There is a recommendation for grams of protein per day though – from memory I think it’s around 50g. And there’s some research on VLCDs that suggests that you do need to make sure you have at least 7g fat a day (and preferably more) in order to reduce the risk of gallstones – http://www.foodedsoc.org/marks/MARKS34.htm
I’d go for at least 20g of fat, and there’s no reason to be scared of having much more than that now that we know fat doesn’t make you fat.
So, given there’s 4 calories per gram of protein and 9 calories per gram of fat…
4 x 50 = 200 calories
20 x 9 = 180
Total intake from protein and fat = 380 calories.
Which leaves a maximum of 420 calories for carbs – so up to 105g of carb a day (given carbs are 4 calories per gram).
According to many low carb gurus, anything less than 100g carb a day is considered a low carb diet.
But to be honest, it’s probably not worth worrying exactly how you spend your calories (quantities of fat and protein aside) provided you eat a good range of foods each day.