"But what about the long term?"
It seems that every study of low-carbohydrate diets, which almost always show positive results, ends with words of warning that a low-carb diet cannot be recommended for the long term because of lack of data. The problem, of course, is that it takes a long time to get long-term data! So, those of us who have experienced positive effects from reducing carbohydrates just have to wait for the people in white coats to crunch those numbers. Well, wait no longer! In November of 2006 a report of a very long-term study was published in the New England Journal of Medicine.
The StudyThe data were drawn from a large study of over 120,000 female nurses which has been going on since 1976. Six years ago, this same group of researchers analyzed the carbohydrate intake over a 10 year period of the study, and found that glycemic load was the biggest factor in determining the effect of carbohydrate on health, rather than the composition of the carbohydrate (simple vs complex). In that previous study, it was found that people eating the diet with the highest glycemic load had almost twice the incidence of heart disease as those eating the lowest glycemic load. The evidence from this new study confirms and builds upon what was found earlier, drawing from data from an 18 year period following 82,802 women.
This time, the researchers aimed to find answers to some new questions. One of the worries about low-carb diets has to do with eating more protein and fat in the longer term, especially if that protein and fat comes from animal sources, which are usually higher in saturated fat. In the short run, research seems to indicate that the markers for heart disease risk mostly improve with low-carb diets, but no one has felt safe recommending them for longer periods. (Note that low-carb diets don't necessarily have high levels of saturated fat.) So the researchers were trying to differentiate low-carb diets which had higher amounts of protein and fat from animal sources from those which had more protein and fat from vegetable sources.