Strength/Weight

[dms]

For someone who is naturally thin, so that exercise is not likely to cause much weight loss (let's assume none for this discussion), how strong is the correlation between strength gains and weight gains when lifting?

If such a person is not seeing much improvement in strength or an increase in weight after lifting for 1-3 months, is there a good chance that he simply isn't taking in enough calories? Or would strength be expected to increase a fair amount even on a very limited diet?

(If it helps to keep things simple, let's think of "strength" as measured by 1 set of 8-12 reps doing as much as one can do.)