For starters, it's not 400g, it's 0.4lbs.
Secondly, 7lbs weight-loss in 1 week is damned fuckin good. General rule of thumb is 2% of body weight is the ideal target for consistent gains (or losses depending on your view).
I'll take Kade's comment a step further - don't even stress over the
weelkly numbers. I only weigh-in once/week (usually on Sundays - first thing in the morning, before consuming anything, and after I drop the kids off at the pool
... do the same thing consistently, so that a glass of water or cup of coffee don't skew things). I've had weeks where I was 100% clean in my eating, worked out like a fiend, and ended up gaining weight... and then weeks where I slacked on my workout, and was sloppy with my nutrition (booze, sweets, fatty foods - or all three!), and LOST weight.
The body is a fickle mistress.