The past few years there has been quite a lot of hype about insulin and how it affects fat storage. It's super-confusing, but I think I've managed to whittle it down to something both understandable and practical for the every day person.
Here goes...... (Er, this isn't going to be real technical, so if you are into splitting hairs or are going to suggest I should have included more information, you may just want to skip this blog.)
Anyhow......
Carbohydrates make your blood sugar go up. Your body doesn't like this (high blood sugar is dangerous), so it sends out a storage hormone we call insulin to bring it back down. (BTW- the pancreas is what produces insulin, so that's why you hear so much about the pancreas when people talk about blood sugar.)
Insulin turns the carbs into glycogen and stores the glycogen in different parts of the body, namely the muscles and liver. BUT it also turns any excess glycogen that doesn't fit into the muscles and liver into fat and stores them in your fat cells. If there aren't enough fat cells to hold the fat that has been made, the body has to do something with it, so it makes more fat cells to store it in. And who wants more fat cells?
Okay, now lets add in one more thing Insulin does: It keeps another chemical, called hormone-sensitive lipase, from doing it's job properly. And that job is releasing fat from your fat tissues to be used as energy.
Sooooo..... when you eat a ton of fast-burning carbs (generally the kind that don't have much fiber in them), not only are you promoting fat storage because the muscles and liver can only hold so much, but you are also KEEPING the fat you do have from being burned off as energy. This is the main reason why low-carb diets work so well for weight loss.
Having said all of this, you don't need to run from carbs like they are the enemy. Slow-digesting carbs- like oatmeal, whole-grain breads (the real whole-grain stuff, not the kind that has white flour in it, too) and starchy vegetables- are just that: Slow digesting. They release the carbs slowly into your body so that you don't have an excess all at one time to be stored as fat.
Also, when you exercise heavily the body uses up the glycogen in your muscles very quickly. So you need to eat carbs to replace them so that you have power to not only get through your workout, but also through your day.
If you are anything like me, you are asking "So why do people go low-carb when they are exercising heavily?" The reason for that is another big, long technical explanation, but I'm gonna give the very-condensed-but-not-very-scientific answer: The body will turn fat into glycogen and burn it when your muscles and liver run out of it. And the process of turning the fat into glycogen burns calories in and of itself, so it's kinda like you are getting a little calorie-burning bonus when this happens.
The thing with this is that you want to be very careful: When I have gone too low-carb I have wound up with all sorts of not-so pleasant side effects, the scariest of which is that I started to lose my long-distance vision. It was to a point where I was beginning to question whether I should drive at night because depth perception was thrown off. Other interesting side effects for me were running out of steam very quickly, getting confused easily, feeling mentally "fuzzy", headaches, becoming incredibly irritable (my daughter thought this was the worst side effect- She'd of rather I be blind than a wench), tripping over things, falling down frequently when doing cardio (Once I fell off a bench when doing step-ups, making quite a racket. People were rushing from all of the gym to help me- embarrassing!), and general lack of coordination. Clearly, super-low carb (under about 100g a day) for me is not healthy. I think different people have different thresholds, but if you are experiencing things like this while on a low-carb eating plan, I'd suggest adding a little whole-grain, fruit, or starchy veggie into every meal. Non-starchy veggies ARE a carb source, but they are not a very condensed form of carbs and would take so much of them that you would no longer be practicing portion control, which I believe to be a key factor in losing weight and getting fit.
And as a final and fairly unrelated note, if you are working with a coach who is helping you with your eating and experience any of these symptoms, TELL THEM! Any responsible coach will alter your diet and get you out of the too-low-danger-zone. If they don't, dump them immediately and find someone else to help you. Your health is not worth having a super-svelte appearance.
