Why Do We Eat?

  • to satisfy hunger
  • for pleasure, eg the love of sweet or salty
  • for social significance (companionship, to impress, culture, traditions, availability–season and geography, positive and negative associations, cost)
  • concern for health to obtain food energy and the essential nutrients (specific chemical substances that we must have available in our body because they can’t be synthesized by our body cells or cannot be synthesized at a sufficient rate to satisfy our needs).
  • to promote growth and maintenance of body tissues
  • to regulate processes of the body

Body composition of an average 65 kg male:

Water, 61.5 %; protein, 17%; fat, 13.8 %, mineral, 6.2%; carbohydrate, 1.5%.

So, how do we use this information? Well,

  • drink at least six cups of water each day.
  • don’t forget to take your daily required amount of protein for without it you can’t even maintain muscle tone, let alone develop muscles. Meat, protein shakes, whatever, to meet your needs.
  • fat isn’t the enemy. Quality of fat and portion control are the key.
  • minerals (and vitamins) are needed and are often provided in food supplement capsules to compensate for over-processed food, nutrient poor soil, and toxic pesticides and herbicides on and in foods. Carbohydrates are found in fruits and vegetables as well as breads. Avoid over-indulging in the starchy foods because the colours in the fruits and vegetables indicate special nutrients your body can use is preferred. Excess weight gain often is related to too much starch in the diet as well as too many toxins which are stored in fat cells in attempts to protect body organs from damage.

Where Does It All Go?

Often when we try to improve our health nutritionally, we have “fast food” thinking. We want results right away. Sometimes we feel results quickly. Other times, it could take weeks to months before significant improvement. A quick review of the organisation of the human body may help you to visualize the various levels of the body the nutrients need to get to and repair, and that takes time.

In the order of increasing complexity, we have: atoms, ions and simple molecules, macromolecules (protein, nucleic acids, polysaccharides, long carbohydrate units), macromolecular complexes (cell ribosomes, chromosomes, etc.), cell organelles (major components of a cell – nucleus, mitochondria…), cells, tissues (muscle, adipose etc.), organs, organ systems (digestive etc.), living organism (human).


  • cell membrane (consists of protein and lipid, acts as barrier or fence),
  • nucleus (plural nuclei),
  • mitochondrion (plural mitochondria) to generate energy for the cell, to use by breaking down fuel molecule in presence of oxygen (controlled combustion),
  • chromosomes (specifies what a cell can be and do, a blueprint for specific proteins)
  • ribosomes (protein and nucleic acid)
  • cytoplasm (medium within cell membrane: a viscous liquid like material containing dissolved ions, metabolic intermediates and enzymes wherein many of cell’s chemical reactions occur


  • composed of a collection of cells
  • adipose tissue (fat tissue – adiposites)
  • muscle tissue
  • role of connective tissue to bind cells in tissues and act as a support system
  • blood vessels and nerves run in the connective tissue

Digestion and Absorption


  • a mechanical and chemical process that reduces complex food molecules to simpler, absorbable substances
  • begins in mouth with chewing creating a bolus with the salivary glands distributing salivary amylase (acts on starch)
  • goes down esophagus, the bolus passes to stomach
  • rapid strong churning, food mixed with gastric juice turning the bolus into chyme, very acidic, some protein digestion
  • pylorus (pyloric valve) allows food into small intestine 
  • small intestine, a coiled tube 9 feet by 1 1/2 inches, inner folds, three sections: 8″ duodenum, 3′ jejunum, 5′ ileum
  • villi on the bowel wall: millions of projections, covered with epithelial cells
  •  pancreatic, intestinal and gall bladder secretions enter small intestine, neutralize acid chyme from stomach making it slightly alkaline
  • secretions contain enzymes which attack specific food constituents
  • the continual turnover of intestinal cells are digested as well. Said to be a six week turnover.
  • other terms: lumen, microvilli, brush border


  • occurs primarily in the small intestine, and some in the stomach
  • nutrients pass into epithelial cells of villi by passive diffusion (down the concentration gradient), facilitated diffusion (carrier molecules through membrane down concentrated gradient), active transport (against concentration gradient requiring energy and a carrier substance – eg. calcium, glucose and some amino acids)
  • water soluble nutrients are picked up by capillaries in the villi where the nutrients eventually pass via the portal blood to the liver
  • lipid soluble nutrients are taken up by the lacteals by-passing the liver, and enter the general circulation via the thoracic duct
  • colon 4′ by 2.5 inches and consists of the ascending, transverse and descending segments
  • colon re-absorbs back much of the water from the 7 litres of digestive secretions, and colon also a storage site for fecal matter….then of course there is the circulatory system not entered into here.

Stay tuned for blog on metabolism. Hopefully it won’t be like watching cement dry.


University of Waterloo Kinesiology notes (a long time ago…), Waterloo, Ontario, Canada

Janet Wiebe