Carbohydrates have been a hot topic for decades. Like fats, they’ve been villainized by fad diets and picked apart by anyone interested in nutrition, from scientists to your next door neighbor who’s trying Atkins. Low-carb diets have gained traction as a possible way to lose weight and reduce the risk of heart disease. Understanding the science will help you navigate the controversy and make the best food choices for your health.

At its most basic, a carbohydrate is a molecule composed of carbon, hydrogen, and oxygen. There are three types of dietary carbohydrates: sugar, starch, and fiber:

Sugar: Single unit carbohydrates such as glucose and fructose are called monosaccharides; “mono” meaning one and “saccharide” meaning sugar. Glucose, commonly referred to as “blood sugar,” is the body’s main source of fuel. Monosaccharides can join together to form disaccharides. For example, sucrose (table sugar) is made up of glucose and fructose; lactose (the main sugar found in milk) consists of glucose and another monosaccharide called galactose. 

Starch: Monosaccharides can also form chains called polysaccharides, one type of which is starch. Starch is composed of chains of glucose molecules. When you eat starch, the body breaks down those chains and oxidizes glucose to produce energy in the form of ATP. You’ll find starch in non-sweet carbohydrate foods such as bread, potatoes, and pasta.

Fiber: Fiber also consists of  polysaccharides, but, unlike sugar and starch, is indigestible. There are two types of fiber to be aware of: soluble and insoluble. Soluble fiber absorbs water, thus forming a gel-like material in the digestive tract. This slows down digestion and helps you feel full. It can also lower blood sugar and cholesterol levels, therefore decreasing the risk of diseases such as diabetes and heart disease. Some of the foods highest in soluble fiber include oranges, oatmeal, brussels sprouts, and beans. Insoluble fiber does not dissolve in water. It adds bulk to the stool and can help prevent constipation. You can get it from fruit and vegetable skins, onions, leafy greens, and cabbage. Fiber can also serve as fuel for good gut bacteria and help reduce inflammation in the digestive tract. According to the most recent Dietary Guidelines for Americans, adults should aim for 25 to 30 grams of fiber per day. There’s no need to crunch numbers; eating a variety of foods from each food group (especially fruits and vegetables) will give you your recommended daily allowance.

Carbohydrates and weight loss

People often say that cutting carbohydrates can help you lose weight. Like almost everything else in nutrition, it depends. If you drastically reduce your carb intake your body will begin to burn more fat for fuel (this is the basis of the ketogenic diet). The oxidation of fat for energy produces acidic molecules called ketone bodies as a byproduct; if too much of these build up, it can disrupt the pH balance of the blood and be dangerous. However, the average person is unlikely to build up ketone bodies to this point, and eating fewer carbohydrates (especially refined carbohydrates) may be a good strategy for those looking to eat less overall. 

Complex carbohydrates and weight loss

You may have heard that you should choose complex carbohydrates over refined carbohydrates, but what’s the difference? Complex carbohydrates are less processed than refined carbohydrates and therefore contain more vitamins, minerals, and fiber. Examples of complex carbs are whole grain bread, whole fruit, and starchy vegetables such as sweet potatoes. Refined carbohydrates (think white bread, cake, cookies, and candy) contain a higher proportion of simple sugars than complex carbohydrates do and therefore raise your blood sugar more rapidly. This “spike and crash” can leave you feeling tired and irritable. The glycemic index is a tool that measures how quickly a carbohydrate food raises your blood sugar. It uses pure glucose as a reference point, giving it a score of 100. Foods with higher scores raise your blood sugar more quickly than those with lower scores. For example, white baguette has a score of 95, whereas an apple has a score of 36. You can find a more detailed explanation of the glycemic index and a sample reference chart here.

Final thoughts

How much carbohydrate  you should eat depends on your level of activity and how carbs make you feel. The Institute of Medicine recommends eating 45%-65% of your daily calories as carbohydrate. Carbohydrates have 4 calories per gram, so if you eat 2000 calories per day this works out to about 275 grams. One slice of bread has about 15 grams of carbohydrate (although many packaged brands have more, so don’t forget to read the food label); so does a small apple. This is just a guideline, however; some people will feel better with less and some with more. Focusing on complex carbohydrates will help ensure that you maximize your intake of vitamins, minerals, and fiber. 

Healthy Sources of Complex Carbohydrates

  • Medium boiled sweet potato: 24 g carbohydrate, 4 g fiber
  • ½ Cup cooked brown rice: 23 g carbohydrate, 2 g fiber
  • Medium raw apple: 25 g carbohydrate, 4 g fiber
  • ½ Cup cooked barley: 22 g carbohydrate, 3 g fiber
  • ½ Cup canned garbanzo beans: 16 g carbohydrate, 5 g fiber
  • Medium raw orange: 18 g carbohydrate, 3 g fiber
  • ½ Cup dry oatmeal: 28 g carbohydrate, 4 g fiber
  • 1 Cup baked butternut squash: 22 g carbohydrate, 7 g fiber
  • 1 Cup raw raspberries: 15 g carbohydrate, 8 g fiber
  • ½ Cup cooked quinoa: 20 g carbohydrate, 3 g fiber
Spotlight on Carbohydrate
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