Wednesday, January 27, 2010

Glyceroneogenesis, and Other Reasons for Fat Storage on Zero Carb

This week I have an extra set of responsibilities in real life and have had a hard time finding time for a new blog post. Fortunately I recently learned of an excellent article by LynMarie Daye, Is the Fable of Unfettered Fat Burning Derailing Your Low Carb Diet?

The author explains in clear and well-referenced terms how the body is able to store fat in the relative absence of insulin. As she says, only type-1 diabetics have a total absence of insulin, and it is true that they cannot store fat. However, the rest of us have a low baseline level of insulin at all times, and in that situation, Acylation Stimulating Protein is able to promote fat storage even when blood insulin levels remain low.

It is also true that fat storage requires the presence glycerol 3-phosphate to form the backbone of the triglyceride molecule. However, simply refraining from eating carbs is not sufficient to stop the synthesis of glycerol 3-phosphate. Even in a state of prolonged fasting, the body is able to use its own muscle protein to synthesize glycerol 3-phosphate. This metabolic pathway is called glyceroneogenesis, and it is illustrated in the figure above.

If you have ever wondered how it is possible to eat no carbs whatsoever and still gain weight, LynMarie Daye provides a thorough treatment of the issue. I highly recommend her article.


Mike said...

Excellent link! I have many of your blog posts "starred" in my Reader for reference. Please keep up the great work!

Stargazey said...

Thanks, Mike!

anne h said...

Another great article, Stargazey!

Stargazey said...

Thanks, anne h! (I wish I'd written it myself!)

One of the comments there suggested that it was somewhat difficult to understand. If any of my readers finds that to be the case and has a question, please ask in the comments here and I'll do my best to explain it.

LynMarie Daye said...

Wow, I'm truly honored! Thanks so much for recommending my blog post!

And yes, if anyone has any question, please ask Stargazey for clarification. She will do a great job explaining the complex material in the article.


Stargazey said...

Thanks, LynMarie! It's great to "see" you here!

gn said...

"Even in a state of prolonged fasting, the body is able to use its own muscle protein to synthesize glycerol 3-phosphate."

does this mean that during fasting body can dissolve muscles, and potentially make fat out of resulted glucose? that would be scary

Stargazey said...

Yes. Energy is most efficiently stored in fat at nine calories per gram, but it is also stored in muscle at four calories per gram.

The body can and does use muscle protein for its metabolic needs when our diet does not include sufficient protein. Fat cannot be used to make glucose, for instance, so the body will use whatever protein source it can find to make the glucose required by the brain and other glucose-obligate tissues.

The reason that muscle is converted to fat during prolonged fasting is that muscle has a high metabolic requirement. To minimize that, the body will convert some of its muscle into fat, which requires less metabolic support but still provides a storage form of energy.

Mike said...

"Fat cannot be used to make glucose, for instance, so the body will use whatever protein source it can find to make the glucose required by the brain and other glucose-obligate tissues."

Just to clarify, free fatty acids cannot be used, but glycerol from triglycerides can be used through gluconeogensis.

Stargazey said...

Yes. I was speaking in general terms and should have been clearer. The glycerol backbone can be used to make glucose, but the fatty acids attached to it cannot. Because the glycerol portion makes up only 5-10% of a triglyceride, a very large fraction of fats is unavailable for conversion to glucose.

Fluxtopia Mars said...

Hi! I am new to low-carbing, and was looking for info on metabolism of fats and proteins when I stumbled across your amazing blog. After reading the linked article, I have a few questions for you:
1) If protein stimulates a glucagon response, and needs insulin to build muscle, what would happen if caffeine were consumed with a protein shake which would stimulate adrenaline response and block the release of insulin? Do we still release insulin from ingesting protein on a low-carb diet?
2) Assuming the low-carber is not diabetic, does that mean there always be glycogen present in liver and muscles, hence sugar to stimulate insulin release during anaerobic activity? Or does ketogenesis result in an entirely different form of stored energy?

I ask because the formula of cutting calories plus exercise previously hasn't resulted in as much weight loss as it logically should have for me, and I am looking for more specific knowledge about how I could be metabolizing the things I eat. I tend to drink a lot of green tea, and some coffee, and if I use an artificial sweetener, it's stevia, which are generally touted as weight loss assistants, but I can't find any good information on how that works. Could I be hurting my weight-loss efforts by consuming caffeine, even on a low-carb diet, or would the adrenaline release help suppress insulin and induce ketogensis?

Stargazey said...

Fluxtopia Mars--good questions! I'll make a stab at answering them, but if you keep reading the more science-related low-carb blogs, you'll eventually come to understand what's going on. I have lots of posts here that will be helpful, but don't try to read them all at once. It's best if you read a bit at a time, assimilate it, and then come back for more.

1. The release of adrenaline and/or glucagon does not block the release of insulin. Excess glucose and excess amino acids in the blood can be thought of as kind of a poison. The body needs to get them into storage as quickly as possible, and insulin is the hormone that does it.

2. Glycogen is present in muscles and is available to provide a quick energy source. Once it's made, its glucose building blocks stay in the muscles and are not secreted into the blood. Glycogen in liver can be converted back into gluose and released into the blood, however. Because of gluconeogenesis, the body is able to make glycogen even when zero carbs are eaten. Amino acids can be converted to glucose, taken up, and converted into glycogen in the liver and muscles.

Ketogenesis results from the incomplete metabolism of fatty acids. It is NOT ketoacidosis and is not to be feared. Google the terms and you will learn more.

I've written a couple of blogposts on caffeine: Caffeine and Weight Loss and Managing Hunger. Perhaps those will be helpful for you.