What you'll learn
This topic examines how the human body requires specific nutrients in correct proportions to maintain health, and what happens when dietary intake becomes inadequate or excessive. CXC CSEC Integrated Science papers frequently test nutrient classification, functions, deficiency diseases, and the ability to plan appropriate diets for different population groups across the Caribbean region.
Key terms and definitions
Balanced diet — a diet containing all essential nutrients (carbohydrates, proteins, fats, vitamins, minerals, water, and dietary fibre) in the correct proportions to meet the body's metabolic needs and maintain optimal health.
Malnutrition — a condition resulting from an unbalanced diet where one or more nutrients are either deficient, in excess, or in wrong proportions; includes both undernutrition and overnutrition.
Deficiency disease — a disorder caused by the prolonged lack of a specific nutrient in the diet, such as scurvy from vitamin C deficiency or kwashiorkor from protein deficiency.
Macronutrients — nutrients required by the body in large amounts (carbohydrates, proteins, and fats) that provide energy and structural materials for growth and repair.
Micronutrients — nutrients needed in small quantities (vitamins and minerals) that regulate metabolic processes but do not provide energy directly.
Basal Metabolic Rate (BMR) — the minimum amount of energy required to maintain essential life processes such as breathing, circulation, and cell metabolism while at complete rest.
Body Mass Index (BMI) — a numerical value calculated from a person's mass and height (BMI = mass in kg ÷ height² in m²) used to classify weight status and assess health risks.
Nutrient density — the concentration of essential nutrients relative to the energy content of a food; nutrient-dense foods provide substantial vitamins and minerals with relatively few calories.
Core concepts
Classification and functions of nutrients
The human body requires six main classes of nutrients, each performing specific physiological roles:
Carbohydrates
- Primary energy source providing 17 kJ per gram
- Stored as glycogen in liver and muscles for short-term energy reserves
- Simple carbohydrates: glucose, fructose, sucrose found in fruits, sugar cane (major Caribbean crop)
- Complex carbohydrates: starch in breadfruit, cassava, yam, green banana, sweet potato
- Dietary fibre (non-starch polysaccharide): aids peristalsis, prevents constipation, reduces bowel cancer risk
Proteins
- Growth and repair of body tissues; enzyme and hormone synthesis
- Provide 17 kJ per gram when carbohydrates are depleted
- Complete proteins (containing all essential amino acids): fish, chicken, beef, eggs, milk
- Incomplete proteins: peas, beans (red kidney beans, black-eyed peas), lentils common in Caribbean cuisine
- Children, pregnant women, and athletes require higher protein intake
Fats (lipids)
- Concentrated energy source providing 38 kJ per gram
- Insulation and protection of vital organs
- Synthesis of cell membranes and steroid hormones
- Storage and absorption of fat-soluble vitamins (A, D, E, K)
- Saturated fats: coconut oil, butter, fatty meats (increase cardiovascular disease risk)
- Unsaturated fats: olive oil, avocado, nuts, oily fish (protective cardiovascular effects)
Vitamins
| Vitamin | Function | Deficiency Disease | Food Sources |
|---|---|---|---|
| A (retinol) | Vision in dim light; healthy skin and mucous membranes | Night blindness; xerophthalmia | Liver, carrots, mangoes, pumpkin, callaloo |
| B₁ (thiamine) | Carbohydrate metabolism; nerve function | Beri-beri (muscle weakness, heart failure) | Whole grains, peas, pork |
| C (ascorbic acid) | Collagen synthesis; wound healing; antioxidant | Scurvy (bleeding gums, slow healing) | Citrus fruits, guava, soursop, tomatoes |
| D (calciferol) | Calcium absorption; bone mineralization | Rickets (children), osteomalacia (adults) | Oily fish, fortified milk, UV synthesis |
Minerals
| Mineral | Function | Deficiency Effects | Sources |
|---|---|---|---|
| Calcium | Bone and teeth formation; blood clotting; muscle contraction | Rickets, osteoporosis, poor clotting | Milk, cheese, sardines, callaloo |
| Iron | Haemoglobin synthesis for oxygen transport | Anaemia (fatigue, pale skin) | Red meat, liver, dark leafy greens, beans |
| Iodine | Thyroid hormone synthesis (thyroxine) | Goitre (thyroid enlargement), cretinism | Iodized salt, seafood |
Water
- Solvent for biochemical reactions and transport medium
- Temperature regulation through sweating (critical in Caribbean climate)
- Approximately 60-70% of body mass
- Daily requirement: 2-3 litres, increased during physical activity
Dietary requirements across different groups
Energy and nutrient needs vary based on age, sex, activity level, and physiological state:
Infants (0-12 months)
- High energy per kg body mass for rapid growth
- Breast milk provides complete nutrition for first 6 months
- Gradually introduce solid foods rich in iron after 6 months
Children and adolescents
- Increased protein for growth spurts
- Calcium and vitamin D for bone development
- Iron for expanding blood volume
- Common Caribbean breakfast of porridge, eggs, and fruit juice meets morning energy demands
Pregnant and lactating women
- Additional protein for fetal tissue development
- Increased calcium and iron requirements
- Folate to prevent neural tube defects
- Extra 1200-2000 kJ daily during pregnancy
Manual labourers and athletes
- High carbohydrate intake for sustained energy
- Increased protein for muscle repair
- Adequate hydration in hot Caribbean working conditions
- Construction workers and cane cutters require 12,000-15,000 kJ daily
Elderly persons
- Lower energy needs due to reduced metabolism
- Maintained protein requirements to prevent muscle wasting
- Calcium and vitamin D to reduce osteoporosis risk
- Increased dietary fibre for digestive health
Nutritional disorders: deficiency conditions
Protein-Energy Malnutrition (PEM)
Marasmus
- Severe deficiency of both protein and energy
- Extreme weight loss with muscle wasting
- Visible ribs, shrunken face, dry wrinkled skin
- Alert but irritable; occurs primarily in infants under 18 months
- Still present in some Caribbean communities despite economic development
Kwashiorkor
- Adequate energy intake but severe protein deficiency
- Oedema (fluid retention) causing swollen belly
- Reddish discoloured hair, flaky skin with lesions
- Apathy and irritability
- Typically affects children aged 1-3 years after weaning
- Name derived from Ghanaian language meaning "disease of the displaced child"
Vitamin deficiency diseases
Scurvy
- Vitamin C deficiency affecting collagen synthesis
- Bleeding gums, loose teeth
- Slow wound healing, joint pain
- Historically affected sailors on long voyages
- Prevention: daily consumption of fresh fruits (oranges, guava, julie mango)
Night blindness
- Vitamin A deficiency impairing rod cell function in retina
- Difficulty seeing in dim light or twilight
- Can progress to complete blindness (xerophthalmia)
- Caribbean sources: ripe papaya, mango, pumpkin, callaloo
Rickets and osteomalacia
- Vitamin D deficiency reducing calcium absorption
- Rickets in children: soft, deformed bones (bowed legs, malformed skull)
- Osteomalacia in adults: bone pain, muscle weakness
- Less common in Caribbean due to year-round sunshine enabling vitamin D synthesis
Mineral deficiency diseases
Anaemia
- Iron deficiency reducing haemoglobin production
- Fatigue, weakness, pale conjunctiva and nail beds
- Reduced oxygen-carrying capacity of blood
- Particularly affects menstruating women and pregnant mothers
- Treatment: iron supplements, diet rich in red meat, callaloo, beans
Goitre
- Iodine deficiency preventing adequate thyroxine synthesis
- Visible swelling of thyroid gland in neck
- Reduced metabolic rate, weight gain, mental sluggishness
- Controlled through iodized salt programs across Caribbean nations
Nutritional disorders: excess and lifestyle-related conditions
Obesity
- Excessive accumulation of body fat (BMI > 30 kg/m²)
- Causes: energy intake consistently exceeds energy expenditure
- Risk factors: sedentary lifestyle, high consumption of processed foods, sugary beverages
- Health consequences: type 2 diabetes, hypertension, cardiovascular disease, joint problems
- Growing concern across Caribbean with increased availability of fast food
Type 2 diabetes mellitus
- Insulin resistance preventing effective glucose uptake
- Blood glucose levels remain elevated (hyperglycaemia)
- Linked to obesity, high sugar diets, physical inactivity
- Symptoms: excessive thirst, frequent urination, fatigue
- Caribbean has some of world's highest diabetes rates (Jamaica, Trinidad, Barbados)
- Prevention: balanced diet with complex carbohydrates, regular exercise, maintaining healthy BMI
Cardiovascular diseases
- High intake of saturated fats increases blood cholesterol
- Atherosclerosis: cholesterol deposits narrow arteries
- Increases risk of heart attack and stroke
- Hypertension linked to excessive salt intake
- Traditional Caribbean diet (fish, ground provisions, callaloo) protective; Western-style diet increases risk
Dental caries (tooth decay)
- Bacterial fermentation of sugars produces acids
- Acid demineralizes tooth enamel causing cavities
- High consumption of sugar cane products, sweetened beverages in Caribbean
- Prevention: reduced sugar intake, regular brushing, fluoridated water
Planning balanced diets
A balanced diet must include:
- 55-60% carbohydrates (emphasis on complex carbohydrates)
- 10-15% proteins (mix of animal and plant sources)
- 25-30% fats (predominantly unsaturated)
- Adequate vitamins, minerals, water, and dietary fibre
Sample balanced Caribbean meal plan:
Breakfast
- Cornmeal porridge with milk and cinnamon
- Boiled egg
- Sliced pawpaw
Lunch
- Grilled fish seasoned with local herbs
- Rice and red kidney beans
- Steamed callaloo and carrots
- Fresh orange juice
Dinner
- Baked chicken breast
- Roasted breadfruit and sweet potato
- Garden salad with tomatoes and cucumbers
- Soursop juice
This combination provides complete proteins, complex carbohydrates, essential vitamins and minerals, while limiting saturated fats and excess sugar.
Worked examples
Example 1: Identifying nutrient deficiencies (6 marks)
Question: A 7-year-old child living in a rural Caribbean community shows the following symptoms: swollen abdomen, reddish hair, skin lesions, and appears apathetic. The child consumes mainly cassava with very little fish or meat.
(a) Name the nutritional disorder affecting this child. (1 mark) (b) Identify the nutrient that is lacking in the child's diet. (1 mark) (c) Explain why consuming mainly cassava has led to this condition. (2 marks) (d) Suggest TWO dietary changes to correct this disorder. (2 marks)
Model answer:
(a) Kwashiorkor (1 mark)
(b) Protein (1 mark)
(c) Cassava is high in carbohydrates but contains very little protein. While the child receives adequate energy, the absence of fish or meat means insufficient intake of essential amino acids required for growth and tissue repair. This protein deficiency causes the characteristic symptoms of kwashiorkor. (2 marks — 1 for identifying cassava as poor protein source, 1 for explaining need for complete proteins)
(d)
- Include protein-rich foods such as fish, chicken, eggs, or beans in daily meals
- Add milk or cheese to provide complete proteins and calcium (2 marks — 1 mark each for two appropriate suggestions)
Example 2: Diet planning (8 marks)
Question: A pregnant woman in Jamaica requires nutritional advice during her second trimester.
(a) State TWO reasons why a pregnant woman requires more nutrients than a non-pregnant woman. (2 marks) (b) Name TWO specific nutrients needed in increased amounts during pregnancy and explain why each is important. (4 marks) (c) Suggest ONE Caribbean meal that would provide these nutrients. (2 marks)
Model answer:
(a)
- Development and growth of the fetus requires building materials
- Formation of the placenta requires additional nutrients (2 marks — any two valid reasons)
(b)
- Protein: required for building fetal tissues, organs, and muscles
- Iron: needed for increased blood volume and preventing maternal anaemia
- Calcium: essential for developing fetal bones and teeth
- Folate: prevents neural tube defects in the developing baby (4 marks — 1 mark for each nutrient named, 1 mark for each explanation; any two nutrients)
(c) Callaloo with saltfish, rice and peas, with fresh mango for dessert (2 marks — 1 for complete meal, 1 for appropriate nutrient sources)
Example 3: Calculating BMI (5 marks)
Question: A 35-year-old office worker in Trinidad has a mass of 92 kg and height of 1.75 m.
(a) Calculate this person's BMI. Show your working. (3 marks) (b) State the weight classification for this BMI value. (1 mark) (c) Identify ONE health risk associated with this BMI category. (1 mark)
Model answer:
(a) BMI = mass (kg) ÷ height² (m²) BMI = 92 ÷ (1.75)² BMI = 92 ÷ 3.06 BMI = 30.07 kg/m² (3 marks — 1 for correct formula, 1 for substitution, 1 for answer)
(b) Obese (1 mark)
(c) Type 2 diabetes / cardiovascular disease / hypertension / joint problems (1 mark — any one valid health risk)
Common mistakes and how to avoid them
Confusing marasmus and kwashiorkor: Students often mix up these two forms of protein-energy malnutrition. Remember: marasmus results from total energy and protein deficiency (extreme thinness), while kwashiorkor results from protein deficiency with adequate calories (swollen belly). The oedema distinguishes kwashiorkor.
Stating vitamin D deficiency causes anaemia: Vitamin D deficiency causes rickets/osteomalacia affecting bones. Iron deficiency causes anaemia affecting blood. Keep mineral and vitamin deficiencies distinct — know which nutrient affects which body system.
Claiming fats are unnecessary or harmful: While excess saturated fat poses health risks, fats are essential macronutrients. Unsaturated fats are necessary for cell membranes, hormone synthesis, and fat-soluble vitamin absorption. A balanced diet requires 25-30% fat content.
Forgetting that proteins can provide energy: Students correctly identify carbohydrates and fats as energy sources but forget proteins also yield 17 kJ per gram when metabolized. Though primarily for growth and repair, proteins serve as energy sources when carbohydrates are depleted.
Misidentifying food sources of nutrients: Know Caribbean foods specifically — callaloo is rich in iron and calcium, not just "leafy vegetables." Breadfruit and cassava provide complex carbohydrates. Saltfish provides protein but is high in sodium. Exam questions use regional foods.
Calculating BMI incorrectly: Always square the height before dividing. BMI = mass ÷ height², not mass ÷ (height × 2). Use consistent units (kg and metres). Show all working steps for method marks even if the final answer is incorrect.
Exam technique for "Balanced Diet and Nutritional Disorders"
"State" and "Name" questions (1 mark): Require only the term itself — kwashiorkor, rickets, protein. No explanation needed. Write the specific scientific term, not a description. Common command words for nutrient names and deficiency diseases.
"Explain" and "Account for" questions (2-4 marks): Must provide reasons and mechanisms. Structure answers as: identify the nutrient/condition, state its function, explain what happens without it. Use linking words: "because," "therefore," "this causes." Example: "Iron deficiency causes anaemia because iron is required for haemoglobin synthesis, therefore less oxygen is transported."
Diet planning questions: Always specify actual Caribbean foods, not just food groups. "Fish" is better than "protein source." "Callaloo and carrots" is better than "vegetables." Include preparation methods when relevant — grilled, steamed, baked rather than fried demonstrates nutritional awareness.
Table and data questions: When given nutrient tables or food composition data, extract information systematically. Check units carefully. BMI calculations appear regularly — memorize the formula and show complete working. Mark schemes award method marks separately from accuracy marks.
Quick revision summary
A balanced diet contains correct proportions of six nutrient classes: carbohydrates (55-60%, main energy), proteins (10-15%, growth/repair), fats (25-30%, concentrated energy), vitamins, minerals, and water. Deficiency diseases include kwashiorkor (protein), scurvy (vitamin C), rickets (vitamin D), anaemia (iron), and goitre (iodine). Excess conditions include obesity, type 2 diabetes, and cardiovascular disease from high energy, sugar, and saturated fat intake. Requirements vary by age, activity, and physiological state (pregnancy, lactation). Caribbean foods like callaloo, breadfruit, fish, and tropical fruits provide excellent nutrient sources. BMI = mass(kg) ÷ height²(m²) classifies weight status.