The rising prevalence of obesity and type 2 diabetes has led consumer interest in lowcarbohydrate diets (LCDs) to surge. LCDs, as defined by the National Institutes of Health, have no more than 130 g of carbohydrate per day or less than 26% of daily calories from carbohydrates.
A growing body of evidence has linked LCDs to weight loss, reduced cardiovascular risk, and improved lipid profiles. This has led to increased consumer demand for low-carbohydrate food products.
In response, food manufacturers started marketing products with claims regarding “net carbs,” which is different from the total carbohydrate noted in nutrition labels. For example, a snack bar may have 30 g of total carbohydrate per bar and contain 4 g of net carbs.
But what exactly are net carbs? Where did they come from, and more importantly, why do they matter?
The 3 main types of carbohydrate are (1) sugar, (2) starch, and (3) fiber. “Total carbohydrate,” as reported on nutrition labels, represents a combination of all 3 types of carbohydrate in the food.
Each gram of carbohydrate is assumed to contain 4 calories. However, not all carbohydrates are created equal. Simple carbohydrates, such as sugar, are digested easily and absorbed quickly, providing a short-term burst of energy, as seen in postprandial blood glucose spikes. Conversely, complex carbohydrates, such as starch and fiber, are digested more slowly than simple carbohydrates. Starch provides long-term energy, and fiber serves as a bulking agent.
Due to individual differences in age, medical history, dietary preferences, and physical activity level, there are no set daily requirements for carbohydrate intake. The American Diabetes Association (ADA) recommends choosing whole grains and nutrient-dense carbohydrate foods over refined and processed carbohydrate foods, including those with added sugars. The Dietary Guidelines for Americans 2020-2025 and the American Heart Association advise limiting added sugars to at most 10% and 6% of daily caloric intake, respectively.
Carbohydrate counting helps with meal planning and blood glucose management for people with diabetes (PWD). It remains a safe and effective method in reducing A1C levels without increasing hypoglycemia risk in both adult and pediatric populations. In addition, it allows greater individualization and flexibility regarding dietary choices. Continuing education in carbohydrate counting is important to improve or maintain precision when estimating intake.
When using a nutrition label in basic carbohydrate counting, the main items to pay attention to are (1) serving size and (2) total carbohydrate.
PWD may also exhibit individual responses to different carbohydrate-containing foods. For some PWD, advanced carbohydrate counting may be taught to achieve target postprandial glucose levels. It also aims to further increase the precision of quantifying carbohydrate intake by requiring additional calculations involving fibers and sugar alcohols.
Fiber is a complex carbohydrate that maintains gut health, increases satiety, and acts as a bulking agent. It is usually categorized into 2 types: (1) insoluble and (2) soluble. Both insoluble and soluble fibers are beneficial in managing constipation and improving digestion. Additionally, soluble fibers have been shown to lessen postprandial blood glucose spiking and reduce cholesterol levels.
In practice, the fiber rule is variable across institutions and between health care practitioners. Some practitioners subtract all or half the grams of dietary fiber from the grams of total carbohydrate, whereas others prefer implementing the fiber rule only if the product contains at least 5 g of dietary fiber per serving.
A myriad of benefits regarding a high fiber intake has been well established over the years, including risk reduction for several chronic diseases, including type 2 diabetes, obesity, gastrointestinal diseases, and some cancers. The Dietary Guidelines for Americans 2020-2025 currently recommend individuals consume at least 14 g of fiber per 1000 calories (equal to 28 g of fiber for 2000 calories).
Studies have shown that as little as 5% of the population is estimated to meet the daily fiber requirement. When looking at fiber in nutrition labels, US Food and Drug Administration (FDA) regulations state a product can be labeled as a “good source” when it has a minimum of 2.5 g or 10% of the daily value of fiber per serving; an “excellent source” has at least 5 g or 20% of the daily value of fiber per serving.
Sugar alcohols, or polyols, are frequently added in sugar-free or low-sugar products as a low-calorie sweetener or bulking agent. Small amounts of sugar alcohols occur naturally in some fruits and vegetables, although most are commercially manufactured. Examples of manufactured sugar alcohols include xylitol, mannitol, erythritol, and sorbitol. Many sugar-free chewing gums contain sugar alcohols in place of sugar because they are not associated with tooth decay.
It is estimated that about half of the sugar in sugar alcohols will be absorbed; therefore, the sugar alcohol rule is to subtract half of the sugar alcohol content from the total carbohydrate per serving. For example, a product may contain 30 g of total carbohydrate and 14 g of sugar alcohols per serving, which results in 23 g of digestible carbohydrate.
The ADA recommends eating sugar alcohols in moderation because of high amounts being associated with a potential rise in blood glucose levels and gastrointestinal adverse effects, such as bloating, gas, and osmotic diarrhea. Different types of sugar alcohol can exhibit different glycemic responses, which may be clinically significant if consumed in large amounts. Also, unlike some artificial sweeteners with zero calories, sugar alcohols contain a small number of calories as they are partially digested and absorbed by the body. Per the FDA, a gram of sugar alcohol consists of 0 to 3.0 calories depending on the type.
The main concept behind net carbs is that some carbohydrates are indigestible and not metabolized by the body and therefore can be excluded. Manufacturers often use the term “net carbs” to claim a minimal impact on the consumer’s blood glucose.
Manufacturers calculate net carbs by subtracting indigestible carbohydrates, such as fiber, sugar alcohols, allulose, and glycerin, from the total carbohydrate on the nutrition label. However, this calculation assumes all subtracted carbohydrates to be nondigestible and an insignificant source of calories, which may not be the case. One such example would be soluble fibers, which are fermented into short chain fatty acids and then absorbed by gut microbiota and colonic cells. Therefore, they are still an indirect energy source for the body. In fact, the FDA’s nutrition labeling regulations designate all soluble fibers (except polydextrose) to contain 2 calories per gram.
The terms “low carb,” “reduced carb,” and “carb free” are categorized as “nutrient content claims” by the FDA, and there are currently no legal definitions regarding the amount of carbohydrate required for such claims, unlike for “low calorie” or “fat free.
The lack of scrutiny on the use of these terms makes it challenging for health care professionals and consumers to determine the accuracy of the claims. Furthermore, the type of fiber and sugar alcohol in the product are often not specified by manufacturers, because it is not mandatory, making it challenging for practitioners and consumers to conclude how blood glucose levels may be impacted. This holds particularly true for PWD taking insulin because either underestimation or overestimation can result in postprandial hyperglycemia or hypoglycemia, respectively.
The FDA does regulate total carbohydrate on nutrition labels and therefore recommends all consumers to refer to this value rather than net carbs or other nutrient content claims.
Sweeteners are nonnutritive sugar substitutes that have grown in popularity among manufacturers as a low-calorie yet intensively sweet-tasting alternative to sugar. The FDA has approved 6 artificial sweeteners as food additives: (1) aspartame, (2) acesulfame potassium, (3) sucralose, (4) neotame, (5) advantame, and (6) saccharin.
The safety of artificial sweeteners has been heavily debated in recent years. Some past studies, including a recent review by Iizuka, have demonstrated benefits in managing oral health, diabetes, and weight; however, there has been growing evidence that suggests potential links between artificial sweeteners and increased risk of several chronic diseases, including cardiovascular disease and cancer.
In response, plant-derived sweeteners have been introduced as a more “natural” replacement to sugar and its artificial counterparts. Examples include allulose, monk fruit, and stevia. Plantderived sweeteners are recognized as safe for consumption by the FDA, and they contain almost no calories because they are excreted either by the gastrointestinal tract or in the urine.
No safety levels for plant-derived sweeteners have been officially established; however, the ADA 2024 Standards of Care do allow nonnutritive sweeteners to be “consumed in moderation.” Due to the minimal caloric value, artificial and plant-derived sweeteners are not included in the carbohydrate counting process.
The term “net carbs” is increasingly used among food manufacturers to advertise the “actual” amount of fully digestible carbohydrate in their products. The calculation for net carbs by food manufacturers may not be fully accurate based on their assumptions regarding nondigestible carbohydrates; however, it can still provide a learning point for PWD to try and choose products that have a higher fiber content and therefore a lower net carb value. It is also important to encourage PWD to choose products with highquality carbohydrates that are rich in fiber, vitamins, and minerals and low in added sugars, sodium, and fat.
Total carbohydrates remains the focus when counting carbohydrates, as recommended by both the FDA and ADA. Regular monitoring of postprandial blood glucose levels can also be useful in determining the need for individualized education. Health care practitioners may consider providing advanced carbohydrate counting education with the fiber and sugar alcohol rules to enhance precision in achieving target postprandial blood glucose levels.
V. J. Lam, MS, RD, CNSC, CDCES, BC-ADM, is with Huntington Health Physicians in Pasadena, CA.
The authors declare having no professional or financial association or interest in an entity, product, or service related to the content or development of this article.
The authors declare having received no specific grant from a funding agency in the public, commercial, or not-for-profit sectors related to the content or development of this article.
V. J. Lam https://orcid.org/0009-0000-6674-6647
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