What Happens During Fast PUFA Loss Studies?

[Luann]

These are the two I'm talking about.

Development of hepatic steatosis and essential fatty acid deficiency in rats with hypercaloric, fat-free parenteral nutrition — UC Davis

"..hepatic essential fatty acid deficiency (EFAD) developed by day 4; liver linoleic acid levels had dropped from 20 to 1% of total fatty acids, and liver triene:tetraene ratio was 0.68. Similar changes in hepatic phospholipid fatty acids were observed."

EFA Deficiency Achievable In 2 Weeks On Fat Free Diet

"EFA deficiency was detected by decreases in linoleic acid and by the appearance of 5, 8, 11-eicosatrienoic acid in lipid fractions of plasma. Linoleic acid decreased significantly during 2 wk of the fat-free diet given intravenously from 48.8 to 9.8% (percent of total fatty acids) in cholesterol esters, from 21.2 to 3.2% in phospholipids, from 9.6 to 2.0% in free fatty acids, and from 14.1 to 2.6% in triglycerides. Eicosatrienoic acid, normally undetectable, appeared..."


I thought the rats might have really cleared most of the PUFA in their body in four days, since they grew up on chow rather than the standard western diet. But the humans couldn't have, even in two weeks. What caused PUFA levels to drop so low in both groups? Were the fatty acids hiding elsewhere?

 

[shepherdgirl]

Hi @Liubo - have you seen this thread by @haidut that cites an old PUFA depletion study on monkeys?

PUFA Depletion Can (probably) Be Accomplished In 30 Days!

The monkeys depleted PUFA in their serum and cholesterol in 4 days. There was still PUFA in their tissues which took significantly longer to deplete.
In the rat studies you cited it seemed like they were not measuring PUFA depletion in the tissues but rather in the blood and liver, which seems to me would be the "first tier" of depletion. That's my guess as to why it only took 4 days.
Interesting that the rats developed enlarged livers - is that supposed to happen on a low PUFA diet in general? Would explain my "5 months prego" belly...

 

[Hugh Johnson]

Rats have huge livers, and monkeys have next to no stored fat. Humans have lots of stored fat, and a mediocre liver.

 

[shepherdgirl]

Saw this today at
Errors in Nutrition: Essential Fatty Acids – Functional Performance Systems (FPS) in regards to William Brown, who followed a pufa depletion diet for six months:

His blood lipids became more saturated and their concentrations of linoleic and arachidonic acids were cut in half.

I don't know the details of when his blood lipids were measured, but if after 6 months "linoleic and arachidonic acids were cut in half," it sounds to me like @Hugh Johnson could be right, and human depletion could take a lot longer than monkey depletion. Of course it's a study of only one guy.