I received this question on Reddit via personal message:

Via private message, someone asked me this question:

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But the thing is, since last Thursday, when I started the 1500, I’ve gained 0.8 lbs. I’m still only 131.8, and I know weight fluctuates, but it’s still got me pissing my pants and trying to find any excuse not to eat. I’m making myself, though. … I shouldn’t be gaining weight. I know that logically and empirically, but I still feel disgusting, still feel impossibly, ridiculously huge. Part of the problem is that some of my calories everyday are coming from sugar, mostly because I’d the holiday season.

So my question is, did I fuck something up when I was eating so little? Theoretically, to maintain even if I was sedentary, I should have an extra 250 calories. There’s no way in hell I should be gaining, but that’s what the trend has been. I’m trying to get better, but it’s so hard when things like this happen when you try to eat more.

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The person is referring to adding in 100 calories steadily in weekly increments to build up to a more normal caloric intake as we talked about. Weight gain, especially for people with anorexia, is a very scary issue indeed; however, when it comes to weight gain, there are a lot of factors that come into play for something like 0.8 pounds. It could be any of the following:

Water retention from too much salt.

Some kind of allergy or sickness causing an inflammatory response.

Hormonal changes causing you to retain water.

A shit you need to take.

As for the question on metabolism, people who recover from restrictive eating tend to have higher metabolic rates than others once they get back to a normal body weight. That means you would need even more calories than someone your height/weight/gender, and sometimes that causes a relapse because of all the calories you need to take in. Your metabolism returns to normal soon after proper re-feeding. You can read more about these studies here.

In other words, this gain of 0.8lbs is not likely due to your metabolism. If you are concerned, hit the weights or do some other strength-building exercises. Muscle is a very easy factor to control for your metabolism.