The new Dietary Guidelines for Americans 2005 is specifically targeted towards preventing obesity. The previous food guide pyramid from 1992 emphasized a reduction in saturated fats to prevent heart disease. With an estimated 300 million worldwide expected to be afflicted with Type 2 diabetes in the near future, mostly due to obesity, we have a new priority. The guidelines recommend a diet that is high in fruits and vegetables, low in fat, and low in sugar. The latter recommendation was especially contentious with the food industry.
As expected, low carbohydrate diets like the Atkins diet were not held in high regard. However, there really isn't overly strong evidence that they are unhealthy and in some cases they have been found to actually lower blood lipid levels! As a weight loss measure, low carb diets do seem to work although keeping that weight off is another matter as I discussed previously.
The Atkins idea is that carbohydrates make you fat. When you eat carbohydrates they get broken down to glucose (except fructose) which then triggers an insulin response. Insulin allows muscles to uptake and burn glucose (instead of fat). At the same time it suppresses the release of free fatty acids from adipocytes (fat cells). Thus when insulin levels are low, the muscles mostly burn fat (except during exercise). Glucose is thus spared for the brain which cannot burn fat. This much is true. However, Atkins also claims that when insulin levels drop after a meal, you get a strong hunger response. The data is not so clear on this point.
To make up for the lack of carbohydrates, you must eat more protein and a lot more fat. Thus low carb diets are high fat diets. The traditional Inuit diet is an Atkins diet. When you begin a low carb diet, the first thing that happens is that you get depleted of your glycogen (which is the body's only store of carbohydrates). This is accompanied by a loss of water so you lose a lot of weight quickly. Your body then goes into a state of ketosis where the liver makes ketones. The brain only burns glucose or ketones. No one knows if maintaining ketosis for prolonged periods of time is detrimental. The fact that the Inuit did it for generations probably means it's okay.
There may be other reasons for why the Atkins diet works. For one, the diet does limit calories. Secondly, there is some data that shows that restricting food choices can result in eating less. Thirdly, until recently, there were very few snacks that are low in carbs. Finally, the quick weight loss in glycogen and water may motivate people to stay on the diet.
However, people do eventually give up and the weight inevitably returns after two years.
I personally think, from a health point of view, that controlling the total amount of calories consumed is more important than the composition of the diet. If you are in energy balance, you will basically burn everything you eat so it doesn't really matter if it is mostly fat or carbs. When you overeat, you are going to store that extra energy as fat. The data shows that losing just a little bit of weight can greatly reduce insulin resistance which is a precursor to Type 2 diabetes. Exercise also seems to confer benefits that go beyond the extra calories burned. So although eating lots of fruits and vegetables is probably good for you, if eating pork rinds helps you lose weight, then stick with that.