Chapter 5--Carbohydrates: Sugars, Starches, and Fiber

Photosynthesis

The metabolic process by which plants trap energy from the sun and use it to make sugars from carbon dioxide and water

Chlorophyll

The green pigment in plants that captures the sun's energy

Transformation of energy in photosynthesis

The light energy that's "captured" from the sun becomes the chemical energy of the bonds that allow water and carbon dioxide to combine and form glucose, a single sugar. The remaining oxygen is released into the air.

The function of water in photosynthesis

It is absorbed by the roots of plants and donates its hydrogen and some oxygen.

The function of carbon dioxide in photosynthesis

It is absorbed into the air, donating the carbon and additional oxygen.

Where and how do plants get their energy?

Glucose, through the breaking of energy-containing bonds in starch.

What is the storage form of glucose in plants?

starch

Do plants use all the starch?

No, the starch and its energy are available to us when we consume plants.

Carbohydrate

the class of nutrients that is a major source of energy for the body; CHO

Sources of CHOs

Mainly plant-derived, with the exception being milk/milk products (lactose). Milk is the only animal-derived food that contains a large amount of CHO

What is the most important monosaccharide in the human body?

Glucose because it is the primary fuel for muscle cells, among others. Under normal conditions, RBCs, brain cells, and nervous system cells burn mostly glucose for energy.

Disaccharides

Simple CHOs that are made up of monosaccharides. All of them contain at least 1 glucose molecule.

Monosaccharides

The simplest type of sugar, and the basic chemical unit of CHOs.

Types of monosaccharides

glucose, fructose, galactose

Fructose

Fruit sugar, the sweetest of the monosaccharides, and the least needed by the body

galactose

an important component of lactose, but not commonly found in foods

Three major dietary disaccharides

Lactose, sucrose, maltose

lactose

milk sugar-->glucose + galactose

sucrose

naturally found in some foods (e.g., honey, maple syrup, carrots); commonly refined from sugarcane or sugarbeets --> glucose + fructose

maltose

a disaccharide that remains after the hydrolysis of starch -->glucose + glucose

sugar alcohols

alternative sweeteners used to replace sugar in some sugar-free products. NOT fully absorbed by the intestinal tract, and so may cause diarrhea

non-nutritive sweeteners

type of alternative sweetener made from a group of compounds that taste intensely sweet but do not contribute calories. EX: aspartame, Splenda, etc.

complex carbohydrates

carbohydrates that are composed of 3 or more monosaccharides bonded together

polysaccharides

complex CHOs comprised of more than 10 monosaccharides bonded together.

oligosaccharide

complex CHO comprised of 3 to 10 monosaccharides bonded together

starch

CHO found in plants, made up of many glucose molecules linked in straight or branched chains. It is a plant's storage form of glucose.

glycogen

Storage form of glucose made in the liver and stored in the liver and muscle tissue.

Fiber

nondigestible plant material that's bonds can't be broken by human digestive enzymes. Bacteria in the large intestine can break down "some" via a process called fermentation with remnants from such being absorbed.

insoluble fiber

Fiber that does not dissolve in water, form gels, or have viscosity. It is less likely to be broken down by bacteria in the large intestine, and it's the tough fibrous structural components of fruits, veggies, and whole grains

Functions of insoluble fiber

Increases fecal bulk & the rate of passage of fecal matter through the large intestine

Health benefits of insoluble fiber

* alleviates constipation by increasing the frequency of defecation

* reduces bowel pressure via regular bowel movements

* strengthens the muscles of the large intestine to prevent diverticulitis

soluble fiber

viscous, slow-flowing fiber that dissolves in water and that is easily broken down by bacteria in the large intestine and is found in plants

functions of soluble fiber

Decreases the rate of glucose absorption via...

>alteration of pancreatic and intestinal enzymes.

>forming a gel with glucose

Decreases the risk of developing diabetes thereby.

health benefits of soluble fiber

> slows the passage of food through the upper GI tract (by delaying gastric emptying)

> aids in moisture retention in feces

> provides energy for the colon by being fermented

> helps lower blood cholesterol levels

Fiber Adequate Intake (AI) general recommendations

Women (19-50): 25g/day

Men (19-50): 38g/day

How does a diet high in fiber lower heart disease risk?

> lowers blood cholesterol levels

> reduces blood pressure

> normalizes blood glucose levels

> may reduce the risk of developing obesity

unrefined foods

foods eaten either just as they are found in nature or with minimal processing

refined foods

foods that have undergone processing that changes or removes various components of the original food

empty calories

Calories from solid fats (saturated and trans) and added sugars

whole grain

A grain milled in its entirety, excluding the husk. Contains the bran, endosperm, and germ

bran

the rich multi-layered outer skin of the edible kernel in whole grains. contains most of the fiber plus B vitamins, minerals, antioxidants, and phytochemicals

endosperm

the bulk (~83%) of the edible portion of a whole grain. It is starchy, soft in texture, and whitish in color. It contains most of the CHOs and protein. Contains a small amount of some B vitamins and minerals.

germ

Located at the base of the kernel, it is the embryo that has the potential to sprout into a new plant. It is rich in oils and vitamin E. It contains some vitamins and phytochemicals.

enrichment of refined grain products

Legislation requires the fortification of grains with some of the nutrients that were removed during processing: Some B vitamins (thiamin, riboflavin, niacin, and folic acid) and iron (a mineral).

fortification

in general, the addition of nutrients to foods

enrichment

the addition of specific amounts of nutrients; a type of fortification

indigestible carbohydrates

Carbs that cannot be digested by human digestive enzymes and are not readily absorbed

Types of indigestible carbs

a) fiber (soluble and insoluble)

b) some oligosaccharides

c) resistant starch

resistant starch

a starch that escapes digestion either because the natural structure of the grain protects the starch molecules or because cooking and processing alter their digestibility.

What breaks down indigestible CHOs?

Bacteria in the large intestine

Do indigestible carbohydrates raise blood glucose levels?

No, they do not raise blood glucose levels because they aren't digested or absorbed.

How do indigestible carbohydrates affect stomach emptying?

They delay stomach emptying by slowing the absorption of nutrients in the small intestine.

What effect do indigestible carbohydrates have on feces?

They add water and bulk to feces, which stimulates peristalsis and increases the speed at which material passes through.

absorption of monosaccharides

enterocytes directly absorb single sugars via the capillary network of each villus in transit to the liver by the hepatic portal vein

digestion/absorption of disaccharides

enzymes within the microvilli split double-sugars into monosaccharides, which are digested via enterocytes.

CHO digestion in mouth

maltase breaks starch into maltose, and amylase breaks down shorter polysaccharides.

What happens to CHOs in the stomach?

hydrochloric acid decreases the pH in the stomach which deactivates salivary amylase, stopping CHO digestion

What happens to CHOs in the small intestine?

Bicarbonate in pancreatic juice neutralizes the pH of the gastric juice, and CHO digestion resumes

What happens to indigestible CHOs in the large intestine?

Some fiber, some oligosaccharides, and resistant starch are broken down by bacteria, producing short chain fatty acids and gas via fermentation

Main Function of CHO

providing energy; the AMDR for it = 45-65% of total calories

What is the role of galactose in the body?

Galactose is needed for nerve cell function.

What are ribose and deoxyribose?

They are monosaccharides that are components of RNA and DNA.

What is the function of some oligosaccharides in cell membranes?

Some oligosaccharides in cell membranes convey information about cells via signals.

What is the role of large polysaccharides found in connective tissue?

They provide cushion and lubrication.

What do brain, nerve, and red blood cells have in common with regard to nutrition?

They all prefer glucose as their main source of energy

RDA for CHOs + why?

130 grams/day for adults and children

This amount is based on the average minimum amount of glucose used by JUST the brain. This amount of CHOs is also enough to prevent ketosis, which is an adaptive metabolic state in which the body uses fat for energy, primarily.

What two organs regulate blood glucose?

The liver and the pancreas (insulin and glucagon)

Properties of insulin

-it allows glucose to enter the cells

-promotes fat synthesis in fat-storing cells

-stimulates protein synthesis

insulin

a pancreatic hormone that is secreted in response to blood glucose levels increasing after eating

glucagon

a pancreatic hormone secreted when blood glucose levels drop, which occurs a few hours after eating

function of glucagon

Increase blood glucose levels by signaling liver cells to break down glycogen into glucose, which is released in the blood

energy metabolism

the sum of all the chemical pathways in the body that break down molecules to release energy (catabolism) and use energy to build new molecules (anabolism)

chemical pathways

specific chemical reactions that occur in sequence

cellular respiration

the reactions that break down CHOs, fats, and proteins to produce carbon dioxide, water, and energy in the form of ATP

coenzymes

organic compounds that assist enzymes with chemical reactions

glycolysis

an anaerobic metabolic pathway that occurs in the cytoplasm and splits the 6-carbon glucose into two 3-carbon pyruvates to produce 2 ATP

What is the fate of the pyruvates made in glycolysis in the absence of oxygen?

They are converted to lactic acids (3-carbon molecules), which enter the bloodstream on their way to the liver. There they can be used toward ATP production

What is the fate of the pyruvates made in glycolysis in the presence of oxygen?

They are converted to acetyl-CoA in the mitochondria, producing carbon dioxide and high-energy electrons

Can acetyl-CoA be converted back into glucose?

No because it only has 2 carbons

Citric Acid Cycle

in the presence of oxygen, one acetyl-CoA enters the cycle, one at a time, producing a small number of high energy electrons, ATP, and CO2

electron transport system

after the energy from the high-energy electrons in Krebs cycle is transferred to the chemical bonds of ATP, the remaining electrons combine with oxygen and hydrogen to form water.

Two possible sources of glucose in the body

1. breakdown of liver glycogen

2. conversion of pyruvate back to glucose

What is significant about fats?

They are the main storage form of energy in the body

Products of a fat molecule being disassembled

Fatty acids and glycerol that are released into the blood

Fate of fatty acids with "adequate" CHO and oxygen

They are broken down into 2-carbon units that form acetyl-CoA, which proceed through aerobic metabolism

Fate of fatty acids with "inadequate" CHO

Acetyl-CoA molecules react with each other to form ketone bodies, acidic molecules formed from the metabolism of fat.

ketosis

an adaptive, normal metabolic state in which the body primarily uses fat for energy

ketoacidosis

a life-threatening condition in which high ketone levels in the blood increase the acidity level of blood, which could lead to a coma and death

what does the body do with extra glucose?

the body uses it for energy instead of fat, which increases fat circulation in the blood

what happens to circulating fat and any extra-extra glucose?

some fat is taken up into fatty tissue where it is stored. The liver or fat cells convert the glucose to fat, which will be released into the bloodstream and deposited in fat tissue.

diabetes mellitus

a group of serious, chronic diseases characterized by abnormal glucose, fat, and protein metabolism

hyperglycemia

abnormally elevated blood glucose levels

Cause of diabetes mellitus

Insufficient production of insulin or decreased sensitivity of cells to insulin

Signs and symptoms of diabetes mellitus

Excessive thirst, frequent urination, blurred vision, and poor wound healing

Long-term effects of untreated blood glucose levels

Damage to nerves, organs, and blood vessels

Long-term effects of poorly controlled blood glucose levels

Heart disease, kidney failure, blindness, and poor blood circulation (especially in lower limbs, possibly requiring amputation)

Type I diabetes

An autoimmune disease that results in the destruction of beta cells of the pancreas; exogenous insulin is usually required for treatment

autoimmune disease

a disease that results from immune reactions that destroy normal body cells

What happens if cells lack glucose and need energy?

Ketones are formed for energy

Type II diabetes

the most common type of diabetes, where beta cells in the pancreas produce less insulin or the body has insulin resistance