, potatoes are nutritious and not high in calories.
Fresh fruits and berries usually have natural fruit sugars, but they also contain dietary fiber in their coverings and seeds, along with lots of vitamins, minerals and natural phytochemicals that may have health benefits.
Vegetables are usually lower in starch and sugar than fruits, but some of the sweeter vegetables like sweet corn, potatoes and sweet potatoes are high in starch. They're still good for you as long as you prepare them with healthy cooking methods and watch your serving sizes. Grains and cereals are high in starch, but if you choose 100-percent whole grain products, you'll get more nutrition and fiber than if you pick refined versions.
Refined carbohydrate-rich foods that are low in fiber and heavily processed are bad for you. Potato chips, for example, are high in starch, as well as fat and sodium, and candy and sweets are generally high in sugar, but not nutritious. Soft drinks get all their calories from sugar, but there's nothing else of nutritional value. These types of high sugar, nutrition-poor foods are sometimes said to contain "empty calories."
When people talk about cutting out carbs, they're usually talking about giving up only those foods that are high in sugar and starch, but low in fiber. However, some people try to give up almost all carbohydrates, including all fruits and some vegetables. This isn't necessary, or even a good idea since fruits, vegetables and berries are nutritious and not high in calories when you eat them in their natural whole form.
Harvard School of Public Health. "Carbohydrates: Good Carbs Guide the Way." Accessed August 22, 2012. http://www.hsph.harvard.edu/nutritionsource/what-should-you-eat/carbohydrates-full-story/.
United States Departments of Agriculture. "ChooseMyPlay.gov - Fruits." Accessed August 22, 2012. http://www.choosemyplate.gov/food-groups/fruits.html.