Macronutrients

Macronutrients

1. Carbohydrates

   • Classification of carbohydrates:
     • Monosaccharide e.g. glucose and fructose
     • Disaccharides e.g. sucrose, maltose and lactose
     • Polysaccharides e.g. starch and glycogen
     • Non starch polysaccharides (Fiber) : components of dietary plants that cannot be broken down by human digestive enzymes, e.g. cellulose and pectin.
   • Importance of carbohydrates:
     • A. It is the major source of energy in most of the tissues, allowing protein to be used for growth and maintenance (protein- sparing)
     • B. The only source of energy for RBCs, and is also needed for proper brain function.
     • C. A small amount is needed to prevent ketosis.
     • Fiber has several beneficial effects on health.
   • dietary fibers
     • Several different types
     • Each has different chemical and physical properties, and different effects on body function or metabolism
     • Some are partially broken down by intestinal bacteria.
     • Those that have been shown to have beneficial effects in humans are termed functional fiber
     • Recommended intake (AI) for total fiber:
       • 38 g/d for men ages 14 - 50 y
       • 25 g/d for women ages 19 - 50 y
   • physiological effects of undigested CHO
     • 1. Increase fecal weights (Soluble fibre is readily fermented Leading to increased bacterial population, but Insoluble fibers directly increase weight, thus more important as a laxative )
     • 2. Effect on intestinal transit time:
       • -The intestinal transit time is the time taken for a meal to pass from the mouth to the anus
         • -Colonic transit takes approximately ten times as long as mouth-to-caecum transit
           • -Mouth-to-caecum transit time is increased by viscous polysaccharides leading to:
             • a. prolonged gastric emptying resulting in greater satiety
             • b. delay in the absorption of low-molecular-weight nutrients, e.g. glucose
             • -Colonic transit is reduced by insoluble fibers
     • 3.Effect on serum Cholesterol (mainly sol. fibers)
       • - Physiological studies show that the addition of certain plant fibres to the diet is accompanied by significant reductions in serum cholesterol concentrations
         • The reduction in cholesterol is seen mostly in the low denisty lipoprotien function (LDL) , and is accompined be decrease in the cholesterol content of the liver, aorta, and other tissues

2. Fats.

3. Proteins.

4. Water

5. Carbohydrates and Fats are the principal energy sources.

6. Dietary proteins serve many roles including energy production.

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