If energy in (from food consumed) equals energy out, body weight will remain stable. Any change to this balance equation causes changes in body weight. Most commonly today, the energy balance is tipped towards excess consumption and therefore weight gain. But are all calories equal or should we be looking at the individual nutrients that provide us with calories?  

Calories are just a way to measure energy

 Energy expenditure is usually measured in units of kilojoules or kilocalories, often simply abbreviated to ‘Calories’. Typical energy expenditure of an adult with low-moderate levels of physical activity is about 2000 Calories. 

People expend energy continuously. Even when sleeping the body is using energy. The lowest level of energy usage is known as the basal metabolic rate, or BMR. The BMR of every individual is unique and influenced by a number of factors, including percentage of muscle tissue, growth and repair demands, state of health and ambient temperature. (See Table 1). 

Physical activity levels also vary and have an immediate and direct impact on energy expenditure. The more vigorous the activity, the longer it is continued, and the more muscles in the body that are used, the greater the total energy expenditure.  

The other side of the energy balance is energy intake and this is wholly determined by the energy consumed from eating. Energy content of foods and diets is also measured in calories or kilojoules. Three types of macronutrients – proteins, fats and carbohydrates – supply calories. Alcohol is also a contributor of calories (See Table 2).  

The important thing to remember is that a calorie is a calorie regardless of whether it comes from fat, protein or carbohydrate – over-consumption of nay food can tip the balance towards weight gain! 

Energy content of foods

Most foods are a mix of carbohydrate, fat and protein and also contain water. Many plant foods contain indigestible fibrous parts. Water and indigestible dietary fibre are essential to good health, but do not provide calories. Similarly, vitamins and minerals which are needed for good health contain no calories. 

The energy/Calorie content of any food can be measured using analytical techniques in a laboratory. The energy content of a food can also be calculated by multiplying the each macronutrient in the food by the Calorie values in Table 2, and then adding the totals together. 

Many packaged foods make calculating calories easy, by carrying information about the energy content of the food on the label. This information is usually described in calories per serving or per given weight (usually 100 g).  

Choosing Foods to Maintain Energy Balance

There are 3 characteristics of food that can influence total energy consumption: 

1. Energy Density – Foods with low energy density are foods with relatively low Calorie content per given weight. Foods with high water content and foods with high non-digestible dietary fibre are bulkier making you feel fuller. Fruit, vegetables and wholegrains or foods made with a high proportion of these ingredients are good examples of less energy dense foods.  Foods with high fat or sugar content are much more energy dense, and so make the overconsumption of calories from these foods relatively easy. For example, 3 small boiled wontons contain about 420 calories while just one fried wonton provides the same amount of calories.  Similarly, a fresh rambutan has only 2/3 the calories of a rambutan preserved in sugar syrup, but is equally filling.

2. Appetite Influencers- Foods that have higher protein content or a high proportion of complex, starchy, carbohydrates are more satiating for longer than foods with higher fat or simple (non-starch) carbohydrate content. This means that choosing these foods more often will result in delayed hunger and less temptation to eat. These effects are quite subtle, but when recurring on a regular basis (for example in a diet with lots of fried foods) can result in slow but consistent overconsumption of calories. 

3. The “More” Factor – The desirability of a food can over-ride any built-in appetite controls. Foods that are especially delicious, or where there is little or no desire to limit quantities eaten such as a generous buffet, are more likely to be eaten in excess of the quantity needed to satisfy appetite. Lack of control of portion size is increasingly recognized as an important contributor of over-consumption. 

Variable Calorie Needs

The amount of calories that a person needs changes throughout the life cycle. During periods of rapid growth such as childhood, adolescence and pregnancy, energy needs are relatively higher than during adulthood.  

Calorie needs are also heavily influenced by lifestyle.  Physically active individuals require more energy than those who have a more sedentary lifestyle. The extra energy demands are not only to fuel the extra activity, but also to sustain higher BMR, even when at rest.  There are a number of reasons for this, but one important reason is that those who are physically active develop more muscle tissue. Muscle tissue is more metabolically active than fat tissue, so a body which is more muscular than another body of the same weight will burn more energy at all times than the more ‘fatty’ body. Male hormones encourage the development of muscle tissue, hence men have relatively more muscle and less fat than women, and a man weighing 60kgs can eat slightly more calories each day than a woman without gaining weight! 

Nutrient and Energy Needs

As well as protein, fat and carbohydrate, the body also needs small amounts of over 40 different minerals and vitamins. Most of these vitamins and minerals, which are collectively described as micronutrients are present in foods in relatively small amounts. Many foods that are less energy dense are micronutrient rich. For example, fruits and vegetables are the most concentrated sources of many of the B vitamins, as well as vitamin C; low fat dairy contains just as much calcium and phosphorous as full fat milk but less calories; lean meat is an excellent source of essential minerals such as iron and zinc. So including generous quantities of these foods in your regular diet will help to ensure a diet balanced both in energy, and also overall nutrition. 

Balance on all fronts

So, calories in = calories out = weight maintenance. And choosing nutrient-rich foods as the basis of the diet with additional snacks and treats occasionally is the key to following a healthy diet. Evidence also suggests that maintaining a healthy balanced diet long term, is most easily achieved by also remembering to balance some other essential ingredients, such as pleasure, social motivations and convenience. Balance on all fronts is the key to a healthy lifestyle!

For more information and further reading:

IFIC exploratory research on consumer perceptions of energy balance:

http://www.ific.org/research/energybalres.cfm

Human energy requirement – Report of Joint FAO/WHO/UNU Expert Consultation:

http://www.fao.org/docrep/007/y5686e/y5686e00.htm

Astrup, A.:“The Satiating Power of Protein – a Key to Obesity Prevention?” The American Journal of Clinical Nutrition, Vol. 82, No. 1, 1-2 July 2005