CH. 4 Learning Objectives

Explain why carbohydrates are needed in the diet (Part 1)

The body tissues use carbohydrate for energy and other critical functions. The brain and nerve tissues prefer carbohydrate as fuel, and red blood cells can use nothing else. Intakes of refined carbohydrates should be limited. Soluble fibers dissolve in water, form viscous gels, and are easily fermented by colonic bacteria. Soluble fibers and products of their fermentation play roles in maintaining the body's health. Insoluble fibers do not dissolve in water; they form structural parts of plants and resist fermentation by colonic bacteria. Insoluble fibers support digestive tract health. Foods rich in soluble fibers help control blood cholesterol. Foods rich in soluble fibers help to modulate the rate of glucose absorption. Soluble fibers help to sustain intestinal colonies of beneficial bacteria.

Identify foods that are rich in carbohydrates.

The recommended intake for carbohydrates is 45-65% of your energy requirement. Breads and cereals, starchy vegetables, fruit, and milk are all rich sources of carbohydrates.

Explain how plants synthesize carbohydrates.

Through photosynthesis, plants combine carbon dioxide, water, and the sun's energy to form glucose. Carbohydrates are made of carbon, hydrogen, and oxygen held together by energy-containing bonds: carbo- means "carbon"; -hydrate means "water." Glucose is the most important monosaccharide in the human body. Monosaccharides can be converted by the liver to other needed molecules. Starch is the storage form of glucose in plants; it also yields glucose for the body's use. Glycogen is the storage form of glucose in the body. Fibers lend structure to plants and perform other functions. Human digestive enzymes cannot break the chemical bonds of fibers. Some fiber is susceptible to fermentation by bacteria in the colon.

Describe how carbohydrates are converted to glucose in the human body.

A main task of the human digestive system is to convert starch and sugars to glucose for absorption. Other body systems transport and store glucose; all cells can split glucose for energy. In lactose intolerance, the body fails to produce sufficient amounts of the enzyme lactase, needed to digest the sugar of milk, which leads to uncomfortable symptoms. People with lactose intolerance or milk allergy need alternatives that provide the nutrients of milk.

Itemize the effects of added sugars on health

Added sugars are empty calories and, when consumed in large amounts, can contribute to health problems. Added sugar intake is linked to increased body fat, heart disease, and type 2 diabetes.

Explain why carbohydrates are needed in the diet (Part 2)

Both soluble and insoluble fibers ease elimination by enlarging and softening stools, which helps maintain digestive tract health. Adequate dietary fiber may reduce the risks of colon and rectal cancers. Plant foods supply fiber, nutrients, and phytochemicals that may oppose cancers in many ways. A diet with adequate fiber-rich whole foods may help to manage body weight. Few people consume sufficient fiber. The best fiber sources are whole foods from plants. Very-high-fiber all-plant diets can pose nutritional risks for people who are old or malnourished, and for young children. Whole-grain flours retain all edible parts of grain kernels. Refined grain products are less nutritious than whole grains. A diet rich in whole grains is associated with reduced risks of overweight and certain chronic diseases.

Briefly summarize the differences among type 1 diabetes, type 2 diabetes, and hypoglycemia.

In type 1 diabetes, blood glucose stays too high because insulin is lacking. In type 2 diabetes, blood glucose stays too high because the cells do not respond to normal insulin levels. In hypoglycemia, blood glucose falls below normal, usually as a result of poorly controlled diabetes or other diseases.

Describe the body's handling of glucose.

Lacking glucose, the body is forced to alter its uses of protein and fat. To help supply the brain with glucose, the body breaks down its protein to make glucose and converts its fats into ketone bodies, incurring ketosis. The muscles and liver store glucose as glycogen; the liver can release glucose from its glycogen into the bloodstream. The hormones insulin and glucagon regulate blood glucose concentrations. The liver has the ability to convert glucose into fat, but most excess glucose is stored as glycogen or used to meet the body's immediate needs for fuel. The glycemic index reflects the degree to which a food raises blood glucose. A steady diet of high-glycemic ultra-processed foods may be linked with chronic diseases. The concept of good and bad foods based solely on the glycemic response is an oversimplification.