Nutrition

What you'll learn

Nutrition is a fundamental topic in CXC CSEC Human and Social Biology that examines how the body obtains and uses nutrients for growth, energy, and maintenance. This guide covers the six classes of nutrients, their functions and sources, balanced diets appropriate for Caribbean populations, and the consequences of malnutrition. You will learn to analyse food tests, interpret dietary requirements, and apply nutritional knowledge to real-world scenarios common in examination questions.

Key terms and definitions

Nutrient — a chemical substance obtained from food that is necessary for life processes including growth, energy production, repair, and regulation of body functions.

Balanced diet — a diet that contains all six classes of nutrients in the correct proportions, along with adequate water and dietary fibre, to maintain good health.

Malnutrition — a condition resulting from an unbalanced diet where certain nutrients are deficient, in excess, or in wrong proportions.

Deficiency disease — an illness caused by the lack or insufficient intake of a specific nutrient over an extended period.

Basal metabolic rate (BMR) — the minimum amount of energy required to maintain essential life processes in the body at rest.

Macronutrients — nutrients required by the body in large amounts, including carbohydrates, proteins, and lipids.

Micronutrients — nutrients required by the body in small amounts, including vitamins and mineral salts.

Dietary fibre — indigestible plant material (roughage) that aids in the movement of food through the digestive system and prevents constipation.

Core concepts

The six classes of nutrients

Carbohydrates

Carbohydrates are organic compounds composed of carbon, hydrogen, and oxygen. They serve as the primary source of energy for the body.

Types and sources:

• Simple sugars (monosaccharides): glucose, fructose found in fruits and honey
• Double sugars (disaccharides): sucrose in sugar cane, lactose in milk, maltose in germinating seeds
• Complex carbohydrates (polysaccharides): starch in cassava, yam, sweet potato, breadfruit, rice, and plantain; glycogen stored in liver and muscles

Functions:

• Provide energy (1 gram yields 17 kJ or 4 kcal)
• Glucose is essential for cellular respiration
• Excess converted to glycogen or fat for storage
• Cellulose provides dietary fibre

Caribbean food sources: Dasheen, eddoes, green banana, cornmeal, provision grounds produce

Proteins

Proteins are large organic molecules composed of carbon, hydrogen, oxygen, nitrogen, and sometimes sulfur. They consist of chains of amino acids.

Types:

• Complete proteins contain all essential amino acids (animal sources)
• Incomplete proteins lack one or more essential amino acids (plant sources)

Functions:

• Growth and repair of tissues
• Formation of enzymes, hormones, and antibodies
• Secondary energy source (1 gram yields 17 kJ or 4 kcal)
• Component of haemoglobin, plasma, and muscle tissue

Caribbean food sources: Red beans, pigeon peas, saltfish, chicken, eggs, cow's milk, cheese, soybeans, peanuts

Lipids (Fats and Oils)

Lipids are composed of carbon, hydrogen, and oxygen, but with proportionally less oxygen than carbohydrates.

Types:

• Saturated fats (solid at room temperature): animal fats, coconut oil
• Unsaturated fats (liquid at room temperature): vegetable oils, fish oils

Functions:

• Concentrated energy source (1 gram yields 38 kJ or 9 kcal)
• Insulation to reduce heat loss
• Protection of delicate organs
• Formation of cell membranes
• Storage of fat-soluble vitamins (A, D, E, K)
• Source of essential fatty acids

Caribbean food sources: Coconut oil, avocado, cooking oil, butter, margarine, fatty fish like kingfish and tuna

Vitamins

Vitamins are organic compounds required in small amounts for specific metabolic functions.

Vitamin A (Retinol):

• Sources: Liver, milk, butter, egg yolk, yellow/orange fruits (mango, papaya, pumpkin), green leafy vegetables (callaloo)
• Functions: Formation of visual pigment in retina, healthy skin and mucous membranes, normal growth
• Deficiency: Night blindness, xerophthalmia, dry skin, retarded growth

Vitamin B Complex (including Thiamine - B₁):

• Sources: Whole grains, yeast, liver, meat, nuts, legumes
• Functions: Cellular respiration, healthy nervous system
• Deficiency: Beri-beri (nerve damage, muscle weakness), pellagra

Vitamin C (Ascorbic acid):

• Sources: Citrus fruits (oranges, limes, grapefruits), tomatoes, guava, sorrel, green peppers
• Functions: Formation of connective tissue, healthy gums and teeth, wound healing, iron absorption
• Deficiency: Scurvy (bleeding gums, poor wound healing, loose teeth, anaemia)

Vitamin D (Calciferol):

• Sources: Fish liver oils, egg yolk, fortified milk; synthesized in skin by sunlight
• Functions: Absorption and use of calcium and phosphorus for bone and tooth formation
• Deficiency: Rickets in children (soft, deformed bones), osteomalacia in adults

Mineral salts

Mineral salts are inorganic elements needed in varying amounts for body functions.

Calcium:

• Sources: Milk, cheese, sardines with bones, green leafy vegetables
• Functions: Formation of bones and teeth, blood clotting, muscle contraction, nerve impulse transmission
• Deficiency: Rickets, osteoporosis, poor blood clotting, tetany

Iron:

• Sources: Liver, red meat, dark green vegetables (callaloo), red beans, dried fruits
• Functions: Component of haemoglobin for oxygen transport, component of enzymes
• Deficiency: Anaemia (fatigue, pale skin, shortness of breath)

Iodine:

• Sources: Seafood, iodized salt, sea vegetables
• Functions: Component of thyroxine hormone controlling metabolic rate
• Deficiency: Goitre (enlarged thyroid gland), cretinism in infants

Phosphorus:

• Sources: Milk, cheese, meat, fish, whole grains
• Functions: Bone and tooth formation, component of ATP, DNA, and RNA
• Deficiency: Rare but affects bone and tooth development

Water

Water comprises 60-70% of body mass and is essential for all life processes.

Functions:

• Medium for chemical reactions
• Transport of substances in blood and lymph
• Temperature regulation through sweating
• Removal of metabolic waste
• Lubrication of joints
• Maintenance of turgidity in cells

Requirements: Approximately 2-3 litres daily from drinks and food

Balanced diet and dietary requirements

A balanced diet must provide:

• All six nutrient classes in appropriate proportions
• Adequate energy for daily activities and BMR
• Sufficient water and dietary fibre

Factors affecting dietary requirements:

Age:

• Infants and children: High protein for growth, calcium for bone development, energy for activity
• Adolescents: Increased protein and calcium during growth spurts, iron for menstruating females
• Adults: Balanced intake to maintain health and support work activities
• Elderly: Lower energy needs, calcium to prevent osteoporosis, vitamin D

Sex:

• Males generally require more energy due to larger body size and muscle mass
• Females require iron to replace losses during menstruation, extra calcium during pregnancy and lactation

Activity level:

• Manual labourers (farmers, construction workers) require more carbohydrates and fats for energy
• Sedentary workers (office employees) need less energy to prevent obesity
• Athletes require increased carbohydrates, proteins, and water

Physiological state:

• Pregnancy: Extra protein for fetal growth, calcium and iron, folic acid
• Lactation: Increased protein, calcium, vitamins, and water for milk production
• Illness: Additional protein for tissue repair, vitamins to boost immunity

Climate:

• Hot Caribbean climate increases water requirements due to perspiration
• Less energy from fats needed compared to cold climates

Malnutrition and deficiency diseases

Protein-energy malnutrition (PEM):

Kwashiorkor:

• Cause: Severe protein deficiency despite adequate energy intake
• Common in Caribbean children after weaning onto starchy diet
• Symptoms: Oedema (swollen abdomen, feet, face), discoloured hair, fatty liver, skin lesions, growth retardation, apathy
• Prevention: Adequate protein from legumes, eggs, fish, milk

Marasmus:

• Cause: Severe deficiency of both protein and energy
• Symptoms: Extreme wasting of muscles and fat, "skin and bones" appearance, low weight, stunted growth, no oedema
• Prevention: Adequate total food intake

Obesity:

• Cause: Excessive energy intake exceeding energy expenditure over prolonged periods
• Complications: Type 2 diabetes, hypertension, heart disease, joint problems
• Common in Caribbean countries with increased consumption of processed foods
• Prevention: Balanced diet, regular exercise, portion control

Anaemia:

• Iron-deficiency anaemia most common in Caribbean region
• Symptoms: Fatigue, pale skin and mucous membranes, shortness of breath, dizziness
• Prevention: Iron-rich foods (liver, red beans, callaloo), vitamin C to enhance absorption

Food tests

Food tests identify the presence of specific nutrients in food samples.

Starch test:

• Reagent: Iodine solution (brown/yellow)
• Positive result: Blue-black colour
• Example: Testing cassava, yam, or breadfruit

Reducing sugar test (Benedict's test):

• Reagent: Benedict's solution (blue)
• Method: Heat food solution with Benedict's solution
• Positive result: Colour change from blue → green → yellow → orange → brick-red precipitate
• Tests for glucose, fructose, maltose

Protein test (Biuret test):

• Reagents: Sodium hydroxide solution + copper sulfate solution
• Positive result: Purple/violet colour
• Example: Testing cow's milk or egg white

Lipid test (Grease spot test):

• Method: Rub food on paper, allow to dry
• Positive result: Translucent grease spot remains
• Alternative: Ethanol emulsion test (white cloudy emulsion when added to water)

Vitamin C test:

• Reagent: DCPIP (blue dye)
• Method: Add food extract drop by drop to DCPIP
• Positive result: Blue colour decolorizes to colourless/pale pink
• Tests for ascorbic acid in citrus fruits, sorrel

Worked examples

Example 1: Dietary analysis question

Question: A 14-year-old Caribbean female athlete trains for 2 hours daily. Her diet consists mainly of rice, fried plantain, and small portions of chicken twice weekly.

(a) Identify TWO nutrients likely to be deficient in this diet. (2 marks)

(b) Explain why EACH nutrient identified is important for this individual. (4 marks)

Answer:

(a)

• Iron (1 mark)
• Calcium (1 mark) [Accept also: protein, vitamin C, water]

(b)

• Iron is needed to form haemoglobin in red blood cells (1 mark) which transports oxygen to muscles during exercise/prevents anaemia (1 mark)
• Calcium is required for bone development/growth during adolescence (1 mark) and for muscle contraction during athletic training (1 mark)

Example 2: Deficiency disease question

Question: A child in rural Jamaica shows signs of oedema, has discoloured reddish hair, and appears apathetic. The child's diet consists mainly of green bananas and yam with little protein.

(a) Name the deficiency disease affecting this child. (1 mark)

(b) State TWO foods available in Jamaica that could prevent this condition. (2 marks)

(c) Explain why this disease commonly occurs after weaning. (2 marks)

Answer:

(a) Kwashiorkor (1 mark)

(b) Any TWO from: Red beans/kidney beans, pigeon peas, eggs, fish/saltfish, chicken, milk, cheese, peanuts (2 marks - 1 each)

(c) After weaning, children transition from protein-rich breast milk (1 mark) to starchy staple foods like yam, banana, cassava which are low in protein (1 mark)

Example 3: Balanced diet question

Question: Explain why a pregnant woman in Trinidad requires a different diet compared to when she was not pregnant. (6 marks)

Answer:

• Increased protein required for growth and development of the fetus/formation of fetal tissues (1 mark)
• Extra protein needed for growth of placenta and uterus (1 mark)
• Additional calcium needed for fetal bone and tooth development (1 mark)
• Increased iron requirement to prevent anaemia/produce haemoglobin for increased blood volume (1 mark)
• Extra folic acid required to prevent neural tube defects in the developing fetus (1 mark)
• More energy needed to support metabolic demands of pregnancy/growth of fetus (1 mark)

Common mistakes and how to avoid them

• Confusing kwashiorkor and marasmus: Remember kwashiorkor shows oedema (swelling) and results from protein deficiency specifically, while marasmus shows extreme wasting and results from overall energy and protein deficiency with no oedema.

• Mixing up vitamin deficiency diseases: Create a table linking each vitamin to its specific deficiency disease (A → night blindness, C → scurvy, D → rickets, B₁ → beri-beri) and memorize Caribbean food sources for each.

• Stating functions too vaguely: Instead of writing "protein is for growth," specify "protein provides amino acids for synthesis of new cells and tissues during growth" or "protein is required for repair of damaged tissues."

• Forgetting to use Caribbean examples: When questions ask for food sources, use regional foods (callaloo, dasheen, ackee, saltfish, provision) rather than only generic answers to demonstrate contextual knowledge.

• Confusing energy values: Remember the correct values: carbohydrates and proteins yield 17 kJ/g (4 kcal/g) while lipids yield 38 kJ/g (9 kcal/g). Lipids provide more than twice the energy.

• Incomplete food test descriptions: Always state the initial colour of the reagent, the method (especially if heating is required), and the positive result colour change completely. For Benedict's test, mention heating is essential.

Exam technique for Nutrition

• Command words matter: "State" requires brief factual answers (1 mark each); "Explain" requires reasons or mechanisms (usually 2 marks); "Describe" needs characteristics or processes in sequence. Allocate your detail accordingly.

• Use mark allocations strategically: If a question is worth 4 marks, provide at least 4 distinct points. For a 6-mark "explain" question, aim for 3 points with explanations (2 marks each: statement + elaboration).

• Structure dietary requirement answers systematically: Use the framework: state the nutrient → explain its function → link to the specific needs of the individual's age/sex/activity level/condition. This ensures comprehensive responses.

• Draw clear tables for comparisons: When comparing kwashiorkor and marasmus, or different dietary needs, tabular format with clear headings earns marks for organization and ensures you cover all required points.

Quick revision summary

Nutrition involves six essential nutrient classes: carbohydrates and lipids for energy; proteins for growth and repair; vitamins and minerals for regulation; water for all processes. A balanced diet provides these in correct proportions based on age, sex, activity, and physiological state. Deficiency diseases include kwashiorkor (protein deficiency with oedema), marasmus (protein-energy malnutrition), scurvy (vitamin C), rickets (vitamin D/calcium), and anaemia (iron). Caribbean diets utilize provisions, legumes, callaloo, and fruits to meet nutritional needs. Food tests identify nutrients using specific reagents and colour changes.