1. A. Human
nutrition and
health
A2: Energy in human diets

2. Energy in diets
 Cell respiration involves the release of
energy from foods such as
fat, carbohydrate or protein.
 Foods eaten in bulk to supply energy are
called staple foods. Human societies are
very diverse in their choice of staple
energy sources.

3. What is food energy and how is it
measured?
Humans are autotrophs and get energy
from organic molecules from other
organisms. Typically these are fats,
lipids and carbohydrates.
One food Calorie = 1kcal or 1000 cal
One calorie is the energy needed to raise 1g
of water by 1°C
One food Calorie = 4.18kJ (kilo joules) SI
unit

4. Compare the energy content
per100 g of carbohydrate, fat
and protein
 Energy in 100 g
Fats Carbohydrates Proteins
4 000 kJ 1 760 kJ 1 720 kJ
956kcal 421kcal 411kcal

5. How is food energy metabolized?

6. Why are fats so energy rich?
 Energy in 100 g
Fats Carbohydrates Proteins
4 000 kJ 1 760 kJ 1 720 kJ
956kcal 421kcal 411kcal

7. Let’s check the
food label again!
 What percentage calories from
fat are in this burger?
 (295/563) x 100 = 52.4%
 Whatpercentage of fat by
weight is in this burger?
 (33/219) x 100 = 15.1%

8. How much energy do we
need?
 Energy needs vary according to
size, age, gender and level of activity, but
you can calculate the amount you take
in and the amount you need.
 Amount taken in – amount used = amount stored

9. Staple diets vary by geographical
region and culture
 Availability and
sustainability of
land are major
factors in the food
energy source of a
population
 Initiatives like
«Golden Rice» can
use genetic
engineering to
supplement staple
foods to reduce
malnutrition

10. Carbohydrate-rich diets
 Two types:
 Large amounts of sugar: increase the risk of
developing type II diabetes and tooth decay.
 Large amounts of starch: usually from cereals
or root crops (tubers). If digested slowly, it can
be a healthy diet. If digested quickly, promtes
the development of type II diabetes.
 All diets with excessive amounts of
carbohydrates can cause obesity

11. Fat-rich diets
 They can cause obesity
 Other consequences depend on the type
of fatty acids contained in the fats. Fats,
unlike carbohydrates, cannot be used for
anaerobic respiration, so they are
unsuitable for athletes in strength events,
like running and weight lifting.

12. Protein-rich diets
 Protein is only used as an energy source if
it is present in the diet in excess or if
amounts of carbohydrates and fat are
very small.
 Weight lifters and body builders
sometimes have a high-protein diets and
they are sometimes used as a method for
slimming.

13. Eating and apetite
 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.

14. Nervous-hormonal pathway

15. Calculating Body Mass Index
(BMI)
 BMI= body mass (kg)  Calculate your BMI
height (m)
BMI Below 18.5 18.5 – 24.9 25.0 – 29.9 30.0 and above
Category Underweight Normal Overweight Obese
 Limitations of the BMI using this table:
 Race, gender and age are not considered
 No distinction is made on body
fat/water/muscle composition

16. Obesity
 A BMI of 30.0 or above is catalogued as obesity.
 In some countries rates of clinical obesity are
increasing for many reasons:
 Availability of cheap, high-energy food (junk food)
 Large portion sizes served in restaurants (super size)
 Increase use of vehicles for transport instead of
walking
 Increase in office-based jobs replacing jobs
involving physical activity
 Sedentary recreation (videogames) replacing
active recreation (sports)

17. Anorexia nervosa - causes
 Anorexia nervosa is an eating disorder in
which the patient severely limits food intake
(voluntary starvation).
 It is a medical condition with complex mental
and physiological causes.
 It is closely associated with body image and
meeting aesthetic standards imposed by
culture.
 It is most common in females, but does occur
in males.

18. Anorexia nervosa -
consequences
 Since the amount of carbohydrates and
fats consumed are too small, the body
starts breaking down its own proteins.
 Hair becomes thinner and can drop out.
 Skin becomes dry and bruises easily
 Blood pressure is reduced, slow heart rate
and poor circulation
 No ovulation or menstrual cycles and
infertility.