Energy, exercise and weight control
Published by Bupa's health information team, healthinfo@bupa.com, April 2008
This article looks at how calories and exercise are linked. It discusses how many calories you need each day, how these calories are used and which food groups are the best sources of energy.
What is a calorie?
Calories are units of energy. To fuel our bodies, we need thousands of calories: a thousand calories is a kilocalorie (kcal). To make things easier, people often refer to kilocalories simply as "calories". Joules are also used to measure energy. You will often see energy listed in both kilocalories and kilojoules on nutritional information labels.
How many calories do I need each day?
The average man consumes around 2,300 calories per day in food and drink. For women, the average is around 1,600. Everyone is different and you will need more or less than this depending on your basal metabolic rate (BMR) and how active you are. Working out your actual calorie requirement uses an equation that takes into account your age, weight, height and level of physical activity.
Where should I get my calories from?
The food and drink you take in supply energy (in calories) from four main sources.
| Energy source | Calories per gram |
|---|---|
| Fats | 9 |
| Carbohydrates | 3.75 |
| Protein | 4 |
| Alcohol | 7 |
For your body to function at its best, you need to eat a healthy diet. The table below shows how your calorie intake should be divided between the food groups for a balanced diet.
| Food source | Contribution to daily calorie intake |
|---|---|
| Fat | No more than 35 percent |
| Carbohydrate | Approximately 50 percent |
| Protein | Approximately 15 percent |
How are the calories used?
The calories you take in are used to meet three energy needs.
Basal metabolic rate
Even when you aren't exercising, you need energy. Your BMR (also known as resting metabolic rate) is the rate at which you use energy during rest and sleep to maintain basic bodily functions such as breathing and organ and cellular function. BMR accounts for about 60 to 70 percent of your energy needs.
BMR varies from person to person and depends on several factors including your weight, age and gender. The factor with the biggest effect on BMR is the level of fat-free mass in your body - that means all tissue that isn't fat, such as your muscles and organs.
Thermic effect of food
This is the extra energy your body uses to digest, absorb and store food.
Physical activity
This is the energy you use for movement or exercise, such as lifting, walking and running. It accounts for the rest of your energy expenditure - around 25 to 35 percent.
Why do we gain or lose weight?
Calories you don't burn are stored as fat. So you gain weight if you consume more calories in food and drink than you burn. You lose weight if you burn more calories than you consume and you maintain a steady weight if you use up the same number as you take in. This is true whether you exercise or not.
| Calories taken in | Calories used up | |
|---|---|---|
| 3,000 | 2,500 | Gain weight |
| 3,000 | 3,000 | Stable weight |
| 3,000 | 3,500 | Lose weight |
In practice, it's difficult to monitor exactly how many calories you eat and drink. One way to make sure you are getting it right is to keep an eye on your weight and try to keep your body mass index (BMI) within the healthy range. Use our online BMI calculator.
How can I burn more calories?
Doing more physical activity will mean you use more energy - exercise burns up calories as you do it. Exercising can also mean that you use more calories even when you are resting because it builds muscle, which burns more calories than fat.
What is the best way to replace calories used by exercise?
Unless you are trying to lose weight, if you exercise regularly and intensively, you will need more energy. The best way to get this is by eating more carbohydrates. Athletes and people who exercise intensively should get a minimum of 60 to 70 percent of their dietary energy from carbohydrates. So fill up on wholegrain, starchy foods such as brown bread, wholemeal pasta and brown rice.
Key points
- Aim to keep your body weight within the healthy range for your height.
- Weight loss, gain or maintenance, depends on the number of calories you take in compared with the number of calories you use up.
- You should try to get your calorie intake from a range of energy sources.
Further information
- Weightwise
www.bdaweightwise.com - Food Standards Agency
www.eatwell.gov.uk - British Heart Foundation
08450 70 80 70
www.bhf.org.uk
Related information
- Benefits of exercise
- Exercise - what type, how much?
- GI approach to weight management
- Healthy weight and exercise
