Energy is required by all living creatures to support their lives. In common with all other animals, humans take in energy (measured in calories or joules; 1 kcal = 4.2 kJ) released from food and beverages to provide fuel for bodily functions and various physical activities.

Sources

Dietary energy mainly comes from carbohydrates, proteins and fats in foods and beverages. After digestion, they provide different amount of energy to our body.

Energy density values of different nutrients (kcal/gram)
Carbohydrates Protein Fat
Each g of carbohydrates provides 4 kcal Each g of protein provides 4 kcal Each g of fat provides 9 kcal

Energy Requirement

Daily energy requirement of a person is the amount of energy intake required per day to balance the energy used to maintain his/her daily activities, bodily functions and growth. It varies according to the person’s sex, age, weight, height, health status, as well as level of physical activity. For example, a breastfeeding infant weighing 8 kilograms (kg) requires about 720 kcal a day for optimal growth; a highly active 30-year-old lactating mother may need to take in about 2 900 kcal from foods and beverages a day; while a healthy 60-year-old man with a low level of physical activity may require about 2 100 kcal a day to maintain energy balance.

If you take in more energy than you use to maintain daily activities, bodily functions and growth, you will gain weight (mainly as body fat), leading to overweight and obesity in the long term. Conversely, you will lose weight when you take in less energy than you use. To maintain a healthy weight, you need to balance your energy intake and output - that is, energy intake from food and beverages should be equal to the energy you use.

The Chinese Nutrition Society has estimated the daily energy requirements for the average-built Chinese as shown in the following table.

Estimated daily energy requirement (kcal/day)
for healthy individuals with no chronic disease and specific nutritional requirement
Age (year) Male (kcal/day) Female (kcal/day)
  Level of physical activity Level of physical activity
  Light Moderate High Light Moderate High
0 -
90 kcal/kg/day 90 kcal/kg/day
0.5 - 80 kcal/kg/day 80 kcal/kg/day
1 - 900 800
2 - 1100 1000
3 - 1 250 1 200
4 - 1 300 1 250
5 - 1 400 1 300
6 - 1 400 1 600 1 800 1 250 1 450 1 650
7 - 1 500 1 700 1 900 1 350 1 550 1 750
8 - 1 650 1 850 2 100 1 450 1 700 1 900
9 - 1 750 2 000 2 250 1 550 1 800 2 000
10 - 1 800 2 050 2 300 1 650 1 900 2 150
11 - 13 2 050 2 350 2 600 1 800 2 050 2 300
14 - 17 2 500 2 850 3 200 2 000 2 300 2 550
18 - 49 2 250 2 600 3 000 1 800 2 100 2 400
Pregnant women            
- 1st trimester   -     + 0  
- 2nd trimester   -     + 300  
- 3rd trimester   -     + 450  
Lactating mothers   -     + 500  
50 - 64 2 100 2 450 2 800 1 750 2 050 2 350
65 - 79 2 050 2 350 - 1 700 1 950 -
80 and above 1 900 2 200 - 1 500 1 750 -

Source: Chinese DRIs 2013. Chinese Nutrition Society.

Health Alert

Being obese may shorten life expectancy and increase the risk of various chronic diseases, including type 2 diabetes, coronary heart disease, hypertension, certain cancers such as colon cancer and breast cancer (in post-menopausal women), gallbladder disease and osteoarthritis (knees). However, underweight due to long-term inadequate energy intake may increase the risk of anemia, heart beat irregularities, osteoporosis and bone fracture.

Practical Tips for Eating Well for Fewer Calories

To maintain an optimal weight, it is important to control your energy intake by ‘eating well’. Eating well is not only about what and how much you eat, but also about when and how you eat. The following are some suggestions for eating well:

What to eat?

 
 

How much to eat?

 
 

When to eat?

 
 

How to eat?

 
 

Go and review your own eating practices and find out what changes you could make to eat well.

Reference

Chinese DRIs 2013. Chinese Nutrition Society.