Food Science and Metabolism
5. Nutrition in Health and Disease
Learning outcomes
- I can explain the relationship between nutrition and overall health.
- I can identify how poor nutrition can contribute to disease.
- I can describe the role of nutrition in preventing chronic illnesses.
- I can evaluate dietary choices using scientific evidence.
- I can propose nutritional strategies that support long-term health and well-being.
What Is Nutrition?
Nutrition is the process by which organisms obtain and use nutrients from food.
The body requires nutrients for many different purposes, including:
- Providing energy.
- Growth and development.
- Repairing tissues.
- Producing enzymes and hormones.
- Maintaining bones and muscles.
- Supporting the immune system.
- Producing blood cells.
- Maintaining normal cellular processes.
Good nutrition does not mean eating one particular "healthy" food. It involves obtaining an appropriate balance and variety of nutrients over time.
Nutrients Required by the Body
The human body requires several major categories of nutrients.
These include:
- Carbohydrates
- Proteins
- Lipids
- Vitamins
- Minerals
- Water
Dietary fibre is also important for maintaining digestive health.
Different nutrients have different functions, so one nutrient cannot simply substitute for all the others.
Carbohydrates
Carbohydrates are an important source of energy.
Many carbohydrates are digested into simple sugars such as glucose, which can be used during cellular respiration.
Sources include:
- Rice
- Bread
- Pasta
- Potatoes
- Cereals
- Fruits
- Legumes
Whole-grain and minimally processed carbohydrate sources can also provide fibre, vitamins, and minerals.
Proteins
Proteins provide amino acids that the body uses to make its own proteins.
Proteins are important for:
- Growth
- Tissue repair
- Enzymes
- Antibodies
- Transport proteins
- Some hormones
- Muscle and other body structures
Sources include meat, fish, eggs, dairy products, beans, lentils, soy products, nuts, and seeds.
Lipids
Lipids provide a concentrated source of energy and have many other biological functions.
They are important for:
- Long-term energy storage.
- Cell membranes.
- Insulation.
- Protection of organs.
- Absorption of fat-soluble vitamins.
- Production of certain signalling molecules.
Different types of dietary fats can have different effects on health, so simply classifying all fat as "unhealthy" is misleading.
Micronutrients
Micronutrients are nutrients required in relatively small quantities.
They include:
- Vitamins
- Minerals
Although they are required in small amounts, they are essential for normal body function.
A deficiency can cause disease.
Vitamins
Vitamins are organic substances required for normal physiological processes.
Different vitamins perform different functions.
For example:
| Vitamin | Important role | Some sources |
|---|---|---|
| Vitamin A | Vision and normal cell function | Carrots, leafy vegetables, liver, dairy |
| Vitamin C | Collagen production and tissue maintenance | Citrus fruits, peppers, many vegetables |
| Vitamin D | Calcium regulation and bone health | Sunlight exposure, oily fish, fortified foods |
| Vitamin K | Normal blood clotting | Leafy green vegetables |
| Folate | DNA synthesis and cell division | Leafy vegetables, legumes, fortified foods |
The body does not need enormous quantities of vitamins. More is not automatically better.
Minerals
Minerals are inorganic nutrients required for many body functions.
Examples include:
Calcium
Important for:
- Bones and teeth
- Muscle contraction
- Cell signalling
Iron
Required for haemoglobin, which helps transport oxygen in the blood.
Iodine
Required for the production of thyroid hormones.
Sodium and Potassium
Important for:
- Nerve impulses
- Muscle function
- Fluid balance
Malnutrition
Malnutrition occurs when nutrient or energy intake does not appropriately meet the body's requirements.
It does not simply mean "not eating enough."
Malnutrition can result from:
- Insufficient total energy.
- Insufficient protein.
- Vitamin or mineral deficiencies.
- Excessive energy intake over time.
- An unbalanced diet.
- Diseases that interfere with digestion or absorption.
A person can consume plenty of energy while still being deficient in particular nutrients.
Undernutrition
Undernutrition occurs when the body does not receive sufficient energy or essential nutrients.
Possible consequences include:
- Reduced growth in children.
- Loss of body mass.
- Muscle wasting.
- Reduced ability to repair tissues.
- Weakened immune function.
- Fatigue.
- Micronutrient deficiencies.
The effects depend on which nutrients are lacking, how severe the deficiency is, and how long it continues.
Deficiency Diseases
A deficiency disease can develop when the body does not receive or absorb enough of a particular nutrient.
Understanding these diseases provides clear evidence of the connection between nutrition and health.
Iron-Deficiency Anaemia
Iron is required to produce haemoglobin.
Haemoglobin in red blood cells transports oxygen.
Insufficient available iron can contribute to iron-deficiency anaemia.
Possible symptoms include:
- Fatigue
- Weakness
- Reduced exercise tolerance
- Shortness of breath
The underlying cause matters: low dietary intake is one possibility, but blood loss or problems with absorption can also cause iron deficiency.
Vitamin D Deficiency
Vitamin D plays an important role in calcium regulation and bone mineralisation.
Severe deficiency in children can contribute to rickets, in which developing bones become poorly mineralised and may deform.
In adults, severe deficiency can contribute to osteomalacia.
Vitamin C Deficiency
Vitamin C is required for normal collagen production.
Severe, prolonged deficiency causes scurvy.
Possible effects include:
- Bleeding gums
- Poor wound healing
- Easy bruising
- Weakness
Historically, scurvy was a major problem among sailors on long voyages when fresh fruits and vegetables were unavailable.
Iodine Deficiency
Iodine is needed to produce thyroid hormones.
Insufficient iodine can interfere with normal thyroid function.
In some cases, the thyroid gland enlarges, producing a goitre.
Iodine deficiency during fetal and early childhood development can have particularly serious effects on growth and neurological development.
Excess Nutrition Can Also Affect Health
Poor nutrition can also involve consuming more energy or certain nutrients than the body requires over long periods.
When energy intake consistently exceeds energy expenditure, energy stores tend to increase.
Much of this excess energy can eventually be stored as fat.
However, body mass and disease risk are influenced by many interacting factors, including:
- Genetics
- Hormones
- Physical activity
- Sleep
- Medications
- Food environment
- Health conditions
- Socioeconomic factors
Nutrition is important, but health outcomes should not be reduced to one simple cause.
Nutrition and Cardiovascular Disease
Cardiovascular disease includes disorders affecting the heart and blood vessels.
Diet is one of several factors that can influence cardiovascular risk.
Dietary patterns containing appropriate amounts of:
- Fruits
- Vegetables
- Whole grains
- Legumes
- Nuts
- Unsaturated fats
are associated with cardiovascular health.
High intakes of certain dietary components, particularly excessive sodium and diets high in some saturated and trans fats, can contribute to risk factors in some populations.
Saturated and Unsaturated Fats
Fats should not all be treated as identical.
Saturated Fats
Saturated fats are found in varying amounts in foods including:
- Fatty meats
- Butter
- Some dairy products
- Coconut and palm oils
High intake can raise LDL cholesterol in many people, although the overall dietary pattern and replacement nutrient matter.
Unsaturated Fats
Unsaturated fats are found in foods such as:
- Nuts
- Seeds
- Fish
- Avocados
- Many vegetable oils
Replacing some saturated fats with unsaturated fats can improve some cardiovascular risk markers.
Trans Fats
Some trans fats, particularly industrially produced trans fats, have strongly adverse effects on cardiovascular health.
They can:
- Increase LDL cholesterol.
- Reduce HDL cholesterol.
- Increase cardiovascular disease risk.
Many countries have therefore restricted or eliminated industrially produced trans fats from much of the food supply.
Sodium and Blood Pressure
Sodium is essential for normal body function.
However, high sodium intake can contribute to elevated blood pressure in susceptible individuals and populations.
Common sources can include:
- Processed foods
- Packaged snacks
- Sauces
- Processed meats
- Restaurant foods
This illustrates an important nutritional principle:
A substance can be essential in appropriate amounts but harmful when intake is excessive.
Nutrition and Type 2 Diabetes
Type 2 diabetes is a metabolic disease involving impaired regulation of blood glucose.
Its development is influenced by multiple factors, including:
- Genetics
- Age
- Body composition
- Physical activity
- Overall dietary patterns
- Other metabolic and environmental factors
Dietary patterns can influence risk, but no single food can be identified as the sole cause of type 2 diabetes.
Dietary Fibre and Chronic Disease
Fibre is important for more than preventing constipation.
Fibre-rich foods include:
- Whole grains
- Fruits
- Vegetables
- Legumes
- Nuts
- Seeds
Higher-fibre dietary patterns are associated with benefits including improved digestive health and reduced risk of several chronic diseases.
Some soluble fibres can also influence blood cholesterol and glucose absorption.
Nutrition and Bone Health
Healthy bones require more than just calcium.
Important factors include:
- Calcium
- Vitamin D
- Protein
- Physical activity
- Hormonal health
Weight-bearing exercise helps stimulate bone maintenance.
Therefore:
Nutrition + physical activity + physiology → bone health
Focusing on a single nutrient can overlook the way multiple factors work together.
Nutrition and the Immune System
The immune system requires adequate nutrients to function normally.
Important nutrients include:
- Protein
- Vitamin A
- Vitamin C
- Vitamin D
- Zinc
- Iron
- Several B vitamins
Deficiencies can interfere with normal immune function.
However, consuming very large quantities of a vitamin does not necessarily make the immune system "stronger."
Once nutritional requirements are met, additional intake may provide little benefit and can sometimes cause harm.
Dietary Patterns Matter
Nutrition research increasingly considers dietary patterns rather than focusing only on individual foods.
This is because people do not eat nutrients separately.
A meal might contain:
- Carbohydrates
- Proteins
- Fats
- Fibre
- Vitamins
- Minerals
- Water
These components interact.
Long-term eating patterns are therefore often more informative than asking whether one particular food is "good" or "bad."
Evaluating Dietary Choices Scientifically
Nutrition information is everywhere.
Social media, advertisements, influencers, friends, and websites may all make dietary claims.
These claims vary greatly in scientific quality.
Useful questions include:
- What exactly is being claimed?
- What evidence supports the claim?
- Was the research conducted in humans?
- How many participants were studied?
- Was there a control group?
- How long did the study last?
- Was the study independently reviewed?
- Does one study agree with the wider body of evidence?
- Is the source selling the product being promoted?
Correlation Does Not Necessarily Mean Causation
Suppose researchers observe that people who eat more vegetables have lower rates of a particular disease.
This is a correlation.
It does not automatically prove that vegetables alone caused the difference.
People who eat more vegetables may also differ in:
- Physical activity
- Smoking
- Income
- Healthcare access
- Sleep
- Other dietary habits
Researchers attempt to control for these confounding variables, but observational nutrition research can be difficult to interpret.
Strong conclusions usually require evidence from multiple studies using different methods.
Example: Evaluating a Health Claim
Imagine an advertisement states:
"This juice prevents heart disease."
A scientific evaluation should ask:
What evidence supports this?
Was the juice compared with a control?
How many people participated?
Were actual cardiovascular outcomes measured?
How long were participants studied?
Could another lifestyle factor explain the results?
Was the research funded by the company selling the juice?
One small study or personal testimonial would not provide strong evidence that a food prevents disease.
Food Labels as Evidence
Nutrition labels provide useful quantitative information.
They can show:
- Energy
- Protein
- Fat
- Saturated fat
- Carbohydrate
- Sugars
- Fibre
- Sodium
- Certain vitamins and minerals
When comparing foods, values per 100 g or 100 mL can be especially useful because serving sizes may differ.
However, labels should be interpreted in the context of the whole diet.
Worked Example: Comparing Breakfast Cereals
Consider two hypothetical cereals.
| Nutrient per 100 g | Cereal A | Cereal B |
|---|---|---|
| Sugars | 24 g | 8 g |
| Fibre | 3 g | 10 g |
| Protein | 7 g | 11 g |
| Sodium | 500 mg | 220 mg |
From these data we can state that, per 100 g:
- Cereal A contains more sugar.
- Cereal B contains more fibre.
- Cereal B contains more protein.
- Cereal A contains more sodium.
These are conclusions supported directly by the data.
It would be less scientifically justified to simply declare one cereal "healthy" and the other "unhealthy" without considering portion size, other nutrients, the person's needs, and the rest of their diet.
Long-Term Nutritional Strategies
Rather than concentrating on one "perfect" food, long-term health is generally better supported by an overall dietary pattern.
Useful strategies include:
- Eating a variety of foods.
- Including fruits and vegetables regularly.
- Choosing fibre-rich carbohydrate sources.
- Including suitable protein sources.
- Including appropriate sources of unsaturated fats.
- Drinking adequate water.
- Limiting excessive sodium.
- Limiting foods high in added sugars when they displace more nutrient-dense choices.
- Avoiding excessive energy intake over long periods.
- Matching energy intake reasonably with individual energy needs.
Nutrition Is Individual
Nutritional requirements are not identical for everyone.
They can vary according to:
- Age
- Body size
- Physical activity
- Growth
- Pregnancy
- Health conditions
- Allergies and intolerances
- Cultural dietary patterns
- Food availability
For example, an adolescent athlete may have very different energy requirements from an older sedentary adult.
A dietary strategy should therefore be evaluated in relation to the person's needs rather than treated as universally appropriate.
Supplements and Nutrition
Vitamin and mineral supplements can be valuable when there is a specific need.
Examples can include:
- Treating diagnosed deficiencies.
- Providing folic acid around pregnancy.
- Providing certain nutrients when dietary intake or absorption is inadequate.
However, supplements do not automatically improve health in someone whose nutritional requirements are already being met.
Some nutrients can also be harmful in excessive doses.
More is not always better.
Food, Disease and Risk
Nutrition usually affects risk rather than determining exactly what will happen to an individual.
For example, a particular dietary pattern may be associated with a lower risk of a disease.
That does not mean:
"Everyone following this diet will avoid the disease."
Likewise, developing a disease does not prove that someone had a poor diet.
Disease usually results from interactions among many factors, including:
genetics + environment + behaviour + physiology + chance + nutrition
This distinction is important when interpreting health information.
Worked Example: Improving a Dietary Pattern
Consider a student whose usual daily diet contains:
- Very few vegetables.
- Little fruit.
- Mostly refined grains.
- Few fibre-rich foods.
- Large quantities of sugary drinks.
- Very little water.
Rather than banning one particular food, a more evidence-based strategy might include:
- Gradually increasing vegetables and fruit.
- Replacing some refined grains with whole-grain options.
- Adding legumes or other fibre-rich foods.
- Drinking more water.
- Reducing reliance on sugary drinks.
- Maintaining adequate protein and overall energy intake.
The goal is to improve the overall dietary pattern rather than label individual foods as forbidden.
Nutrition Across a Lifetime
Nutritional needs change throughout life.
Childhood and Adolescence
Nutrition must support:
- Growth
- Brain development
- Bone development
- Physical activity
- Puberty
Adulthood
Nutrition supports:
- Tissue maintenance
- Metabolism
- Physical activity
- Long-term disease prevention
Older Adulthood
Factors such as energy requirements, muscle maintenance, bone health, appetite, and nutrient absorption can become increasingly important.
Good nutrition is therefore a lifelong process rather than a short-term diet.
Common Mistakes
Thinking Malnutrition Only Means Starvation
Malnutrition can involve insufficient energy, excessive energy, or an imbalance or deficiency of particular nutrients.
Labelling Individual Foods as Simply "Good" or "Bad"
Overall dietary patterns, amounts, frequency, and individual needs are more informative.
Assuming Fat Is Always Unhealthy
Lipids are essential nutrients. Different types and amounts of fat have different effects.
Assuming Vitamins Provide Energy
Vitamins help regulate biological processes but do not provide food energy in the way carbohydrates, fats, and proteins do.
Assuming Supplements Are Always Better Than Food
Supplements can be useful in particular circumstances, but they do not replace the many nutrients and other components supplied by a varied diet.
Assuming More Vitamins Must Be Better
Some vitamins and minerals can be harmful at excessive doses.
Assuming One Food Causes or Prevents a Chronic Disease
Chronic diseases usually have multiple contributing factors.
Confusing Correlation With Causation
An association between a food and a health outcome does not automatically demonstrate that the food caused the outcome.
Check Your Understanding
1. Explain the relationship between nutrition and health.
2. What is malnutrition?
3. Explain why someone can consume enough energy but still be malnourished.
4. Give two examples of deficiency diseases and identify the nutrients involved.
5. Explain why iron deficiency can cause fatigue.
6. Describe two ways nutrition can influence cardiovascular health.
7. Why is dietary fibre important for long-term health?
8. Explain why vitamins do not provide energy even though they are essential nutrients.
9. Why can excessive intake of some nutrients be harmful?
10. Explain the difference between correlation and causation in nutrition research.
11. Give three questions you should ask when evaluating a nutritional health claim.
12. Why are values per 100 g useful when comparing food labels?
13. Explain why the term "balanced diet" cannot refer to exactly the same quantities for every person.
14. Give four dietary strategies that could support long-term health.
15. Evaluate the claim: "If a food contains vitamins, eating more of it will always make you healthier."
Key Terms
- Nutrition – the process of obtaining and using nutrients.
- Nutrient – a substance required by the body for energy, growth, repair, regulation, or normal function.
- Macronutrient – a nutrient required in relatively large quantities, including carbohydrates, proteins, and lipids.
- Micronutrient – a nutrient required in relatively small quantities, including vitamins and minerals.
- Malnutrition – a condition resulting from inadequate, excessive, or imbalanced nutrient or energy intake or utilisation.
- Undernutrition – insufficient intake or availability of energy or essential nutrients.
- Deficiency disease – disease caused by insufficient availability of a particular nutrient.
- Anaemia – a condition involving insufficient healthy red blood cells or haemoglobin; iron deficiency is one possible cause.
- Rickets – impaired mineralisation of developing bones, commonly associated with severe vitamin D deficiency.
- Scurvy – disease caused by severe vitamin C deficiency.
- Cardiovascular disease – diseases affecting the heart and blood vessels.
- Dietary fibre – plant-derived food components that resist complete digestion by human digestive enzymes.
- Saturated fat – fats containing fatty acids without carbon-carbon double bonds.
- Unsaturated fat – fats containing one or more carbon-carbon double bonds in their fatty acids.
- Correlation – an association between two measured variables.
- Causation – a relationship in which one factor contributes directly to producing a change in another.
- Confounding variable – an additional factor that can influence an observed relationship.
- Chronic disease – a disease that develops or persists over a long period.
Key Takeaways
- Nutrition affects growth, metabolism, tissue repair, immunity, bone health, and long-term disease risk.
- A healthy diet provides an appropriate combination of macronutrients, micronutrients, fibre, and water.
- Poor nutrition can involve both deficiency and excess.
- Nutrient deficiencies can produce specific diseases, such as iron-deficiency anaemia, scurvy, and rickets.
- Nutrition can influence the risk of chronic diseases, including cardiovascular disease and type 2 diabetes.
- Different types of dietary fats have different biological effects.
- Fibre-rich foods can support digestive, metabolic, and cardiovascular health.
- Dietary patterns are generally more informative than labelling individual foods as simply "healthy" or "unhealthy."
- Nutritional requirements vary according to factors such as age, activity, growth, and health.
- Supplements can be useful when there is a specific need, but more is not automatically better.
- Food labels provide quantitative evidence that can help compare foods.
- Nutrition claims should be evaluated using scientific evidence rather than advertising, testimonials, or popularity.
- Correlation does not automatically demonstrate causation.
- Nutrition influences disease risk, but it is rarely the only factor determining whether a person develops a disease.
- Long-term health is best supported by sustainable overall dietary patterns rather than extreme or short-term diets.