The jury's still out on the Atkins diet's efficacy and long-term health effects, in large part due to resistance from the AMA's inflexible mindset--as research studies on ideas which run counter to prevailing AMA "doctrine" are quite difficult to get funded. The diet is difficult to maintain for those who have to eat out a lot (like pilots), because so much of the American food industry revolves around carbohydrates--and not for the reasons you'd think; it has more to do with the agriculture and food manufacturing industries than anything else. The diet itself is unrestricted fats and proteins, accompanied by daily vitamin and fish oil supplements. Carbohydrate intake is limited to <20g during the first two weeks (known as the "induction diet", intended to jolt your body into what Atkins calls "benign dietary ketosis"); afterward, carbs are gradually reintroduced to the diet until an individual's "balance point" is reached, that which sustains ketosis.
The theory behind ketosis and the Atkins diet in general is that carbohydrates are far more easily converted to blood glucose, your body's fuel source, than dietary fats or proteins. Given a choice between carbs, fats and proteins, your body will first turn to DIETARY carbs, then BODY fat, then BODY protein for energy. (Fats and proteins are not readily converted to blood glucose and have other dietary functions, anyway. More on that later.) On a carbohydrate-rich diet, your body maintains a blood glucose level of 2 or 3 days' worth. Carbohydrates in excess of that needed to maintain this level are stored as body fat. When carbohydrate intake is severely restricted, blood glucose levels begin to drop as your body depletes its supply.
Once blood glucose levels drop below a certain point (and in the absence of your body's preferred source of blood glucose--carbohydrates), your body turns to its stores of body fat and begins to convert it to blood glucose. The breakdown of body fat into blood glucose--a process called ketosis--produces a byproduct called a ketone which your body eliminates through urination (one reason why water intake is a large part of this or any diet--your body needs to get rid of those ketones). In diabetics, ketosis is a precursor to a condition called ketoacidosis, which can lead to coma and death. Because the presence of excess ketones is a serious condition for diabetics, urine test strips which detect the volume of ketones in urine are widely available at most drug stores. For low-carb dieters, these test strips are useful in determining when your body has turned to stored body fat for energy--and in determining your body's carbohydrate balance point when carbs are reintroduced to the diet.
According to Atkins, the irony to all the low-fat diets is that dietary fat doesn't make a person fat--excess carbohydrates do, as explained above. Dietary fat is necessary for absorption of the fat-soluble vitamins (Vitamins A, E, D and K) and also controls our sense of satiety; in his book, Atkins points out how most people, after a large meal of pasta or other carbs usually crave sweets, whereas after consuming a steak, they don't crave anything. And since the Atkins diet is a qualitative one rather than quantitative (meaning that WHAT you eat is at issue, not how much--you can eat all the fats and proteins you want on this diet), this appetite satiety effect means that after a while, people tend to begin eating less, which also contributes to weight loss.
Now, as this pertains to pilots and medical certificates, Atkins--a cardiologist by training--says his patients have seen improvements in their cholesterol levels as a result of the diet. This is the most controversial aspect of the Atkins diet as the AMA has long held that dietary fat intake is bad for your cholesterol levels and by extension, your heart. This is the area which begs for more research--which, like I said, is less likely to be funded since high fat intake is so strongly connected to poor cholesterol numbers in the AMA mindset.
The other medical aspect important to pilots is the diet's effect on blood glucose-related problems, specifically Type II Diabetes--which is usually the kiss of death for a pilot's medical certificate. Atkins claims that his patients with glucose tolerance problems, even those which rise to the level of diagnosable Type II Diabetes, have been able to reduce or eliminate symptoms of these problems, even to the point of being no longer diagnosable.
Aside from that, many healthy people experience mild symptoms of glucose intolerance. On a typical carb-rich diet, I'd "bottom-out" a couple hours after lunch every afternoon, usually using caffeine to perk back up. I then tried restricting carbs for a couple days to see if I felt any effect, and in the middle of the afternoon on the third day, it occurred to me that I was not the least bit tired or fatigued as usual for me at that time of day. As a glucose tolerance test later bore out (recommended by Atkins in his book), I have a mild glucose intolerance, which means that for a given rise in blood glucose levels brought on by intake of sugar or other carbs, my body produces too much insulin--which causes too much blood glucose to be metabolized, resulting in that tired or fatigued feeling. Restricting carbs in the diet seems to have the effect of stabilizing blood glucose levels, stemming those wide swings and raising one's general feeling of alertness, as chperplt experienced.
Anyway, that's my take on it. I'm no expert, but I did stay at a Holiday Inn Express last night.
