Final answer:
The French ban on the sale of substituted milk was limited by the ECJ based on the health protection argument, with the key point being that trade restrictions must have a scientific basis and cannot discriminate between similar conditions in different countries.
Step-by-step explanation:
The issue in the case of the French ban on the sale of substituted milk revolved around the health protection argument. The European Court of Justice (ECJ) reduced the extent of exceptions that member states could use to impose bans on national trade. In particular, it adjudicated that the low nutritional value of a product does not provide sufficient justification for a member state to enact a ban on national trade under the health protection premise. Such regulations, as posited by the World Trade Organization (WTO), must be based on science and cannot discriminate unjustifiably between countries with similar conditions. The WTO permits nations to set their safety standards, but they must apply equally to both imported and domestically produced goods and have a scientific basis.