- ACRONYMS AND DEFINITIONS
- CC- Carbohydrate counting
- Carb- carbohydrate
- OS - Oligosaccharides
- USDA - United States Dept of Agriculture
- CARBOHYDRATE OVERVIEW
- Macronutrients
- There are 3 types of macronutrients:
- Carbohydrates can be subdivided into 3 main categories:
- Energy
- Macronutrients supply the following amounts of energy:
- Carbohydrates - 4 calories/gram
- Fats - 9 calories/gram
- Protein - 4 calories/gram
- Carbohydrate utilization
- Glucose is the fundamental energy source in humans
- Certain forms of carbohydrates (sugars and some starches) are easily absorbed and broken down into glucose by the body
- Because of this, carbohydrates have the most direct effect on blood sugar levels
- RECOMMENDED DIETARY INTAKE
- USDA recommended intake
- The USDA recommends that 45 - 65% of total calories come from carbohydrates
- The USDA recommends that added sugars be limited to < 10% of total calories [14]
- See calories for a guide on calculating daily caloric requirements
- SUGARS
- Sugar categories
- Sugars can be divided into 3 main groups:
- Monosaccharides (1 sugar unit)
- Monosaccharides are easily absorbed and turned into glucose, therefore they have a direct effect on blood sugar
- Glucose (also called dextrose)
- The main energy source of most living organisms
- Found naturally in fruits and vegetables - grapes, peaches, pears, bananas, sweet onions, corn, etc.
- Pure corn syrup is pure glucose
- Sweeteners used in food are often a combination of glucose and fructose - honey, molasses, high-fructose corn syrup, invert sugars
- Fructose
- Fructose has the highest sweetness (sensation of tasting sweet) of all the sugars
- Found naturally in fruits and vegetables - apples, pears, tree fruits, grapes, carrots, sweet pepper, corn, etc.
- Found in sweeteners - high fructose corn syrup, honey, invert sugars
- Galactose
- Galactose is found mainly in dairy products
- A galactose molecule is joined with a glucose molecule to make lactose
- Disaccharides (2 sugar units joined together)
- Disaccharides are easily absorbed and turned into glucose, therefore they have a direct effect on blood sugar
- Sucrose
- Sucrose is a glucose and a fructose molecule joined together
- Found naturally in fruits and vegetables - sugar cane, sugar beets, pineapples, peaches, green peas, etc.
- Table sugar is sucrose derived from sugar cane or sugar beets
- Main component of food sweeteners - table sugar, brown sugar, maple syrup, powdered sugar
- Lactose
- Lactose is a galactose and a glucose molecule joined together
- Main carbohydrate found in dairy products
- Lactose must be metabolized by the lactase enzyme to be absorbed from the intestine
- People who are lactase deficient cannot metabolize lactose and may have gastrointestinal symptoms
- Maltose
- Maltose is two glucose molecules joined together
- Maltose is fermented by yeast to ethanol so it is often used to brew beer
- Maltose corn syrup can be added to foods as a sweetener
- Oligosaccharides (3 - 10 sugar units joined together)
- Oligosaccharides (OS) are short chains (typically 3-10 units) of monosaccharides joined together
- Naturally occurring OS include raffinose, stachyose, low molecular weight fructans, and verbascose
- OS are not digestible by the upper intestinal tract, and they pass unchanged into the colon where they are fermented by bacteria. Because of this process, OS only yield around 1.5 - 2 calories/gram.
- They also produce methane gas which can lead to flatulence
- Oligosaccharides have less of an effect on blood glucose levels than other sugars
- Foods containing OS:
- Raffinose - beans, cabbage, Brussels sprouts, broccoli, asparagus
- Stachyose - green beans, soybeans
- Fructans (fructo-oligosaccharides) - Jerusalem artichoke, onions, wheat, rye [1,2]
- STARCHES
- Starches
- Starches are chains of many glucose molecules linked together (also called polysaccharides)
- Starches are found naturally in many foods - grains (corn, barley, wheat, rye, rice), potatoes, squash, green peas, beans, banana
- Starch bioavailability
- Food processing is a large determinant in whether the starch in a food will be available for absorption and utilization by humans (bioavailability)
- Examples of processes that affect starch bioavailability include:
- Heating and cooking - a baked potato will yield more starch than a raw potato
- Milling and grinding - grinding grains into flour will increase their starch bioavailability compared to consuming them as whole grain
- Food storage - the longer food is stored, the more starch becomes bioavailable
- Ripeness - The riper a food, the more starch is bioavailable
- Other foods consumed with starches - fiber consumed with starches can decrease the bioavailability of starch
- Other starches
- Resistant starches
- Resistant starches are starches that resist digestion in the small intestine and pass into the large intestine undigested
- Because of this property, some resistant starches are considered fibers
- Resistant starches can be naturally occurring or synthetic. Naturally occurring resistant starches include many unprocessed starches (e.g. starches in whole grains and beans, starches in uncooked vegetables). Other resistant starches are produced through food processing (pasta, Hi-maize®) [2]
- Modified starches
- Modified starches are treated chemically or physically to create a functionally desirable characteristic (e.g. viscosity, binding, texture)
- Modified starches are added to foods and other materials (e.g. adhesives, paper, pharmaceuticals) to impart their characteristic on that substance. [1,2]
- Complex carbohydrates
- Term used to refer to oligosaccharides and starches
- FIBERS
- Overview
- Fibers are nondigestible carbohydrates that pass relatively unchanged through the upper digestive tract
- Because fibers are not digested in the upper digestive tract, they do not have a direct effect on blood sugars
- The USDA recommends adults consume 14 grams of fiber per 1000 calories consumed
- Food labeling requirements for fiber are as follows:
- Good source of Fiber - defined as foods that provide 2.5 grams of fiber/serving
- Excellent source of fiber - defined as foods that provide 5 grams of fiber/serving [3,4]
- Types of fiber
- Fibers can be divided into three main groups:
- Soluble (viscous) fiber
- Insoluble (nonviscous) fiber
- Mixed fibers
- Soluble (viscous) fiber
- Soluble fiber passes undigested through the small intestine into the colon
- Soluble fiber is fermented in the colon by bacteria to short chain fatty acids which can then be used as energy. After this process, soluble fiber only yields 1.5 - 2.5 calories/gram compared to 4 calories/gram for other carbohydrates [1]
- Soluble fibers include psyllium, guar gum, pectin, glucomannan, xanthan
- Insoluble (nonviscous) fiber
- Insoluble fiber is not fermented in the colon and therefore does not yield any bioavailable energy
- Insoluble fibers include cellulose, hemicellulose, corn bran, rice bran, wheat bran, lignin
- Mixed fiber (soluble and insoluble)
- Mixed fibers share properties of both soluble fibers and insoluble fibers
- Mixed fibers include soybean and oat bran [5]
- Sources of fiber
- Vegetables, fruits, whole grains, dry beans, peas, nuts, seeds, supplements (e.g. Metamucil), cereals (e.g. All Bran)
- SUGAR ALCOHOLS
- Sugar alcohols are monosaccharides and disaccharides that have been altered slightly
- Sugar alcohols are added to foods as sweeteners
- They have limited absorption in the intestine and may produce a laxative effect if consumed in large quantities
- Sugar alcohols only yield about 2 calories/gram as opposed to 4 calories/gram for other carbs
- Examples of sugar alcohols include sorbitol, mannitol, xylitol, lactitol, maltitol [2]
- CARBOHYDRATES ON FOOD LABELS
- FDA requirements
- The FDA requires manufacturers to list certain nutrient values on food labels
- Some nutrients are required and some are voluntary
- For carbohydrates, the following is true:
- Required
- Total Carbohydrates
- Dietary Fiber
- Total sugars
- Added sugars
- Voluntary
- Soluble fiber
- Insoluble fiber
- Sugar alcohol
- Other carbohydrate
- Exceptions
- Certain foods that contain an insignificant amount of nutrients (e.g. Diet Coke®) are exempt from the requirements
- Exempt foods are only required to list total calories, total fat, total carbs, protein and sodium
- Carbohydrate categories
- On food labels, there are 8 different categories of carbohydrates that may be listed
- An example of a food label is given below along with the definition for each carbohydrate category
- Example food label:
Nutrition Facts Serving size 30g |
Total Carbohydrate 25g Dietary Fiber 8g Soluble Fiber 1g Total sugars 6g includes 5g Added Sugars Other Carbohydrate 5g Sugar Alcohol 6g |
- Total carbohydrates (required)
- The sum total of all the different types of carbohydrates in a food (sugars, starches, and fibers)
- It is important to note that when the grams of carbs from the subcategories of carbohydrates (ex. Fiber, Total Sugars) are added up, they may be less than the total carbohydrates. This occurs because the category "Other Carbohydrate" is voluntary and not always listed.
- Dietary fiber (required)
- Listed as "Dietary fiber" or "Fiber"
- Total Sugars (required)
- Total sugars is the sum of added sugars and sugars found naturally in the food
- Added Sugars (required)
- Added sugars are sugars that are added during the processing of foods
- Added sugars typically include monosaccharides and disaccharides that are found in syrups, honey, and concentrated fruit and vegetable juices
- Soluble fiber (voluntary)
- Soluble fiber is typically only listed on high fiber foods
- Insoluble fiber (voluntary)
- Insoluble fiber is typically only listed on high fiber foods
- Sugar alcohols (voluntary)
- Sugar alcohols consist of lower calorie sweeteners like sorbitol and mannitol
- Because sugar alcohols are not a required listing, they may be present in the food, but not listed separately on the label
- Sugar alcohols may also be counted under "Other Carbohydrate"
- Other carbohydrates (voluntary)
- Defined as the "difference between total carbohydrate and the sum of dietary fiber, sugars, and sugar alcohol"
- Other Carbohydrates = Total Carbohydrate - Dietary Fiber - Sugars - Sugar Alcohol
- Other carbohydrates typically include starches and oligosaccharides
- If sugar alcohols are not listed separately, they may be a part of other carbohydrates
- CARBOHYDRATES AND SATIETY
- Satiety is defined as the sense of fullness or satisfaction a person feels after eating food
- Because of the obesity epidemic, there has been interest in the satiety of macronutrients (protein, carbohydrates, and fat) as a means to control weight gain
- A number of studies of varying designs have been performed to measure the effect of different macronutrients on satiety
- In short, there is no conclusive evidence that one macronutrient is superior to another in providing satiety that leads to reduced calorie intake [1,7]
- GLYCEMIC INDEX
- Sugars, starches, and fibers are absorbed differently, and therefore, they have varying effects on blood sugar levels
- The glycemic index was developed to quantify the direct effect of different foods on blood sugar levels
- See glycemic index for a review
- CARBOHYDRATE COUNTING
- Carbohydrate counting is a method used by diabetics to help dose insulin
- See carbohydrate counting for a review
- RESOURCES FOR FOOD CONTENT
- USDA food composition database - extensive nutritional information about numerous foods including restaurant foods
- myfitnesspal - commercial website that has extensive database of food calorie content
- Lose it! - commercial website that has extensive database of food calorie content
- BIBLIOGRAPHY
- 1 - Dietary Reference Intakes, Institute of Medicine, 2005
- 2 - Carbohydrates in human nutrition, FAO food and nutrition paper - 66, 1997
- 3 - Report of the Dietary Guidelines Advisory Committee on the Dietary Guidelines for Americans, 2010
- 4 - USDA Dietary Guidelines for Americans 2005
- 5 - PMID 8283297
- 6 - PMID 16935851
- 7 - PMID 12499328
- 8 - PMID 8862476
- 9 - PMID 10435117
- 10 - PMID 7900695
- 11 - PMID 7661908
- 12 - PMID 1728818
- 12 - PMID 20167238
- 13 - Code of Federal Regulations, Title 21, Sec 101.9
- 14 - Scientific Report of the 2015 Dietary Guidelines Advisory Committee