It is a blissful time where the weight seems to stay off no matter what you eat. For RNY patients, it is because the intestines are lined with hair like appendages called villi. Those villi grab food as it goes through the intestines and hold it up against the sides of the intestines. That allows the body to grab the calories and absorb them.
After RNY surgery, many of those appendages are no longer there. So food slides right though and the calories do not get absorbed. The body is in a state of artificial starvation and weight falls off and stays off.
The body is smart and figures out how to overcome this state of starvation by growing new and stronger villi. That process takes between 18 months and 30 months. It is a slow process but steady and one day the scale goes up.
After the honeymoon, it is much harder to lose and to maintain the loss. Because the person now has to rely on diet and exercise to control their weight. While VSG patients may believe they have a similar honeymoon, they do not not. They only lose weight if they diet and exercise from day one. There is no malabsorption for them.
Real life begins where your comfort zone ends