Calculating energy content of foods
Without mathematics, there’s nothing you can do. Everything around you is mathematics. Numbers rule the universe. Neither fitness nor bodybuilding are exceptions to this rule. The two most important numbers in fitness and bodybuilding relate to our daily calorie intake (computing the energy value of foods) and to our daily calorie expenditure (computing how many calories you burn during the day). These two numbers alone do not have any special importance. However, as soon as we compare these two numbers we’re getting a clear picture of whether we are approaching toward or moving away from our goals (this is an energy-balancing equation). For some of us these goals include increase in muscles mass and gaining weight. For others this can be losing extra pounds or simply maintain the status quo.
Correct calorie counting is an important step in reaching your goals. Therefore, the main purpose of this article is to teach you how to calculate the energy value of food – your total daily calorie intake. Knowing how many calories you eat each day is essential to finding out if you’ll lose weight or gain weight. Off course, calculating daily caloric intake (energy content of food) is just part of the equation. It’s obvious that you will have to compare this value with your daily expenditure to see where you stand.
Let’s start with computing the energy value of foods, or simply to say – counting the calories…
Components of energy intake (“energy in”)
The math is quite simple here. Much like a car needs gasoline to work; your body needs energy every day. The energy in food and beverages is the only contributor to the “energy in” side of the energy balance equation. There is no other way for your body to get the energy it needs. Once you eat your food or drink your beverage, your body gets the energy it needs in the form of calories.
What are calories? Calories are the energy currency used by your body. They measure how much energy you get from food. In other words, the same way you need money to buy things at the store, your body needs calories to keep working. Think of calories as meaning “the energy your body uses every day”.
A calorie reflects food energy regardless of the food source. Thus, 100 calories from mayonnaise equals (the same) 100 calories in 20 celery stalks. The more food you consume, the more calories you consume.
From an energy standpoint, 500 kCal of chocolate ice cream topped with whipped cream and chocolate chips is no more fattening than 500 kCal of watermelon, 500 kCal of cheese and sausage pizza, or 500 kCal of a bagel with salmon, onions, and sour cream. Even celery would become a “fattening” food if consumed in excess. Whether this is a healthy product or not, no idea! That will depend on all the other nutrients present in this product.
Before you can decide how much food will supply the energy your body needs in a day, you must first become familiar with the amounts of energy in foods and beverages. There are several ways to achieve this. So let’s examine some popular methods for computing the energy value of foods.
DETERMINING A FOOD’S MACRONUTRIENT COMPOSITION AND ENERGY CONTRIBUTION
As you will see from the methods below, computing the energy value of foods is not rocket science.
LOOKING AT FOOD LABELS AS METHOD OF COMPUTING THE ENERGY VALUE OF FOODS
Food labels usually carry information on the energy content of the food. They also must indicate a food’s macronutrient content (how many grams of protein, carbohydrates and fat per 100 grams of food portion). Look at the “Nutrition information” or “Nutrition – typical values” on a selection of food labels. The food’s energy content is often called its energy value, and is usually given in kilojoules (kj) or kilocalories (kcal) per 100g of food. Kilojoules (kJ) and kilocalories (kcal) are simply two different units for measuring energy. One calorie is equal to approximately 4.2 kilojoules. Often you’ll also be able to find energy value per serving.
In this example, a plastic pot contains 300 grams of low fat cottage cheese. On the food label you can see that 1/3 of a pot (100 g) contains 12.4 grams of protein, 0.8 grams of fat, and 3.1 grams of carbohydrate. In the second column you can see the typical values per serving (30 g). Serving sizes are based on the amount of food people typically consume, rather than how much they should consume. Therefore, 100 grams of this cottage cheese contains 69 kcal (energy value). Knowing that, it’s easy to calculate the energy value for any other quantity of cottage cheese you decide to eat. If 100 grams has 69 calories, how much calories would 75 or 85 grams have? Such type of questions must be solved using unitary method.
As you can see, all foods contain a mixture of nutrients, and the energy value of a particular food depends on the amount of carbohydrate, fat and protein it contains. For example, one slice of wholemeal bread provides roughly the same amount of energy (kcal) as one pat (7 g) of butter. However, their composition is very different. In bread, most energy (75%) comes from carbohydrate, while in butter, virtually all (99.7%) comes from fat.
COMPUTING THE ENERGY VALUE OF FOODS MANUALLY
Some foods do not need to have a nutrition facts table. For example, many fruits and vegetables do not come in a package, so they do not have labels. The same goes for the row meat and poultry, raw seafood, milk sold in refillable glass containers, etc.
However, for foods that don’t have information about energy content printed on the label, as long as you have access to information about the masses of different nutrients in the food, you can easily calculate energy content. Unfortunately this is sometimes time consuming.
Different foods provide different amounts of energy for a given weight. The energy value of a food depends on the amount of carbohydrate, protein, fat, fiber and alcohol it contains. Because these nutrients have different chemical structures, they provide different amounts of energy.
| Nutrient | Kilocalories per gram (kCal/g) | Kilojoules per gram (kJ/g) |
|---|---|---|
| Protein | 4 | 17 |
| Carbohydrate | 4 | 16 |
| Fat | 9 | 37 |
| Alcohol | 7 | 29 |
| Water | 0 | 0 |
The energy values for carbohydrate and protein are approximately 4 kcal (17 kjoule) per gram. Note that 1 g of fat contains more than twice the number of kcalories as 1 g of carbohydrate or protein. The fuel factor for alcohol (7 kcal/g) falls midway between fat and that of carbohydrate and protein. Hence if the amounts (grams) of carbohydrate, fat, protein and alcohol in a meal are known, the energy value of the meal can be calculated easily. Micro nutrients such as vitamins, minerals and water do not contribute to energy intake.
Add the energy from carbohydrate, protein and fat. The total, in calories, is the energy content of the food. This is the same information available on a nutritional label, for those foods that provide nutritional information.
Example:
The energy value for 100 g of cottage cheese containing 12.4 grams of protein, 0.8 grams of fat, and 3.1 grams of carbohydrate would be calculated as follows:
- Calculate the energy provided by carbohydrates: 3.1 g x 4 kcal = 12.40 kcal
- Determine the energy provided by fats : 0.8 g x 9 kcal = 7.20 kcal
- Finally, calculate the energy provided by protein: 12.4 g x 4 kcal = 49.60 kcal
- Total energy value for 100 g is: 12.40 + 7.20 + 49.60 = 69,20 kcal
As you can see this is indeed the same information available on a nutritional label.
USING CALORIE COUNTER CHARTS (CALORIE TABLES FOR COMMON FOODS)
If you are not sure of the calories in certain foods, find a good food calorie list by using the web. Even better, consider going to your local book store and browse for a good book on nutrition to fill in gaps in your knowledge. A good book will likely have food lists their calorie count. The NutriBase Nutrition Facts Desk Reference is an essential tool for monitoring the nutritional value of your diet. It is recognized by health experts as the best source of information on food values and is used widely by physicians, nutritionists, and health-conscious consumers alike.
The calorie table is a table of the caloric value of the foods and beverages we have in our daily diet.
In addition to the caloric value of most foods we have in our daily diet, these charts also show us the exact macronutrient content of specific foods (grams of protein, carbohydrate and fat) per 100 grams or 100 milliliters of many of our everyday foods/beverages. Sometimes these tables contain even the values of glycemic load and glycemic index.
For better visibility and easier navigation among many food items, these tables are organized according to certain food categories. Some of these categories include: milk and dairy products, meat and meat products, fish, fruit, vegetables, cereal products, eggs, sweets, etc.
Example:
Let’s assume your lunch constitutes from the following food items:
| Food items in lunch | Weight in grams (use a kitchen scale) |
| 1 large baked potato (peel not eaten) | 225 g |
| 2 tsp olive oil spread | 10 g |
| 1 small tin tuna in brine | 100 g |
| 1 bowl salad (mixed salad greens) | 125 g |
| 1 tbsp Italian oil/vinegar dressing | 11 g |
| 2 kiwi fruit | 152 g |
We’re using FoodData Central to find the energy values and the exact macronutrient content for the following food items:
| Food item | Quantity | Calories | Fat (g) | Carbs (g) | Protein (g) | Water (g) |
|---|---|---|---|---|---|---|
| Potato, baked, peel not eaten | 100 g | 93 | 0,10 | 21,45 | 1,95 | 75,08 |
| Olive oil (spread) | 1 tbsp (14 g) | 124 | 14 | 0 | 0 | 0 |
| Tuna, canned, water pack | 100 g | 90 | 0,94 | 0,08 | 19 | 79 |
| Mixed salad greens, raw | 100 g | 16 | 0,22 | 2,93 | 1,61 | 94,42 |
| Italian salad dressing, made with vinegar and oil | 1 tbsp (14 g) | 35 | 3,10 | 1,78 | 0,06 | 9,32 |
| Kiwi fruit | 100 g | 58 | 0,44 | 14 | 1,06 | 83,9 |
Now all we have to do is recalculate everything to the actual weights of individual foods from our lunch menu. For our needs, it is enough to recalculate only the column showing the caloric values. Recalculation of other columns only makes sense if you are interested in finding out how much of the total caloric value of your lunch is coming from individual components (fats, carbs, and proteins).
| Food item | Quantity | Calories | Fat (g) | Carbs (g) | Protein (g) | Water (g) |
|---|---|---|---|---|---|---|
| Potato, baked, peel not eaten | 225 g | 209 | 0,23 | 48,26 | 4,39 | 168,93 |
| Olive oil (spread) | 10 g | 89 | 10 | 0 | 0 | 0 |
| Tuna, canned, water pack | 100 g | 90 | 0,94 | 0,08 | 19 | 79 |
| Mixed salad greens, raw | 125 g | 20 | 0,28 | 3,66 | 2,01 | 118,03 |
| Italian salad dressing, made with vinegar and oil | 11 g | 28 | 2,44 | 1,40 | 0,05 | 7,32 |
| Kiwi fruit | 152 g | 88 | 0,67 | 21,28 | 1,61 | 127,53 |
| TOTAL | 623 g | 524 | 14,6 g | 74,68 g | 27,06 g | 500,81 g |
FOOD CALORIE AND NUTRITION CALCULATOR
Alternatively, computer programs (calorie counter calculator) can readily provide this information.
MyFitnessPal is one of the most popular calorie counters right now. MyFitnessPal’s nutrition database is very extensive, containing over 5 million foods. However, some of its features can only be accessed in the premium version, which is $49.99 per year.
Closing thoughts: computing the energy value of foods
By computing calories, you can determine the energy value of the foods you eat. The great thing about calorie counting is that you will learn so much about what you eat, and make so many important changes to your eating and drinking habits, that you’ll probably find it difficult to go back to your old ways. For weight loss you simply have to consume fewer calories than you burn each day. The types of foods and calories you choose to eat and how you burn those calories (this is where exercise and other factors enter the picture) is up to you. You can lose weight even if you eat only chocolates, as long as you burn more calories. This is the reason why it’s so important to know these two numbers: (a) your daily calorie intake, and (b) your daily calorie expenditure.
It doesn’t matter how you count calories, whether you use high tech apps or a simple pen or paper method. Try to be as consistent as possible. An accurate number will help you get the health or weight loss results you want. In our next post we’ll show you how to calculate energy expenditure.
