BIO 39.1 DIGESTIVE SYSTEM

Your Body’s Need for Food

FOOD

Food:

Your body uses energy to move, to grow, and even to lie still and sleep.

The amount of energy you need depends on many factors, including your age, your sex, your rate of growth, and your level of physical activity.

Different activities use different amounts of energy.

FOOD

Food:

You obtain your energy from the nutrients in the foods and beverages you consume.

A nutrient is a substance required by the body for energy, growth, repair, or maintenance.

Nutrients in food and beverages include carbohydrates, lipids, proteins, vitamins, and minerals.

Each nutrient plays a different role in keeping your body healthy. Water is also essential for health and maintaining life.

FOOD

The large molecules in food must be broken down in order to be absorbed into the blood and carried to cells throughout the body.

The process of breaking down food into molecules the body can use is called digestion.

FOOD

Your cells than break the chemical bonds of the digested food particles and use the energy that is released to make ATP during the process of cellular respiration.

The energy available in food is measured by a unit called a calorie.

A calorie is the amount of heat energy required to raise the temperature of 1 gram of water 1 degree centigrade ( or 1.8 F).

The greater the number of calories in a quantity of food, the more energy the food contains.

FOOD

Calories:

Because a calorie represents a very small amount of energy, nutritionists use a unit called the Calorie (with a C) which is equal to 1000 calories.

On food labels in the grocery store, and throughout this book, the word calories represent Calories (1000 calories).

ENERGY AND BUILDING MATERIALS

Carbohydrates:

Carbohydrates that exist as single sugar molecules are called monosaccharides or simple carbohydrates.

Carbohydrates made of two or more sugars linked together by chemical bonds are called complex carbohydrates.

Complex carbohydrates must be digested (broken down) into simple sugars before cells can use their energy.

CARBOHYDRATESMost foods contain carbohydrates; in particular breads, grains, cereals, potatoes and fruits are all carbohydrate rich.

Glucose, fructose, and other simple sugars are found in fruits, honey and onions.

Glucose, a simple sugar (monosaccharide), is used by cells for energy, and it can be directly absorbed into your bloodstream.

Table sugar contains sucrose, two simple sugars linked together (disaccharide).

Starches are long chains of sugars (polysaccharides) found in cereal grains and in vegetables such as potatoes, beans and corn.

CARBOHYDRATES

Cellulose is a major component of plant cell walls and is found in all foods that come from plants.

Cellulose, which is a major part of fiber, does not provide energy because we do not have enzymes that can digest it.

However, cellulose aids in human digestion by stimulating the walls of the digestive tract to secrete mucus, which helps food pass through the digestive tract.

CARBOHYDRATES

If excess carbohydrates are consumed, they are stored as the carbohydrate glycogen in the liver and in some muscle tissue.

Glycogen can later be broken back down into glucose when the body needs energy.

The remainder of the excess glucose is converted to fat and stored in fatty tissue.

PROTEINS

The digestive products of proteins, amino acids, are normally used by the body for making other protein molecules, such as enzymes and antibodies.

When more protein is eaten than is needed by the cells, the amino acids are used for energy or converted to fat.

The body requires 20 different amino acids to function. A child’s or teen’s body can make 10 of the amino acids from the other amino acids.

PROTEINS

The other 10, called essential amino acids, must be obtained directly from food.

Most animal products, such as eggs, milk, fish, poultry and beef, contain all the essential amino acids.

Eating certain combinations of two or more plant products can also supply all the essential amino acids. No single plant food contains all the essential amino acids.

Adults must get 8 essential amino acids from food.

LIPIDS

Lipids, organic compounds that are insoluble in water, are used to make steroid hormones and cell membranes and to store energy.

Fats are lipids that store energy in plants and animals.

Fats are stored around organs and act as padding and insulation.

Fats also act as solvents for fat-soluble vitamins.

Lipid bilayer

Saturated and unsaturated fats

LIPIDS

Although lipids are essential nutrients, too much fat in the diet is known to harm several body systems.

For example, a diet high in saturated fats is linked to high cholesterol levels, which in turn may be connected to cardiovascular diseases.

It is recommended that a person limits his or her consumption of saturated fats and that most of the fats in the diet be unsaturated.

Fatty foods high in cholesterol

Clogged arteries

BALANCING NUTRITION AND ENERGY

Regardless of their source, the excess calories you eat will be stored as either glycogen or body fat, and you will gain weight.

If you use more calories than you take in, additional energy will be obtained from your body’s energy stores, and you will loose weight.

Your diet and overall activity level determine in part whether you store excess calories as glycogen or as fat.

For optimal health, 45 to 65 percent of each days calories should come from carbohydrates, 10 to 15 percent from protein, and 25 to 35 percent from fats.

BALANCING NUTRIENTS AND ENERGY

Obesity is described as being more than 20 percent heavier than your ideal body weight.

Obesity significantly increases an individuals risk of diabetes, heart disease, osteoarthritis, and many other disorders.

Regular exercise is important in maintaining the balance of your body’s energy.

VITAMINS, MINERALS AND WATER

Vitamins, minerals and water are also required in our diets.

They do not provide energy but they contribute to many different functions, including regulating the reactions that release energy.

Many different vitamins, organic substances that occur in many foods in small amounts, are necessary in small amounts for the normal metabolic functioning of the body.

Vitamins can dissolve in either water of fats.

VITAMINS, MINERALS AND WATER

Vitamins can dissolve in either water of fats.

Fat soluble vitamins; vitamins A, D, E, and K, can be stored in body fat.

Excessive amounts of vitamins A and D can be toxic.

Excess water soluble vitamins, C and B vitamins, are excreted in urine and must be replenished by the diet.

MINERALS

Different minerals are required to maintain a healthy body.

Minerals are naturally occurring inorganic substances that are used to make certain body structures and substances.

They also provide for proper nerve and muscle function, and to maintain osmotic balance.

Some minerals are essential for enzyme function.

MINERALS

Minerals are not produced by living organisms.

Minerals must be replaced on a daily basis because they are soluble in water. Minerals are required by many body systems to function properly, among them:

•Teeth and bones require the minerals calcium and phosphorus.• Iron is required for transporting oxygen. •Magnesium, calcium, sodium, potassium, and zinc help regulate the function of the nerves and cells.

TRACE ELEMENTS

Trace elements are minerals present in the body in small amounts.

Humans usually obtain adequate amounts of required trace elements directly from the plants they eat directly or indirectly from eating animals that have eaten plants.

Trace elements we get from plants include iodine, cobalt, zinc, molybdnum, manganese, and selenium.

WATER

You can survive only a few days without water, though you can live several weeks without food.

Water is used by the body as a medium to transport gases, nutrients, and waste products.

Water also plays a role in regulating body temperature (homeostasis).

Two-thirds of the body’s weight is water.