Carbohydrates: Deficiency and Excess

This lesson covers the effects of carbohydrate deficiency (not enough carbohydrate) and carbohydrate excess (too much carbohydrate) on the body, as required by AQA GCSE Food Preparation and Nutrition specification 8585 (section 3.2.1). You will also learn the Dietary Reference Values for carbohydrate and understand how to apply this knowledge to diet analysis questions.

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Carbohydrate Deficiency

Carbohydrate deficiency occurs when a person does not consume enough carbohydrate to meet the body's energy needs. Since carbohydrate is the body's primary energy source, a shortage has significant effects.

Effects of Carbohydrate Deficiency

Effect	Explanation
Lack of energy and tiredness	Carbohydrate is the body's preferred fuel. Without enough, the body has less glucose available for respiration, leading to fatigue, lethargy, and difficulty concentrating.
Use of protein for energy	If carbohydrate stores are depleted, the body breaks down protein for energy instead. This diverts protein from its primary functions of growth and repair, leading to muscle wasting.
Use of fat for energy (ketosis)	When carbohydrate is very low, the body relies on breaking down fat for energy. This produces ketone bodies as a by-product. An excess of ketones in the blood is called ketosis, which can cause nausea, headaches, bad breath, and in extreme cases can be dangerous.
Constipation	A diet low in carbohydrate is often low in dietary fibre (since fibre is a type of carbohydrate). This reduces stool bulk and slows peristalsis, leading to constipation.
Low blood sugar (hypoglycaemia)	Symptoms include dizziness, shakiness, confusion, irritability, sweating, and in severe cases, fainting. The brain relies almost exclusively on glucose, so it is particularly affected.
Poor concentration and mood changes	The brain uses approximately 120 g of glucose per day. Insufficient carbohydrate intake impairs cognitive function, concentration, and mood.
Poor exercise performance	Glycogen stores in muscles are depleted, reducing the body's capacity for physical activity. Athletes on very low-carbohydrate diets often experience reduced endurance and performance.

Exam Tip: A common question asks what happens if someone does not eat enough carbohydrate. The key points are: tiredness/lack of energy, the body uses protein for energy (diverting it from growth/repair), ketosis, and constipation (due to low fibre). Always explain why each effect occurs, not just name it.

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What Happens When Carbohydrate Is Insufficient: The Energy Hierarchy

When carbohydrate intake is inadequate, the body uses alternative fuels in a specific order:

graph TD
    A["Carbohydrate intake is low"] --> B["Glycogen stores in liver and muscles are used first"]
    B --> C["Glycogen stores depleted"]
    C --> D["Body breaks down FAT for energy"]
    D --> E["Ketone bodies produced — KETOSIS"]
    C --> F["Body breaks down PROTEIN for energy"]
    F --> G["Less protein available for growth and repair"]
    G --> H["Muscle wasting"]

    style A fill:#c0392b,color:#fff
    style E fill:#e67e22,color:#fff
    style H fill:#8e44ad,color:#fff

This sequence is important: the body first uses glycogen, then fat (producing ketones), and then protein (causing muscle wasting). Using protein for energy is the body's last resort and is undesirable because it compromises growth and repair.

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Who Is Most at Risk of Carbohydrate Deficiency?

At-Risk Group	Reason
People on very low-carbohydrate diets	Diets like keto or Atkins severely restrict carbohydrate intake
People with eating disorders	Anorexia nervosa involves severe food restriction
People in poverty or famine	Limited access to food means insufficient energy intake overall
Athletes with poor nutrition	May not consume enough carbohydrate to replace glycogen used during intense exercise
People with uncontrolled diabetes	May have difficulty utilising the carbohydrate they consume

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Carbohydrate Excess

In the UK, excessive consumption of carbohydrate — particularly free sugars — is a significant public health concern. While starch in moderate amounts is an important part of a healthy diet, excess carbohydrate (especially sugar) has serious health consequences.

Effects of Carbohydrate Excess

Effect	Explanation
Obesity	Excess carbohydrate that is not used for energy is first stored as glycogen in the liver and muscles. When glycogen stores are full, the excess is converted to fat and stored in adipose tissue. Over time, this leads to weight gain and obesity.
Tooth decay (dental caries)	Free sugars are fermented by bacteria in the mouth, producing acid. This acid attacks the enamel on teeth, causing cavities. Frequent consumption of sugary foods and drinks is the main cause of tooth decay.
Type 2 diabetes	Excess sugar consumption contributes to obesity, which is the biggest risk factor for type 2 diabetes. In type 2 diabetes, the body either does not produce enough insulin or becomes resistant to insulin, meaning blood glucose levels remain dangerously high.
High blood sugar levels	Frequent consumption of high-GI sugary foods causes repeated blood sugar spikes, which over time can lead to insulin resistance.
Increased risk of cardiovascular disease	Obesity and type 2 diabetes (both linked to excess carbohydrate) increase the risk of heart disease and stroke.
Nutritional imbalances	Filling up on sugary foods may displace more nutritious foods from the diet, leading to deficiencies in vitamins, minerals, and protein.

Tooth Decay in Detail

Tooth decay is one of the most directly tested consequences of excess sugar:

1. Bacteria in the mouth (particularly Streptococcus mutans) feed on free sugars from food and drinks
2. The bacteria produce lactic acid as a waste product
3. The acid demineralises the tooth enamel (dissolves the calcium and phosphate)
4. Over time, a cavity forms in the tooth
5. If untreated, the cavity can reach the dentine and pulp, causing pain and infection