Under EU regulations, any claim that a food is a source of a vitamin or mineral must only be made when the product contains a significant amount, defined as at least 15% of the Nutrient Reference Value, or NRV (used to be called the Recommended Dietary Allowance, or RDA), which is an EU guidance level on the daily amount of vitamins/minerals needed, to meet the needs of 98% of the population. For a claim to be ‘high in’ or a ‘rich’ source of a nutrient the food must provide 30% of the NRV.
With protein it is a little different and for a to claim to be made that a food is a source of protein, 10% of the energy (measured in calories) must be derived from protein. For a claim to be made that a food is a rich source of protein, 20% of the energy in the food must be derived from protein.
Iron deserves a special mention as the iron in red meat is in the haem form which is well absorbed (or more “bioavailable”).
The non-haem form of iron is less well absorbed and can be inhibited by tannins in items such as tea or oxalates from certain vegetables like spinach and rhubarb.
Red meat also has a special trick regarding iron absorption as it contains a special protein called the “meat factor” which helps the absorption of non- haem iron. Therefore for example the meat factor in some roast pork in a meal will help you to absorb more iron from the vegetables you serve with it.