Confused About Carbohydrates?

Glucose, fructose, sucrose…sugar, starch, fiber: All these different terms can be confusing. Here’s a guide to help you sort through the pieces of the carbohydrate puzzle.

You need carbs to survive; they’re the body’s main source of fuel to power your muscles, your nervous system, and your brain. But you’ve probably heard that eating too many carbs can be unhealthy. And you’ve probably also heard that most sugar is bad, but some starches are OK. But what’s a complex carb, and are they all good? And what about fructose, sucrose and glucose? “Carb lingo” can be really confusing. Here’s a guide to understanding the different faces of this important macronutrient so you can better determine which carbohydrate foods are healthy for you and which are less so.

What are carbohydrates? 

In biological circles, a carbohydrate is most often defined as an organic compound (made up of carbon, hydrogen and oxygen usually in the ratio of CH2O) found in foods and beverages that can be broken down to release energy in human or animal bodies. 

Carbohydrates comprise one of the six essential macronutrients found in food. Protein and fats are two of the other big categories; vitamins, minerals and water make up the rest. Learn more about these essential nutrients: What Is Protein?, Dietary Fats; and then learn how they all function and interact to drive your metabolic health

Simple sugars 

Within the carbohydrate category, “simple sugars” refer to two types of carbohydrate molecules:

  • Monosaccharides — such as glucose, fructose and galactose — don’t need to be broken down further in the digestive process. 
  • Disaccharides — including sucrose (table sugar), lactose and maltose — contain two carb molecules, but are still considered simple sugars because the body very quickly breaks them down into direct glucose molecules. 

Simple sugars are found in a variety of natural foods including fruits, vegetables, milk and honey, and they are also processed and added to hundreds of foods like cakes, candies, soda, fruit juice, ketchup, sauces, ice cream, even yogurt. 

Because they are “simple,” these carbs provide a quick source of energy to the cells, which happens when the production of insulin is triggered. In healthy individuals, when simple sugars are consumed in excess, they are most often converted into energy stores that can be kept and used later, either as glycogen (stored by the liver and muscles) or fat (ectopically stored as triglycerides in adipose tissue, liver, and muscle). However, even if individuals can successfully process large amounts of sugar without developing diabetes, they may become obese — which in and of itself is associated with a host of metabolic and cardiovascular disorders. 

For those individuals who don’t have enough insulin to move glucose out of the blood, or the insulin is ineffective (aka insulin resistance), blood glucose levels can stay chronically high — leading to a host of health issues, including diabetes. Learn more: The Link Between Blood Sugar and Diabetes.

Natural versus “refined” or added/processed sugars

Understand that the three primary carbohydrate molecules (glucose, fructose and sucrose) are just that: molecules, and not food sources or food categories. That is, there really isn’t a food source that is made up of just one of these molecules; rather, foods contain various quantities and combinations of these molecules — either naturally or by being added in the processing steps before the food or beverage gets to the table. And foods may contain many other types of molecules, such as various acids and minerals; or proteins or fats.

The food source which comes closest to being all one sugar molecule is table sugar, which is sucrose — a combination of glucose and fructose. While derived from natural plant sources, table sugar is “refined” because it has been processed commercially from sugar cane and sugar beets. Table sugar is actually just one type of refined sugar; others include brown sugar, coconut sugar, and palm sugar. High-fructose corn syrup (HFCS) is an example of a highly processed (and very concentrated) sugar. 

Honey is a natural, typically unprocessed simple sugar. Like table sugar, it is also made up predominantly of glucose and fructose, but with a higher ratio of fructose to glucose. (Honey also contains trace amounts of several B vitamins and minerals, including calcium and zinc.) 

Whether unprocessed, like honey, or refined, like table sugar, all of these sugars represent very high concentrations of simple sugars that your body converts directly to glucose soon after consumption. Accordingly, were you to gobble down large quantities of honey or white sugar, you’d be a metabolic mess.

Whole fruits and vegetables: the healthier simple sugars

But what about natural whole foods that contain simple sugars, like fruits and vegetables? It is important to understand that these natural whole foods do contain many of the same molecules as the various sugars that are added to processed foods; that is, they contain varying quantities and concentrations of glucose, fructose and sucrose. They may even provide the same number of calories when consumed, and their sugar molecules may be used by the body in much the same way as processed sugars. For example, the sucrose found naturally in a banana is the same sucrose added to flavored yogurt. In either case, your body converts that sucrose to glucose very quickly after consumption.

Therefore, whole fruits and vegetables can and do cause your blood glucose levels to rise, and the degree to which they do so varies greatly from fruit to fruit and vegetable to vegetable. For example, a fruit like a grapefruit or a tomato has a lower sugar concentration than, say, a banana. (See our reports detailing What Is the Glycemic Index? and explaining how foods compare relative to Glycemic Index vs. Glycemic Load.) 

Furthermore, the way sugar is metabolized can vary significantly from individual to individual. Certainly, those with diabetes — who either can’t make enough insulin or can no longer properly use the insulin they produce — cannot readily rid their bloodstream of sugar, so less of it gets offloaded into cells. And amongst those with diabetes, there are also significant individual variations in how various carbohydrate-rich foods affect their blood glucose levels and other health parameters. (Individualized responses to food are what is driving the growth in the use of such medical technologies as continuous glucose monitors, or CGMs.)

Source: Canadian Sugar Institute

It seems more and more clear to scientists that the natural, simple sugars found in “whole” fruits and vegetables are not as detrimental to your metabolic health as foods with added, processed sugars. In fact, an important 2015 research review concluded that whole foods containing fructose (e.g., fruits and vegetables) “pose no problem for health and are likely protective against diabetes and adverse CV [cardiovascular] outcomes,” whereas “added sugars (e.g., sucrose and high-fructose corn syrup)…may pose the greatest problem for incident diabetes, diabetes-related metabolic abnormalities, and CV risk.”
See also: What Is Sucrose?, What Is Fructose? and What Is Glucose?.

Don’t forget, too, that whole fruits and vegetables — irrespective of their sugar composition — contain many beneficial compounds like fiber, vitamins, minerals and various bioactives, such as polyphenols. That banana we referenced, which does contain a relatively high concentration of all three sugar molecules (particularly sucrose), also contains a healthy quantity of fiber and a host of other nutrients, such as potassium. Thus, it’s important to consider what’s in the whole food, not just how much sugar (and what type) it may contain.

Complex starches 

Starches are essentially complex sugars; they are polysaccharides — long chains of various sugars (monosaccharides and disaccharides). Consequently, after consumption, they will be broken down into sugars at a much slower rate, tending to spike blood sugar levels less than do simple sugars.

Many starches also contain fiber, to varying degrees. Fiber is a type of carb that your body can’t digest. In other words, it can’t be broken down into sugar molecules, so it hasn’t been shown to have any negative effect on your blood sugar levels. Furthermore, fiber becomes food for your gut microbiome, resulting in important byproducts such as short-chain fatty acids (SCFAs), signaling molecules that appear to play a role in producing bioactives that help steady blood glucose, regulate hunger, and reduce inflammation — all important for diabetes management. Learn more about fiber and its importance in diabetes management.

Complex carbs that are high in starch compounds, but not as high in fiber, include many cereals, white bread, corn, refined pasta and white rice. While complex, remember that even these foods, being polysaccharides, do ultimately get broken down in your body to glucose (as well as some fiber and other types of molecules). Therefore, complex carbs that are especially low in fiber and above-average or high on an easy-to-look up Glycemic Index (GI) could very well contribute to higher blood glucose levels — and are thus “carbs to eat less of.” An example of one complex carb offender: white rice. See our article Rice and Diabetes for details. 

By contrast, complex carbs that are much higher in fiber and lower on the Glycemic Index include many whole fruits, vegetables, nuts, lentils, beans and whole grains. Many of these are “the good carbs,” such as broccoli, brussels sprouts, almonds, avocados, chickpeas and kidney beans. 

The “in between” complex carbs, those with a decent amount of fiber and not terribly high on the glycemic index, include sweet potatoes (healthier than white), brown rice, whole wheat pasta and pure bran cereals.

The big carb culprits: “added sugars” and “ultra-processed” foods

Most of us realize that processed foods containing high quantities of “added sugars,” like candy or sugar-sweetened beverages (SSBs), are the carb foods we should seek to avoid or consume only minimally. But many starchy, complex carbs — such as white bread, potato chips, white rice and many breakfast cereals — are also highly processed: they may not only contain polysaccharides that convert into glucose when fully digested, but they may also contain added sugars as well as added salt, fats, additives, preservatives, and artificial coloring. 

In fact, such “ultra-processed foods” account for 90% of the added sugars we consume, according to one study. See our report, The Truth About Processed Foods, for details on which foods are ultra-processed (and therefore the least healthy) versus those that are minimally processed (e.g., a can of beans or a loaf of whole wheat bread) and so still considered relatively healthy. A recent study of more than 100,000 participants found that those who had a diet high in heavily processed foods (accounting for more than 22% of their overall intake) were significantly more likely to develop type 2 diabetes compared to those who ate the least amount of processed foods (roughly 11% of their diet). 

Looking just at processed and ultra-processed foods that are carbohydrate-rich, there continues to be debate about the relative roles that added glucose, sucrose and fructose (and fructose-derivatives) play in disease risk, morbidity and mortality. While a 2021 meta-analysis concluded that “chronic consumption of fructose is no worse or better than equivalent doses of sucrose or glucose for glycemic and other metabolic outcomes,” the authors also clearly pointed out that “we are not stating that consumption of sugar, especially as refined carbohydrates, is advisable or beneficial.” But many studies, including a 2021 perspective, do single out the exponential increase of high-fructose corn syrup (HFCS) consumption as the prime culprit in the increased incidence of obesity and type 2 diabetes in countries who have adopted the Western diet — even if the mechanistic link has not been fully proven.

A majority of recent clinical researchers come to agreement on these three principal conclusions:

  1. Above-average consumption of sugar-sweetened beverages (SSBs) with HFCS or added sucrose correlates highly with increased risk for both cardiovascular mortality as well as nonalcoholic fatty liver disease (NAFLD) and type 2 diabetes (T2D). On the other hand, as discussed previously, consumption of natural whole fruits and vegetables, and even fruit juices, at normal dietary levels, does not correlate with these same cardiometabolic indicators.
  1. Other highly processed or ultra-processed foods, including those high in carbohydrate composition, also appear to increase the risk of developing T2D.
  1. Beyond these previous two categories (SSBs and ultra-processed high-carb foods), the health impact of one carbohydrate food source vs. another continues to be debated, even after consideration of the food’s GI and GL ratings. However, the current recommendation continues to be: Restrict overall dietary carbohydrate consumption, particularly of foods with added sugars, because it is the most promising strategy for reducing the risks of obesity, diabetes and metabolic syndrome. 

The U.S. has an added sugar problem

In the United States, an estimated 15% of total energy intake is derived from “added sugars” — with a higher proportion of over 20% among adolescents.

Seeing that these percentages have been steadily rising for the past 20 years, the USDA Dietary Guidelines for Americans 2020–2025 reduced its recommended daily added sugar intake to less than 10% of calories per day, down from the 13% level it recommended in 2005.  The American Heart Association has proposed limiting sugar calories even more drastically, to 150 kcal/day for men or 100 kcal/day for women, which equates to no more than 6% of calories each day. Similarly, the World Health Organization, which officially advises that less than 10% of energy come from the consumption of “free sugars,” has also advised that a reduction to below 5%, or roughly 25 grams (6 teaspoons) per day, would be even better. 

Key Takeaways

Those with diabetes need to watch and analyze all the carbs they consume, since any carb can increase your blood glucose level. But certainly not all carbs are bad, and you do need healthy carbs to thrive and survive. A selection of natural, whole carbohydrate foods (such as many fruits and most vegetables, nuts, beans, legumes, and whole grains), especially ones that are high in fiber and score low on the Glycemic Index (GI), can benefit a dietary regimen that also includes lean proteins and healthy fats. For all of us, limiting our consumption of processed foods that have a high amount of added sugar is truly imperative. The consumption of highly energy-dense foods without significant fiber and/or micronutrient content — especially sugar-sweetened beverages and other ultraprocessed carbs — is a sure recipe for getting obese, developing type 2 diabetes, or contracting a host of other cardiometabolic problems.

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