Nutrition, Diet and Weight Loss

Holozoic nutrition – involves the consumption of complex (solid) food which is broken down inside the organism into simple molecules which are then absorbed,

e.g. most animals

Holozoic Nutrition

Holozoic organisms obtain their energy from the consumption of complex organic food which is digested within their bodies.

It involves:

1. Obtaining food  (ingestion)

2. Ingestion       

3. Physical (mechanical) digestion      

4. Chemical digestion                   

5. Absorption                   

6. Assimilation

Elimination (egestion)

According to the type of food ingested, holozoic organisms are classified into:

•          Herbivores - those feed on plant material

•          Carnivores - those feed on other animals

•          Omnivores - those feed on both plants and animals

•          Fluid feeders - those consume liquid materials

•          Phagotrophs - those (majority) take in solid food

•          Microphagous - phagotrophs taking in very small particles,

•          e.g. by filter feeding mechanism

•          Macrophagous - phagotrophs taking in relatively large particles,

e.g. most animals

Clam (mussel)

See Figure 1:

Diet

•          In mammals carbohydrates and fats are needed in relatively large quantities as energy source, and

•          proteins for growth and repair.

•          Vitamins and minerals are required in much smaller quantities for a variety of specific functions.

•          Water is a vital constituent of the diet and

•          roughage is necessary for preventing constipation.

 Carbohydrates and fats (energy requirements)

v  The energy required by an organism varies with age, sex, size and activity.

v  Ideally 2/3 from carbohydrates and 1/3 from fats.

v  A high intake of fats, especially saturated fats, is a contributory factor in causing heart disease.

Proteins

v  Main function: as a source of amino acids which are used to synthesized new proteins                                                              

v  Plants are able to synthesize all their own amino acids but animals are more limited.

v  Thus man requires essential amino acids in the diet.

v  Although plant food contains proportionately fewer proteins, a properly balanced diet can nevertheless provide all the essential amino acids.

Vitamins - group of organic compounds with the following features:

1. no energy value

2. essential in very small quantities for maintenance of good health

3. not structural materials in body

4. work as cofactors in enzymatic reactions

Two groups of vitamins:

A.    Fat soluble vitamins and

B.     Water soluble vitamins
 

VITAMIN               SOURCES                              DEFICIENCY

A                  MILK, CARROT, SOURCES                         DRY SKIN, POOR VISION

B₁                   CEREALS,YEAST, LIVER                                BERI BERI                                                                   

B₂                    MILK, LIVER , VEGETABLE                           SORE THROAT

C                   FRUITS, VEGETABLES                                    SCURVY

D                     EGG-YOLK, COD-LIVER OIL                           RICKETS

E                    BUTTER, PEANUT, EGG YOLK                      ANAEMIA

K                  FISH, LIVER, VEGETABLES                             INABILITY OF THE BLOOD TO CLOT

Too much vitamins, e.g. vitamin A, may be harmful to our body

**Vitamins B & C are water soluble; others fat soluble

**Vitamin C could be destroyed by prolonged heating; tested by decolorizing deep blue colour of DCPIP;  and vitamin C has relatively larger daily requirement than other vitamins

Minerals

v  needed to regulate the metabolism of the body

v  essential for health

v  needed in small amounts

MINERAL                                          SOURCE                  FUNCTION/DEFICIENCY DISEASES

1. CALCIUM & PHOSPHORUS       CHEESE, MILK, VEGETABLE           BONES& TEETH  FORMATION/BLOOD CLOTTING

2. IRON                       LIVER, EGG, BEEF FORMS      HAEMOGLOBIN/ ANAEMIA

3. IODINE                    SEA FOOD    THYROXINE FORMATION/ GOITRE

4. SODIUM & POTASSIUM   TABLE SALT & VEGETABLES          ANION & CATION BALANCE,

/MUSCLE CONTRACTION

5. CHLORINE             TABLE SALT                           ANION & CATION BALANCE / FORMS HCL

Water

ü  - makes up about 75% of body weight

ü  - importance:

ü  as a solvent;      

ü  for transport;      

ü  as a reaction medium;  

ü  as a reactant;

ü  dilutes wastes & poisons;

ü  forms urine

Roughage/Dietary fibre

ü  - consists of cellulose

ü  - indigestible because

ü  - human body has no enzyme for its digestion

ü  - stimulate peristalsis;

ü  - absence will lead constipation

 Milk

Milk is a balanced diet for growth and development of young mammals, but it cannot sustain healthy development indefinitely because:

1. It contains little if any iron - new born baby has Fe accumulated from mother, but store becomes deficient in later life

2. It contains no roughage - constipation results with its long-term absence from diet

3. It contains a high proportion of fat  - ideal for young and actively growing organisms, but as energy demand decreases, more fat deposits around the body would increase risk of heart disease

•          Food additives – examples:

1. colourings,
2. preservative,
3. antioxidants,
4. texture enhancers,
5. synthetic flavourings,
6. flavour enhancers and sweeteners

Feeding mechanisms

A. Small-particle feeders – microscopic food, e.g. bacteria, unicellular algae or small invertebrate larvae, etc., are eaten by unicellular organisms like amoeba, paramecium

B. Filter feeding mechanism: microscopic foods are removed from the surrounding water by some form of filtration mechanism, e.g. mussel

See Figure 2 and 3

C. Large-particle feeders - involving ingestion of particles which are relatively large, e.g. most mammals

D. Fluid and soft-tissue feeders - a mechanism to pierce their 'host' in some way and then use a specialized suction apparatus for drawing  food into their bodies, e.g. mosquito

See Figure 4, 5 and 6

Teeth and dentition in man

•          The structure of the tooth

•          Enamel - non-living substance containing 97% calcium salt & 3% organic matter; cement forms the root of enamel;  fibres attach to jawbone for anchorage forming periodontal membrane

•          dentine - hard but softer than enamel;  with channels of living cytoplasm from pulp cavity

•          pulp cavity - contains living cells with blood vessels (supply food & O₂) and nerves (sensation)

TYPES OF TEETH

See figure 7:

Types of teeth

•          Incisors - at the front;   chisel-like for biting & cutting

•          Canines - pointed, curved & long for tearing flesh; in carnivores, they are well developed for killing preys

Premolars - with one or two cusps for grinding & crushing food

Molars - have 4 cusps for grinding & crushing food

Wisdom teeth - last 4 molars; grow after the age of 20

Milk Teeth and Permanent Teeth

•          - man is diphyodont: two sets of teeth

1.      Milk teeth - appear in babies;  totally 20 in man

2.      Permanent teeth - replace milk teeth in later years; cannot replaced if damaged; totally 32 in man

TOOTH DECAY

See Figure 8:

Dental decay (dental caries)

•          Cause of tooth decay - results from a chemical reaction between bacteria & food debris in mouth; bacteria forms a sticky, invisible film (plaque) reacting with sugars to produce an acid which dissolves enamel, dentine & pulp cavity

          ¾®    toothache  ¾® more serious   ¾®    periodontal disease    ¾® teeth falling off

Calculus: hard deposits due to interaction of plaque & salts in saliva

 Principles of Digestion

•          Mechanical breakdown of food has the effect of giving the food a large surface area which aids later digestion.  The food must be made small enough to pass through cell membranes. Thus chemical digestion with the aid of enzymes occurs.

Amylase - breaks down starch into maltose

See  Diagram A:

Peptidases – break down peptides into amino acids

Endopeptidases – break down peptide bonds in the middle of peptides

Endopeptidases hydrolyse peptide bonds at points along the protein

See Diagram B:

                                                *

*Carboxypeptidase liberates      Exopeptidases acts on                   Aminopeptidase breaks

terminal amino acids                      terminal amino acids                      terminal amino acids with –NH₂ group

Exopeptidases – break down peptide bonds on terminal amino acids

Aminopeptidases – break down amino acids with a free amino (-NH₂) group

Carboxypeptidases – break down amino acids with a free carboxyl (-COOH) group

Lipase - breaks down fats into fatty acids and glycerol

The food vacuoles of Protozoans represent the simplest form of digestive system:

•          Advantages:

allows the organism to achieve the optimum concentration of enzymes in a small space within the vacuole

•          Disadvantages:

1 The organism is restricted to food small enough to be ingested by phagocytosis

2 All enzymes operate within the vacuole without specialization of certain regions

3 Acidic and alkaline phases must be taken within the same vacuole at separate times

Digestion in Humans

A.     Digestion in the mouth

Mechanical digestion of food begins in the buccal cavity. The tongue manipulates the food during chewing with saliva produced from 3 pairs of salivary glands.

The human digestive system

See Figure 9 and 10:

Saliva contains:

1. Water – over 99%

2. Salivary amylase – enzyme

3. Mineral salts

   – maintain optimum pH for amylase

4. Mucin

    – bind food particles together and

       lubricates food for swallowing

•          5. Taste buds allow food to be selected.

The thoroughly chewed food (bolus) is passed to the back of the mouth for swallowing.

Swallowing and peristalsis

- pharynx leads to both trachea & oesophagus

When swallowing food, epiglottis closes entrance to trachea to prevent food going into lungs

See Figure 11 and 12:

Peristalsis - longitudinal & circular muscles contract & relax alternately to drive food down oesophagus, small intestine, large intestine & out of the anus as faeces

See Figure 13 and 14 and 15:

 Digestion in the stomach

•          The stomach is a muscular sac with a folded inner layer (gastric mucosa) with holes (gastric pits) lined with secretory cells which secrete gastric juice:

1. Water - the bulk of the secretion

2. Hydrochloric acid - secreted by the oxyntic cells

Functions:

1.      Gives an acid pH  to kill bacteria and activates enzymes in the stomach (pepsinogen & prorennin);

Initiates the hydrolysis of sucrose & nucleoproteins

See Figure 16A B and C:

2. Pepsinogen - secreted by the zymogen (chief cells) in an inactive form to pepsin

3. It is activated by HCl                             

4. Prorennin - secreted by zymogen cells; activated by HCl to rennin to coagulate milk by converting caseinogen (soluble protein in milk) to casein (insoluble)

5. Mucus - secreted by goblet cells to produce a protective layer to prevent autodigestion of the gastric mucosa (thus preventing ulcer). It also lubricates food in the stomach

What is peptic ulcer?

It is a disease in which a hole has been made in the mucous membrane lining the stomach or duodenum.

 Causes:

Too much HCl because of nervous tension, irregular meals, smoking, alcohols, lack of sleeps, etc.

Cure: Antacids

The churning and mixing action of the muscular stomach wall changes the bolus of food into a creamy fluid (chyme).

The chyme from any one meal takes 3-4 hours to be released little by little into the duodenum.

This provides a continuous supply of food for absorption throughout the period between meals.

Digestion in the small intestine

• Duodenum: for digestion
• Ileum: chiefly for absorption
• The walls of the small intestine are folded with villi which contain fibres of smooth muscle.
• These muscles regularly contract and relax to mix food and enzymes so as to facilitate absorption.

The global spread of obesity has been fueled in large part by the growing availability and popularity of the Western-style diet, which is characterized by foods with high contents of sugars, salt, and fat — particularly from processed foods and red meat.

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