Your top carbohydrate questions, answered

Pop culture’s view on carbs has been quite the roller-coaster. On one hand, many of us who grew up doing sports were told to carbo-load before a race and heard through most of the 1980s that carbs wouldn’t cause weight gain. Since the Atkins diet became popular in the ‘90s through keto in the 2010s, we’ve also heard preaching about low-carb and no-carb diets. Oh, and the whole simple-versus-complex carbs concept. So what in the carb is really going on here?

It turns out that the category of carbohydrates isn't inherently good or bad. Carbs come in many forms, with various implications for health. Once you better understand the science behind carbohydrates, you’ll be empowered to make informed food choices that support your wellness goals. (And no, we’re never going to say you have to swear off bread.)

What are carbohydrates?

Carbs are essentially sugar molecules — groupings of carbon, hydrogen, and oxygen — that occur either alone or linked together in different combinations. Most of the carbs we eat are digested and broken down into glucose to provide energy for our muscles and brain; in fact, carbohydrates are the body’s preferred source of fuel, says Silvia Klinger, M.S., RDN, a nutritionist based in Hinsdale, Illinois. Some carb types support digestion, gut health, and other functions. Carbohydrates are classified as macronutrients, meaning the body needs relatively high amounts for energy.

What should my daily carb intake be?

The latest Dietary Guidelines for Americans recommend that carbs compose between 45% and 65% of total calories. The optimal proportion of carbs for you depends on your lifestyle and personal health picture, Mitchell says. For example, if you are living with type 2 diabetes, your optimal carb intake might be on the lower end of that bracket to help keep blood glucose level within a healthy range, she explains. Lifestyle factors such as physical activity can increase the need for carbs. Your doctor or the nutritionists at Weight Watchers can advise you on the carb intake that makes sense for you.

What are the different types of carbs?

Some of us hear the word “carbs” and immediately think “bread.” But the world of carbs is diverse, Klinger says. Carbohydrates fall into one of three main groups, though many foods contain some of the other types as well.

• Starches. For most adults in the U.S., starches are the most widely consumed type of carbohydrate. This includes rice, oats, and barley, as well as grain-based products such as bread, cereal, and pasta. Potatoes, beans, peas, and corn are major sources of starch, too.
  
  
• Sugars. This carb group also includes sugars that occur naturally in whole foods, such as the fructose in fruits and lactose in yogurt. Also in the sugar category: caloric sweeteners found in commercially made foods and drinks, from candy and soda to salad dressing and pasta sauce. On ingredient labels, sugar goes by a number of names, including corn syrup, dextrose, and molasses.
  
  
• Fibers. Found only in plant-based foods like fruits, veggies, and grains, fiber adds bulk to your diet. It has a number of subtypes (for example, there’s pectin in citrus fruits, inulin in onions, and cellulose in kale), which are classified as either soluble or insoluble, depending on how they interact with water. Different types of dietary fiber support health in different ways.

What makes a simple versus complex carb?

Nutrition experts love to classify, so they also divide carbs by whether they’re simple or complex, all depending on the number of sugar molecules the carbs contain. Sugars fall into the simple category because they’re made up of just one or two molecules. Starches and fibers, meanwhile, comprise at least three sugar molecules and are therefore classified as complex carbs. Here’s a little more about what that means for your body.

• Simple carbohydrates (sugar): Thanks to their basic molecular structure, sugars require little or no digestive breakdown, so their glucose enters the bloodstream soon after a person eats. “Simple carbs can be beneficial, especially for people who are very active physically and need quick bursts of energy during exercise,” says Mindy Hermann, RDN, a nutritionist based in Somers, New York.
  
  The presence of fiber in a food can slow the release of simple sugars to result in a more sustained energy release and greater satiety, Hermann notes. That’s one reason she recommends fiber-rich whole foods such as apples over sweetened fare like cookies, which tend to lack fiber. Because of that lack of fiber, “processed foods with added sugar really aren’t that filling,” Hermann says. “So some people find that it can lead to overeating.”
  
  
• Complex carbohydrates (starch, fiber): For starches, digestive enzymes in the gut take more time to break the longer chains of sugar molecules in these types of carbs down into single units, so starches tend to provide a steadier and more gradual source of glucose energy than simple sugars do, says Susan Mitchell, PhD, RDN.
  
  Dietary fiber, meanwhile, works a little differently from starches and sugars. Our bodies lack the enzymes needed to divvy up fiber chains into simple sugars, Mitchell explains. As a result, fiber passes through the gut without being broken down into glucose and keeps moving, undigested. That’s good because it can help keep you regular as well as keeping hunger and blood sugar in check.

What are “good” vs. “bad” carb foods?

At Weight Watchers, we steer clear of value judgments concerning individual foods. After all, it’s more about having an overall healthy pattern of eating, which includes a variety of foods.

That said, some healthier carbohydrate-containing foods below can boost your overall nutrient intake.

• Tubers. ​Skeptics may scoff that potatoes, yams, and sweet potatoes are starchy, but again, that’s not an inherently negative quality. (Remember, starch is a complex carb.) Depending on the variety, a tuber might be a good source of potassium, vitamin C, vitamin B6, and more.
• Vegetables.​ “Veggies provide a mix of naturally occurring plant compounds called phytonutrients, which help protect us from heart disease, cancer, and other disease,” Mitchell says. And yep, from Brussels sprouts to beets, all veggies contain some carbs.
• Whole fruits. The fiber in any given fruit slows the release of its simple sugars, making fruit a nutritious option for those of us with a sweet tooth. And though some people may worry that fruits’ naturally occurring simple sugars will cause weight gain, research following U.S. men and women for 24 years found that the more produce people ate, the less weight they gained over time.
• Pulses.​ The edible seeds of beans, peas, and lentils boast a unique combination of starch, fiber, and protein, which helps satisfy appetite and keep post-meal munchies at bay. A meta-analysis of 11 clinical trials found that people who regularly ate pulses had a reduced risk of developing cardiovascular disease, possibly due to beneficial effects on blood pressure, cholesterol, blood sugar, and more.
• Whole grains. In addition to delivering complex carbs, including fiber, whole grains are rich in magnesium, antioxidants, and vitamin E. Research suggests that a diet high in whole grains can help lower the risk of developing type 2 diabetes.

How do carbs affect the body?

Carbohydrates can affect our energy level, mood, blood sugar, weight, digestion, and more. Here’s how they affect the body.

Carbs and energy

After you eat a food that contains a carb, it travels to the small intestine for digestion. Any complex carbs are broken down into single units of glucose, which then enter the bloodstream (sugars do the same without having to be broken down). Once glucose makes its way into cells, it’s synthesized into a molecule called ATP (adenosine triphosphate), a cell’s main carrier of chemical energy. Although cells can also make ATP from the building blocks of protein- and fat-based foods, glucose from carbs is the body’s preferred and most widely-used source.

Not all glucose ends up being used for ATP production. The liver and muscles also stash some glucose away in the form of glycogen to protect against future shortages. Any glucose not needed after that is stored as fat.

Carbs, blood sugar, and insulin

Glucose can’t do its job without a major assist from insulin. In healthy people, the pancreas secretes this hormone in response to rising blood levels of glucose after a carb-containing meal or snack. Insulin then “unlocks” the body’s cells so glucose can enter. In some people, however, the body’s cells don’t respond well to insulin, a condition known as insulin resistance. This can lead to chronically high blood sugar — and health impacts such as prediabetes and type 2 diabetes. Many people are able to improve their insulin response through lifestyle changes.

Carbs and digestion

It’s not glamorous, but fiber is probably most famous for preventing constipation. By taking on water, the soluble type of fiber helps form soft, bulky stools. Insoluble fiber adds further bulk and, with a broom-like effect, keeps waste material moving along.

That’s not all fiber does during the digestive process. When some types of fiber (such as pectin) reach the colon, they help feed the resident population of beneficial bacteria (probiotics) through a process of fermentation. As those bacteria feast on the fiber, some produce short-chain fatty acids believed to play a role in immunity, inflammation control, and more.

Many adults in the U.S. fall short of getting the recommended 22g to 38g of fiber per day, depending on age and sex. You can boost your fiber intake by eating whole grains and whole-grain foods, as well as legumes, fruits, vegetables, nuts, and seeds.

Carbs and weight control

“Carbs can be a part of a weight-loss plan,” says Klinger. After all, even diets billed as “low-carb” contain some carbs. (Keep reading for more on low-carb diets.)

“Simple carbs provide a lot of calories but not a lot of nutrition,” Hermann says. That’s not a reason to ban all carbs, but to choose complex carbs over simple ones for weight management. She recommends choosing foods that contain complex carbs because they tend to be digested and absorbed more slowly than foods that are low in fiber and high in simple sugars (think white bread and sweets).

Carbs, brain function, and mood

Despite your brain accounting for around just 2% of your body’s total weight, it uses about 20% of the body’s glucose, making it a major consumer. That energy goes toward maintaining neurons, generating neurotransmitters, and calculating the percentage you should tip on your friend’s birthday dinner. The brain’s reliance on glucose (which — reminder — often comes from carbs) likely explains why lower-than-normal blood levels of glucose, a condition known as hypoglycemia, can make people feel confused, tired, or irritable. (Hypoglycemia warrants prompt medical attention; contact your doctor if you experience symptoms.)

What’s the truth about low-carb diets?

Atkins, keto, paleo, carnivore — low-carb diets likely persist in popularity because they often result in short-term weight loss. The problem is, they’re tough to maintain because they’re so restrictive, Hermann says. Low-carb diets vary in their degree of carb restriction, but the long-term gist is the same: if someone returns to their former eating habits, any weight that was lost tends to come back.

In truth, there’s little scientific evidence that low-carb diets are the best way to go for weight loss. A 2019 research review concluded that low-carb diets are no more effective than other dietary approaches to weight loss.

Other studies have raised questions about the long-term safety of strictly limiting carbs (more on that below). One risk is that diets that limit carbs generally lead to eating more fat, including saturated fat, which is linked to coronary heart disease. For example, bacon contains zero carbs, so it’s diet compliant…but it’s high in saturated fats, so likely isn’t contributing to someone’s overall health.

Hermann says the most sensible approach to a low-carb weight-loss diet would encourage people to limit carbs with added sugars, which are often high in calories and low in nutrients, while still encouraging consumption of nutritious whole foods that contain carbs.

Potential side effects and risks of low-carb diets

Low-carbohydrate diets vary in their intensity and affect people in different ways. It’s best to consult with your doctor before switching to a low-carb eating plan (or making any radical change to your diet). Below are some potential pros and cons to consider.

Potential benefits of a low-carb diet:

• Short-term weight loss
• Improved blood sugar control in people with type 2 diabetes
• Reduced blood pressure in people with hypertension
• Improvement in levels of blood lipids

Potential side effects of a low-carb diet:

• Vitamin and mineral deficiencies
• Digestive difficulties, particularly constipation
• Headaches
• Halitosis (bad breath)
• Muscle cramps
• Difficulty sticking to the diet long-term, leading to weight regain

The bottom line

So, should you eat carbohydrates? You betcha, given that they’re the preferred energy source for our muscles and brain, among other important functions. Carbohydrates are key in a healthy pattern of eating.

Despite the omnipresence of low-carb diets, the evidence shows it’s difficult to maintain long-term. The healthier way to approach a diet is finding one that’s sustainable for the rest of your life and includes a variety of whole foods, and allows for personal choices in what to eat.

That said, there are benefits to limiting your intake of carbs from added sugars and refined grains. Instead, consider centering your diet on whole foods that deliver good-for-you vitamins, minerals, and phytonutrients along with carbs like fruits, veggies, whole grains, and legumes.