How much food is absorbed, and how much comes out again?

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I always thought that most of the food comes out again after nutrients are absorbed.

For example, here is a can of noodles. It says the 800gr in the can have a total of something like 600kcal. If the entire can would be converted into fat, this would have to be about 5500 kcal. That would mean that about 90% of it comes out again.

But sometimes I eat and eat and eat and a lot less is coming out then went in.

So, how much food is actually coming out again after being processed in the body?

In: 128

24 Answers

Anonymous 0 Comments

Really depends on what you eat. All simple sugars will either be used to fuel your metabolism or be stored as fat. Fibers are by definition indigestible so they’ll do that their thing and be excreted. Say you eat a 100g apple that’s 80% water, 10 grams of fiber and 10 grams of sugar; you’ll excrete at least 10 grams of fiber (+some water and dead bacteria from your gut). The rest will either be used immediately, stored as glycogen or fat, and most of the water will evaporate or be excreted by your kidneys.

Anonymous 0 Comments

Depends on the food. With foods that we’re great at digesting, we actually breath out most of them as CO2 & H2O.

Anonymous 0 Comments

This is quite complex and depends on a lot of things. Firstly a lot of the food is just water and will be absorbed into the blood stream and end up in the urine. Similarly a lot of vitamins and minerals will take the same way unless it is actually used in the body. And then there is protein which can be converted to carbohydrates but only through a process that uses energy. So you might start with two amino acids and get one glucose molecule from it, the remainder will turn into carbon dioxide which you breathe out or other molecules that goes out with the urine. There is also some loss when breaking down longer carbohydrates like starch and fibers as well as when converting carbohydrates into fat.

Anonymous 0 Comments

Really depends on what you eat. All simple sugars will either be used to fuel your metabolism or be stored as fat. Fibers are by definition indigestible so they’ll do that their thing and be excreted. Say you eat a 100g apple that’s 80% water, 10 grams of fiber and 10 grams of sugar; you’ll excrete at least 10 grams of fiber (+some water and dead bacteria from your gut). The rest will either be used immediately, stored as glycogen or fat, and most of the water will evaporate or be excreted by your kidneys.

Anonymous 0 Comments

This is quite complex and depends on a lot of things. Firstly a lot of the food is just water and will be absorbed into the blood stream and end up in the urine. Similarly a lot of vitamins and minerals will take the same way unless it is actually used in the body. And then there is protein which can be converted to carbohydrates but only through a process that uses energy. So you might start with two amino acids and get one glucose molecule from it, the remainder will turn into carbon dioxide which you breathe out or other molecules that goes out with the urine. There is also some loss when breaking down longer carbohydrates like starch and fibers as well as when converting carbohydrates into fat.

Anonymous 0 Comments

Depends on the food. With foods that we’re great at digesting, we actually breath out most of them as CO2 & H2O.

Anonymous 0 Comments

In ecology we use the 10% rule, which says that approximately 10% of what is consumed at one tropic level is transferred to the next. So as a rule of thumb you can say approximately 10%.

Anonymous 0 Comments

Most of what comes out is not the food that goes in. Most of the fiber comes back out, but the rest is bacterial growth, dead intestinal cells, and excreted gunk pushed out from your liver in the bile and not resorbed. (Bilirubin related compounds are in the last category and give feces it’s distinctive brown color).

Digestion is a ton more effective with a dozen bacterial species assisting in the breakdown, each doing things you genetically can’t. When those bacteria die they’re excreted. They grow best when there’s good fiber- insoluble for them to grow on and soluble they can partially digest. What’s left of the fiber comes out with them.

Anonymous 0 Comments

In ecology we use the 10% rule, which says that approximately 10% of what is consumed at one tropic level is transferred to the next. So as a rule of thumb you can say approximately 10%.

Anonymous 0 Comments

Pretty much everything involved in this process is >50% water trapped in a network of other stuff. The food, you, the waste, all of it. It’s going to contribute a lot to bulk going in and coming out.

Even food that isn’t packed in water/soup is usually pretty wet. Because water can leave you in a variety of ways (sweat, exhalation, urine, feces), it’s hard to measure exactly how much of your food is leaving you in any way at any time. Plus, at any time your body could be retaining very different amounts of water, which will also affect the flows in and out.

The solid parts of food (what isn’t converted to energy or fat) do exit as feces, but even that is pretty wet. If you’re dehydrated or not eating enough fiber (which is great at absorbing and trapping water), your bowel movements will be smaller, especially if you were expecting exactly the same mass of food to come out the other end.