why do ppl do low carb for weight loss?

This is just in from National Geographic:
http://ngm.nationalgeographic.com/2013/08/sugar/cohen-text

It confirms that the boogeyman is Fructose, also known as fruit sugar. Fructose is in almost every fruit and plant we eat, although obviously the percentage is highest in fruits. When you eat low carb, you automatically eat low Fructose as well as long as you properly count the carb in fruits.

Yeah, fructose is something that some researchers are looking into.

Having done a lot of reading on the subject (I can be geeky that way) the issue with fructose doesn't seem to be saying to run screaming from fruit. It is perhaps a good reason to start wondering about high fructose corn syrup being placed into so many things these days. From what I've read, the center of research on the subject seems to arise from the way that fructose is metabolized by the body. (And I'm going to be really oversimplyfing this. I realize there's all sorts of things concerning ATP that I'm bypassing. I know that I'm over simplifying to an extreme degree, but it's complicated).

Fructose can only be metabolilzed by the liver, which does so by more or less splitting fructose into both glucose and fat. So basically, in order for your body to deal with fructose at all, part of it has to be turned into fat. The rest is turned into glucose.

Glucose can be absorbed without being shunted off to your liver the way that fructose is (where, again, fructose is turned into glucose + fat as the method of dealing with it). All the heavy work out folks complaining about low carb diets, saying that they have to have the carbs for their workouts, there's truth to that. Aerobic exercises depletes your glycogen stores in your muscles. If you're eating carbs, your body has a quick, efficient way to smoothely replinish the glycogen.

Where you start running into some of the low carb concept is that when glucose isn't readily available to replenish glycogen, your body can begin converting part of your consumed protein or consumed fat or can even start burning your body fat (or muscle) to do so. But, as your body prefers to use glucose -- and there are reasons for that that I'll get to in a minute -- if you have a lot of glucose available, you're body is going to default to the glucose first.

Burning fat or protein is far less efficient than converting readily available glucose, so if your focus is on athletic performance, you probably prefer the readily available carbs. If your object is to burn off fat stores that you already have, you may be willing to sacrifice atheltic performance for fat burning.

Where fructose comes in is that, again, the only part of your body capable of dealing with fructose is your liver. Fructose cannot be converted into glycogen without first having been metabolized by the liver which "splits" it into fat and glucose.

Sucrose (old fashioned table sugar) is metabolized by first splitting it into fructose and glucose, with the fructose then having to be split into fat and glucose.

Factoring this out into an equation (that is NOT proportionally accurate, it's just a 'thought experiment' representation), in order for your body to metabolize these sugars what you roughly have is something like

glucose = glucose
fructose = glucose + fat
sucrose = glucose + (glucose+fat)

So if your object is to replish glycogen stores for atheltic performance, best choice may be starchy carbs. Your body can metabolize it most efficiently and your liver doesn't immediately convert part of it to fat.

Flipping this around, though, fructose -- PURE fructose -- which is handled by the liver isn't regulated by insulin, meaning it's going to be far slower to trigger an insulin response than something starchy (after all, your liver has to 'convert' fructose into fat and glucose first). This is why less starchy fruits are lower on the glycemic index than starchy ones.

Once you start getting into insulin issues, however, you start talking about a whole host of other things.

Excesss glucose in your bloodstream is bad. It's toxic. That's diabetes. A healthy body prevents there being too much sugar in your bloodstream by releasing insulin which tells your body to stop poking around,burning your fat, etc, and burn this excess blood sugar instead. Right NOW! It keeps your blood sugar in the heathy range by your muscles using what they can burning through glycogen, your body fat absorbing/expanding as it can, and other parts of it converted into triglycerides (fat) in your blood. When you're body more or less goes '*ahem* I'm aborbing all that I can!' and there's still yet. more. suger., your body makes yet MORE insulin trying to try to make your cells absorb the excess... and now you're on the way to insulin resistance, requiring more and more insulin to accomplish the same result until your pancreas cries uncle because it's taking more insulin than it can produce to lower your blood sugar... at which point you are the owner of Type 2 diabetes.

So the resulting contradictions are that glucose stimulates your insulin faster than fructose, which stimulates your body to deal with the blood sugar NOW, which -- if you're taking in more sugar than your brain and muscles need -- is stored as fat.

Fructose on the other hand, doesn't immediately stimulate insulin, but to handle it at all, part of it is metabolized as fat ...and part of it is turned into glucose which in turn stimulates insulin, and so on.

So basically, what you're left with is: your body needs glucose but not too much glucose (and how much you need is going to depend on how much you're burning). Try to avoid sugar spikes. You don't want to over-stimulate insulin. You don't want more glucose in your bloodstream than your body can use. So yeah, calories in/calories out is part of the equation.

Now the pro-side of fruit is that between the FIBER they contain and the fact that fructose doesn't immediately stimulate an insulin response, fruit it a bit of a time release capsule. Your blood sugar load is strung out over a longer period of time which minimizes sugar spikes by spreading it out. This was the way that your body was meant to behave (and it's the way that your body deals with fructose, but yeah, to metabolize it, it's still going to be split into fat and glucose).

Glucose is handled far more efficiently by the body, but excessive amounts of it are going to cause sugar spikes that will stimulate insulin that... well, we've been there already.

Basically, don't overconsume.

Eat fruit. It has a lot to recommend it.

But maybe think about avoiding high fructose corn syrup. It looks like it could possibly be the worst of both worlds... but that hasn't been proven which why they're researching the subject.

Excellent and interesting post, thank you for taking the time.

Because they believe that carbs are unhealthy. It's not true of course.

but a lot of people dont eat low carb and arent overweight?
so then why would carbs make some humans fat but not all of them?
just had this thought today at work
corworker is doing a low carb diet to lose weight
and there i was shoveling rice in my mouth and just shrugging. works for me.