I would suspect that the concern that is referenced pertains to the difference between ketosis and ketoacidosis.

Here's Atkins take on it:

http://atkins.com/helpatkins/faqs/f...ysis/index.html

Lipolysis and Ketosis
FAQ 1-12 of 12
What is ketosis?
Ketosis is really a shortening of the term lipolysis/ketosis. Lipolysis simply means that you're burning your fat stores and using them as the source of fuel they were meant to be. The by-products of burning fat are ketones, so ketosis is a secondary process of lipolysis. When your body releases ketones in your urine, it is chemical proof that you’re consuming your own stored fat. And the more ketones you release, the more fat you have dissolved.

If you are restricting the amount of carbohydrates you eat, your body turns to fat as its alternative source of energy. In effect, lipolysis/ketosis has replaced the alternative of burning glucose for energy. Both are perfectly normal processes.

People (and even some ill-informed doctors) often confuse ketosis, which is a perfectly normal metabolic process, with ketoacidosis, which is a life-threatening condition. The latter is the consequence of insulin-deficient subjects having out-of-control blood sugar levels, a condition that can occur as well in alcoholics and people in a state of extreme starvation. Ketosis and ketoacidosis may sound vaguely alike, but the two conditions are virtually polar opposites and can always be distinguished from each other by the fact that the diabetic has been consuming excessive carbohydrates and has high blood sugar, in sharp contrast to the fortunate person who is doing Atkins.