January 18, 2005

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What the heck is ketosis? And how important is it to my low carb diet?

You hear the word "ketosis" bandied about a lot. Some low carbers consider it to be the Holy Grail, while anti-low-carbers claim it's the ultimate proof that a low carb diet is horribly unhealthy. So what the heck is ketosis, anyway?

More accurately called "dietary ketosis," the term simply means a state when enough ketones are being produced in your body that they are spilled in your urine in detectable amounts. They're detected by means of test strips, available at any drug store, which you pass through your urine stream.

"Oh, great," I can hear you groan. "So what the heck is a "ketone," why would my body make one, and is it dangerous?"

A ketone is a perfectly normal byproduct of metabolism. They're made in your liver, and your liver is actually manufacturing ketones all the time. They're a by-product of fat metabolism. However, since your body will always choose carbohydrate for fuel over fat, if you give your body some carbohydrate every few hours, as most people do, you don't burn much fat, and you don't make many ketones. When you restrict carbohydrate intake, your body switches over to burning fat for fuel - a good thing! - and as a result, makes more ketones. Your body then uses those ketones for fuel - the vast majority of tissues in your body can burn ketones for fuel as happily as they would burn glucose or free fatty acids.

So spilling ketones in your urine is proof that your body is burning fat as its primary fuel, and this is why Dr. Atkins wanted people to test their urine for ketones - it was a sure-fire way of knowing whether they'd cut their carb intake low enough to be running a fat-burning metabolism instead of a glucose-burning metabolism.

Being in ketosis has some interesting effects. Most people find that ketosis suppresses appetite, always a good thing when you're trying to lose weight. And many folks, me among them, have found that ketosis causes a mild euphoria, a state of high energy and feeling very "clear." Since we know that the body goes into ketosis during starvation, because in the absence of food all it has to burn is body fat, I suspect that this state of cheerful energy and focus is a survival mechanism - it helped our ancestors get out there to hunt and gather.

Some low carb critics turn this around, and say that a low carb diet puts your body into "starvation mode," as if this were some sort of terrible thing. As my pal Johnny Bowden says in his superb book Living The Low Carb Life (a book that is so well-written and informative, I keenly wish I had written it myself), saying that because starvation is bad, ketones are bad, is like blaming umbrellas for rain.

It is very important to understand that while testing for ketones in your urine can give you an idea if you're burning fat, it cannot tell you whether you are burning body fat or dietary fat. You can burn fat all day long, and if you're taking in 10,000 calories a day, you'll gain weight - because you're not burning anywhere near as much fat as you're taking in. So please, don't just test your urine, think "Oh, I'm in ketosis, I'm burning fat!" and assume that "burning fat" is the same thing as "losing weight." It is not.

Too, not testing positive for ketosis is not proof that you're not burning fat - you may just not be burning enough to test positive, or you may have burned up a lot of your ketones by exercising, or you may have drunk so many fluids you diluted your urine to the point where you tested negative. The point is, ketosis is a useful tool, but not the be-all and end-all of low carb dieting.

Not all low carb diets involve ketosis anyway. I generally eat 50 or so grams of non-fiber carbs per day, mostly as vegetables, and that's enough that I'm not in ketosis. If you're on one of the diets that stresses "good carbs" over restriction of the total quantity of carbs, you may not go into ketosis, either. If you feel good and you're losing weight, not to worry.

What about those horrible, dire warnings about ketosis? There's even a warning on the jar of ketosis test strips! Breathe easy. The warnings are about ketoacidosis. This is a very dangerous thing, but it only happens to type 1 (insulin dependant) diabetics.

Here's the deal: There are two opposing hormones - insulin, which you've heard of, and glucagon, which is less well known. Insulin is responsible for storing fat, and glucagon is responsible for releasing it into the bloodstream to be burned. In the total absence of insulin, which only happens in type 1 diabetics, the body dumps too much fat into the bloodstream and starts to make ketones. But at the same time the diabetic, because he or she has no insulin, is running very high blood sugar levels. Since the body will always burn glucose first, the ketones pile up in the bloodstream to extreme levels that cannot occur with a low carb diet. There is simply no reason to equate what is a disease state to dietary restriction in a healthy person.

So there you go: Ketosis is a way of knowing if you're burning fat for fuel. It is a useful indicator, and can even be an aid to dieting by making you less hungry and more energetic. But it is not proof that you are burning body fat, and it is not essential to low carb success, though it can be helpful.

And ketosis certainly isn't a dangerous, abnormal state - indeed, there's every reason to believe that our hunter-gatherer ancestors were frequently in ketosis.

Posted by HoldTheToast at January 18, 2005 09:40 PM