I rarely buy ready meals and perhaps this is slightly cross posting with the Paul McKenna/sugar thread but, as an example, I happen to have a box of Belvita breakfast biscuits in the cupboard. Looking at the nutrition information, they contain, per biscuit, 55 calories, of each 12.5gm biscuit 3% is fat and 1% of that fat is saturated, 3 % is sugars and 3% is salt. 2% is protein. I do realise that adds up to 11! That aside I suppose my point is that processed foods often contain sugar and salt to make them tasty along with fats. The latter are often saturated and unhealthy, in particular, palm oil is used in virtually everything now because it's cheap but it's a saturated fat and it can increase cholesterol levels. So I can shrug and take note only of the 55 calories or I can look at the rest of the ingredients which are unhealthy and unbalanced. Sugar and salt are addictive and have effects on body weight, fat composition, mood and appetite.
I'm not saying all ready meals and perhaps not the high quality ones but a lot of ready meal type eating is not healthy at all. To read the marketing hype on the Belvita biscuits you'd think they were the food of Royalty!