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Food and Feeding
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Covers why animals eat, described in proximate and ultimate reasons, and rewards.
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Comparative Anatomy and Physiology of AnimalsLecture 15 Food and Feeding 08/12/20
Why do animals eat?
- Ultimate explanation: to provide the nutrients needed to maintain the body and to perform
processes/activities.
- Proximate explanation: homeostasis, nerve signals, hormones, hunger, hedonic rewards.
Ultimate explanation
All foods have the same basic constituents
- Around 90% of the dry weight of food is comprised of protein, Macronutrients provide energy:
carbs and fats, and these provide the energy required by the Protein 17kJ (4.1 kcal) per gram
Carbohydrate 17kJ (4.1 kcal) per gram
animal for metabolism.
Fat 37kJ (8.8 kcal) per gram
- Macronutrients provide the building blocks for growth, repair
Ethanol 29kJ (7.0 kcal) per gram
and defence.
- Proteins: large complex molecules comprised of long chains of amino acids linked together
by peptide bonds. There are 23 amino acids that can be arranged in any
combination to give an almost infinite variety of naturally occurring
proteins. Essential amino acids – AAs that are unable to be synthesised at
a sufficient rate for optimal performance. (NE= Non-essential,
E=Essential).
- Lipids: they are the most concentrated source of energy. Glycerol
backbone, 3 chains of fatty acids. Provider of EFA’s (Essential Fatty Acids)
absorption, storage and transport of fat-soluble vitamins. EFAs are
important for kidney function and reproduction. Essential cell membrane
component and are needed for prostaglandin synthesis. Fats are also
important for the absorption, storage and transport of fat-soluble
vitamins (A, D, E and K). Type of fat important to health, saturated fats
are solid at room temperature and are more prone to forming plaques
and blocking arteries, and as such should be limited in the diet. They also
contribute to the biosynthesis of LDL or ‘bad cholesterol’. Mono and polyunsaturated fats
are an important part of the diet.
- Carbohydrates: classified as absorbable these are the monosaccharides: glucose, fructose
and galactose. Digestible, the disaccharides, such as sucrose, and the polysaccharide, starch.
These are broken down by enzymes in the mouth and gut into monosaccharides that can be
absorbed. Carbohydrates that cannot be digested are transported to the intestine where gut
flora break them down by fermentation into short chain fatty acids. These can then be
absorbed by the gut cells and used in metabolism and other processes. These include soluble
“fibre” or NSPs such as pectin, gums and hemicelluloses. Non-fermentable carbs include
insoluble fibre such as cellulose. Carbs that cannot be fermented pass through the gut
undigested. Fibre is especially important in increasing the transit rate through the gut and
reducing constipation.
Functions of carbohydrates
- Primary energy source, even for carnivores.
- Insulin regulates blood glucose levels.
- Storage as glycogen.
- Used to build amino acids and fatty acids.
- Protects proteins.
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