Diet trends come and go, but the age-old question still stands: how do you lose belly fat — and fast? Well, hate to break it to you, but there isn't a quick, safe solution to tightening up stubborn areas. However, it is possible to begin seeing small changes in your waist in as little as two weeks with the right workout and diet regimen, according to personal trainer and registered dietitian Jim White, RD, ACSM. You won't necessarily lose inches, but with a little more patience, you may be able to accelerate your timeline by doing the following.