If a banana is said to have 100kcal and you and I eat it are we going to get:
1. all of those calories?
2. the same amount of energy or it varies person to person?
In: Biology
1. No
2. No
First of all, my understanding is that the FDA only requires the calories listed on a nutrition label to be 80% accurate.
Furthermore, the caloric content of food is determined by literally burning it in a bomb calorimeter and measuring how much energy was released by measuring the increase in temperature. Your body is not 100% efficient, and also cannot absorb 100% of the nutrition in the food that we eat. So the calories of a food measured in a lab is only an upper bound on the number of calories you would obtain by eating it.
If every digestible carb, fat, and protein in that banana were converted and then oxidized for energy, then you could expect the energy gain to be 100kcals.
Calorimeters measure how much energy is released from burning a piece of food. How much of that piece of food’s stored energy (in carbon bonds) being used for life functions will vary from person to person. It’s more of an average thing that you or a healthcare provider have to adjust for.
Think of calories as food energy money. A banana is worth 100kcal, but that money comes from different sources – sugar, fat, protein. And the body spends it all differently.
If you get 100kcal, you dont just store it in your bank as fat. Some goes to pay energy bills, some goes to build muscle, a little may go to fat storage. Some may go to feeding but bacteria.
Calories indicate how much energy is in a food. But only a small amount of that energy will go to storage, and usually only when you’ve already eaten too much and haven’t spent it with exercise.
Calories aren’t actual energy tho – like money they mean nothing without the goods you want to buy. Calories represent the energy released when breaking down a unit of a macronutrient, like a carb. 1 gram of carbs costs or yields 4 calories. That means when you eat a gram of sugar, the body breaks down the chemical bonds and releases 4 calories of heat.
The amount of calories is determined by burning the food in a device called a bomb calorimeter that measures how much heat is given off while burning the food. It’s a very simple way of measuring the energy in something.
How much you absorb versus what you pee and poop out, depends on a number of things. Exactly how much energy a person will extract from it (and whether they use it quickly or store it as fat) depends on a lot of things: what you ate, how quickly it passes through your GI tract, hormones, general health, etc. You might get absorb as much as 90% of the energy, but probably a bit less, and it’s going to vary from person to person.
You’ll never get 100% of the calories, but you’ll get most of them if you’re in decent health. On the other hand, if for example you have norovirus and are vomiting and pooping uncontrollably, you just aren’t going to have a chance to absorb anything.
It’s how much energy is in the food and not how much your body gets out of them. Here’s how they calculate calories:
The calorie content of food is measured in kilocalories (kcals), which is the amount of energy needed to raise 1 kilogram of water 1 degree Celsius.
A sample of food is placed in a sealed container filled with oxygen and surrounded by water. The food is ignited and the temperature increase of the water is measured to calculate the calorie content. This method is called direct calorimeter.
Now this process isn’t at all how our bodies process food. We use energy to break things down, some stuff can only get absorbed if other things are also present, lots of processing is dependent on the bacteria in your digestive tract and what kind of bacteria it is, etc…. So many factors determine what and how much your body can extract from food.
There are even plenty of foods that are considered negative calories in terms of what the body gains from digesting them as it takes so much energy to break them down. You may loose total calories eating them but gain lots of nutrients.
(Below stolen from Google AI search)
“Negative calorie” foods are foods that require more calories to digest than they contain, resulting in a net negative calorie intake. Some examples of negative calorie foods include:
Cucumbers
High in vitamins, minerals, and electrolytes, and contain around 16 calories per 100 grams.
Celery
Low on the glycemic index, meaning it has a slow, steady effect on blood sugar.
Broccoli
One cup of broccoli contains just 25 calories, but requires up to 80 calories to digest.
Apples
Contain very few calories, with 100 grams of apples containing only 50 calories.
Watermelon
94 percent of the weight in watermelon is water.
Lettuce
Contains only 5 calories per 100 grams, and has essential nutrients like vitamin C, iron, and calcium.
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