Protein: Deficiency and Excess

This lesson covers the effects of protein deficiency (not enough protein) and protein excess (too much protein) on the body, as required by AQA GCSE Food Preparation and Nutrition specification 8585 (section 3.2.1). You will learn to identify the symptoms and health consequences of both under- and over-consumption, and understand which groups of people are most at risk.

Protein Deficiency

Protein deficiency occurs when a person does not consume enough protein to meet the body's needs. This can happen because of:

Inadequate food intake (poverty, famine)
A very restricted diet that lacks variety
Increased requirements not being met (e.g. during growth, pregnancy, or recovery from illness)
Poor-quality protein sources without complementation

Effects of Protein Deficiency

Effect	Explanation
Kwashiorkor	A severe protein deficiency disease, most common in developing countries. Symptoms include a swollen belly (oedema caused by fluid retention), thin arms and legs, flaky skin, and discoloured hair. Primarily affects young children after weaning.
Slow growth	Children who lack protein may not grow to their expected height and weight. Growth is stunted because the body cannot build new tissues.
Wasting (loss of muscle mass)	The body breaks down its own muscle tissue to obtain amino acids, leading to muscle wasting and weakness.
Weakened immune system	Antibodies are made of protein. Without sufficient protein, the body produces fewer antibodies, making a person more susceptible to infections and illnesses.
Poor wound healing	Repair of damaged tissue requires protein. Deficiency slows down the healing of cuts, wounds, and surgical incisions.
Oedema	Protein helps maintain the balance of fluid in the body. Deficiency causes fluid to leak into tissues, resulting in swelling (oedema), particularly in the abdomen, hands, and feet.
Thin, brittle hair and weak nails	Hair and nails are made of the protein keratin. Without adequate protein, they become thin, dry, and break easily.
Fatigue and weakness	The body lacks the amino acids needed to maintain muscles and produce enzymes, leading to tiredness and physical weakness.

Kwashiorkor in Detail

Kwashiorkor is the most severe form of protein deficiency and is most commonly seen in children aged 1–4 years in developing countries, particularly in sub-Saharan Africa and South Asia.

It typically occurs when a child is weaned from breast milk (which is HBV protein) onto a diet that is high in starchy carbohydrates but very low in protein. The name "kwashiorkor" comes from the Ga language of Ghana, meaning "the disease the first child gets when the second child is born" — referring to the older child being weaned when a new baby arrives.

Key symptoms of kwashiorkor:

Distended (swollen) abdomen due to oedema and an enlarged liver
Thin, wasted limbs despite the swollen belly
Discoloured, sparse hair (sometimes reddish or grey)
Flaky, peeling skin with dark patches
Irritability, lethargy, and loss of appetite
Increased vulnerability to infections
Can be fatal if untreated

Exam Tip: Kwashiorkor is a protein energy malnutrition disease. Do not confuse it with marasmus, which is caused by an overall lack of food (energy and protein). In kwashiorkor, the child may be getting enough calories from starchy food but not enough protein.

Who Is Most at Risk of Protein Deficiency?

At-Risk Group	Reason
Children in developing countries	Limited access to protein-rich foods; weaned onto starchy diets
Elderly people	Reduced appetite, difficulty chewing, living alone, poverty
People with eating disorders	Severely restricted food intake
Vegans with poorly planned diets	Risk of insufficient protein if diet lacks variety and complementation
People with digestive disorders	Conditions like Crohn's disease or coeliac disease can impair protein absorption
People recovering from surgery or illness	Increased protein requirements that may not be met

Protein Excess

In the UK, most people consume more protein than they need. While the body can tolerate a moderate excess, consistently consuming far too much protein over a long period can have negative health effects.

Effects of Protein Excess

Effect	Explanation
Stored as fat	Excess protein cannot be stored as protein in the body. The amino acids are deaminated (the nitrogen-containing amino group is removed) in the liver, and the remaining carbon skeleton is converted to fat and stored in adipose tissue. This can contribute to weight gain and obesity.
Kidney strain	The nitrogen removed during deamination is converted to urea in the liver, which is then filtered out of the blood by the kidneys. A very high protein intake means the kidneys must work harder to excrete the extra urea. Over time, this can put strain on the kidneys, which is particularly concerning for people with existing kidney disease.
High saturated fat intake	Many high-protein animal foods (red meat, cheese, full-fat dairy) are also high in saturated fat. Excess saturated fat raises blood cholesterol, increasing the risk of coronary heart disease (CHD).
Calcium loss	Some research suggests that very high protein diets may increase calcium excretion in urine, potentially affecting bone health over time (though this is debated).
Dehydration	The body needs water to process and excrete the extra urea produced from protein metabolism. Very high protein intake without adequate water can lead to dehydration.

The Process of Deamination

When excess protein is consumed, the body cannot store it as protein. Instead, a process called deamination occurs in the liver:

graph TD
    A["Excess amino acids in blood"] --> B["Liver: DEAMINATION"]
    B --> C["Amino group removed"]
    B --> D["Carbon skeleton remaining"]
    C --> E["Converted to UREA"]
    D --> F["Converted to FAT or used for ENERGY"]
    E --> G["Transported to kidneys"]
    G --> H["Excreted in urine"]
    F --> I["Stored in adipose tissue"]

    style A fill:#e67e22,color:#fff
    style B fill:#c0392b,color:#fff
    style E fill:#4a90d9,color:#fff
    style F fill:#27ae60,color:#fff

Key points about deamination:

It occurs in the liver
The nitrogen-containing part of the amino acid becomes urea
Urea is a waste product carried in the blood to the kidneys
The remaining part can be used for energy or converted to fat
This is why excess protein contributes to weight gain

Exam Tip: "Deamination" is a key term that examiners look for. If asked what happens to excess protein, you must mention that it is deaminated in the liver, producing urea (excreted by the kidneys) and a carbon skeleton (used for energy or stored as fat).

Balancing Protein Intake

The goal is to consume enough protein to meet the body's needs without significant excess:

Situation	Recommendation
Growing children	Ensure adequate HBV or complementary LBV protein for growth
Teenagers	Increased needs during growth spurts; include protein at every meal
Adults	Maintain intake around the RNI (approximately 45–55 g per day)
Pregnant women	Additional 6 g per day to support foetal growth
Elderly	Maintain adequate protein to prevent muscle wasting (sarcopenia)
Athletes	May need slightly more protein for muscle repair, but extreme intakes are unnecessary

Protein Deficiency vs Excess: Comparison Table

Aspect	Deficiency	Excess
Cause	Not enough protein in the diet	Too much protein in the diet
Energy effect	Lack of energy, fatigue	Excess stored as fat (weight gain)
Growth	Stunted growth in children	No direct benefit to growth
Muscles	Muscle wasting	No extra muscle gain (without exercise)
Immune system	Weakened (fewer antibodies)	Not directly affected
Organs	Oedema, enlarged liver	Kidney strain (urea excretion)
Serious condition	Kwashiorkor	Obesity, potential kidney problems
Most at risk	Children in developing countries	People in developed countries with high-meat diets

Protein: Deficiency and Excess

Protein: Deficiency and Excess