This is the difference between weight loss and fat loss. On Atkins, your body lost fat while preserving your muscles. When you starve yourself, your body cannibalizes the muscle tissue, the bones--everything. So you will weigh less, but this means that you'll still have excess fat, so you won't be as small as you'd think you should be at that weight. Muscle is more compact than fat, which is why you looked better at the same weight on Atkins than on your current eating regimen. When the body believes that it's starving, its response is to increase your insulin levels to try to induce hunger in the hopes that you will eat to satisfy the hunger. A side effect of this increased insulin is that it prevents your body from burning your fat tissue for energy.

Hopefully that makes sense. Suffice it to say that there is a biological reason why you have observed this difference in your body at the same weight on two different eating regimens, and that you are far from the only one. You will lose weight quickly while starving until your body's metabolism slows to match the new lower energy intake. Then your weight plateaus at the lower level and you would have to eat even less to continue losing weight. This is problematic since most people cannot sustain the lower level of food intake indefinitely. Once you start eating more again, you will gain weight. Often, you gain it all back plus more since your metabolism had been reset lower and the amount of food that you ate before you began starving is now no longer in balance with your body's energy needs. This is why calorie restricted diets inevitably fail and why people often gain back everything they lost plus some extra pounds when they stop dieting.

Check out the user anyway's photos. She has a great photo of herself side-by-side on two different diets. On Atkins, she weighs 30 pounds more but looks substantially smaller. Here's a link:

Compare and Contrast

Also, there is a photo on the forum somewhere that shows the difference in size between 5 pounds of fat and 5 pounds of muscle--the muscle is much more compact. I can't find it at the moment but will update if I do.

I hope that this helps.

--Melissa