In order to calculate the calories of a meal, we must first understand the nature and differences of this meal (this is also the way of thinking of fitness people). In other words, what ingredients in food are calories, carbohydrates, protein, fat, etc. These three nutrients basically occupy all the sources of dietary calories.

Knowing the nature of heat in food, corresponding it to actual food, and then using the heat values of three nutrients, we can quickly calculate the heat of a meal.

1. Carbohydrate ≈ protein ≈ 4 kcal/g; Oil ≈9 kcal/g (this value must be kept in mind), and it can also be approximately considered that the calories of carbohydrates and protein are half that of oil.

2. 1 kcal = 1 kcal (kcal) ≈4.2 kJ (kJ)

Look at the following common breakfast combinations.

2 slices of bread +2 boiled eggs (whole eggs)+a cup of instant coffee.

1 slice of bread (50g) contains carbohydrate 2 1.6g, protein 4.5g and fat 0.8g, and the calorie is: 21.6 * 4+4.5 * 4+0.8 * 9 =11.

1 standard size egg (edible part 53g), containing carbohydrate 1.5g, protein 7g, fat 4.7g, and calorie: 1.5*4+7*4+4.7*9=76.3 calories.

Take a brand of coffee as an example. 1 cup of instant coffee contains 9.5g of carbohydrate, 0.5g of protein, 7g of fat 1.7g, and the calorie is 9.5 * 4+0.5 * 4+1.7 * 9 = 55.3kcal ≈ 232.26kj. ..

To sum up, the calories of this breakfast are:11.6 * 2+76.3 * 2+55.3 = 431.1calorie, carbohydrate 55.7g, protein 23.5g and fat.

Note: In order to make people adopt the thinking mode of nutritional structure, the calories in the nutritional table are not directly used in this calculation.

Let's look at the last example, which is also a complicated situation in daily application.

1 bowl of rice +2 chicken legs (with skin)+some vegetables

1 bowl of rice (200g) contains 5 1.2g of carbohydrate, 5.2g of protein and 0.6g of fat, and the calorie is 51.2 * 4+5.2 * 4+0.6 * 9 = 231calorie.

1 chicken leg (edible part 83g), containing carbohydrate 0g, protein 13.3g, fat 10.8g, and calorie:13.3 * 4+10.8 * 9 =1.

The calories of green leafy vegetables are almost zero, which is not included.

To sum up, the calories of this meal are: 231+150.4 * 2 = 531.8 calories, carbohydrate 5 1.2g, protein 3 1.8g, and fat 22.2g

Note: Generally, the carbohydrate content of rice is 25%, excluding protein and fat.

The above is a quick way to calculate the calories of a meal. What seems complicated is actually the relationship among carbohydrate, protein and fat. In addition, because different foods contain different moisture, the proportion of nutrients is also different, but the general staple food contains 25-50% carbohydrates (depending on the dry humidity of the food), and meat products contain about 20% protein and about 5% fat.