# Calculate Energy Intake

1. Dec 20, 2015

### Physicsrapper

I've read somewhere that 100 g of tomatoes have approximately 1 g protein, 2.6 g carbohydrates and 0.2 g fat. So it has 4*1 + 4*2.6 + 9*0.2 = 16.2 kcal

A fried egg (~50 g) has 89 kcal, 4 g protein, 0.4 g carbohydrates, 6.7 g fat. So it has 4*4+4*0.4+9*6.7 = 77.9 kcal

The sum of the kcals is 16.2 + 77.9 = 94.1 kcal
I have to write the total of the energy intake. Is it the same as the sum of the kcals, 94.1 kcal?
If not, then how can I calculate it?

2. Dec 21, 2015

### BvU

Yes. Energies can be added.

In fact you have used that twice already when adding up the contributions from the constituents...

3. Dec 21, 2015

### Staff: Mentor

In your example: total energy intake is the sum of the kcal calculation for each food item, summed over all food items.

If you are taking a nutrition course note:

1. Food antagonisms and environmental/genetic factors (bioavailability) reduce the uptake of macronutrients: fat, protein, carbohydrate content. Example: phytates in raw, or undercooked legumes.
This talks mainly about phytates and micronutrients. Micronutrient deficiencies can lead to reduced uptake/usage of macronutrients.
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2266880/

2. 2.2kg of your body weight comes from gut bacteria. They consume food energy and alter uptake rates of some nutrients + or -.
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3601187/

3. Not all of what you eat is "yours", so to speak.

FWIW - a lot of calorie data originated from data based on finding the heat of combustion of constituents of food items using a bomb calorimeter.
https://en.wikipedia.org/wiki/Calorimeter

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