If you're doing Atkins, eating steak is not a threat to your weight. However, I think I know what you mean.

Of course it's not a good idea to weigh yourself right after you eat because everything is still in there, undigested. It's best to weigh yourself on an empty stomach and bladder, the same time of day in the same place, with no clothes on so you can gauge accurately. There will be slight water weight fluctuations. That's normal. I weigh myself right after I wake up each morning.