Nutrients Definition and Function


Definition and Function

Energy (Calorie)
  • Calorie is an energy measurement unit.
  • One calorie of heat energy is required to raise one gram of water by one degree Celsius.
  • 1,000 calories equal 1 kilocalorie (kcal), which is commonly used in measuring food energy.
  • Estimation of energy requirements for healthy individuals takes account of age, gender, body weight and activity level.
    Age    Men  Women    
   (year)     (kcal/day)
  1. The above values are based on an average body weight of 65kg for men and 55kg for women with a low activity level assumed.1
  2. Adjustment may be necessary for:
    • individuals who require weight management;
    • individuals with increased activity level;
    • pregnant or lactating women; and
    • individuals with illness, chronic diseases or in post-operative rehabilitation.
  • Protein is mainly used for growth and body repair.
  • When there is an insufficient intake of energy, protein would be broken down and used as body fuel, which may lead to protein-energy malnutrition.
  • One gram of protein provides 4 kcal.
  • Contributes 10%-15% of daily energy intake.2
  1. Protein intake of 0.83 g/kg body weight per day would be expected to meet the requirements of most (97.5%) of the healthy adult population.3
  • Meat
  • Milk
  • Eggs
  • Legumes
  • Carbohydrate is the major energy source in an average diet, which is also the preferred fuel.
  • One gram of carbohydrate provides 4 kcal.
  • When adequate carbohydrate is provided in the diet, protein would be spared for growth and repair.
  • Carbohydrate can be divided into three main types: monosaccharides, disaccharides and complex carbohydrate (starches and dietary fibres).
  • Contributes 55%-75% of daily energy intake.2,4
  1. A lower limit of around 50% total energy was accepted in the 2007 FAO/WHO Scientific Update.4
Monosaccharides and disaccharides:
  • Sugar
  • Syrup
  • Honey
  • Molasses
Complex carbohydrate:
  • Cereal, grains and their products (e.g. rice)
  • Starchy vegetables (e.g. potato)
Total fat
  • Fat is technically known as triglycerides, which is a class of lipids
  • Fat is a concentrated energy source, which provides 9 kcal for each gram of fat.
  • Fat carries fat-soluble vitamins, i.e. vitamin A, D, E and K.
  • Fat prevents heat loss in extreme temperatures and protects organs against shock.
  • Fat can be divided into saturated fat5 and unsaturated fat depending on their chemical structures.
  • Unsaturated fat can be further divided to mono- and poly-unsaturated fats.
  • Excess fat intake has been linked to major health problems, including an increased risk of heart disease, obesity, hypertension, diabetes and certain types of cancers.
  • Contributes 20%-35% of daily energy intake for adults.5
  1. A range of 15%-30% of total energy has also been recommended for preventing non-communicable diseaseses.2
  • Cooking fats and oils
  • Butter
  • Margarine
  • Salad dressings
  • Fried foods
  • High fat animal products
Dietary fibre
  • Dietary fibre is the indigestible part found in plant.
  • Traditionally it can be divided into two main types, i.e. soluble and insoluble.
  • Dietary fibre is important in promoting gastrointestinal health and providing other health benefits.
  • Not less than 25g per day.2
  • Cereals
  • Vegetables
  • Fruits
  • Sugars are simple carbohydrates, technically referring to monosaccharides and disaccharides.
  • Sugars are sources of energy.
  • Contributes not more than 10% of daily energy intake derived from free sugars.2,4
  1. Free sugars means all monosaccharides and disaccharides added to foods by the manufacturer, cook or consumer, plus sugars naturally present in honey, syrups and fruit juices.2,4
  • Honey
  • Syrups
  • Molasses
Saturated fat
  • Saturated fat is one type of fats.
  • It is easily recognised by its solid state at room temperature.
  • Excess saturated fat intake has been linked to increased risk of heart disease.
  • Contributes not more than 10% of daily energy intake.2,5
  • Lard
  • Butter
  • Animal fats
  • Coconut oil
  • Hydrogenated vegetable oil
Trans fat
  • Trans fat is also known as "trans fatty acids".
  • It is a specific type of fat formed when liquid oils are made into solid fats, a process known as "hydrogenation".
  • It is also naturally present in small amount in milk and fats of sheep and cattle.
  • Excess trans fat intake has been linked to increase risk of heart disease.
  • Contributes not more than 1% of daily energy intake.2,5
  • Hydrogenated vegetable oil
  • Margarine
  • Shortening
  • Foods using partially hydrogenated vegetable oil as ingredients (e.g. puffy pastry)
  • Cholesterol is one of the sterols. Sterol is a class of lipids.
  • It can only be found in animal source.
  • It involves in the formation of vitamin D, bile and some hormones.
  • Not all high fat food has high cholesterol content. Contrarily, some low fat foods have appreciable content of cholesterol; e.g. eggs and squids.
  • Not more than 300mg per day.2,5
  1. Cholesterol in the blood and tissues is derived from two sources: diet and endogenous synthesis.2
  • Egg yolk
  • Offals
  • Molluscs
  • Squids
  • Cuttlefish
  • Lard
  • Animal fat
  • Calcium is a mineral necessary for providing rigidity to the skeleton.
  • It also plays roles in nerve transmission, muscle contraction, and blood clotting.
  • Not less than 1000mg per day for adults.6
  • Milk and milk products
  • Green leafy vegetables
  • Fish with edible bones
  • Soy bean
  • Beancurd
  • Copper forms an essential component of enzymes and proteins in the human body.
  • It also involves in many metabolic reactions.
  • Women: Not less than 1.15mg and not more than 10.0 mg per day; Men: Not less than 1.35 mg and not more than 12.0 mg per day.7
  • Seafoods
  • Offals
  • Legumes
  • Nuts
  • Iron is necessary for metabolic functions such as oxygen transport and storage.
  • Insufficient intake may result in iron deficiency anaemia.
  • Women: Not less than 24.5mg per day; Men: Not less than 11.4mg per day.6
  1. The above values are derived basing on the assumption that the diet is consisting of moderate fish or meat in two main meals daily which is of moderate iron bioavailability.6
  • Liver and offal
  • Beef
  • Cereals
  • Pulses
  • Magnesium plays roles in protein synthesis, enzyme action, normal muscular contraction, nerve transmission, and maintaining bone health.
  • Women: Not less than 220mg per day; Men: Not less than 260mg per day.6
  • Green vegetables
  • Nuts
  • Beans
  • Shellfish
  • Manganese plays roles in facilitating enzyme functions.
  • A safe range of intake has not been proposed by WHO/FAO.6,7
  • Unrefined cereals
  • Nuts
  • Leafy vegetables
  • Tea
  • Phosphorus is essential in regulating the body acid-base balance.
  • It is also important for formation of bone and cells.
  • A safe range of intake has not been proposed by WHO/FAO.6,7
  • Milk and milk products
  • Meat
  • Fish
  • Processed foods
  • Potassium is essential in maintaining the body's electrolyte balance and normal cellular function.
  • Adequate potassium intake lowers blood pressure and reduces risk of stroke.
  • Sufficient intake of potassium can be achieved through adequate daily consumption of fruits and vegetables
  • 2.7g - 3.1g (70mmol - 80mmol) per day.2
  • Potatoes
  • Fruit
  • Vegetables
  • Milk and milk products
  • Nuts
  • Sodium is a major electrolyte in the body.
  • It helps in maintaining extracellular fluid balance.
  • Excess sodium intake has been linked to high blood pressure.
  • Not more than 2,000 mg (i.e. 5g of salt) per day.2
  • Salt
  • Soy sauce
  • Processed foods
  • Zinc is essential for growth and development, and testicular maturation.
  • It is also important for neurological function, wound healing and maintenance of the body's immune system.
  • Women: Not less than 4.9mg and no more than 35mg per day; Men: Not less than 7.0mg and no more than 45mg per day. 6,7
  1. The above values are derived basing on the assumption that the diet is of moderate zinc bioavailability which is characterised by mixed diets containing animal or fish protein.6,7
  • Lean red meat
  • Whole grain cereals
  • Legumes
Vitamin C
  • Vitamin C is a water soluble vitamin.
  • Insufficient dietary vitamin C can lead to scurvy.
  • Vitamin C helps iron absorption.
  • Not less than 45mg per day for adults.6
  • Fruits
  • Vegetables
  • Iodine is essential for the production of thyroid hormones which are responsible for normal growth and development.
  • Insufficient dietary iodine can lead to a range of adverse health effects, including goiter, hypothyroidism, etc..
  • Not less than 150 μg and not more than 1,000 μg per day for adults.6,7
  • Seaweeds
  • Seafoods
  • Eggs and egg products
  • Milk and milk products
  • Iodised salt
  • Alcohol has high energy density. One gram of alcohol provides 7 kcal.
  • Excess alcohol intake has been linked to major health problems, including an increased risk of heart disease, osteoporosis and certain types of cancers.
  • Consumption of alcoholic beverages is not recommended by World Health Organization (WHO). If consumed, do not exceed two units per day. 2
  1. One unit is equivalent to approximately 10 g of alcohol and is provided by one glass of beer, wine or spirits.2
  • Beer
  • Wine
  • Spirits
  • Other alcoholic beverages produced by the fermentation process of yeast, using ingredient such as fruit, barley and rye.


  1. United Nations University, World Health Organization, Food and Agriculture Organization of the United Nations. Human energy requirements: Report of a Joint FAO/WHO/UNU Expert Consultation. Rome: UNU/WHO/FAO; 2004.
  2. World Health Organization. Diet, nutrition and the prevention of chronic diseases: Report of a Joint WHO/FAO Expert Consultation. Geneva: WHO; 2003.
  3. World Health Organization, Food and Agriculture Organization of the United Nations, United Nations University. Protein and amino acid requirements in human nutrition: Report of a joint FAO/WHO/UNU expert consultation. Geneva: WHO; 2007.
  4. Mann J et al. FAO/WHO Scientific update on carbohydrates in human nutrition: Conclusions. European Journal of Clinical Nutrition, 61(Suppl 1), S132–S137; 2007.
  5. Food and Agriculture Organization of the United Nations. Fats and fatty acids in human nutrition: Report of an expert consultation. Rome: FAO; 2010.
  6. World Health Organization, Food and Agriculture Organization of the United Nations. Vitamin and mineral requirements in human nutrition. Second edition. Bangkok: WHO/FAO; 2004.
  7. World Health Organization. Trace elements in human nutrition and health. Geneva: WHO; 1996.