The marijuana evidence is poor. The incorrect assumption is that marijuana has been stored uniformly across every adipose tissue. Where is the proof of that? If marijuana is stored only in some tissues, and those tissues end up metabolizing in 77 days, that says nothing about the overall metabolism of the remaining fats.
Where is your experimental evidence that all fats turnover in days? That is your conjecture and if your evidence is marijuana studies that is much poorer evidence than the Hirsch study that your source criticized. And your source didn't even want to make a guess about the real number.
I find several studies that either make their own conjectures at 1 to 4 years, or rely on Hirsch:
http://jn.nutrition..../3/925S.full#T3
http://www.jlr.org/c.../1/103.full.pdf
http://ajcn.nutritio...3/1/81.full.pdf
And here is the "controversial" Hirsch study:
http://ajcn.nutritio.../4/499.full.pdf
I don't find any studies that back your position, which isn't to say they don't exist. But you haven't presented anything, and neither did the blog you quoted.
1. Every single one of those studies either cite Hirsch, or use Hirsch to validate their own assumptions. (look at the notes)
2. Tissue biopsies have shown that MJ metabolites are stored in all fatty tissues, even the TESTES./
3. We do understand biochemical processes much better now. Ingested fat is used for fuel or stored for future use depending on the amount of circulating blood sugar, and muscular energy demand. Yet when fat is used by the body it is not 100% of either ingested or stored.
If you are increasing fat stores, then obviously fat stays in the body longer. But if you are maintaining a stable weight, the fats turn over -- regardless if the % of various length FA remain the same.
If you are ketotic AT ALL FOR ANY REASON -- PURPOSEFUL OR NOT, large amounts of fat can be flushed from the body in days.
600 days is rubbish. All YOUR Evidence uses Hirsch as a basis or outright cites his number.
In the original Hirsch study, when they feed high polyfat diets to subjects for up to 10 WEEKS at a time, there are no changes in the adipose content of the patient. How do you explain that if the adipose turns over rapidly? From the Hirsch Study here:
http://ajcn.nutritio.../4/499.full.pdf
see page 508:
"Effects of Diet In adults in caloric balance, dietary effects on adipose tissue are produced only slowly; in short term studies no effects are seen.... After ten weeks on a formula containing forty percent of calories as corn oil, the adipose tissue of this subject was normal in fatty acid composition. Then, after thirty-eight days on a fat-free high carbohydrate formula, the adipose pattern was still unaffected. During ten weeks on high intakes of corn oil, this patient ingested more than 3.5 kg. of linoleic acid, an amount roughly three times that present in his entire adipose tissue. Yet, the adipose linoleic concentration did not rise. During thirty-eight fat-free days the patients caloric expenditure was of the same order of magnitude as the total caloric value of his entire adipose depot, yet body weight did not change nor was adipose composition altered. Clearly, there must have been intense lipogenesis from carbohydrate; but, the lack of accumulation of 16:0 and 16:1 and lack of decrease in 18:2 strongly argues against the participation of the entire adipose depot in the new synthesis of fatty acids."
From the same page, Hirsch establishes that it took up to 160 WEEKS to make the adipose tissue reflect the polyfat composition of diet! See the passage:
"When formulas rich in corn oil are fed over extremely long periods, slow changes in adipose composition are seen eventually, amid they continue until an adipose pattern is evolved which is very similar to that of the fed corn oil acids. Figure 10 is a composite of the adipose changes in eight different subjects receiving diets rich in corn oil (usually 40 per cent of calories ) from eight to 160 weeks. Changes are almost imperceptible up to twenty weeks. However, at 160 weeks the adipose tissue has become rich in diunsaturated acid (essentially all l8:2) and it closely resembles a mixture of corn oil and normal adipose triglyceride in proportions of 7 to 3. There is no reason to believe that even further adipose changes might not have occurred if the corn oil feedings had been continued for longer periods of time."
It's important to see from these direct measurement of adipose tissue that you cannot change the composition rapidly, either up OR down.
Finally, you are misreading your own blog reference about the criticism of Hirsch. Hirsch was trying to develop a formula to extrapolate experimental data on adipose changes over time. Your blog author never disputed the above experimental evidence of slow adipose changes. His criticism was the formula used to generalize the effect. He has the opinion that the formula overstates the actual turnover period, yet he is unable to commit to any specific number in reply to Hirsch. I have no commitment to Hirsch's formula. I do not care if the right number is two years or five years. But I do respect the evidence, which is very clear that adipose composition changes very slowly over time, no matter what you do to the diet.
Using Marijuana in adipose tissue as a response to a study that actually measures the real fat composition of actual fat is completely ridiculous. We don't know that marijuana is in every single fat cell; that is a completely different point than saying it distributes to different types of adipose tissues. We don't even know that removing the marijuana from the adipose requires full use of the adipose for energy. These marijuana studies measure marijuana metabolism. Using them for adipose metabolism is grade D evidence.
Show us ONE study where they change the adipose fatty acid composition of a subject from diet alone and force a measurable change in polyfat composition of adipose tissues within 90 days. No such study exists. Studies that change polyfat composition rapidly all rely on starvation or exercise, not diet. Ketosis is simulated starvation, so that is the dietary exception, but clearly use of ketosis to clean out fat stores is the stuff of experiments because 95% of the US population doesn't understand ketosis and would never use it.
Edited by pone11, 18 February 2015 - 07:59 PM.