All About Carbohydrates: Are They Really the Villain We've Made Them Out to Be?

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Although carbohydrates have a bad reputation, whole and unprocessed carbohydrates provide many health benefits.

As diet trends come and go, there tends to always be one nutrient that is the villain of the moment — fat was the enemy in the 1990s; now, carbohydrates have a bad reputation. However, carbohydrates tend to be misunderstood. As both spinach and sugar cubes are carbohydrates, it can be difficult to parse out the benefits and consequences when the types of foods under the carbohydrate umbrella are so varied. 

In this article, learn more about the basics of carbohydrates, how they function in the body, the pros and cons of low-carb dieting, and the healthiest carbohydrates to consume. 

What Are Carbohydrates? 

Carbohydrates — also known as carbs — are one of three dietary macronutrients; fat and protein are the other two. Carbohydrates in the diet come from one of three groups: sugar, starch, or fiber. These macronutrients can also be classified based on whether they are simple versus complex carbohydrates, or whole versus refined. 

Simple carbohydrates are mono- or disaccharides, meaning they have just one or two sugar molecules. Sugars, including glucose, fructose, galactose, and sucrose, are simple carbohydrates. In addition to table sugar, simple carbohydrates also include the natural sugar found in fruit and dairy. 

Starches and fiber are complex carbohydrates and polysaccharides, meaning they have multiple sugar molecules linked together. Starches consist of many glucose molecules and include grains, beans, legumes, and starchy vegetables, like peas, corn, and potatoes. 

Fiber is the indigestible part of plant foods, which is essential for intestinal health. High-fiber foods include fruit, vegetables, whole grains, beans, legumes, nuts, and seeds. Whereas starch gets broken down into individual glucose molecules in the digestive system, fiber remains intact and does not provide energy. Instead, fiber provides nutrients for the bacteria in the gut microbiome to flourish. 

Whole Carbs Vs. Refined Carbs 

Another way to define carbohydrates is by whether they are whole or refined. The most significant difference between the two is that whole carbohydrates are minimally or not processed, maintaining their natural fiber. In contrast, refined carbohydrates have their fiber stripped from them. 

For example, white rice is a refined carb, while the less-processed and fiber-filled brown rice is a whole carb. Other whole carbohydrates include fruits, vegetables, whole grains, and beans; refined carbohydrates include juice, white pasta, white bread, and desserts or pastries. 

Whole carbohydrates, which contain their natural fiber, are the healthiest choice for carbs.

Functions of Carbohydrates 

The primary function of carbohydrates is to provide us with energy. All carbohydrates will break down into glucose in the gut, which gets taken up by our cells to produce ATP (adenosine triphosphate) to supply cells with energy. Although the body can and will use ketones from fat to produce ATP in times of low carbohydrate intake, glucose is the preferred source. 

Carbohydrates also spare the muscles from unnecessary breakdown. The liver and muscles store excess glucose as glycogen; this backup storage allows the body to avoid breaking down muscle mass into amino acids for energy. 

Lastly, the fiber in whole carbohydrates is necessary for optimal digestive health. Soluble fiber draws water into the intestine, which softens stool for easier bowel movements. Insoluble fiber adds bulk to the stool, reducing the risk of constipation. 

Fiber has several other benefits, including promoting a healthy weight, lowering cholesterol, slowing the blood sugar rise after meals, promoting satiety, and reducing the risk of heart disease and digestive disorders. 

While dietary fat and the amino acids from muscle can provide the body and brain with energy, they do not provide fiber. Therefore, whole carbohydrates are not only not a villain; they are crucial for overall health. 

Do Low-Carb Diets Work? 

Many people wonder if reducing dietary carbohydrates is the best way to lose weight. The answer is slightly complicated, as most studies don’t differentiate between whole and refined carbohydrates. For example, someone eating a diet high in sugar and white bread will have very different health outcomes than one eating a diet high in vegetables and legumes, even if they are consuming the same number of carbohydrates per day. 

Pros of Low-Carb Diets

For just about everybody, a reduction in refined carbohydrate intake will improve health outcomes, especially for people with type 2 diabetes, metabolic syndrome, obesity, and other cardiometabolic diseases. 

Some studies look at the effects of very-low-carbohydrate diets (VLCD), which entail consuming between 20 to 50 grams of carbs per day. Similarly, a ketogenic (keto) diet, which promotes the production of ketones from fat for energy, requires less than 20 grams of net carbs (not including carbohydrates from fiber) per day — approximately the amount in one small banana. 

In a recent study published in Nutrition & Metabolism in August 2020, obese older adults were randomized to consume either a VLCD with less than 10% of calories coming from carbs or a low-fat diet. After eight weeks, those on the VLCD experienced significant reductions in body weight, adipose tissue, and triglycerides, with significantly increased HDL (healthy) cholesterol and thigh skeletal muscle mass compared to the low-fat dieters. 

Published in the British Journal of Nutrition in February 2016, a meta-analysis analyzed data from 11 randomized controlled trials. The researchers found that those on a low-carb diet (LCD) — with carbohydrate intake at less than 20% of total daily calories — for six months or longer had more significant reductions in body weight and triglycerides and increased HDL cholesterol compared to those on a low-fat diet. However, the LCD group also had significant increases in LDL cholesterol, which is generally considered a risk factor for cardiovascular disease. 

In summary, diets that reduce carbohydrates tend to improve several aspects of cardiometabolic health, including body weight, lipid and cholesterol levels, and glucose control, especially in people who are overweight or with metabolic disorders. However, there also can be potential downsides to reducing carbohydrate levels. 

There are both benefits and downsides to eating a low-carb diet.

Cons of Low-Carb Diets  

In general, LCD and VLCD tend to be unsustainable as a dietary plan for an extended period. People on diets that eliminate or severely restrict one food group or macronutrient potentially run the risk of developing nutrient deficiencies unless they plan out their diets carefully. In addition, there is not a lot of published research analyzing the long-term health effects of these diets. 

Low-carb diets — especially VLCD — may naturally be lower in plant foods, which are known to be healthy components of a diet. People living in the Blue Zones, which are areas in the world with high proportions of centenarians — people living to age 100 and beyond — tend to eat higher carbohydrate diets, emphasizing beans, legumes, and starchy vegetables.

These plant foods provide valuable nutrients, including fiber, vitamin C, B-vitamins, magnesium, potassium, and selenium, as well as antioxidants, polyphenols, and flavonoids. People on LCD or VLCD may not consume adequate amounts of these nutrients and beneficial compounds. However, a low-carb diet that is planned out to contain plentiful amounts of plant foods would be able to consume the recommended amounts of these nutrients.

Another thing to consider is that when you reduce carbohydrate levels, fat and protein intake will naturally increase to maintain the same caloric intake. While this may be fine in the short term, chronically high protein consumption is associated with kidney damage. 

Many studies have also found no differences in weight loss between groups eating LCD or low-fat diets. In a study published in JAMA in February 2018, a 12-month trial of over 600 overweight or obese adults found no significant differences in weight or glucose metabolism between the healthy low-carb and healthy low-fat dieters. 

Both groups focused on maximizing vegetable consumption while minimizing refined grains and added sugars. The researchers indicate that a nutrient-dense diet may be more important to health than the ratios of fat to carbohydrates. 

Researchers found similar results in a February 2009 study published in the New England Journal of Medicine, with no differences in weight loss between low-carb and low-fat dieters after two years. In general, diets that reduce caloric intake will result in weight loss and improved metabolic markers, regardless of which macronutrient was reduced. 

Lastly, some people may be harmed by reducing their carbohydrate intake, including athletes or regular exercisers, underweight individuals, or those who already have impaired kidney health. 

In summary, LCD can be helpful for some individuals, but there are some things to consider, including ensuring adequate nutrient and fiber intake from plant foods and keeping an eye on kidney function. 

A practical and sustainable lower-carb solution would be a diet that supplies between 100 and 150 grams of carbohydrates per day and favors whole over refined carbohydrates. As all individuals could benefit from reducing their intake of refined carbohydrates and sugar, that is one area of nutrition research that is not controversial. 

Key Takeaway

  • Carbohydrates are the body’s preferred energy source; benefits of carbohydrates include minimizing muscle loss and providing beneficial fiber when consumed in their whole forms. 
  • Studies of low-carbohydrate diets (LCD) have shown some benefits, including weight loss and improved metabolic markers, especially in overweight individuals. 
  • Potential downsides to LCD include a heavier burden on the kidneys, potential nutrient deficiencies, and the possibly unsustainable nature of restricting food groups. 
  • While very-low carbohydrate diets are likely unsustainable in the long-term, most people could benefit from reducing their carbohydrate intake — however, the amount of carbohydrates needed will vary individually. 
  • A sustainable way to lower carb intake and improve health would be to replace refined carbs with their whole, unprocessed versions, including fruits, vegetables, beans, legumes, nuts, and seeds in place of added sugar, soda, juice, sweets, desserts, chips, crackers, and white bread, pasta, and rice. 

Show references

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Burke LM, Ross ML, Garvican-Lewis LA, et al. Low carbohydrate, high fat diet impairs exercise economy and negates the performance benefit from intensified training in elite race walkers. J Physiol. 2017;595(9):2785-2807. doi:10.1113/JP273230

Gardner CD, Trepanowski JF, Del Gobbo LC, et al. Effect of Low-Fat vs Low-Carbohydrate Diet on 12-Month Weight Loss in Overweight Adults and the Association With Genotype Pattern or Insulin Secretion: The DIETFITS Randomized Clinical Trial. JAMA. 2018;319(7):667-679. doi:10.1001/jama.2018.0245

Goss AM, Gower B, Soleymani T, et al. Effects of weight loss during a very low carbohydrate diet on specific adipose tissue depots and insulin sensitivity in older adults with obesity: a randomized clinical trial. Nutr Metab (Lond). 2020;17:64. Published 2020 Aug 12. doi:10.1186/s12986-020-00481-9

Mansoor N, Vinknes KJ, Veierød MB, Retterstøl K. Effects of low-carbohydrate diets v. low-fat diets on body weight and cardiovascular risk factors: a meta-analysis of randomised controlled trials. Br J Nutr. 2016;115(3):466-479. doi:10.1017/S0007114515004699

Sacks FM, Bray GA, Carey VJ, et al. Comparison of weight-loss diets with different compositions of fat, protein, and carbohydrates. N Engl J Med. 2009;360(9):859-873. doi:10.1056/NEJMoa0804748

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