I have a theory.

I was keeping this theory a bit quiet as it contradicts Gary Taubes , Michael R Eades & Richard D Feinman and Eugene J Fine.

Please note: This post is not criticising low-carb, high-fat diets in any way, shape or form. I'm just trying to point out that if someone on a low-carb, high-fat diet pigs-out on roast lamb/pork/duck etc, they may not lose as much body fat as they expected & they may even gain some.

I don't particularly want to start a sh*t-storm, but as I am in the "a calorie is a calorie" (when it comes to weight gain/loss) camp and a lot of the people whose blogs I link to aren't, I need to go public. So, here it is, copied & pasted from the comments section of Diet, Carbs, Fat and Weight Loss, corrected for spelling.

"I would like to propose a theory which explains how fat cells can acquire glucose (& thus correct a deficiency in glycerol-3-phosphate) even when serum insulin level is basal.

Consider muscle cells undergoing anaerobic activity:-

Anaerobic activity is very inefficient and uses pyruvate at a very rapid rate. A deficiency in pyruvate up-regulates all of the up-stream processes, including Glu-T4 transporters so as to maximise pyruvate production.

This explains why resistance training with weights greatly increases muscular insulin sensitivity and why resistance training with weights when depleted of muscle glycogen can cause precipitous drops in blood glucose level.

Ditto for glycerol-3-phosphate in fat cells. In this case, blood glucose level is maintained by the liver & kidneys, which convert the glycerol backbone of triacylglycerols (fats) and other substrates such as lactate, pyruvate & glucogenic amino acids into glucose."

In plain terms what this means is that, like muscle cells, fat cells can acquire as much glucose as they need, independently of carbohydrate intake.

Therefore, if an excess (beyond what the body is burning) of dietary fat is eaten, this can be stored in fat cells even if serum insulin level does not increase.

There. I've said it. I expect comments! Moderation is enabled. All comments that are free from ad-hominem, straw men & other logical fallacies will be published.

As a lot of people report that they appear to be able to eat lots of dietary fat without getting fat (& actually getting slim), there's obviously something magical going on. Now, it's generally accepted that fat is the least thermogenic of all the macronutrients (protein being the most thermogenic). I'm wondering whether this is the case for all types of fat and all types of people.

Stephan Guyenet blogged on Butyric Acid: an Ancient Controller of Metabolism, Inflammation and Stress Resistance and Coconut Oil (high in medium chain fats) is also reported as being less fattening/more slimming than long-chain fats.

As Christopher Gardner said 39m 34s into his lecture Battle of the Weight Loss Diets: Who's Winning (at losing), insulin resistant people do better on high-fat, low-carb (HFLC) diets than high-carb, low-fat diets. Insulin sensitive people are the other way round.

So it's quite possible that in people who do well on a HFLC diet, kcals out on the right hand side of the Energy Balance Equation increase a lot. So, keep on keeping on!

See also:-
More evidence comes to light that fat is not fattening
Is there such as thing as a ‘metabolic advantage’?
They're all MAD!
Metabolic Advantage of Ketogenic Diets Debunked? An Intriguing Study You Will Want to Read
Is the Fable of Unfettered Fat Burning Derailing Your Low Carb Diet?

See also How stuff works and Enzymes.