Balanced diet is the best option, but the micronutrient content of foods is hugely dependent upon how they are produced, stored and cooked.
All the fat soluble vitamins (A, D & E) are able to be stored by your body so in a healthy person they will not require supplementation.
Water soluble vits (B complex & C)are not able to be stored to any significant degree. Vit C is relatively easy to come by as long as your diet contains a normal amount of fruit/veg.
B complex can be a useful supplement and is the most common diet related deficiency as many good sources are unprocessed foods.
It is present in meat, pretty much irrespective of it’s “quality” and processed wheat products often have B vits added during the manufacturing process to bring the levels up to (or over) the “natural” level for the particular foodstuff.
Mineral supplementation is the most complex to manage as their metabolism and storage is highly dependent upon their chemical format – so while a multivit can quite legitimately say it has 100mg of mineral X, the mineral may be in a chemical form (sulphate, phosphate, carbonate etc) which make it all but useless to the body.
Fatty acids, ?-3,6 fatty acids are essential nutrients and the best dietary sources are fish, green leafed veg and seeds – all foods which can figure high on peoples “don’t like” lists.
If you take a ?-3,6 supp the I’d go for flaxseed sourced rather than fish oil sourced – more palatable (no fish breath!!) and less liable to be contaminated.
So, a one-a-day multivit/mineral and/or B complex is not going to harm you and may top up any dietary deficiencies and a flaxseed cap is also not a bad idea if you don’t eat much fish or other ?-3,6 sources – the rest, well as a consumer it’s your choice but make sure it’s an informed choice.
There’s plenty of info “out there” on the vit/mineral content of foods, these links are a pretty good place to start…
http://www.ars.usda.gov/main/site_main.htm?modecode=12-35-45-00
http://www.foodcomp.dk/v7/fcdb_default.asp
http://www.hc-sc.gc.ca/fn-an/nutrition/fiche-nutri-data/index-eng.php