THE DIETARY FUELS

Dr Winarsi

THE DIETARY FUELS ARE: - CARBOHYDRATE - LIPID - PROTEIN

THE DIETARY FUELS IN THE GASTROINTESTINAL TRACT ARE HYDROLYZED AND ABSORBED INTO BLOOD STREAM,ENTER THE CELLS, OXIDIZED TO CO2 AND WATER WITH PRODUCTION OF ENERGY (ATP) AND HEAT.

• CO2 IS EXPIRED THROUGH THE LUNG.WATER IS EXCRETED IN URIN, SWEAT AND SECREYED INTO GASTROINTESTINAL TRACT.HEAT IS USED TO MAINTAIN BODY TEMPERATURE.ENERGY (IN THE FORM OF ATP) IS USED FOR ENERGY-CONSUMING PROCESSES IN THE BODY SUCH AS :

• BIOCHEMICAL REACTIONS

- MUSCLE CONTRACTION- ACTIVE TRANSPORT ACROSS

MEMBRANES- BIOSYNTHESIS OF MACROMOLECULES- NERVE TRANSMISSION IN THE ENERGY-CONSUMING PROCESSES, ATP ISCONVERTED BACK TO ADP AND INORGANIC PHOSPHATE (ATP-ADF CYCLE).

MOST OF THE OXIDATION OF FUELS OCCURS IN A SERIES OF REACTION TERMED THE TRICARBOXYLIC ACID CYCLE (CITRIC ACID CYCLE, KREB`S CYCLE).

• CARBOHYDRATE.

MAYOR CARBOHYDRATES IN THE HUMAN DIETS ARE: - STARCH - SUCROSE - LACTOSE - FRUCTOSE - GLUCOSE - INDIGESTIBLE FIBER

• DIGESTION CONVERTS THE LARGER CARBOHYDRATES TO MONOSACCHARIDES TO BE ABSORBED INTO THE BLOODSTREAMGLUCOSE IS THE PREDOMINANT SUGAR IN THE HUMAN BLOOD.

• LIPID.

THE LIPIDS IN THE DIET CONSIST MAINLY TRIACYL GLYSEROL (TRIGLYCERIDES).

THE DIGESTION PRODUCTS OF LIPID ( FATTY ACID, GLYCEROL. MONOACYL GLYCEROL, CHOLESTEROL,etc.) ARE

ABSORBED INTO THE BLOODSTREAM ANDLYMPH FLUID.

• PROTEIN.

DIGESTION CONVERTS PROTEIN TO AMINO ACIDS TOBE ABSORBED INTO THE BLOODSTREAM.

THE OXIDATION OF CARBOHYDRATE, LIPID AND PROTEIN TO CO2 AND H2O IN THE BODY PRODUCE APPROXIMATELY4 KCAL/G, 9 KCAL/G, 4KCAL/G RESPECTIVELY.

• BODY FUELS STORES.

CARBOHYDRATE. - GLYCOGEN IS THE CARBOHYDRATE STORE. - GLYCOGEN CONSIST OF GLUCOSE RESIDUE TO

FORM POLYSACCHARIDES. - GLYCOGEN IS LOCATED MAINLY IN LIVER AND

MUSCLE. - LIVER GLYCOGEN IS USED TO MAINTAIN BLOOD

GLUCOSE LEVELS BETWEEN MEALS. - MUSCLE GLYCOGEN SUPPLIES ENERGY FOR

THE MUSCLE CONTRACTION DURING EXERCISE

• LIPID.- TRIACYLGLYCEROL IS THE MAJOR FUEL STORE

LOCATED IN ADIPOSE TISSUES

• PROTEIN.- PROTEIN SERVES MANY IMPORTANT ROLES IN

THE BODY,NOT SOLELY A FUEL STORE LIKE FAT AND GLYCOGEN.

- MUSCLE PROTEIN IS ESSENTIAL FOR BODY MOVEMENT.

- OTHER PROTEIN SERVE AS ENZYMES, HORMONES, STRUCTURAL COMPONENT OF THE BODY (MEMBRANE, CONNECTIVE TISSUE, ORGANEL IN CELLS).

• FATE OF DIETARY CARBOHYDRATE.

- GLUCOSE IS THE MAJOR METABOLIC FUEL OF MAMMALS ( ATP-GENERATING PATHWAY ).

- GLUCOSE IS THE PRECURSOR FOR SYNTHESIS OF ALL THE OTHER CARBOHYDRATES IN THE BODY INCLUDING :

- GLYCOGEN FOR STORAGE. - RIBOSE AND DEOXYRIBOSE IN NUCLEIC

ACIDS - GALACTOSE IN LACTOSE IN MILK. - GLYCOLIPIDS. - IN COMBINATION WITH PROTEIN IN

GLYCOPROTEIN AND PROTEOGLYCAN.

• FATE OF DIETARY LIPID.

- FAT IS STORED IN ADIPOSE TISSUE. - FAT SERVES AS THERMAL INSULATOR IN

THE SUBCUTANEOUS TISSUE AND

AROUND CERTAIN ORGANS. - NONPOLAR LIPID ACT AS ELETRICAL

INSULATORS, ALLOWING RAPID

PROPAGATION OF DEPOLARIZATION

WAVES ALONG MYELINATED NERVES.

- COMBINATION OF LIPID AND PROTEIN (LIPOPROTEIN) AREIMPORTANT CELLULAR CONSTITUENTS, OCCURING BOTHIN THE CELL MEMBRANE AND IN THE MITOCHONDRIA ANDSERVING AS THE TRANSPORTING LIPID IN THE BLOOD.

- FATS ARE IMPORTANT DIETARY CONSTITUENTS BECAUSE THE FAT SOLUBLE VITAMINES AND ESSENTIAL FATTY ACIDSCONTAINED IN THE FAT OF NATURAL FOODS.

- CHOLESTEROL IS THE PRECURSOR OF BILE ACIDS, ADRENO-CORTICAL HORMONES, SEX HORMONES, D VITAMINES.

FUNCTION OF PROTEIN.

- CYTOSKELETON : INTERNAL PROTEIN NETWORK IN THE CELL, MAINTAIN CELLULAR SHAPE AND PHYSICAL INTEGRITY

- ACTIN AND MYOSIN FILAMENT FROM CONTRACTILE MACHINARY OF MUSCLE.

- CIRCULATING ANTIBODIES SEARCH OUT FOREIGN INVADERS.

- HEMOGLOBIN AS TRANSPORTER FOR OXYGEN.

- ENZYMES CATALYSE REACTION THAT GENERATE ENERGY,

SYNTHESIZE AND DEGRADE BIOMOLECULES.

- REPLICATE AND TRANSCRIBE GENE, PROCESS OF mRNA, etc. RECEPTORS ENABLE CELLS TO SENSE AND RESPONDS TO HORMONES AND OTHER ENVIRONMENTAL CUES.

- ROLES OF AMINO ACIDS : AS PRECURSOR OF HEME, PURIN, PYRIMIDINE, HORMON, NEUROTRANSMITTER AND BIOLOGICALLY ACTIVE PEPTIDES.