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
Everything varies in how our bodies metabolise and process etc etc. it will never be an exact science
They’ll vary in size and composition based on their growing conditions so the nutritional value is based on an average. So you will gain an average of that many calories, minus the cost in calories to process the banana into nutrients in your gut which is not factored into the calculation. That “tax” to convert it into usable nutrients will vary from person to person.
So to answer your question, no, but more or less yes.
Depends on how hungry you are and your metabolism as well as if you already ate and how much.
So if you are starving and you eat a banana with nothing else in your digestive system and assuming you are healthy young individual you will extract around 80-90% of the calories (for some people it will be more, for some it will be less) because nothing is 100% efficient.
Other factors include if you already ate too much because then the food is rushed through your system to make room that is already in your stomach (making you go to bathroom immediately after overeating).
If you are at your daily caloritic limit (body can only process a limited amount) so average 2000-3000 but for people who work extremely physicaly demanding jobs or they work in extreme cold where they burn more calories it can be 4000-5000. Again all of this depends on the individual, their age, size, health etc.
We are all different and operate differently just like our digestive tract.
TL;DR On average our digestion is 80-90% efficient, the rest just passes through.
Well your body is not a 100% efficiency machine (nor anything else in the universe) so losses here/there/everywhere.
Different persons gonna be different efficiencies; think new car engine vs old car engine.
The calories are measured by the generated heat when burning the food. It is a direct conversion of the food into energy. When you consume it, you do not absorb all of it. If you did, we would never have to poop.
As for the second question, the answer is no. There are probably small differences from person to person, but for people with gastrointestinal issues (IBS, crohns, celiac, etc) they do not absorb nutrients in the same way, and have issues absorbing certain types of sugars, proteins, etc. this leads to a difference in total calorie consumption
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Simple answer:
You have to subtract out the fiber calories to get the true calories. Fiber passes through you and is not absorbed, but they are included in calorie counts at 4 calories per gram. So if you eat something that is 100 calories but it has two grams of fiber in it, you’ll really only process 92 calories from it.
Answer with a slight wrinkle:
Soluble fiber provides 2 calories per gram and insoluble fiber provides no calories per gram. So if you know the amount of soluble and insoluble fiber you can subtract 2 calories per gram of insoluble fiber from the total on the label, and subtract 4 calories per gram of soluble fiber from the total on the label.
But this is a huge pain and fiber is good for you, so don’t do that. We don’t want people sweating over fiber calories.
Fun fact, this is one reason why the weight watchers points system assigns fewer points to fiber-rich foods.
The numbers from research are that humans get over 95% of the calories from anything we eat, so for your 100kcal item your body gets approximately 95kcal of energy. The breakdown seems to be that we are ~98% efficient at digesting carbs, 95-97% efficient at digesting fats, and 90-95% efficient at digesting proteins.
This will vary a tiny bit person to person along a normal distribution, but that variation would be so small its negligible for the majority of people, the exception being medical conditions that affect your digestive process. For example, because lactose intolerance affects how the body digests lactose, people with this condition would get less calories from milk than someone without the intolerance.
These efficiencies are not included in the labels on foods, but are also not included in dietary recommendations. So when we say that on average people need 2,500kcal per day, you don’t need to do any math on efficiencies and can just add together what food labels say to reach that value. So if you eat that 100kcal snack, it counts as 100 against that 2500 target.
On the off chance this question was more than just curiosity, you should not need to take caloric efficiency into consideration when thinking about your diet. If you are in a position where these efficiencies matter you should be working closely with a dietician and not trying to do it on your own
Depends on metabolic efficiency so expect losses there. Fiber funnily enough doesn’t get counted as kcal, but some gets broken up into fatty chains and are therefore somewhat caloric albeit negligible and far outweighed by metabolic (in) efficiency.
Your body won’t “absorb” all of those calories, because it isn’t 100% efficient. It also depends on which macro your talking about (protein, carbs or fat) as well as what state your body is in.
For example: if your body’s severely glycogen depleted, and you’re only shovelling lean turkey breast down your throat, your body will try to convert protein to carbs to fill those glycogen stores. This process, gluconeogenesis, if I recall, is about 75% efficient, so 100kcal of protein ends up being 75kcal of glucose.
As with most people, there will be some variation from one to the other, but I’ve never really dug into that side of things.
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