Introduction

Carbohydrates are one of three nutrient groups that provide energy for the body (the others are protein and fat).

Carbohydrates consist of simple sugars (mono- and disaccharides), starch and other complex carbohydrates (polysaccharides) and fiber. Sugar Alcohols and glycerin are also considered carbohydrates.

Simple Sugars

The simplest sugars are the monosaccharides. They are glucose, fructose and galactose. Glucose is the form of sugar used by the body to produce energy. All of the other forms of carbohydrates are converted to glucose by the body to produce energy. The following table lists the monosaccharides:

The disaccharides consist of pairs of monsaccharides. The following table lists the disaccharides:

Sugars contribute 4 calories per gram.

Starch and Other Carbohydrates

Longer chains of glucose form polysaccharides, also known as complex carbohydrates.

Starch is the most common form of polysaccharide. Starch is the means used by plants to store glucose.

In humans and animals, polysaccharides called glycogen store glucose until it is needed for energy production.

Complex carbohydrates contribute 4 calories per gram.

Glycerin

Glycerin is a smooth sticky substance used as a bulking agent for nutrition bars and other products. It also helps hold the bars together. Glycerin is also called glycerol.

Glycerin is considered a carbohydrate, even though its chemical structure is different from the polysaccharides. Glycerin is metabolized more slowly than the other carbohydrates, and provides slightly more energy. In some cases glycerin is only partially metabolized; the remainder is excreted from the body.

Glycerin contributes 4.32 calories per gram.

The FDA (US Food and Drug Administration) requires that glycerin be included in the Total Carbohydrates listed on the Nutrition Facts label.

Fiber

Fiber consists of a class of nutrients that are not easily absorbed by the body. The most common fiber is cellulose, which makes up the cell walls of plants.

In general, digestive enzymes cannot break down fiber, so fiber does not contribute significant calories. However, bacteria in the intestines can metabolize some fiber, so fiber can be a source of a limited number of calories.

Fiber is often classified as water-soluble fiber or water-insoluble fiber. Each has different effects on digestion, but neither contributes calories.

Sugar Alcohols

Sugar Alcohols are chemically similar to both sugar and alcohol. They are metabolized more slowly than other carbohydrates. For this reason they cause less of an increase in blood sugar levels after eating.

Sugar alcohols are classified as carbohydrates. They typically have lower calories per gram than do sugars and starch. The following table lists the calories per gram of the sugar alcohols tracked by nutraCoster

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The FDA (US Food and Drug Administration) requires that sugar alcohols be included in the Total Carbohydrates listed on the Nutrition Facts label.

Sugar alcohols are often used as substitute sweeteners. They are less sweet than sugar, so an equivalent sweetness requires more sugar alcohol than sugar. They are also slowly absorbed by the body, so they tend to linger in the intestines, and are sometimes associated with bloating and gas.

Net Carbohydrates

Because not all carbohydrates contribute calories, the total carbohydrate values listed on Nutrition Facts labels can be misleading. This has lead proponents of low-carbohydrate diets to define a term called Net Carbohydrates (or Effective Carbohydrates).

However, there is no standardized method for calculating Net Carbohydrates. In fact, there is some controversy about what should and should not be considered when calculating net carbohydrates.

In general, carbohydrates that do not contribute calories are subtracted from total carbohydrates to calculate net carbohydrates. Many proponents of low carbohydrate diets also subtract carbohydrates that are metabolized more slowly by the body.

nutraCoster uses 2 techniques to calculate net carbohydrates:

1. A metabolism-based approach which considers how quickly carbohydrates are converted to blood sugar by the body, and
2. A calorie-based approach that considers the total calories contributed by the carbohydrate components.

Net Carbohydrates By Difference - Metabolism-Based Approach

The calculation of Net Carbohydrates is influenced by how quickly the body can digest and utilize different forms of carbohydrate. This is measured by a factor called the Glycemic Index. Foods that are absorbed quickly and cause a sharp rise in blood sugar levels have a high glycemic index. Foods that are absorbed more slowly do not cause a sharp rise in blood sugar and have a lower glycemic index.

The Glycemic Index compares the absorption of foods to that of glucose. Glucose has a Glycemic Index of 100. The following table lists the Glycemic Index for some common foods:

Note that different tables of Glycemic Index often give different values for the same foods.

The body metabolizes both sugar alcohols and glycerin slowly, so they do not cause a sharp rise in blood sugar levels after they are eaten. Fiber is not digested at all. These carbohydrates are subtracted from the total carbohydrates to calculate the net carbohydrates using the metabolism-based approach.

Because these nutrients are subtracted from the total carbohydrates, this technique is called Net Carbohydrates by Difference.

In addition, nutraCoster provides a miscellaneous field called Non-net Carbs which is also subtracted from Total Carbohydrates to calculate Net Carbohydrates.

Note that the Net Carbohydrates by Difference approach is only counting carbohydrates from sugars and starch.

Example: A product has 20 g of total carbohydrates, which consists of 9 g of starch, 5 g of sugar, 3 g of fiber, 2 g of sugar alcohols and 1 g of glycerin. The fiber, sugar alcohol and glycerin (6 g) are subtracted form the total carbohydrates (20 g) to yield a net carbohydrate value of 14 g. The following table summarizes:

Net Carbohydrates - Calorie-Based Approach

Even though the body metabolizes sugar alcohols and glycerin more slowly than other carbohydrates, they still contribute calories. This is an important consideration for weight control.

Since sugar alcohols contribute fewer calories than sugar and starch, the calorie-based approach reduces the contribution from these nutrients, but does not reduce them to 0 like the metabolism-based approach. Glycerin has slightly more calories than sugars and starch, so they cause the net carbohydrates to increase slightly using the calorie-based approach.

The calorie-based approach sums the calories contributed by all of the carbohydrate components, then divides the result by 4. This yields the equivalent grams of sugar and starch that would provide the same total number of calories.

Because this technique calculates net carbohydrates by considering the total calories contributed, it is called Net Carbohydrates by Calories .

Net Carbohydrates by Calories uses the Net Carbohydrates value calculated by the Net Carbohydrates by Difference to determine the calorie contribution from sugars and starch.

Example: In the example above, suppose the sugar alcohols are composed of 2 g of Mannitol. The following table indicates the calories contributed by each nutrient:

In this example, the total calories contributed by all of the carbohydrates is 63.52. At 4 calories per gram, this converts to 15.88 g of equivalent net carbohydrates.

Note that the Net Carbohydrates by Difference approach will result in a lower net carbohydrate number. However, this tends to understate the calorie contributions of the carbohydrates.

Summary and Detail Information

nutraCoster lists several levels of detail for carbohydrates. For example, Total Carbohydrate consists of Total Sugar, Total Fiber, Total Other Carbohydrates and Total Sugar Alcohol. In turn, Total Fiber consists of Soluble Fiber and Insoluble Fiber. The following table lists the summary and detail information tracked by nutraCoster. Note that some values, like Total Sugar, are both summary and detail information.

In general, the sum of the detail values should equal the summary value. The Detail Consistency table on the Carbohydrates page shows the deviation of the detail totals from the summary values.

Entering Detail Values

When you enter or change any of the detail values, nutraCoster checks to see if the associated summary value was equal to the sum of the detail values before the change. If so, nutraCoster updates the summary value to agree with the sum of the detail values after the change. If not, nutraCoster does not update the summary value.

Example: The value for Total Sugar is 10 g, and the value for Sucrose is also 10 g. The following table lists the values:

If you then enter a value of 3 g for Fructose, nutraCoster will update the Total Sugar to be 13 g:

Example: in the above example the Total Carbohydrate consisted of 10 g of Total Sugar and 5 g of Total Fiber before the Fructose was entered. The following table lists the values:

After the 3 g of Fructose was added, the Total Carbohydrate was also updated:

Entering Summary Values

When you enter any of the summary values, nutraCoster cannot know how to update the detail values unless it knows the proportions of the detail values.

If any of the details values are non-zero, and you make a change to a summary value, nutraCoster checks to see if the summary value was equal to the sum of the detail values before the change. If so, nutraCoster updates each of the detail values to make the sum of the detail values equal the new summary value, while keeping the proportions the same.

Example: Total Sugar was 12 g, Fructose was 8 g and Sucrose was 4 g. The following table lists the values:

If you change the Total Sugar to 18 g, nutraCoster will update the detail values as shown in the following table:

In general, when entering nutrition data, enter the detail values first. nutraCoster will automatically calculate the summary values for you.