i'd be really reluctant to agree with that statement! certainly food that has been stored for a while may not cook up as well, but how can frozen vegies be more nutritious than fresh?? especially market fresh?? i'll be first to admit that the convenience of frozen vegies means they are usually in our freezer - but if we have the par boiled veg we've grown and frozen, or fresh from the market and frozen food - well, i'll put my hand on that any day - it just tastes better! we also use the "stock" from the par boiled vegies for soup or casserole cooking (as my nan used) - either fresh. or freeze and reuse later...
As mad as it seems, frozen vegetables in most cases retain mor nutrients than store bought vegies. Obviously this doe not refer to freshly picked from your garden or from the a market they have been at for less than 2-3 days. But certainly to the average shop/supermarket, even some green grocers. It largely depends on where the veg is coming fro mto get to the shop you are buying it. The large supermarkets store their fruit and veg in warehouses for days on end, and to ship it around the country also take days. Add to this the time it takes to get them from the farm to the distribution points themselves.
Vegetables nutrients largely dissipate over time as they begin to break down, light and temperature also affect the nutrient content.
The chlorine solution they wash your lettuce with also affects nutrient content...Especially if you are in WA and any thing coming across the border into WA needs to be quarentined and treated before it is allowed to be sold here. Snap frozen veg is usually frozen almost immediately after being picked and processed, usually with in 4 days of harvest.
So yes, if you want nutrient content, often frozen veges are the way to go.
(they will never beat farm or garden fresh though)