Nutrition

Mr. Arvind Kumar

Introduction

  1. Nutrition is taking in food and converting it into energy and other vital nutrients required for life.
  2. Provide the necessary energy and biomolecules for carrying out various body functions.
  3. All the organisms in the universe need nutrients for proper growth and functioning, but they show divergence in how they fulfil their demand.
  4. Some animals feed on inorganic compounds to meet nutrient requirements, while others utilize complex compounds.

 

Importance of nutrition

  1. Keeps us healthy & free of disease and psychological and behavioural issues.
  2. Nothing heals the body more than the body itself; for this reason, we need to nourish our cells properly.
  3. Boost the immune system
  4. Delay the effects of ageing
  5. Help beat tiredness and fatigue
  6. Enhance ability to concentrate and possibly alter mood
  7. Keep one active and fit into old age
  8. Ward off serious illnesses like heart disease, certain cancers, mature-age onset diabetes, gallbladder disease, etc.

 

Types of Nutrition

  • Autotrophic mode
  • Heterotrophic mode

Nutritional Importance of Carbohydrates

  1. Available or digestible carbohydrate
  2. Unavailable or undigestible carbohydrates.
    • The digestible carbohydrates are a major source of food energy, yielding 4 kcal/gm and providing about 50 to 70% of the energy requirement. In addition, these carbohydrates have a protein-sparing effect.
    • Unavailable or undigestible carbohydrates provide dietary fibre.

 

Role of carbohydrates in the body

  • The major source of energy
  • Absolute requirement by the brain: The brain has an obligatory requirement for glucose. It is estimated that it utilises about 100 g of glucose per day.
  • Protein-sparing action: Carbohydrates spare proteins to maintain the body’s structure by acting as the major energy source.
  • Synthesis of nucleic acids: Pentose sugars, the integral components of nucleic acids, are derivatives of carbohydrates.
  • Synthesis of proteins: The intermediates of carbohydrate metabolism (e.g., keto acids) are precursors for synthesising non-essential amino acids.
  • Synthesis of fat: Excess carbohydrate is converted into fat and stored as TAG.
  • Oxidation of fat: Acetyl CoA, the end product of fatty acid oxidation, requires oxaloacetate for further processing via the Krebs cycle. Since oxaloacetate is derived from carbohydrates, it can be deduced that carbohydrates are required to use fats.
  • Nutritional significance of non-digestible carbohydrates: Though the body cannot utilise them, they are important for maintaining health.
  • Cell growth: They play a role in cell growth, cell-to-cell recognition, interaction and adhesion. They lubricate skeletal joints.
  • Taste: Carbohydrates impart sweetness and palatability to food.

 

Dietary fiber

  • Dietary fiber is the name given collectively to indiges­tible carbohydrates present in foods. These carbohy­drates consist of:

  –  Cellulose

  –  Pectin

  –  Gums

  –  Mucilages.

  • The dietary fiber is not digested by the enzyme of the human gastrointestinal tract, where most of the other carbohydrates like starch, sugars are digested and absorbed.
  • Plant foods are the only sources of dietary fiber. It is found in vegetables, fruits, and grains.

 

Importance of fiber

  • Water holding capacity
  • Adsorption of organic molecules
  • It increases stool bulk
  • Hypoglycemic effect of fiber
  • Hypocholesterolemic effects of fiber

 

Significance of dietary fiber

High fiber diet reduces the  risk of:

  • Coronary heart disease (CHD)
  • Colon cancer
  • Diabetes
  • Diverticulosis (inflammation in the wall of the large intestine)
  • Haemorrhoids (piles).

 

Glycemic Index (GI)

  • The glycemic index is defined as the incremental area under the GTT curve after eating 50 g of the test meal (food item to be assessed) compared to the incremental area of the GTT curve with an equal quantity of the reference meal (50 g glucose).

Nutritional importance of lipids

  • Dietary fats are high energy-yielding nutrients that provide 35 to 45% of the caloric intake. Fat yields 9 kcal/gm.
  • Besides satisfying metabolic energy needs, dietary fat has two essential functions.
    1. A vehicle for the absorption of fat-soluble vitamins
    2. Supply essential fatty acids
  • Dietary lipid also increases the palatability of food and produces a feeling of satiety.

 

Nutritional functions of lipids

  • Supply triacylglycerols, which normally constitute about 90% of dietary lipids and are a concentrated fuel source for the body.
  • Provide essential fatty acids and fat-soluble vitamins (A, D, E and K).

 

Function of Essential Fatty Acids

  • Essential fatty acids are the structural components of biological membranes.
  • Participate in the transport and utilization of cholesterol.
  • Prevent fat accumulation in the liver.
  • Required for the synthesis of prostaglandins.
  • Maintain proper growth and reproduction of the organisms.

 

Nutritional Importance of Proteins

Amino acids and their nutritional requirements

Nitrogen Balance

 

  • Nitrogen equilibrium: – In normal adults, nitrogen intake = nitrogen excretion. The subject is said to be in nitrogen equilibrium or balance.
  • Positive nitrogen balance: – In this, > nitrogen intake = nitrogen excretion, i.e., nitrogen intake is more than excretion. This occurs in growing infants and pregnant women.
  • Negative nitrogen balance: – In this, < nitrogen intake = nitrogen excretion, i.e. nitrogen output exceeds input, this occurs during serious illness and major injury and trauma, in advanced cancer and following failure to ingest adequate or sufficient high-quality protein, e.g. in kwashiorkor and marasmus. If the situation is prolonged, it will ultimately lead to death.

 

Assessment of Protein Quality

The quality of a protein is assessed by comparison to the “reference protein”, usually egg protein. Four methods of assessment of protein quality are:

  1. Biological value (BV).
  2. Net protein utilization (NPU)
  3. Protein efficiency ratio (PER)
  4. Chemical score or amino acid

Biological Value (BV)

  • Biological value is the ratio of nitrogen retained in the body and nitrogen absorbed.

  • Though BV is a widely used index to express the nutritional value of proteins, it has certain inherent defects. It does not consider the nitrogen lost during digestion, and hence, it may not provide an accurate nutritional assessment of proteins.

 

Net Protein Utilisation (NPU)

  • This is a better nutritional index compared to BV as it takes into account the factor of digestion.

  • It is the ratio between the nitrogen retained in the body to total nitrogen ingested.

 

Protein Efficiency Ratio (PER)

  • The quality of a protein can be determined by its ability to produce growth. It is the assessment of weight gain per gram of protein taken.

  • PER is the measurement of the ability of a protein to promote growth in an animal.

 

Chemical score

  • It measures the concentration of each essential amino acid in the test protein, which is then compared with the reference protein.

  • This chemical assessment mode does not consider the digestibility of dietary proteins. Hence, biological methods based on growth or nitrogen (N) retention are used to determine the overall quality of a protein.

 

Balanced Diet

  • A balanced diet is composed of a variety of foods that contain all the essential nutrients, such as carbohydrates, fats, proteins and micronutrients, in the right proportions.

Principles of prescribing a diet

  • Choose a diet with plenty of whole grains, vegetables fruits and green leafy foods which contain both digestible carbohydrates and dietary fibre.
  • Ideally, 55%–65% of calories can be obtained from a carbohydrate diet.

Basal Metabolic Rate

  • BMR is defined as the minimum amount of energy required by the body to maintain life at complete physical and mental rest.
  • While determining the BMR, the person should be awake and post-absorptive.

Significance of BMR

  • BMR is the major determinant of energy requirements and hence plays a role in the calculation of the calorie requirements of an individual.
  • It prescribes diets for individuals and diet planning for communities.
  • BMR can be used for assessing the functioning of the thyroid gland.
  • BMR may increase in leukemias, polycythemia and hypertension.

Factors affecting BMR

  • Age
  • Gender
  • Body surface area
  • Built
  • Climate
  • Physical activity and exercise
  • Starvation
  • Fever
  • Hormones
  • Stress

 

Metabolic Syndrome

  • This is an associated condition with diabetes characterised by insulin resistance.
  • It is usually associated with a sedentary lifestyle, obesity, alcoholism, elevated TAG levels, low HDL levels, hyperuricemia, microalbuminuria, hypertension and polycystic ovarian disease (PCOD).
  • Mostly among the urban middle-class of developing countries
  • The affected persons cannot effectively metabolise glucose despite normal insulin levels.
  • Such individuals are at a high risk of developing atherosclerosis, coronary heart disease and type 2 diabetes.
  • Corrective measures include weight reduction, moderate exercise and low-fat intake

 

Protein-Energy Malnutrition (PEM)

PEM is mostly seen in young children due to malnutrition. The clinical picture of PEM is manifested in two forms.

Kwashiorkor: Kwashiorkor represents protein malnutrition in children characterised by oedema.

Marasmus: Marasmus results from severe malnutrition in infants with severe muscle wasting.

Nutritional anaemias

  • Microcytic anaemia—most common, with reduced RBC size. Occurs due to the deficiency of iron, copper and pyridoxine.
  • Macrocytic anaemia—RBCs are large and immature. Mostly due to the deficiency of folic acid and vitamin B12.
  • Normocytic anaemia—The size of the RBC is normal, but the quantity in the blood is low. Mostly found in protein-energy malnutrition

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