You'll gain weight in the beginning, but you'll end up losing weight little by little.
ーIf you start lifting weights and eat three well-balanced meals a day, you'll gain weight in the beginning, but you'll end up losing weight little by little.
「筋トレして、3食バランスの良い食事を食べるようになると、最初は太るけど、だんだん痩せてくるよ。」
to lift weights で「筋トレをする」
to eat three well-balanced meals a day で「1日に3食バランスの良い食事を食べる」
to gain weight で「太る・体重が増える」
to end up losing weight で「最終的に痩せる・体重が落ちる」
little by little「少しずつ・だんだん」
ご参考まで!