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Carbohydrates are one of the three macronutrients that occur naturally in plant foods, including peas and beans, nuts and seeds, grains, dairy and dairy products, fruits, and vegetables.

The other two macronutrients are dietary fats and proteins.

Carbohydrates are considered essential nutrients for the body to function properly by several global health organizations, including the World Health Organization (WHO). Their primary role is to provide energy to all cells in the body. In the absence of carbohydrate intake, the body will use an alternative fuel source called ketones.

The word “carbohydrate” is an umbrella term that describes various types of sugar-containing molecules present in foods.

Generally, there are three types of carbohydrates: sugars, starches, and dietary fiber.

It is possible to classify them further as simple or complex carbs, depending on the number and type of sugar molecules — such as glucose — that each structure contains.

Simple carbs

Also called “simple sugars,” “sugars,” or “saccharides,” these carbohydrates contain between one and 10 sugar molecules and are present in fruits, vegetables, and dairy products. Those with one or two sugar molecules are called monosaccharides and disaccharides, respectively, while those containing up to 10 sugar molecules are called oligosaccharides.

Lactose — the main sugar in animal milk — is a disaccharide comprising the monosaccharides glucose and galactose.

Oligosaccharides, however, are mid-length prebiotic carbohydrates that are in fiber-rich foods and human milk.

Complex carbs

Complex carbohydrates are made up of polysaccharides, which are longer, intricate chains of sugar molecules. Complex carbs include both starches and dietary fiber.

Starches are the storage carbohydrates in peas and beans, grains, and vegetables, and they provide the body with energy.

Dietary fiber, or roughage, is the indigestible part of plants — in whole grains, fruits, vegetables, nuts and seeds, and legumes such as peas and beans — that supports good gut health.

Carbohydrates often get a bad rap due to the association of their excessive consumption with weight gain, obesity, metabolic syndrome, and diabetes.

This phenomenon, which some researchers call “carbotoxicity,” promotes the idea that the excessive consumption of all types of carbohydrates favors the development of chronic diseases.

For this reason, many low carbohydrate diets have become popular among people interested in losing weight or managing blood sugar levels. They are even in favor among seasoned athletes.

However, several other studies have demonstrated that the quality of carbohydrates that people consume is as important as the quantity.

This finding suggests that rather than all carbs being “created equal,” some options are better than others for health.

‘Unhealthy’ carbs

Carbohydrates that people may consider unhealthy because they are less nutritious include:

  • refined carbohydrates, such as polished rice and flour
  • sugar-sweetened beverages, such as sodas and juices
  • highly processed snacks, including cookies and pastries

According to existing research, a diet with a higher intake of these types of carbohydrates and fewer of the more nutritious options can increase markers of inflammation and perpetuate hormonal imbalances in people with polycystic ovary syndrome (PCOS).

The excessive consumption of simple added sugars is also linked with an increased risk of insulin resistance, non-alcohol-related fatty liver disease, heart disease, stroke, diabetes, and cancer.

However, studies distinguish that added sugars and simple sugars that occur naturally in foods may not have the same negative effects.

A 2018 study even suggests that natural sources of sugar, such as honey, may be effective in reducing blood sugar levels and lowering the risk of developing type 2 diabetes.

Emerging research continues to shine a light on the adverse health effects of these so-called unhealthy carbohydrate foods.

Experts recommend eating a balanced diet that consists primarily of nutritious foods and includes these types of carbohydrates only in moderation.

‘Healthy’ carbs

More nutrient-dense sources of carbohydrates that people typically see as healthy include:

  • fruits, such as bananas, apples, and berries
  • nonstarchy vegetables, such as spinach, carrots, and tomatoes
  • whole grains, such as whole grain flour, brown rice, and quinoa
  • peas and beans, such as black beans, lentil peas, or garbanzo beans
  • dairy and dairy products, such as low fat milk, and yogurt

Research has linked diets rich in these complex carbohydrates — such as the Mediterranean diet — with anti-inflammatory benefits, lowered insulin resistance, and a reduced risk of chronic diseases.

The researchers attribute many of these benefits to the dietary fiber content of complex carbohydrates.

For instance, the dietary fiber in whole fruits improves long-term weight management and supports regular bowel movements and healthy aging.

Furthermore, boosting the quality of the diet by including more complex carbs and dietary fiber can lead to improvements in some of the effects of PCOS, such as insulin resistance and elevated androgens.

A 2020 review found that the dietary fiber in whole grain foods confers several health benefits, including a reduced risk of heart disease, gut disorders, cancer, and diabetes.

The glycemic index (GI) and glycemic load (GL) are two measures that people have used to establish the quality of carbohydrate foods and categorize them as “healthy” or “unhealthy.”

The GI is a measure of the blood sugar-raising potential of a single carbohydrate food compared with pure glucose.

Low GI foods, which primarily consist of complex carbs, have minimal effects on blood sugar levels. They include whole grains and nonstarchy vegetables. High GI foods include potatoes and foods with added sugars.

Likewise, people use the GL to assess how much a particular meal is likely to increase blood sugar levels.

Although people have used both the GI and GL for decades to guide meal planning and manage blood sugar levels for people with diabetes, the science is inconclusive.

Many studies suggest that an increased intake of low GI foods improves health outcomes, but other studies demonstrate that differences in daily glucose tolerance and individual responses are responsible for blood sugar levels rather than the GI of the foods themselves.

A food’s GI may, therefore, not be a direct predictor of an individual’s glycemic response.

Differences in glycemic response between individuals make it challenging to determine which carbs are truly the healthiest, since even whole grains may not be a consistent and reliable measure of GI and GL.

Despite the popularity of low carbohydrate diets, they are not suitable for everyone, and some populations still benefit from a carbohydrate-rich diet.

For example, endurance athletic performance becomes compromised on a low carbohydrate diet, and a high carbohydrate intake remains the most evidence-backed choice for elite athletes.

Among members of the general population with high carbohydrate intake, significant reductions in blood sugar levels — potentially promoting the remission of prediabetes — occur when the daily intake of carbohydrates is reduced.

Therefore, for populations that consume 65–75% of their daily calories from carbohydrates, experts recommend reducing carbohydrate calories to 50–55% of daily intake and increasing protein.

A carbohydrate restriction of 45% or less of daily calories is more effective for short-term blood sugar control, but it may be unsustainable and does not provide greater long-term results than a range of 50–55% of daily calories from carbohydrates.

Before making changes to their diet, people should speak with a doctor or registered dietitian to determine their specific carbohydrate needs to optimize their health outcomes.

Carbohydrates are an essential macronutrient, providing the body with energy and dietary fiber to support good health.

Excessive consumption of carbohydrates is associated with weight gain and an increased risk of the development of chronic diseases, such as heart disease and diabetes.

Despite their bad rap, however, carbohydrates offer many health benefits when a person frequently consumes sources of complex carbs and dietary fiber in favor of refined carbs and sugar-sweetened beverages.

Also, the ideal diet varies among individuals. For example, a carbohydrate-rich diet optimizes athletic performance.

However, nonathletic populations that consume 65–75% of their daily calories from carbohydrates see the greatest reduction in blood sugar levels when they reduce their calorie intake from carbohydrates to 50–55% of their daily energy intake.

Carbohydrates are not bad when people manage the amount and types that they consume and tailor these to their specific needs.