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HUMAN NUTRITION
STUDY NOTES
Human nutrition is the provision to obtain the essential nutrients necessary to support life and health.
People can survive for two to eight weeks without food, depending on stored body fat, water and muscle
mass.
Poor nutrition is a chronic problem linked to poverty, poor nutrition understanding and practices, and
deficient sanitation and food security. Promoting good nutrition promotes growth, human development
and advances economic growth and eradication of poverty.
Nutritional science investigates the metabolic and physiological responses of the body to diet. It is the
science that deals with the foods which a living organism requires how it utilizes them and how it deals
with the waste products due to its activities. Part of the food consumed will be unusable (not assimilable)
and will have to be extruded (defecation).the remainder of the food is changed so that the organism can
utilize it will be absorbed. The many changes it undergoes after it has been absorbed is metabolismprocess of building up or breaking down .those changes that involve building up the tissues of the
organism are called anabolic and the process anabolism. Those that involve breaking down of food
substances are called catabolic.
Nutrition is the process of nourishing or being nourished, especially the process by which a living
organism assimilates food and uses it for growth and for replacement of tissues.
Food is any substance, solid or liquid, usually of plant or animal origin that contains or consists of
essential body nutrients, such as carbohydrates, fats, proteins, vitamins, or minerals, and is ingested and
assimilated by an organism to produce energy, stimulate growth, and maintain life.
Nutrients: Is a chemical component in food that an organism needs to live and grow or a substance used
in an organism's metabolism which must be taken in from its environment.
Nutrients can be organic or inorganic.

Organic nutrients include carbohydrates, fats, proteins (or their building blocks, amino
acids), and vitamins.

Inorganic nutrients such as dietary minerals and water.
Optimal nutrition means that a person is receiving and using the essential nutrients needed to maintain
health and well being at the highest possible level.
Malnutrition refers to the physical effects on the human body of a dietary intake inadequate in quantity
and/or quality. It results from a deficiency, excess or imbalance of nutrients.
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A balanced diet is one that provides an adequate intake of energy and nutrients for maintenance of the
body and therefore good health. A diet can easily be adequate for normal bodily functioning, yet may not
be a balanced diet. An ideal human diet contains fat, protein, carbohydrates, vitamins, minerals, water and
fibre all in correct proportions. These proportions vary for each individual because everyone has different
metabolic rates and levels of activity.
Malnutrition results from an unbalanced diet, this can be due to an excess of some dietary components
and lack of other components, not just a complete lack of food. Too much of one component can be as
much harm to the body as too little. Deficiency diseases occur when there is a lack of a specific nutrient,
although some diet related disorders are a result of eating an excess.
Importance of nutrition
The concern of why people eat and what nutrients they obtain from their food is of major importance.
People eat for various reasons:
a) For physiological needs - proper functioning of our bodies. These functions will only proceed
normally if the environment inside and outside the body cells is well controlled. Maintaining this
constant environment requires the input of energy and nutrients. If we are deprived off food for
long periods of time then the body has got to raw from its reserves and weight is lost.
b) Habit: eating by the clock e.g. 3 major meals per day
c) Psychological influences e.g. boredom, depression and for comfort.
d) Sensory appeal by appearance smell and taste we feel like eating.
e) Social influences- food can be used either to bring people together.
After eating food is digested by the enzymes of the GIT and broken down to release it basic constituentsthe nutrients. Without an adequate supply of nutrients optimal growth and development to adulthood
would not be possible. Nutrients are important in the body for:
a) Energy provision
b) Build and repair body tissues
c) Regulation of body processes.
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There are seven major classes of nutrients: carbohydrates, fats, dietary fiber, minerals, proteins, vitamins,
and water. They help give us energy to perform daily functions, as well as fuel to build tissues and grow.
These nutrients, however, are broken up into two distinct categories.
Macronutrients are substances that provide caloric value (calories) which are metabolized for energy.
Macronutrients are called “macro” because we need them in large amounts and because they are large in
molecular standards:
Micronutrients are nutrients we need in smaller quantities: hence, -micro, which is Greek for “small”.
These are just as important as macronutrients in the sense that we need them, but the key difference lies in
the sheer amount of the nutrients we need to digest.
Macronutrients are vital for every function we perform in the body because they provide us with fuel for
the body. Without that energy, our bodies would not be able to perform the constant upkeep required and
we would eventually perish.
We have three main macronutrients in our diet, each with their own caloric value. They are as follows:
i) Carbohydrate: 4 kcal/gm(4 kcal of energy per gram,)
ii) Fat: 9 kcal/gm (9 kcal per gram)
iii) Protein: 4 kcal/gm (4 kcal/gm)
The net energy from either depends on such factors as absorption and digestive effort, which vary
substantially from instance to instance.
Most foods contain a mix of some or all of the nutrient classes, together with other substances. Poor
health can be caused by a lack of required nutrients or, in extreme cases, too much of a required nutrient.
For example, both salt and water (both absolutely required) will cause illness or even death in too large
amounts.
Essential and non-essential nutrients
Nutrients are frequently categorized as essential or nonessential.
An essential nutrient is a nutrient that the body cannot synthesize on its own or not to an adequate amount
and must be provided by the diet. These nutrients are necessary for the body to function properly. The six
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essential nutrients include carbohydrates, protein, fat, vitamins, minerals and water.
Nonessential nutrients are those nutrients that can be made by the body; they may often also be absorbed
from consumed food. For humans, these include essential fatty acids, essential amino acids, vitamins,
and certain dietary minerals.
Non-essential substances within foods can still have a significant impact on health, whether beneficial or
toxic. For example, most dietary fiber is not absorbed by the human digestive tract, but is important in
digestion and absorption of otherwise harmful substances. The non-essential amino acids include
Alanine, Arginine, Asparagine, Aspartic acid, L-Cysteine, Glutamic Acid, Glutamine, Glycine, Histidine,
Ornithine, Proline, Selenocysteine, Serine, Taurine and Tyrosine.
Deficiencies and toxicity
An inadequate amount of a nutrient is a deficiency. Deficiencies can be due to a number of causes
including inadequacy in nutrient intake called dietary deficiency, or conditions that interfere with the
utilization of a nutrient within an individual. Some of the conditions that can interfere with nutrient
utilization include problems with nutrient absorption, substances that cause a greater than normal need for
a nutrient, conditions that cause nutrient destruction, and conditions that cause greater nutrient excretion.
Nutrient toxicity occurs when an excess of a nutrient does harm to an organism.
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