Diana,
The subject of fat storage is a complex one. It is true that when we eat a high carb diet, the main hormone regulating fat storage is insulin, however, when eating a high fat diet with little or no carbs then there are other mechanisms. Much of my Journal is about testing Taubs theory of "no carbs, no insulin, no fat gain". I found this to be wrong.
First, it appears that there is a lot of fat loss because initially our bodies are conditioned to process carbs. Since there is plenty of glucose in our blood, our cells are conditioned to utilize this as their primary fuel. Metabolizing glucose is a rather simple process much like yeast and fermentation.
For our cells to use fatty acids as the primary fuel is much more complex. Mitochondria are needed for this process. Since most of our lives we’ve had plenty of glucose available as fuel, we only have the minimum level of mitochondria in our cells and not near enough to convert fatty acids directly to fuel.
When we stop eating carbs and start eating fats, our bodies are very inefficient in using the new fuel. Our cells are demanding glucose as they can’t use fatty acids efficiently until they create more mitochondria which takes time (often several months). The fat we eat (and the body fat we store) is in the form of triglycerides. This is three fatty acids clustered around a glycerol molecule. Glycerol can be converted to glucose, but it is very inefficient. It takes 2 glycerol molecules to make one glucose molecule. Our liver will take the triglycerides we are eating (as well as some from body fat), strip off the fatty acids and convert the glycerol to glucose as this is what our cells need until they adapt and make more mitochondria to be able to use fatty acids directly. This means that the body needs two triglycerides and is throwing away 6 fatty acids (75% of the energy) just to be able to make one molecule of glucose. And, you guess it, we start rapidly loosing weight. (the excess fatty acids are turned into ketones and eliminated through sweat, breath, and urine.) If the body is still short glucose it will use dietary protein as well as sacrifice muscle tissue to create the needed glucose through the process of gluconeogenisis. We get the impression that calories don’t count because we just can’t eat enough food to create the necessary glucose that our body wants from the fat we are eating when 75% of the energy is being thrown away because the cells can’t use it. Therefore, the body consumes body fat and some muscle tissue to make up the short fall in glucose and we lose weight.
Over time, our bodies begin to adapt to the new fuel source. The cells add mitochondria and most of our body tissues will convert to using fatty acids and/or ketones as fuel rather than glucose. When this happens we find that the level of ketones being thrown away in the urine drop to very low levels (because our body is now using them), and weight loss slows or stops completely. Suddenly calories start to count again, and in a big way because now our bodies are using 100% of the energy contained in the fat as the cells are using the three fatty acids directly as fuel and the left over glycerol is still being converted to glucose. Body fat is no longer being used to fill in the energy gap.
Now comes the issue of body fat storage. When we are eating fat and protein and little or no carbohydrate, fat storage is accomplished through an enzyme called ASP (Acylation Stimulating Protein). This little jewel has the ability to directly store fat in the fat cells completely bypassing the glucose and insulin pathways.
On a zero carb diet, excess fatty acids not immediately needed for energy will be directly stored in the fat cells through ASP. This stored fat will then be called upon as the body needs energy and is mobilized out of the fat cells through Hormone Sensitive Lipase (HSL) which will only allow body fat metabolism if insulin, a hormone, is low, hence ‘hormone sensitive’.
As long as the total fat stored is equal to the total fat consumed, body fat will not accumulate. However, if, on average, less energy is needed than was stored, not all fat stored by ASP from the ZC meals will be remobilized by HSL and body fat will rise.
When I first converted to Paleo/VLC/ZC, I could easily eat 4,000 to 5,000 calories per day and I lost weight. My body couldn’t use most of the energy so it threw it away. The ketones in my urine were running the darkest color on the Ketostix, and my breath had an acetone smell from ketones being eliminated through my breath.
After about 18 months my body had adapted to using fatty acids rather than glucose as its primary fuel and the ketone levels dropped to Trace levels and the acetone breath went away. I was eating until I was satisfied and that was about 2,000 calories per day. My weight had dropped from 215 and stabilized at 160. This is when I decided to test Taubes theory and raised the fat in my diet while keeping the amount of food I was eating the same to see if it was impossible to gain weight as there were no carbs to create insulin. Raising the fat raised the calories from 2,000 per day to about 3,000 per day and I started putting on weight. I gained about 20 lbs in 2 or 3 months. The only way I could loose the weight was to reduce the amount of food I was eating so that even with the higher fat I was only eating 2,000 calories per day. Other Zero Carber’s have had the same experience. Once their bodies are fully adapted to using fatty acids as their primary fuel, they start to gain weight unless they reduce their calorie intake.
Hope this makes sense. If not, feel free to ask questions and I’ll do my best to answer.
Lex
