CARBOHYDRATES. The term “carbohydrate” refers to a group of molecules composed of carbon, hydrogen, and oxygen. There are two groups: Simple carbohydrates

CARBOHYDRATES

The term “carbohydrate” refers to a group of molecules composed of carbon, hydrogen, and oxygen.

There are two groups: Simple carbohydrates (also called “sugars”) Complex carbohydrates

The term “carbohydrate” refers to a group of molecules composed of carbon, hydrogen, and oxygen.

There are two groups: Simple carbohydrates (also called “sugars”) Complex carbohydrates

In fact, they are related: 1. The complex carbohydrates are formed by linking together many simple carbohyrates and2. The simple carbohydrates can be formed by breaking apart the complex carbohydrates

We get carbohydrates in our diets from eatingplants and, to smaller degree from milk and meat.

Simple Carbohydrates:

The simple carbohydrates are the monosaccharides and the disaccharides

Simple Carbohydrates:

The simple carbohydrates are the monosaccharides and the disaccharides

Although there are dozens of known monosaccharides and disaccharides, only a small number are important nutritionally because they are found in our food.

Monosaccharides: All have formula C6H12O6

Glucose (also called “dextrose”) is the most abundant and most important monosaccharide.

Simple Carbohydrates: Monosaccharides

Glucose (also called “dextrose”) is the most abundant and most important monosaccharide.

All green plants produce glucose from carbon dioxide, water, and sunlight (energy) Gives food a sweet taste

Glucose is the primary “fuel molecule” our cells use to produce energy soIt is the sugar carried around the body in the blood


Fructose (also called “levulose” or “fruit sugar”) is also very sweet


Fructose (also called “levulose” or “fruit sugar”) is also very sweet

Occurs naturally in fruits, vegetables,honey, and corn syrup.

Some cells can use fructose as a fuel molecule, but most cells convert it to glucose instead


Galactose - rarely found alone in natureUsually combined with glucose


Galactose - rarely found alone in natureUsually combined with glucose

Found in milk

Cells convert galactose to glucose for energyMay be part of cell membranes


Simple Carbohydrates: Disaccharides

Disaccharides are two monosaccharides linked together


Disaccharides are two monosaccharides linked together

Three disaccharides are dietarily important:

Sucrose

Lactose

Maltose

All have formula C12H22O11


Sucrose = glucose + fructose

Found in sugarcane, sugarbeets

“Table Sugar” – only sweetener that can be called “sugar” on food labels in United States


Lactose = glucose + galactose

“Milk Sugar”


Maltose = glucose + glucose

Found in partially digested starch and in germinating cereal grains

Chains of two or more monosaccharides

Oligosaccharides = shorter chains

Polysaccharides = longer chains

Complex Carbohydrates

Complex Carbohydrates: Oligosaccharides

Consist of 3-10 monosaccharides

Found in legumes, milkForms receptors on many cell membranes

Not digestible by humans = fiber

May be added to food: inulin oligofructose raffinose maltotriose

Starch: How plants store energy Found in grains, legumes, and tubers

Long chains of glucose units:

Amylose—straight chains

Amylopectin—branched chains

Complex Carbohydrates: Polysaccharides

Glycogen How animals (including humans) store energy Found in meat, liver

Long, branching chains of glucose units:

Formed in liver and muscle when blood glucose levels are high

Can be broken down to provide glucose when blood glucose levels get low


Cellulose


Indigestible chains of monosaccharides = “fiber” - speeds up gastrointestinal movement - increases fecal mass - slows breakdown of starch - slows absorption of glucose

Found in all plants,

“Functional” fiber: isolated and added to foods

Can be use as a supplement

Other forms of fiber


= Indigestible chains of monosaccharides Pectins Gums Lignans Beta glucans Chitins

Found in all plants,

“Functional” fiber: isolated and added to foods

Can be use as a supplement

Complex Carbohydrates

Dietary fiber:

Possible role in weight control

Better control of blood glucose

Reduced risk of heart disease

Healthier gastrointestinal functioning

Negative effects of excess fiber

Increased water consumption

Can bind small amounts of minerals

Complex Carbohydrates:

Complex carbohydrates (amylose, amylopectin) broken down to form disaccharides and monosaccharides:

Mouth: Salivary amylase begins digestion

Stomach: No carbohydrate digestion

Small intestine: Pancreatic amylase finishes digestion

Carbohydrate Digestion:

Disaccharides (sucrose, maltose, lactose) broken down to form monosaccharides:

Small intestine: Pancreatic enzymes

Enzymes from intestinal cells (sucrase, maltase, lactase)


These enzymes are highly specific

For example: - Amylase digests amylose but not amylopectin - Lactase digests lactose but not maltose or sucrose - Maltase digests maltose but not lactose or sucrose - Sucrase digests sucrose but not maltose or lactose

Remember: Some carbohydrates can not be digested; fiber & “resistant” starch


Monosaccharides are absorbed from the small intestine

Carbohydrate Absorption:


and carried by the blood to the liver





Liver: Converts other monsaccharides to glucose

Stores excess glucose as glycogen




Liver: Converts other monsaccharides to glucose

Stores excess glucose as glycogen

Liver: Breaks down glycogen to release glucose back into theblood when needed.

Glucose is our primary fuel source soIt is important to maintain normal blood glucose levels andIt is important for glucose to get from the blood into cells

Carbohydrate Metabolism:

Glucose is our primary fuel source soIt is important to maintain normal blood glucose levels andIt is important for glucose to get from the blood into cells

These processes are primarily regulated by two hormones Insulin GlucagonBoth are secreted by the pancreatic islets



Insulin promotes:

(i) Energy storage

glucose glycogen (glycogenesis)

(ii) Protein synthesis

glucose amino acids protein

(iii) Fat synthesis

glucose fatty acids triglycerides(fat)


Carbohydrate Metabolism: Disorders

Normal Blood Glucose: 70-110 mg/100 ml of blood

Persistent high blood glucose levels = Hyperglycemia Insufficient insulin >125 mg/100 ml

Too much glucagon Most common cause = diabetes mellitus



Persistent high blood glucose levels = Hyperglycemia Insufficient insulin >125 mg/100 ml

Too much glucagon Most common cause = diabetes mellitus

Persistent low blood glucose levels = Hypoglycemia Too much insulin <50 mg/100 ml

Insufficient glucagon Most common causes = insulin overdose in diabetes starvation

strenuous exercise



Diabetes Mellitus:

Glucose unable to enter cells

so

Blood glucose levels rise (hyperglycemia)

Complications: Hypertension Heart damage Kidney damage Nerve damage Blood vessel damage Eye damage


Diabetes mellitus:

Type 1 or “insulin dependent” diabetes: Lack of insulin production

Type 2 or “insulin independent” diabetes: Cells are resistant to insulin


Diabetes mellitus:

Type 1 or “insulin dependent” diabetes: Lack of insulin production

Type 2 or “insulin independent” diabetes: Cells are resistant to insulin

Usually present as “prediabetes” first

Gestational diabetes: occurs during pregnancy


Diabetes mellitus:

Best prevention:

Healthful diet

Regular exercise

Healthy weight

Don’t smoke

Monitor blood sugar if you have genetic predisposition


Recommended carbohydrate intake:

Recommended Daily Allowance = 130 grams per day

Acceptable Macronutrient Distribution Range = 45–65% of calories

Carbohydrates:

Recommended carbohydrate intake: Recommended Daily Allowance = 130 grams per day Acceptable Macronutrient Distribution Range = 45–65% of calories

Choose carbohydrates wisely: fiber-rich fruits vegetables whole grains high-fiber cereal Because:

Not all carbohydrate sources have the same effect on blood glucose levels

Carbohydrates:

Carbohydrates:

Each type of food has a glycemic index which measures its effects on blood sugar levels.

Carbohydrates:


Carbohydrates that break down quickly during digestion and release glucose rapidly for absorption into the bloodstream have a high glycemic index

Carbohydrates:


Carbohydrates that break down quickly during digestion and release glucose rapidly for absorption into the bloodstream have a high glycemic index

Carbohydrates that break down more slowly, releasing glucose more gradually for absorption into the bloodstream, have a low glycemic index.

Low glycemic index: Most vegetables, fruits, legumes,(55 or less) whole grains, nuts, milk, citrus juices, foods low in carbohydrates Moderate glycemic index: Whole wheat products, honey, (56 to 69) brown or basmati rice, bran, baked potato, sweet potato

High glycemic index: White bread, white rice, breakfast(70 and above) cereals, waffles, chips, candy, table sugar

(Pure glucose: glycemic index = 100)

Carbohydrates:

Moderating sugar intake: Choose food with lower glycemic index

Use less added sugarLimit soft drinks, sugary cereals, and candyChoose fresh fruits or those canned in water or juice

Carbohydrates:

Nutritive sweeteners

Natural sugars

Sugar alcohols

Non-nutritive sweeteners

Saccharin

Aspartame

Acesulfame K

Sucralose

Carbohydrates: Natural and Artificial Sweeteners

Let’s move on to the lipids next

Documents

CARBOHYDRATES. The term “carbohydrate” refers to a group of molecules composed of carbon, hydrogen, and oxygen. There are two groups: Simple carbohydrates