An Overview of Ingredients in Low Carb Foods

With the low carbohydrate diet craze in full swing, there have been a plethora of new product introductions aimed at consumers on low carbohydrate diets. This article will provide an overview of ingredients in low carbohydrate products and how they are used in formulation and labeling of low carbohydrate foods.

First, it is important to define what a carbohydrate is. A carbohydrate is a molecule that consists of carbon, hydrogen and oxygen molecules. The types of molecules range from simple sugars to very complex fibrous polymers. Carbohydrates are the major energy source for the planet and range from starches in plants such as wheat and potatoes, to cellulose as a structural material in plants, to chitin as a structural material for insects and shellfish.

The Nutrition Facts panel on a food product is required to list Total Carbohydrates and then indent underneath and label Sugars and Dietary Fiber. Total carbohydrates in a food are determined by analyzing for crude fat, crude protein, ash and water and then subtracting from each from the total to obtain the number for total carbohydrates. Thus, this number encompasses a wide variety of substances, including sugars, dietary fiber, sugar alcohols and other carbohydrates.

It is voluntary to indent under Dietary Fiber and label Soluble and Insoluble Dietary Fiber. In addition to Sugars, it is also voluntary to label Sugar Alcohols separately. Another voluntary line is Other Carbohydrates, which consists of subtracting sugars, sugar alcohols and dietary fiber from Total Carbohydrates. Each of these types of carbohydrates is determined by specialized analytical methods that are standardized by the Association of Official Analytical Chemists (AOAC).

There are different types of carbohydrates. They are usually described as simple or complex carbohydrates. Simple carbohydrates are composed of simple sugars or monosaccharides, such as glucose (dextrose) and fructose. Sucrose and lactose are disaccharides (two sugar molecules together). Polysaccharides consist of several sugars together in a chain and therefore are considered complex carbohydrates. Complex carbohydrates may be classified as either starches with alpha-glycosidic linkages, which are readily digested by intestinal amylases, or as dietary fiber with beta-linkages, which are resistant to these enzymes.

Refined carbohydrates are sources of simple sugars that are produced through processing. Sucrose and high fructose corn syrup are examples of refined carbohydrates. These carbohydrates are characterized by greater solubility in a food product and they typically have lower dietary fiber content. Refined sugars and starches are the types of carbohydrates that are typically avoided first in low carbohydrate diets as they have the most potential impact on blood glucose after ingestion.

Another way to describe the impact of carbohydrates on blood glucose is by using the glycemic index. The glycemic indices is a ranking of carbohydrates based on their immediate effect on blood glucose (blood sugar) levels. Glucose is given an arbitrary glycemic index of 100 and other foods are compared to it. Carbohydrates and starches that breakdown quickly during digestion, such as those in white bread (70) have the highest glycemic indices. Carbohydrates that break down slowly, releasing glucose gradually into the bloodstream, such as those in lentils (30) have low glycemic indices.

In an attempt to distinguish total carbohydrates from those with a high glycemic index, manufacturers are using terms such as net carbs, effective carbs or net impact carbs. Often, dietary fiber and sugar alcohols are subtracted from total carbs to get net carbs. The Food and Drug Administration (FDA) permits factual statements about the total number of carbs in a product and net carb statements, provided that there is a clear explanation on the package as to how these terms are defined.

Formulating Low Carb Foods

Low carbohydrate products are formulated in many ways. Techniques include using artificial sweeteners or sugar alcohols to replace sugars, increasing the protein level of the product by incorporating high protein ingredients, and substituting dietary fiber for other carbohydrates. A brief description of some of the ingredients used in formulating reduced carbohydrate products follows.

Sweeteners

Sugars, both refined and unrefined, are considered to be nutritive sweeteners as they generally impart sweetness with an energy value of 4 kcal/g as carbohydrate. Therefore, one of the easiest options used to reduce carbohydrates in a product is to substitute other sweet ingredients for sugars.

Sugar alcohols (or polyols) are nutritive sweeteners that impart sweetness, but with reduced calories (1.5-2 kcal/g) because they are not fully absorbed in the gut. Sugar alcohols include sorbitol, mannitol, xylitol and lactitol. They occur in small amounts in nature and the body can break them down, but they are usually only commercially available in synthetic forms. Erythritol and possibly some sources of xylitol and mannitol are exceptions as they are produced via fermentation and therefore meet the definition of natural. These sugar alcohols work in many food systems, but they produce unpleasant digestive side effects with as little as 10 g/serving, so they must be used judiciously in reduced carbohydrate products.

Nonnutritive sweeteners offer no energy or insignificant energy because they sweeten with little volume since they are typically 200-600 times as sweet as sucrose. These include aspartame, sucralose and saccharin. Many controlled carbohydrate products use a combination of these sweeteners in order to mimic the taste profile of sucrose.

Sugar alcohols and nonnutritive sweeteners can be called sugar substitutes, sugar replacers, artificial or alternative sweeteners. Products containing these sweeteners can be labeled as sugar-free, since these sweeteners are not technically sugars as defined in the Nutrition Facts panel of a food product. There are also novel sugars called D-tagatose and trehalose. Dtagatose is not absorbed fully and therefore provides 1.5 kcal/g and is starting to show up in reduced carbohydrate products. Trehalose is absorbed completely and therefore provides 4 kcal/g. Products containing these two sugars cannot be labeled sugarfree, as these are considered to meet the definition of sugars by FDA. Currently, many low carb products fully subtract polyols from the Total Carbs on the label to get net carbs.

For consumers looking for natural reduced-calorie or sugar-free products, there are very few options. The South American herb stevia contains the sweet component stevioside, but is considered an unapproved food additive and only allowed in dietary supplements. Therefore, it is used in products only when labeled as a dietary supplement. Lo Han Kuo (LHK) is a sweet fruit extract from China that has been self-affirmed GRAS (generally recognized as safe) for use in foods. Thaumatin is a mixture of sweet proteins from a West African fruit. In the United States, it is approved as a flavor enhancer for products such as beverages, jams and jellies, condiments, milk products, yogurt, cheese, instant coffee and tea, and chewing gum. Because it is a protein, its sweet taste is destroyed by heat.

Bulking/Thickening Agents

Sucrose also imparts thickening, mouthfeel and humectancy (water-binding) in many products. Therefore, when sugars are removed, very often bulking or thickening agents are used to replace those properties. A common bulking agent used is polydextrose. Polydextrose is a polymer of d-glucose with bound sorbitol and citric acid and it is often used in low fat or reduced carbohydrate products to provide mouthfeel, dietary fiber and humectancy. It provides 1 kcal/g.

Other common thickeners used alone or in combination in low carb products are gums such as xanthan, locust bean and guar. These plant gums may be derived from their natural source or chemically modified to impart specific thickening characteristics.

High Protein Ingredients

Many reduced carbohydrate products, such as cookies, breads and pastas, use high protein ingredients to substitute for the usual flours used. Use of soy proteins, soy protein isolates, whey protein concentrates, wheat gluten and other high protein ingredients is quite common. Use of high levels of these ingredients may have a significantly negative impact on texture and mouthfeel and is one of the reasons why many reduced calorie counterparts do not measure up to their full carbohydrate versions.

High Fiber Ingredients

A popular way to reduce net carbs in a product is to increase the fiber content of the product since dietary fiber is subtracted out to determine net carbs. Fiber is notoriously deficient in most diets and it is well-known fiber consumption moderates blood glucose levels and benefits colon health.

A wide variety of dietary fibers is now available for use by product developers. A type of fiber called resistant starch is becoming more popular. Resistant starches are relatively new to the market, but these ingredients provide excellent functional characteristics, while providing an insoluble fiber and non-digestible carbohydrate.

Fibers derived from whole grains, such as soy, wheat, oat and barley, continue to be used as ingredient replacements in reduced carbohydrate foods. Careful choice of ingredients to maximize functionality in the finished product is critical.

Inulin, a prebiotic fiber that supports the growth of beneficial bacteria in the gut, is a non-digestible soluble fiber and a complex carbohydrate that provides about 1.5 kcal/g. It is used to replace simple sugars in many formulations and is also used in combination with probiotic ingredients to support intestinal health.

Many specialty fibers have hit the market in recent years. One is a digestion-resistant maltodextrin fiber with 90 percent soluble fiber and a low glycemic index. This ingredient is odorless, tasteless and is very stable to many processing conditions. It has been used in many beverages, for example.

Food product developers have many options when it comes to developing reduced carbohydrate foods. The ultimate test for these products, however, is satisfying the consumer. As with the low fat craze, products which do not meet the taste and texture expectations of consumers will not be successful in the marketplace.

Mary C. Mulry, Ph.D., is senior director of research, development and standards for Wild Oats Markets Inc. Mulry is responsible for developing packaged goods and Wild Oats branded products, overseeing the standards and quality assurance programs and directing the food science, nutrition and safety initiatives. She can be reached via e-mail at [email protected].