South Beach vs. AtkinsThe South Beach diet begins very similarly to Atkins - with a 2 week initiation phase that radically restricts carbohydrates (and which, Dr. Agatston brashly asserts, should result in a 13-pound weight loss). But after this initiation phase South Beach differs from Atkins (at least the classic Atkins diet) in two significant ways: under South Beach, "good" carbohydrates are not discouraged, and "bad" fats are. (Classic Atkins doesn't like any carbs, and scooping lard from a bucket is a perfectly legitimate snacking strategy.)
South Beach relies on the glycemic index to determine good carbs from bad carbs. Essentially, the glycemic index estimates how rapidly blood glucose levels (and hence, insulin levels) rise after eating a carbohydrate. This is important since keeping insulin levels low is the central principle behind all low carbohydrate diets. (To read why, click here.) So under South Beach, bad carbs with a high glycemic index (like refined flour products, potatoes, pasta, and white rice) are forbidden, while good carbs with a low glycemic index (like whole wheat products and wild rice) are OK.
South Beach also chooses not to ignore the substantial evidence that saturated fats are bad for you. (Atkins maintains that saturated fats are fine as long as you avoid the carbs.) Thus, South Beach wants you to stay away from butter, fried foods, and sausage and instead pushes unsaturated fats like olive oil and fish.
As DrRich has pointed out in the past, scientific evidence is causing the radical low-carb proponents (as exemplified by Dr. Atkins) and the radical low-fat proponents (as exemplified by Dr. Ornish) to converge. The low-carb guys are having to admit that complex carbohydrates (i.e., the low glycemic carbs) are necessary for a healthy diet. Similarly, the low-fat guys have had to concede that certain fats are essential to good health. So, while these radicals continue to fight viciously, if you listen to what they are saying quietly in the background, they're not all that far apart. DrRich notes with interest that the South Beach diet (after the radical initial 2-week phase) lines up pretty much at the convergence point - the place where the radical low-fats and low-carbs are being dragged together, kicking and screaming all the way.
Nutritionists vs. everybodySo what are nutritionists saying about South Beach? According to the Times, they are carping. Nutritionists hate it when physicians (who, everyone knows, know nothing about nutrition) write best-seller diet books, and when those diet books fall under the category of "low-carb" (an approach that turns the exalted food pyramid on its head) they really go ballistic. So: they complain about the shortcomings of the glycemic index (pointing out that carrots really aren't that bad for you,) and about the unhealthy nature of the radical initial phase, and about the promise of losing 13 pounds during the first 2 weeks (which is indeed reminiscent of the seedier weight loss scams).
But they seem to have a hard time arguing with the later phases of South Beach - as well they might. The long-term part of the South Beach diet looks pretty healthy to me, too.