Here is what Rob says:

The Significance of Ketosis for Fat Burning

ROB SAYS:

Dr. Atkins is credited with having popularized ketones, and the sticks you buy at the drug store, which when peed upon, turn purplish if ketones are present in the urine. Ketone testing has added a much needed element of suspenseful fascination to the otherwise boring and mundane urinary process. Nonetheless, the significance of ketosis for fat burning is overrated in general; and, specifically, it has limited relevance to the NHE Eating Plan.

The questions I get on this subject fall into two categories. 1) NHE practitioners who test negative; and, therefore, infer that they must be doing something wrong. 2) NHE practitioners who test positive; and, therefore, infer that they must be doing something wrong. Both of these groups are wrong in drawing this conclusion. (Logic suggests that there are two other groups of people who test either positive or negative; and, therefore infer that they are doing everything right. This conclusion, too, is unwarranted, but these folks are less motivated to inquire because they believe based on the results of the ketone test that they are succeeding rather than failing - which may or may not be the case.)

To those who fear ketosis because supposedly it is dangerous (and are not diabetic nor have any other metabolic condition): ketosis is neither the hazardous nor unhealthy condition that the high-carbohydrate folks insist on saying it is.

To those who fear ketosis because they believe that ketosis is a catabolic state: it's not. However, chronic low-carbohydrate consumption, which coincides with ketosis, precludes optimal anabolic hormonal enhancement (see p. 139 of NHE). The NHE Eating Plan is not a "chronic" but rather a "cyclical" low-carbohydrate diet, and it is designed to be more anabolic (and more lipolytic), calorie-for-calorie, than a chronic low or high carbohydrate diet.

To those who covet a grape-colored ketone stick, I have news for you as well:

Just because one IS NOT in ketosis does not mean that one IS NOT burning bodyfat; and just because one IS in ketosis does not mean one IS burning bodyfat.

So what does ketosis mean? The short answer is: that fat is being burned incompletely. The longer answer follows.

Ketones are partially burned fat fragments regularly produced by the liver from fatty acids. They then travel through the bloodstream where they are utilized for energy by most of the body's tissues, especially the heart which burns ketones preferentially. When one is in a fat-burning state and insulin is low, fatty acids are mobilized from adipose tissue in greater quantity. This along with a diet comprised of a higher fat/carb ratio makes more raw material available for the liver to produce ketones. However, it is not the greater mobilization so much as the impaired metabolization of fatty acids that causes ketones to accumulate, and consequently appear in the urine, stool, and breath (the three main avenues by which excess ketones are excreted from the body). By impaired metabolization, I don't mean that the body cannot get all the fatty acids/ketones it needs, but rather that it must break down more fat from food and adipose tissue than it needs (because some of it is literally leaking away). In other words, the fat-burning process becomes less efficient (which is actually good from the standpoint that some fat leaves the body without having to be burned). The reason it becomes less efficient is because, as the saying goes, "fat burns in the flame of carbohydrate."

More specifically, the rate-limiting factor for the burning of fatty acids in the Krebs cycle (which is the main process of cellular metabolism by which macronutrients are converted to energy) is oxaloacetate.

Oxaloacetate is formed from pyruvate which is generated when carbohydrate is broken down. When carbohydrate levels decrease, there is less oxaloacetate available, and thus fewer fatty acids can enter the Krebs cycle. Consequently, more fatty acids are transported to the liver where they are broken down to ketones, some of which are excreted in the urine, thereby causing your ketone stick to darken when you pee on it.

For non-diabetics, long before ketones in the blood rise to a dangerous level, insulin is called forth to exert its anti-lipolytic effect, halting the release of fatty acids from adipose tissue so that the ketones in the blood can be disposed of without more being produced. In a Type I diabetic, who has no anti-lipolytic insulin to counterbalance lipolytic glucagon, fatty acids rush from adipose tissue and food unchecked, and get converted by the liver into ketones at a rate that exceeds the body's energy needs and outstrips the body's capacity to get rid of them. Consequently, the blood level of ketones, which are acidic, escalates to toxic levels causing coma then death if not treated quickly. This is called diabetic ketoacidosis. Notice the word "diabetic"; if that doesn't describe you, "ketoacidosis" doesn't apply to you.

Bottom line: the only thing that a purple ketone stick signifies is that fat is being burned in a low-carb environment. Whether the fat burned derives from bodyfat or food (or a percentage from each) is not evident from the result of a ketone test. And just as the presence of ketones in the urine does not prove that bodyfat is being burned, the absence of ketones in the urine does not prove that bodyfat is not being burned.

One final note: the higher one's muscle/fat body composition ratio, the more difficult it is to turn a ketone stick purple.

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