Need to gain weight, but don't want to get fat?

basically i have somehow managed to lose around 7 pounds without realizing and i want to gain back the weight but without getting fatter... just wondering if i were to gain my 7 pounds back, would the change be very noticeable? I know 7 pounds would make a huge difference if i were to gain 7 pounds of fat and no muscle, but what about if were to gain by eating mostly healthy food? is it still possible to get fatter like that?
Need to gain weight, but don't want to get fat?
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