He's not comparing it to a starvation diet. He's saying it actually starves the body, which runs naturally on glucose from carbohydrates. Also, without carbo*hydrates*, many people get very dehydrated on this diet.
GG, if this is what Katz is saying, and I don't believe it is, he is dead wrong.
I actually did a lot of research on this before I even started, because the concept seemed so foreign to me and I was worried it might do more harm than good.
The body is only glucose "starved" on a keto diet for a short period of time - usually no more than a few days. It's then forced to seek out alternative fuel sources. It does this by internally creating ketone bodies from stored fatty acid. On a molecular level, ketones are very closely related to glucose molecules. Enough so that your cells can use them much in the same way. The difference is that ketones don't rely on insulin to be used by cells.
Given the choice between burning glucose or ketones, the body's natural response is to burn glucose, or simple sugar, first. It's an easy fuel, but it also has the disadvantage of burning quickly - sort of like kindling wood. However, your body will easily adapt to burning ketones over time. Part of the reason it takes time to adapt is because in our culture we're accustomed to loading up on carbs, and our ketone burning facilities (within cellular mitochondria) lie dormant most of the time. Once the carbs are depleted, we simply eat more. Life hasn't always been this way, though. It's been speculated that in the time of our primitive ancestors, before fruits, pasta, and starchy vegetables were readily available, humans spent a lot of time in "ketosis" and we've retained this ability. We just don't use it as much anymore.
Once glycogen stores are depleted (This is what actually causes the
temporary dehydration and water weight loss. More on that in a bit.), the body begins to convert stored fatty acids to ketones. With very few exceptions, every cell in your body has the ability to burn ketones just as easily as it burns glucose, although it's not an efficient process in the first stages of the diet.
About dehydration. In the early stages of the diet, as blood glucose is depleted, the body then dips into its glycogen stores, which are mostly in the liver, but also in muscles. Glycogen is a carbohydrate molecule composed of carbon, hydrogen, and oxygen. The body burns the carbon, and the leftover hydrogen and oxygen molecule is released as water. This also has a tendency to flush electrolytes out of your system, the same as when you sweat a lot. But the initial dehydration is only temporary, and is typically not a problem after a couple of weeks. I'll admit, though, that this is the period where there are a lot of drop outs on the diet. It has also led to the myth that people on low carb diets are dehydrated, which simply isn't true, other than in the initial stages.
He acknowledges that it lowers blood sugar, cholesterol, etc., and people generally feel better because they're losing weight. That's what you expect to see when people restrict calories or eliminate a category of food from their diet. But people often don't get enough vitamins and minerals from this diet.
This is somewhat of a myth. First, the weight loss doesn't necessarily come from restricting calories. The keto diet doesn't emphasize calorie counting at all. In fact, just the opposite. The mantra is eat until your full, but no more than that. You tend to be not as hungry on this diet, because you're not dealing with the blood glucose ups and downs, and therefore not having to constantly replenish carbs. Your body starts to rely more on burning its own fat and triglyceride stores as it needs them. At the same time, it relies less on insulin.
Insulin, or the lack of it, is a key part of weight loss on a ketogenic diet. Insulin serves a few purposes in your body. First, it helps shuttle glucose into cells. Hopefully it's shuttling it into muscle cells, where it can be burned as fuel, but when muscle cells can't take up any more glucose, insulin will readily store the excess away in fat tissue as triglycerides. This is what causes bulging bellies and thighs. On a keto diet, the liver utilizes medium-chain triglycerides (MCT) as a source for ketone production. This is why some call it a "fat burning diet," although that's not entirely accurate.
With regard to not getting enough vitamins and minerals, that's not true at all. I eat a ton of vegetables. If anything, I'm eating more leafy greens, which are the lowest carb vegetables, than I ever did in my life. No supplements needed here.