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Dietary Carbohydrate

Primary role of dietary Carbohydrates: provide energy

  • 4 cal/g

Classification

  • Simple sugars

    • monosaccharides

    • disaccharides

  • Complex sugars

    • polysaccharides

  • Fibers

Monosaccharides

Principal monosaccharides found in food:

  • glucose: fruits, sweet corn, corn syrup, honey

  • fructose: found with free glucose in honey and fruits (e.g. apples)

High-fructose corn syrup (HFCS)

  • corn syrup that has undergone enzymatic processing to convert their glucose into fructose and have been mixed with pure corn syrup (100% glucose) to produce a desired sweetness

  • HFCS 55 (55% fructose and 42% glucose): substitute for sucrose on beverages (e.g. soft drinks)

  • HFCS 42 used in processed foods

  • composition of HFCS and surcose are similar

    • major difference: HFCS is ingested as a mixture of monosaccharides

    • no significant difference in either postprandial glucose or insulin responses

Disaccharides

Most abundant:

  • sucrose: table sugar

    • glucose + fructose

  • lactose: principal sugar found in milk

    • glucose + galactose

  • maltose: product of enzymatic digestion of polysaccharides, found in beer and malt liquors

    • glucose + glucose

Polysaccharides

  • complex carbohydrates

  • most often polymers of glucose

  • do not have a sweet taste

  • Sources: starch, wheat, potatoes, dried peas, beans (legumes) and vegetables

Fiber

Dietary fiber: non-digestible, non-starch carbohydrates and lignin present in plants

  • soluble fiber is the edible part of plants

    • resistant to digestion and absorption in the human small intestine

  • insoluble fiber passes through the digestive track largely unchanged

  • provides little energy

  • Recommended intake (AI) for total fiber:

    • 25 g/day for women

    • 38 g/day for men

Type of Fiber

Major Source in Diet

Chemical Properties

Physiological Effects

Cellulose

Unrefined cereals, bran, whole wheat

Nondigestible, water insoluble, absorbs water

Stool bulk, intestinal transit time, intracolonic pressure

Hemicellulose

Unrefined cereals, some fruits and vegetables, whole wheat

Partially digestible, usually water insoluble, absorbs water

Stool bulk, intestinal transit time, intracolonic pressure

Lignin

Woody part of vegetables

Nondigestible, water insoluble, absorbs organic substances

Stool bulk, binds cholesterol, binds carcinogens

Pectin

Fruits

Digestible, water soluble, mucilaginous

Rate of gastric emptying,Rate of sugar uptake, Serum cholesterol

Gums

Dried beans, oats

Digestible,water soluble, mucilaginous

Serum cholesterol, Rate of gastric emptying,Rate of sugar uptake

Benefits

  • adds bulk to diet

  • increasing bowel mobility during exposure of intestines to carcinogens

  • promoting bowel movements (laxation)

  • softens stool: decrease risk for constipation, hemorrhoids, and diverticulosis

  • soluble fiber:

    • delays gastric emptying

      • which can result in a sensation of fullness (satiety)

      • reduce spikes in blood glucose following a meal

    • lower plasma LDL-C levels by increasing fecal bile acid excretion and interfering with bile acid reabsorption

Dietary Carbohydrate and Blood Glucose

  • carbohydrates differ in their glycemic response (GR)

    • carbohydrate-containing foods produce either

      • rapid rise followed by a steep fall in blood glucose

      • gradual rise followed by a slow decline in blood glucose

  • Glycemic index (GI): the area under the blood glucose curve seen after ingestion of meal with carbohydrate-rich food, compared with the area under the blood glucose curve observed after a meal consisting of the same amount of carbohydrate in the form of glucose or white bread.

  • low GI: <50

  • high GI: ≥70

  • low-GI diet improves glycemic control in diabetic individuals

  • foods with low GI tend to create a sense of satiety over a long period of time

    • helpful in limiting caloric intake

Glycemic index (GI)https://www.bda.uk.com/resource/glycaemic-index.html

Carbohydrate Requirements

  • not essential nutrients

  • absence of dietary carbohydrate leads to ketogenesis

  • RD for for carbohydrate: 130 g/day for adults and children

  • adults should consume 45% - 65% of their total calories from carbohydrates

  • added sugars should represent no more than 10% of total energy intake

LA

Dietary Carbohydrate

Primary role of dietary Carbohydrates: provide energy

  • 4 cal/g

Classification

  • Simple sugars

    • monosaccharides

    • disaccharides

  • Complex sugars

    • polysaccharides

  • Fibers

Monosaccharides

Principal monosaccharides found in food:

  • glucose: fruits, sweet corn, corn syrup, honey

  • fructose: found with free glucose in honey and fruits (e.g. apples)

High-fructose corn syrup (HFCS)

  • corn syrup that has undergone enzymatic processing to convert their glucose into fructose and have been mixed with pure corn syrup (100% glucose) to produce a desired sweetness

  • HFCS 55 (55% fructose and 42% glucose): substitute for sucrose on beverages (e.g. soft drinks)

  • HFCS 42 used in processed foods

  • composition of HFCS and surcose are similar

    • major difference: HFCS is ingested as a mixture of monosaccharides

    • no significant difference in either postprandial glucose or insulin responses

Disaccharides

Most abundant:

  • sucrose: table sugar

    • glucose + fructose

  • lactose: principal sugar found in milk

    • glucose + galactose

  • maltose: product of enzymatic digestion of polysaccharides, found in beer and malt liquors

    • glucose + glucose

Polysaccharides

  • complex carbohydrates

  • most often polymers of glucose

  • do not have a sweet taste

  • Sources: starch, wheat, potatoes, dried peas, beans (legumes) and vegetables

Fiber

Dietary fiber: non-digestible, non-starch carbohydrates and lignin present in plants

  • soluble fiber is the edible part of plants

    • resistant to digestion and absorption in the human small intestine

  • insoluble fiber passes through the digestive track largely unchanged

  • provides little energy

  • Recommended intake (AI) for total fiber:

    • 25 g/day for women

    • 38 g/day for men

Type of Fiber

Major Source in Diet

Chemical Properties

Physiological Effects

Cellulose

Unrefined cereals, bran, whole wheat

Nondigestible, water insoluble, absorbs water

Stool bulk, intestinal transit time, intracolonic pressure

Hemicellulose

Unrefined cereals, some fruits and vegetables, whole wheat

Partially digestible, usually water insoluble, absorbs water

Stool bulk, intestinal transit time, intracolonic pressure

Lignin

Woody part of vegetables

Nondigestible, water insoluble, absorbs organic substances

Stool bulk, binds cholesterol, binds carcinogens

Pectin

Fruits

Digestible, water soluble, mucilaginous

Rate of gastric emptying,Rate of sugar uptake, Serum cholesterol

Gums

Dried beans, oats

Digestible,water soluble, mucilaginous

Serum cholesterol, Rate of gastric emptying,Rate of sugar uptake

Benefits

  • adds bulk to diet

  • increasing bowel mobility during exposure of intestines to carcinogens

  • promoting bowel movements (laxation)

  • softens stool: decrease risk for constipation, hemorrhoids, and diverticulosis

  • soluble fiber:

    • delays gastric emptying

      • which can result in a sensation of fullness (satiety)

      • reduce spikes in blood glucose following a meal

    • lower plasma LDL-C levels by increasing fecal bile acid excretion and interfering with bile acid reabsorption

Dietary Carbohydrate and Blood Glucose

  • carbohydrates differ in their glycemic response (GR)

    • carbohydrate-containing foods produce either

      • rapid rise followed by a steep fall in blood glucose

      • gradual rise followed by a slow decline in blood glucose

  • Glycemic index (GI): the area under the blood glucose curve seen after ingestion of meal with carbohydrate-rich food, compared with the area under the blood glucose curve observed after a meal consisting of the same amount of carbohydrate in the form of glucose or white bread.

  • low GI: <50

  • high GI: ≥70

  • low-GI diet improves glycemic control in diabetic individuals

  • foods with low GI tend to create a sense of satiety over a long period of time

    • helpful in limiting caloric intake

Glycemic index (GI)https://www.bda.uk.com/resource/glycaemic-index.html

Carbohydrate Requirements

  • not essential nutrients

  • absence of dietary carbohydrate leads to ketogenesis

  • RD for for carbohydrate: 130 g/day for adults and children

  • adults should consume 45% - 65% of their total calories from carbohydrates

  • added sugars should represent no more than 10% of total energy intake