When a person begins to eat more finally, they may experience increased bloating and even edema. Edema is swelling caused by excess fluid in body tissues, especially in the ankles, feet, and around the eyes. The body will tend to retain more water than usual and cause many pounds of weight gain initially.
People can reach just 10-20 lb of edema (water) weight gain over just a few days (https://eatingdisordersreview.com/causes- and-management-of-edema-in-patients- with-eating-disorders/). So if you seemingly gain weight fast after initially eating more, remember this is mainly water weight. Do not be alarmed at the seemingly “fast” rate of weight gain.
Edema happens because a starving body, suddenly given nutrition, will hoard every bit of it that it can. During a famine, this would help a person survive since the body would be uncertain about if food were truly plentiful.
Edema is especially prevalent in those who binge and purge. This is because those who purge through vomiting or laxative abuse are putting themselves in chronic dehydration, meaning they're volume-depleted. The adrenal glands, which sit above the kidneys, produce extra aldosterone, a hormone that keeps one from urinating away salt and fluids. Purging frequently can cause chronically elevated aldosterone, which will cause edema.
Edema can last for weeks, months, and even longer - but for most people resolves sooner than later. I personally never experienced edema, so not everyone who recovers weight will get it.
The discomfort of gaining weight in recovery is normal, as is edema. The only way to get rid of the edema is to nourish the body more, to continue gaining weight despite the discomfort. Do not purge more, as this will only make the edema worse.
Don't let temporary swelling slow your progress toward achieving the healthy weight and life you deserve!