Re: A limit on the energy transfer rate from the human fat store in hypophagia

[Guest guest]

Hi Bill:

What a very interesting paper. Thank you.

290 kJ is 69·3 kcal I believe.

Now, are you saying that the 290 kJ is calculated per kg of ***fat mass***? Or is it per kg of body weight? The abstract does not make that clear, and that is important and especially so for those like many of us who have lower body fat.

If we could access to the full text it would presumably answer that question.

Rodney.

>> I think this study is significant for those embarking on a CRON> lifestyle. Estimates the maximum amount of fat mass that can be> catabolized for energy while restricting calories before lean tissue> is significantly lost for energy needs. How fast should you permit> weight loss while dieting/CRON? This may help answer that..> > I've read that (290 kJ/kgd is approx 30 calories/lb of fat mass? (Not> 'per lb bodyweight' but 'per lb fat mass'. Can anyone verify this?> > > 1: J Theor Biol. 2005 Mar 7;233(1):1-13. Epub 2004 Dec 8.Click here to> read Links> A limit on the energy transfer rate from the human fat store in> hypophagia.> Alpert SS.> > Department of Physics and Astronomy, University of New Mexico,> Albuquerque, NM 87131-1156, USA. sialpert1@...> > A limit on the maximum energy transfer rate from the human fat> store in hypophagia is deduced from experimental data of underfed> subjects maintaining moderate activity levels and is found to have a> value of (290+/-25) kJ/kgd. A dietary restriction which exceeds the> limited capability of the fat store to compensate for the energy> deficiency results in an immediate decrease in the fat free mass> (FFM). In cases of a less severe dietary deficiency, the FFM will not> be depleted. The transition between these two dietary regions is> developed and a criterion to distinguish the regions is defined. An> exact mathematical solution for the decrease of the FFM is derived for> the case where the fat mass (FM) is in its limited energy transfer> mode. The solution shows a steady-state term which is in agreement> with conventional ideas, a term indicating a slow decrease of much of> the FFM moderated by the limited energy transferred from the fat> store, and a final term showing an unprotected rapid decrease of the> remaining part of the FFM. The average resting metabolic rate of> subjects undergoing hypophagia is shown to decrease linearly as a> function of the FFM with a slope of (249+/-25) kJ/kgd. This value> disagrees with the results of other observers who have measured> metabolic rates of diverse groups. The disagreement is explained in> terms of individual metabolic properties as opposed to those of the> larger population.> > PMID: 15615615>

[Guest guest]

Hi Rodney, Cheers, AlRodney <perspect1111@...> wrote: Hi Bill: What a very interesting paper. Thank you. 290 kJ is 69·3 kcal I believe. Now, are you saying that the 290 kJ is calculated per kg of ***fat mass***? Or is it per kg of body weight? The abstract does not make that clear, and that is important and

especially so for those like many of us who have lower body fat. If we could access to the full text it would presumably answer that question. Rodney. >> I think this study is significant for those embarking on a CRON> lifestyle. Estimates the maximum amount of fat mass that can be> catabolized for energy while restricting calories before lean tissue> is significantly lost for energy needs. How fast should you permit> weight loss while dieting/CRON? This may help answer that..> > I've read that (290 kJ/kgd is approx 30 calories/lb of fat mass? (Not> 'per lb bodyweight' but 'per lb fat mass'. Can anyone verify this?> > > 1: J Theor Biol. 2005 Mar 7;233(1):1-13. Epub 2004 Dec 8.Click here

to> read Links> A limit on the energy transfer rate from the human fat store in> hypophagia.> Alpert SS.> > Department of Physics and Astronomy, University of New Mexico,> Albuquerque, NM 87131-1156, USA. sialpert1@...> > A limit on the maximum energy transfer rate from the human fat> store in hypophagia is deduced from experimental data of underfed> subjects maintaining moderate activity levels and is found to have a> value of (290+/-25) kJ/kgd. A dietary restriction which exceeds the> limited capability of the fat store to compensate for the energy> deficiency results in an immediate decrease in the fat free mass> (FFM). In cases of a less severe dietary deficiency, the FFM will not> be depleted. The transition between these two dietary regions is> developed and a criterion to distinguish the regions is defined. An> exact mathematical

solution for the decrease of the FFM is derived for> the case where the fat mass (FM) is in its limited energy transfer> mode. The solution shows a steady-state term which is in agreement> with conventional ideas, a term indicating a slow decrease of much of> the FFM moderated by the limited energy transferred from the fat> store, and a final term showing an unprotected rapid decrease of the> remaining part of the FFM. The average resting metabolic rate of> subjects undergoing hypophagia is shown to decrease linearly as a> function of the FFM with a slope of (249+/-25) kJ/kgd. This value> disagrees with the results of other observers who have measured> metabolic rates of diverse groups. The disagreement is explained in> terms of individual metabolic properties as opposed to those of the> larger population.> > PMID: 15615615> __________________________________________________

[Guest guest]

Hi folks:

Alpert's paper about the rates of loss of fat and lean body mass during caloric restriction is an interesting one. And as with much else, the jury is still out. Tony, especially, has expressed views on this. The Alpert paper, which is quite long and fairly complicated, provides a view that is somewhat different from Tony's. In this post I am not supporting one side of the argument or the other. But instead will try to show what the implications seem to be for, as an example, if Alpert's analysis is correct.

This issue is important if it is desirable to preserve lean body mass while reaching the kind of body weight usually associated with CR. (While not forgetting, as Warren reported here long ago, that the CR mice which lived the absolute longest in some experiments were those that somehow managed to preserve the largest fat reserves, possibly because they exercised the least or had the lowest metabolic rates?)

It is clear that Alpert's 290 kJ/kg means per kg of body fat. His work is based on the observations in Keys' 1944 Minnesota Experiment, and he concludes that in order to preserve lean body mass the daily caloric deficit should not go beyond 290 kJ/kg of body fat weight. Since one calorie is 0.0041868 kJ, that means the threshold is ~69.3 kcal/kg of body fat. And since one kg of body fat contains ~7716 kcal, it implies that one cannot lose more than 0.898% of one's body fat daily without burning off larger, and possibly excessive, amounts of lean body mass at the same time.

Here is what Alpert's paper seems to be saying, very approximately, for me. Anyone interested in the data for themselves can substitute their biometric numbers for mine:

I have taken a range of body weights: 160, 150, 140 and 130 pounds and calculated the caloric shortfall that would be safe for me, according to Alpert, at each of those weights. The numbers come out as follows (as usual formatting may be a problem):

- - - - - - Body fat - - - - BMR - - BMRx1·3 -Minimum**

- - - - - - -------- fat* --------- ---------- ----------

Wt -BMI - % - lbs -loss -h-b -m-s - h-b -m-s -h-b -m-s

--- ---- ---- ----- ---- ----- ---- ----- ---- ----- ----

160 22·7 ~18 28·8 904 1508 1519 1960 1975 1056 1071

150 21·3 ~14 21·0 659 1446 1474 1880 1916 1220 1257

140 19·9 ~10 14·0 440 1383 1429 1798 1858 1358 1418

130 19·4 ~6 7·8 245 1321 1383 1717 1798 1472 1553

* Number of fat calories that may safely be lost daily according to Alpert's view.

** Minimum number of calories that should be eaten to avoid excessive loss of LBM.

h-b = -Benedict; m-s = Mifflin St. Jeor.

So in conclusion, based on Alpert's paper, at a BMI of 22·7 it is safe for me to drop caloric intake temporarily to ~1050 calories. But the safety threshold rises as weight declines: to ~1250 calories at a BMI of 21·3; ~1400 calories at a BMI of 19·9; and somewhere between 1475 and 1550 calories at a BMI equal to 18·4.

[but bear in mind also that both the -Benedict and Mifflin-St Jeor equations seem to give weird output at unusually low levels of caloric intake. Perhaps this is because they didn't have many such people in the sample they used to develop their equations, and extrapolation from higher caloric intake levels may not have been appropriate.]

This seems like another analysis suggesting those on CR should be cautious about their degree of restriction as body fat declines.

Rodney.> >> > I think this study is significant for those embarking on a CRON> > lifestyle. Estimates the maximum amount of fat mass that can be> > catabolized for energy while restricting calories before lean tissue> > is significantly lost for energy needs. How fast should you permit> > weight loss while dieting/CRON? This may help answer that..> > > > I've read that (290 kJ/kgd is approx 30 calories/lb of fat mass? (Not> > 'per lb bodyweight' but 'per lb fat mass'. Can anyone verify this?> > > > > > 1: J Theor Biol. 2005 Mar 7;233(1):1-13. Epub 2004 Dec 8.Click here to> > read Links> > A limit on the energy transfer rate from the human fat store in> > hypophagia.> > Alpert SS.> > > > Department of Physics and Astronomy, University of New Mexico,> > Albuquerque, NM 87131-1156, USA. sialpert1@> > > > A limit on the maximum energy transfer rate from the human fat> > store in hypophagia is deduced from experimental data of underfed> > subjects maintaining moderate activity levels and is found to have a> > value of (290+/-25) kJ/kgd. A dietary restriction which exceeds the> > limited capability of the fat store to compensate for the energy> > deficiency results in an immediate decrease in the fat free mass> > (FFM). In cases of a less severe dietary deficiency, the FFM will not> > be depleted. The transition between these two dietary regions is> > developed and a criterion to distinguish the regions is defined. An> > exact mathematical solution for the decrease of the FFM is derived for> > the case where the fat mass (FM) is in its limited energy transfer> > mode. The solution shows a steady-state term which is in agreement> > with conventional ideas, a term indicating a slow decrease of much of> > the FFM moderated by the limited energy transferred from the fat> > store, and a final term showing an unprotected rapid decrease of the> > remaining part of the FFM. The average resting metabolic rate of> > subjects undergoing hypophagia is shown to decrease linearly as a> > function of the FFM with a slope of (249+/-25) kJ/kgd. This value> > disagrees with the results of other observers who have measured> > metabolic rates of diverse groups. The disagreement is explained in> > terms of individual metabolic properties as opposed to those of the> > larger population.> > > > PMID: 15615615> >> > > > > > > __________________________________________________>