I can't find the thread now, but we had a discussion about why my exercise bike shows many times the calories consumed verses the energy output, and assumed it was due to inefficiency in me!
Anyway, I came across the following, which suggests a human is about 25% efficient...
In that discussion, your figures suggested 15 to 20% efficiency
528W in 80-110W outBob
I think that is true of mammals as a whole. There was a programme on R4 today that said that to make 1kg of meat takes 10kg of food. To make 1kg of insects, takes 1.6kg of food. They were all confident that insects would be playing a large part in human diet in years to come as the usual meat would be too expensive, just as it was in the 20's/30's when normal families had a roast once a week, and offal/other bits for other meals.
Alan.
once a week? once a month these days.
Probably one of those programmes where I shout questions at the radio interviewer:-) IS THAT 10kg OF FOOD EDIBLE BY HUMANS?
I have forgotten most of what I ought to know about food conversion efficiencies but it is always a *trade off* in terms of protein cost.
Discounting meat and bone meal, Soya Bean meal has about the highest digestible protein level in livestock feeds and grass one of the lowest. However, humans can eat soya but struggle with grass:-)
Soya can't currently be grown here.
regards
In my case almost never, but not because I can't afford the meat, it's because ICBA to wait two hours for something to cook and got for quicker cooking methods.
tim
Googling for "human body"+efficiency brings up loads of stuff. Must be something there to answer your question.
This, from
For an overall efficiency of 20 percent, one watt of mechanical power is equivalent to 4.3 kcal per hour. For example, a manufacturer of rowing equipment shows calories released from 'burning' food as four times the actual mechanical work, plus 300 kcal per hour,[11] which amounts to about 20 percent efficiency at 250 watts of mechanical output.
One of the things that have always puzzled me is why the metrication fascists who are up in arms whenever Imperial units get used in preference to metric never have any problem with calories and frequently don't even seem to appreciate the difference between calories (cgs system)and Kcals (mks system) (not that I am suggesting any of the contributors to this thread are guilty of what is an almost universal error among food faddists).
Anyway I saw that 4.3 above and thought about that experiment that used to be part of the stone age physics I was taught at school - the mechanical equivalent of heat - 4.18 IIRC, not 4.3. Having been caught out by my failing memory several times in the recent past I thought I had better check and found (Wikipedia of course):
"Though a standardised value of 4.1860 J·cal-1 was established in the early 20th century, in the 1920s, it was ultimately realised that the constant is simply the specific heat of water, a quantity that varies with temperature between the values of 4.17 and 4.22 J·g-1·°C-1. The change in unit was the result of the demise of the calorie as a unit in physics and chemistry."
If the calorie died in the 1920s why were we still using it in school circa 1960? Which year incidentally was the year that the ISO adopted SI units and consigned cgs and mks units, along with Imperial units to the junk yard of history.
FWIW I have a heart rate monitor that purports to calculate energy output based on little more than heart rate and body weight. If the exercise bike is checking heart rate it could be working in similar vein rather than using a ratio of the mechanical energy. IIRC the extensive documentation that came with the HRM suggests that efficiency increases with fitness which would tend to undermine any results calculated using a fixed relationship. I could of course had got the wrong end of the stick. I have noticed for instance that my heart rate (flogging up hill) is much higher when I am tired than when I am fresh.
I take it you may have been wondering about GM varieties which could successfully be grown here? (Should cause some excitement).
I am not up to date on Soya trials but efforts to grow it in England some years ago were unsuccessful.
Most effort in the GM field has been to make the crop resistant to cheap broad spectrum weed killers.
My post was a pop at poorly briefed interviewers who fail to ask important questions of interviewees with an agenda. There is a common, unchallenged statement, about the amount of water *used* to grow a kilo of beef or an acre of cereals. Generally this figure is taken as the total rainfall (I think) on the land area involved. In the case of the insect *conversion efficiency* I would like the interviewer to ask what human edible foods make up the 10kg required to produce 1kg of animal protein.
I don't see a commercial problem with using insects as a means of upgrading vegetable protein but there may be consumer resistance:-)
I think the actual protein conversion rate is something like 3:1 for intensive poultry.
regards
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