day fast could regenerate immune system
08-31-2015, 11:33 PM
Quote: (08-31-2015 03:02 PM)Blackwell Wrote:
I'm more interested in the 'regenerating the immune system' part than trying to cut fat. I have great genetics for staying lean I'm not fussed about fasting for that purpose.
Any idea what a 3 day fast to regenerate my immune would do to my weight/overall musculature?
If you're concerned about maintaining muscle, it might be a good idea to go low-carb for three or four days before the beginning of your fast (or however long it takes for your body to enter ketosis). That way, your body will already be using fatty acids for energy before you stop eating, so you won't be spending that three-day fast relying on glucose derived from the breakdown of muscle protein. This should, I think, minimize muscle loss.
I'm a little wary giving this advice, because I haven't seen anyone else give it, even though it seems like it follows from what we know (or think we know) about fasting and its relation to fat and muscle loss.
My conjecture here relies in part on this biochemistry textbook:
http://www.ncbi.nlm.nih.gov/books/NBK22414/
(Italics are in the original. Bold and ellipses are mine.)
Quote:Quote:
The first priority of metabolism in starvation is to provide sufficient glucose to the brain and other tissues (such as red blood cells) that are absolutely dependent on this fuel. … the second priority of metabolism in starvation is to preserve protein, which is accomplished by shifting the fuel being used from glucose to fatty acids and ketone bodies (Figure 30.16).
The metabolic changes on the first day of starvation are like those after an overnight fast. The low blood-sugar level leads to decreased secretion of insulin and increased secretion of glucagon. The dominant metabolic processes are the mobilization of triacylglycerols in adipose tissue and gluconeogenesis by the liver. The liver obtains energy for its own needs by oxidizing fatty acids released from adipose tissue. The concentrations of acetyl CoA and citrate consequently increase, which switches off glycolysis. The uptake of glucose by muscle is markedly diminished because of the low insulin level, whereas fatty acids enter freely. Consequently, muscle shifts almost entirely from glucose to fatty acids for fuel. …
During starvation, degraded proteins are not replenished and serve as carbon sources for glucose synthesis. Initial sources of protein are those that turn over rapidly, such as proteins of the intestinal epithelium and the secretions of the pancreas. Proteolysis of muscle protein provides some of three-carbon precursors of glucose. However, survival for most animals depends on being able to move rapidly, which requires a large muscle mass, and so muscle loss must be minimized.
How is the loss of muscle curtailed? After about 3 days of starvation, the liver forms large amounts of acetoacetate and d-3-hydroxybutyrate (ketone bodies; Figure 30.17). …
The effective conversion of fatty acids into ketone bodies by the liver and their use by the brain markedly diminishes the need for glucose. Hence, less muscle is degraded than in the first days of starvation. The breakdown of 20 g of muscle daily compared with 75 g early in starvation is most important for survival.
If it takes the body the first few days of a fast to switch from using glucose to using ketones, and if it is this switch that minimizes muscle loss, then it seems to follow that switching to using ketones before the fast even begins should minimize muscle loss during those first few days of the fast.
Note the difference that this would make—at least, according to the account I just quoted. It seems that you would normally lose 75g of muscle per day for the first few days, and then 20g per day after switching to using ketones. But if I'm right (and if the numbers from this book are at all accurate for you), then you should only lose 20g per day for your whole three-day fast if you switch to using ketones before the fast begins. So, what's the difference? One pound is about 450 grams. So instead of losing half of a pound of muscle over the course of a three-day fast, you'd lose only a little over one-tenth of a pound.
Granted, I'm not sure where the numbers in this book came from, or how applicable they are to your body specifically. But there should be a difference, if I'm right. That said, I haven't tested this theory for myself because I have no inexpensive method at my disposal for tracking what I've lost (fat, muscle, water), and in what quantities, over the course of my own fasts. Plus, there would be other variables that I cannot control. And besides, my results wouldn't necessarily be your results anyway.
If I had to guess, I'd say that you could expect to lose maybe 2 or 3 pounds in a three-day fast, possibly 4, and this without any additional physical activity. But a lot of that will be water, which you will gain back upon breaking the fast. Maybe total weightloss will be a pound, maybe 2, depending on your metabolism and what your diet is like afterward. But that's just a shot in the dark, since I'm not familiar with your body and what you do with it.
I will say that my own body composition and aesthetic have only ever improved through cutting via fasting followed by a bulk. Since you're already cut, I'm not entirely sure about how it would go for you. Even so, the body in a fast does not start really cannibalizing muscle mass until the body fat reaches about 4% (so I've heard), so you need not worry about that over the course of a short three-day fast.
tl;dr: You should be fine. To preserve muscle mass, consider cutting carbs for four days (or however long it takes for your body to enter ketosis) leading up to the fast.
![[Image: Insulin%20Cortisol%20and%20GH.jpg]](https://lh5.googleusercontent.com/_UYDkSxhditY/TbTdA-ch9ZI/AAAAAAAAAWs/KIvVkHFMfR8/s800/Insulin%20Cortisol%20and%20GH.jpg)
