Even when you know what to eat, the terminology describing how much you should eat can be confusing. Here we clarify them.
Cook books, dietary advice, restaurants and food labels refer to portions, servings and kilojoules when indicating the quantity of foods. What do they mean?
What is a portion?
A portion is the amount of food that you choose to eat for a meal or snack. It can be big or small. In restaurants, the average portion sizes have grown so much over the past 20 years that sometimes the plate arrives and you’re overwhelmed with the amount of food. Gradually consumers start thinking that this is an acceptable amount of food to eat at one sitting at home too!
What is a serving?
A serving is a measured amount of food or drink, such as one slice of bread or one cup (250 ml) of milk, as it is generally served. Servings are indicated on food labels. The label of a box of crisp bread, for example, gives the nutritional value per 100 grams but also the value per serving, which is indicated as 1 biscuit or 5.81 grams. Similarly, the label of a can of condensed milk gives nutritional information for 100 grams, and for a serving of 25 grams. This means that a tin of 385 gram contains 15.4 servings of 25 grams each.
The serving size for meat is approximately 56 to 85 grams (the size of a deck of cards), for eggs it is two eggs, for dry beans it is a third cup. For cereals, the amount is 28 grams and for pasta and rice, it is half a cup. A serving of fruits and vegetables equals on piece or half a cup of chopped fruit or vegetables. For fruit juice, a serving equals 180 ml. A serving of dairy products is one cup and for cheese it is 42 grams.
What are kilojoules?
The foods we eat provide us with energy, which is measured in kilojoules (kJ). A kilojoule therefore is a unit that measures energy, in the same way that kilometres measure distance. [Before South Africa adapted the metrication system, the unit for energy measurement was a calorie (1 kilojoule = 239.005736 calories) and many magazines, books and recipes published in the USA still use calories.]
Just how much energy there is in a product depends on the amount of carbohydrate, protein and fat the food contains. A serving of condensed milk (i.e. 25 grams) will provide 345 kJ of energy and a serving of crisp bread (i.e. 5.81 grams) 90 kJ, according to the respective labels. Fats and alcohol are by far the most energy-dense foods. This is why they should only be consumed in moderation, particularly if you are overweight or obese.
Variable energy requirements
Owing to differences in genetic predisposition, build, gender, age, metabolism, environment and personal activities, energy requirements differ from one person to the next. However, when you regularly consume more energy than your body needs, the excess is stored inside fat cells. One kilogram of body fat contains the equivalent of 37,000 kJ which means that you have to burn an additional 5,000 kJ a day if you want to get rid of it.
Sources
http://en.wikipedia.org
http://nutrition.about.com
http://www.betterhealth.vic.gov.au
http://www.nhlbi.nih.gov