Efficiency of absorption / digestion?

[Daves_Not_Here]

So I've been tracking my energy consumption and expenditure like a fiend, and News Flash, I have lost about 1 pound per 3,500 calorie deficit (after pulling out the water loss contribution).  However, I've been operating under the assumption that 100% of the calories I consume get digested and are available to me as energy (which seems to agree with my results).

I'm curious if anyone has an opinion as to whether this is really a valid assumption.  It would seem that my actual "efficiency of digestion" (is there even a term for this?) could vary.  For example, if I swallowed a balloon containing 1,000 calories of food, it would pass through with no digestion, so my efficiency for that meal would be 0%.  I can imagine that hormones, GI health, GI chemistry, and the presence of other food being digested could all result in less than 100% of my calories being digested.

Also, I can imagine how a "starvation response" might involve an increase in efficiency of digestion.  I know that micro-nutrient absorption varies -- does anyone know if macro-nutrient and overall caloric absorption also varies?

[WavyDavey]

Hi @Daves_Not_Here,

I think that the digestive efficiency won't come into play in your situation. It wouldn't be enough of a difference, unless you had a tapeworm. 🙂

Fiber has calories, and goes largely undigested. So it's never 100% efficient.

What I do know is that as a person ages, their ability to absorb protein lessens, so that those who are strength training will need to eat proportionally more protein as they get over 40 or so.

[Dominique · Accepted solution]

@Daves_Not_Here: this infographics by Precision Nutrition has some answers to your questions.

[Daves_Not_Here]

Thanks @WavyDavey -- I was not previously aware of the reduced absorption of protein by old farts.  I will increase my steak consumption accordingly.

@Dominique - great chart -- provided answers to my original question as well as others.  I kind of like the process of precisely measuring calories if only for experimental verification of weight loss, but will use the "hand" method going forward when I eat out.  Thanks !

[Dominique]

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@Daves_Not_Here wrote:

I kind of like the process of precisely measuring calories if only for experimental verification of weight loss, but will use the "hand" method going forward when I eat out.  Thanks !

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@Daves_Not_Here: yes, the "fist/palm/thumb" method advocated by Precision Nutrition is great for eye-balling things when eating out, because who would want to appear as a freak pulling out their kitchen scale at a restaurant . It’s probably also good when transitioning from rigorous calorie counting to "intuitive eating". 

[Daves_Not_Here]

@Dominique-- Thinking of our calorie measurement discussion, I just had a cross between an "aha" moment and a "wait a minute" moment.

Precision Nutrition and others make an issue of the various errors inherent in attempting to measure caloric intake.  I'm now thinking the response could be: "So what?  This is the concept of observational error."  Just because there are various inaccuracies in measurements doesn't mean we shouldn't measure.  This is what regression analysis is all about.  And, the more data we capture, the better picture we get.

Same response to the complaint about the supposed inaccuracy of FitBit and other tools in measuring energy expenditure.