Bit of a convoluted question. In regards to VLC diets... If you have, say, yogurt in the morning, what process does it follow to replenish glycogen in comparison to consuming a no carb, protein/fat meal? Does the lactose bypass the insulin fat-storage when it becomes stored as glycogen? When you eat the high protein/fat meal, are some of the nutrients there sequestered to replenish glycogen? Which of the two is more energy efficient? Are there any unsavoury by-products of either process? In the former case, would it be more beneficial to consume a small amount of carbs when breaking a fast to replenish so that you don't have create an undo process of other nutrients?
Sorry if this is a horrible question, but I'm terribly curious :)
asked byTaviLola (135)
Get FREE instant access to our Paleo For Beginners Guide & 15 FREE Recipes!
on July 30, 2010
at 08:23 PM
Your question is multi-pronged. Here's a part of the answer:
Glycogen is the storage form of glucose, it is a type of animal "starch" that is found in muscles and the liver. The body uses insulin to pack muscles with glycogen. Insulin takes glucose from the blood and converts it to glycogen right in the muscles themselves.
When you eat carbs, they are broken down into the constituent sugars by enzymes, and then when free glucose enters the blood, insulin levels rise in response, and the insulin then works to store the glucose as glycogen.
If for some reason you don't have enough glycogen stored (e.g. because you've been fasting or doing endurance exercise) then your body will want to store glycogen in the muscles. Your body will still want to fill up the tank, even if you don't eat any carbs. To get glucose in the blood in the absence of dietary carbs, the body uses a process called "gluconeogenesis" which is a process of converting amino acids (free proteins) to glucose. The body will use protein you eat preferentially in this process, or it will break down lean mass and tissues in your body.
Ketosis is a state in which your body manufactures ketones (a type of acetone) from fatty acids to use as a replacement fuel; it substitutes for glucose in the brain. But ketones are not, I think, involved in storing glycogen in the muscles.
Another hitch here is that free fatty acids are available to be used as fuel in the muscles for low intensity exercise at any time; so your body doesn't necessarily need a large store of glycogen to operate. "Fat burning" can take place instead.
In other words, I don't think the body breaks down fats and turns them directly into glucose. The body doesn't need to do this, since breaking down fats yields a fuel (fatty acids) that can substitute for glycogen in the muscles directly.
I suggest you read up on the metabolism on Wikipedia. Start here and follow the connecting links!
on July 31, 2010
at 03:29 AM
Most activity is fat burning type activity. It doesn't deplete glycogen that much so you don't have to worry about rapidly replenishing glycogen. The body can replenish glycogen from fatty acids easily enough. Most of the stuff you do is going to be fat burning type activity. However, intense activity like running and intense cardio will burn glycogen a lot faster and you can become depleted and fatigued. The body can replenish this using gluconeogensis, as others have described, but that process is slower using gluconeogenesis than if you consume carbs which quickly turn to glucose and are quickly turned to glycogen. So for people who need fast recover after intense workouts, they sometimes turn to carbs to get that. Seems like it also varies between individuals as to who seems to really need those extra carbs after intense workouts in order to speed recovery vs who seems to do just as fine recovering without carbs.
What the weight lifters usually say is look at your recover time for intense glycogen burning exercise and note if it is slower on low carb than when eating some carefully timed carbs. The plus side of eating some carefully timed carbs around intense glycogen depleting exercise is it may speed up your recovery and help build muscle. The downside is that it spikes insulin levels.
HOwever, the carefully timed carb consumption regime is generally only needed for elite athletes or someone doing really intense exercise. Sleeping or mowing the lawn doesn't count. Most people can replenish glycogen just fine using gluconeogenesis once their bodies are adapted to low carb.
on July 30, 2010
at 07:53 PM
Ketosis... Your body burns fat and uses ketones
on July 30, 2010
at 09:15 PM
"Does the lactose bypass the insulin fat-storage when it becomes stored as glycogen?"
Insulin doesn't take the carbohydrates you eat and store them directly as fat. There is constantly a stream of fatty acids coming into or going out of the fat cells. When there is insulin in the bloodstream, the process of fat entering the cells becomes preferred over the process of fat exiting the cells. So regardless of what happens to the lactose, during the time when insulin is released in response to your eating it, you will tend to be storing more fat than you are releasing.
You don't need to eat carbs to break a fast.