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^^

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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==

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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

  

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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

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