[Naked Harry (OP)]

We are hungry to hear what you think of a question sent in by Martin.

"I've started my annual lose weight push, but this year I have bought a set of scales and weigh myself daily. I have noticed that my weight fluctuates but that the trend is not straight, more like a staircase despite me eating and exercising similarly each day.

This got me wondering, how long does it the food I eat to become part of me?"

What do you think? Let's start a discussion.

[Bored chemist]

It depends what you eat.
For the water it will get into the blood stream in seconds.
Sugars will take minutes (much like alcohol).
Fats and proteins take longer but it's still only a day or so at most.

[chiralSPO]

As soon as the food is in your mouth (or hand) its weight would be added to your own (if you were on a scale while you were eating, it would tick up every time you picked up your next bite, and then it wouldn't change as thee food moved from hand to mouth to stomach to intestines to blood etc.). If you're not actually on a scale while eating/drinking, but weigh yourself frequently, each meal or beverage would count as a "step up."

As far as loosing wight goes, you have to consider urine and bowel movements (which would show up as steps down), breathing (you exhale quite a bit of CO₂ and H₂O all the time, and if you've been drinking alcohol, then also ethanol and acetaldehyde will be exhaled). Also sweating may play a role in weight if you live somewhere very hot, exercise, or spend time in saunas...

As far as when the food "becomes part of you" that would require better definitions of what "you" are and what "food" is. do the atoms in the food need to become covalently bound with atoms that were already "part of you?"
do water molecules become "part of you" as soon as they are in your body, or must they be incorporated into a body fluid first (like blood, or lymph, or intracellular fluid, etc.) or can water ever be considered "part of you"?
are our gut flora "part of us?" if so, how about multicellular stowaways like demodex?

[Sally Le Page]

We answered this question on our show:

You can listen here: https://www.thenakedscientists.com/podcasts/question-week/how-long-food-i-eat-becomes-me [nofollow]

Hope you can digest it!