Low-calorie diets are safe for bones, but surgery? Not so much.

It said, "markers of bone formation decreased in the more extreme dieters". That sounds very bad to me. It sounds like any bones that might be damaged while on such a restricted diet won't heal as quickly. Given what the article says about the experiment, I think, at best, they have a very short-sighted definition of "safe". I don't think what they said about the data supports their conclusion. At very minimum, I would take this one study's conclusion with a grain of salt unless/until they follow up with all the experiment subjects years from now and check to see whether the extreme dieters were more likely to have worse problems with osteoporosis later in life.

Furthermore, note that the subjects did not stay on the 890 calorie diet the whole six months. They only stayed on the extreme diet long enough to achieve a 15% weight loss and then switched to a "weight maintenance diet". Doing the math, the dieters should've reached their 15% goal before six months, so most of them must've gained weight back on the "weight maintenance" diet. I can only imagine what happened to them after the study was over.

Finally, bone loss is only one of the many possible problems with eating so little. The article said nothing about the other aspects of the extreme dieters' health in general. Eating such a restricted diet may result in weight loss, but is it fat reduction, or did they lose more valuable tissue, such as muscle (or even brain matter)? Did the extreme dieters feel sufficiently energetic to make it through the day? Were they any more or less susceptible to any bacteria or viruses floating around the office? Were there any psychological drawbacks?

The extreme diet seems potentially dangerous in so many ways that, even if I were convinced that the researchers reached the right conclusion in this one experiment, I still would not do it until they test for all the other potential problems too.

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