A.2.1 Compare the energy content per 100g fat, carbohydrate and protein.

Various units of energy can be used on food labels, but we use the unit kJ (kilojoules).

energy in fats, carbos and protein

Notice that fats contain more than double the energy per unit mass than carbohydrates or proteins.

Some food labels use Calories, which is the more common term in public science.
One calorie is the energy required to raise the temperature of 1kg water by 1oC.
One food Calorie is actually 1000 calories (1kcal). One food Calorie is equivalent to 4.18kJ. 


Students might like to consider what the link is between the energy content of fats and their metabolism in respiration? Refer to the role of CoA.

Sources: (1) (17)

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A.2.2 Compare the main dietary sources of energy in different ethnic groups.

Dietary energy can come from various sources, carbohydrates, proteins or fats, depending on the foods available to a population. These staples make up the bulk of a population’s diet, and are generally crops.

dietary sources ethnic groups

This map shows some of the main staple crops around the world

worlds staple crops

Sources: (21) (22) (4)

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A.2.3 Explain the possible health consequences of diets rich in carbohydrates, fats and proteins.

Rich diets

Sources: (17) (6) (23) (8)

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A.2.4 Outline the function of the appetite control centre of the brain.

Link to 6.5

Appetite is controlled in the hypothalamus of the brain. Control is both nervous and hormonal: some hormones trigger appetite-stimulating neurons, others trigger appetite-inhibiting neurons.

An empty stomach releases the hormone gherin, which triggers appetite-stimulating hormones, leading to hunger. When food enters the stomach, gherin production is stopped, reducing hunger.

Appetite is also inhibited when:

appetitie control of

  1. Food entering the intestine stimulates release of PYY3-36 hormone.

  2.  Carbohydrate and protein digestion stimulate release of insulin hormone from the pancreas.

  3. Fat storage stimulates release of leptin hormone from the pancreas. This is enhanced by insulin.

 

 

 

These three hormones trigger appetite-inhibiting neurons in the appetite control centre.
There are strong links to malfunction of any of these pathways and obesity, as the individual eats more than is required.

 

 

Sources: (24)

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A.2.5 Calculate body mass index (BMI) from the body mass and height of a person.

BMI calculation

e.g. 1: 70kg man, 1.8m tall.   BMI = 70 / 1.8 = 21.6

 

 

A.2.6 Distinguish, using the body mass index, between being underweight, normal weight, overweight and obese.

BMI comparisons

Limitations of the BMI using this table:

Examples:

comparative BMI

Source for A.2.5 and A.2.6: (1) (8)

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A.2.7 Outline reasons for increasing rates of clinical obesity in some countries, including availability of cheap high-energy foods, large portion sizes, increasing use of vehicles for transport, and a change from active to sedentary occupations.

There are many contributing factors:

 

Clinical obesity

 

Sources: (25) (24)

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A.2.8 Outline the consequences of anorexia nervosa.


Health consequences include:

Anorexia nervosa

 

Anoerxia

 

Sources: (26) (image from the same source)

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Click4Biology: Option A2: Energy in human diets

A.2 Energy in human diets

The individual sections of this page are cross referenced to their sources.

A.2.1 Compare the energy content per 100g fat, carbohydrate and protein.

A.2.2 Compare the main dietary sources of energy in different ethnic groups.

A.2.3 Explain the possible health consequences of diets rich in carbohydrates, fats and proteins.

A.2.4 Outline the function of the appetite control centre of the brain.

A.2.5 Calculate body mass index (BMI) from the body mass and height of a person.

A.2.6 Distinguish, using the body mass index, between being underweight, normal weight, overweight and obese.

A.2.7 Outline reasons for increasing rates of clinical obesity in some countries, including availability of cheap high-energy foods, large portion sizes, increasing use of vehicles for transport, and a change from active to sedentary occupations.

A.2.8 Outline the consequences of anorexia nervosa.