Body growth, development and functioning are some of the vital and fundamental aspects of life. They cannot be explained without referring to energy: fuel of life is dependent on energy transformations. Our foods bring us the vital energy that our body is burning throughout the day.

What are calories and joules ?

The energy contained in our food is measured in terms of calories (cal) and joules (J). Technically, one calorie is the amount of energy required to raise the temperature of 1 gram of water by 1 degree Celsius (1.8 degrees Fahrenheit). When talking about the energy content of food, we usually work with a higher unit, which is 1000 times bigger than a calorie, the kilocalorie (kcal). However, in non-scientific contexts the kilocalorie is often referred to as a Calorie (capital "C"), or just calories. Another unit to express energy is the joule (J). One joule is the amount of energy expended by a force of 1 newton moving an object 1 metre along the direction of the force. Similarly to calories, a kilojoule (kJ) is the equivalent of 1000 joules.

The relation between kilocalories and kilojoules is: 1 kcal = 4.184 kJ.

The quantity of energy contained in foods and drinks, or spent by doing a certain activity, can both be expressed in kilocalories or kilojoules. According to the current EU regulation on food labelling, both units (kcal and kJ) are to be used for the declaration of the energy value of foodstuffs on pack labels.

Energy Balance: the ins and outs of energy

The fundamental principle of energy balance is:

Changes in energy (fat) stores = energy (Calories) intake - energy (Calories) expenditure

Overweight and obesity are influenced by many factors including hereditary, environmental and behavioural factors, ageing and pregnancy. Despite the fact that obesity is not simply a result of overindulgence in highly palatable foods or of a lack of physical activity, dietary factors and physical activity patterns strongly influence the energy balance equation. Besides, they are also the major modifiable factors. High-fat, energy-dense diets and sedentary lifestyles are the two characteristics most often associated with the increased prevalence of obesity world-wide. Conversely, weight loss occurs when energy intake is less than energy expenditure over an extended period of time. A restricted calorie diet combined with increased physical activity is generally the advice given by dieticians for sustained weight loss.

Miracle or wonder diets that severely limit calories or restrict food groups should be avoided as they are often limiting in important nutrients and/or cannot be sustained for prolonged periods. Besides, they do not teach correct eating habits and can result in yo-yo effect (the gain and loss of weight in cycles resulting from dieting followed by over-eating). This yo-yo effect may be dangerous to long-term physical and mental health. Individuals should not be over-ambitious with their goal setting. A loss of just 10% of initial weight will bring measurable health benefits.

Energy intake

The amount of energy we absorb through our food intake is commonly called the energy intake, and it is the fuel of our body. Each food contains a certain amount of energy which depends on its composition. Macronutrients are nutrients that provide calories or energy. Nutrients are substances needed for growth, metabolism, and for other body functions. Since “macro” means large, macronutrients are nutrients needed in large amounts. There are three macronutrients:

• Carbohydrates
• Protein
• Fat

While each of these macronutrients provides calories, the amount of calories that each one provides varies.

Carbohydrates provide 4 calories per gram.
Protein provides 4 calories per gram.
Fat provides 9 calories per gram.

Besides carbohydrates, protein, and fat, the only other substance that provides calories is alcohol. Alcohol provides 7 calories per gram. Alcohol, however, is not a macronutrient because we do not need it for survival.

This means that if a product contains 5 g of carbohydrates or proteins, it will provide 20 calories, whilst a product containing 5 grams of fat provides 45 calories, and if it contains 5 grams of alcohol it will provide 35 calories. Therefore, it would seem that a good way to decrease the calories in your food is to reduce the amount of alcohol (because it is not a necessary nutrient) and fat (because it is the most energy-dense nutrient). However fats play a very important role in our body functions (carrier of fat-soluble vitamins and essential fatty acids), and they increase the palatability of the diet. So, when attempting to lose weight through reduction in energy intake, none of the macronutrients should be severely decreased, but we should follow the general pattern of 55% carbohydrates, 15% protein and 30% fat of our daily energy intake or tailor the diet to individual needs.

Energy expenditure

Why do we need energy? Our body spends energy continuously, through three ways :

• The amount of energy burned when our body is at rest, also called basal metabolic rate or BMR. In a symbolic way, it is the number of calories we would burn if we stayed in bed all day. More scientifically, it means the energy required for the basal functioning of our vital organs (e.g., heart, lungs, brain). It counts for 60-70% of our total daily requirement.
• A quantity of energy is used for digesting, absorbing and storing the food we eat in our body (also called diet-induced thermogenesis). It accounts for around 10% of our total daily requirement.
• Each motion, action, gesture that we do entails an energy cost. The total cost of physical activity usually accounts for 20 to 30% of our daily energy expenditure and it varies according to our level of physical activity: the more active we are, the more energy we spend.

Total energy expenditure =
Basal Metabolic Rate + Diet-induced Thermogenesis + Physical Activity

So how can we achieve a deficit in the energy balance (weight loss)?

As mentioned above, if we eat fewer calories than we spend, over an extended period of time our body will use the stored fat to fill the gap. Managing energy balance should be based on playing with both food consumption (IN) and physical activity (OUT) instead of concentrating ourselves on counting the calories we eat while neglecting the calories we burn and vice versa. For example, if we want to cut down 100 calories, we could do it by either adding a 15 min walk each day or reducing the portion sizes we eat or a combination of both. Remember that this will only occur if those changes are the only changes you make to your diet and lifestyle and if they are sustained over a certain period of time (e.g. if you start eating an extra biscuit, you should factor that in too, otherwise you might not achieve the energy deficit).

The calorie burner will help you to become aware of the energy you spend through your daily activities. It will help you to plan some extra-activities to achieve small goals (such as cutting 100 calories daily ) to better manage your energy balance.