While many nutritionists believe that "soft drinks and other calorie-rich, nutrient-poor foods can fit into a good diet", it is generally agreed that Coca-Cola and other soft drinks can be harmful if consumed to excess, particularly to young children whose soda consumption competes with, rather than complements, a balanced diet. Studies have shown that regular soft drink users have a lower intake of calcium (which can contribute to osteoporosis), magnesium, ascorbic acid, riboflavin, and vitamin A.
The drink has also aroused criticism for its use of phosphoric acid and caffeine. The soft drink industry dismisses many of these criticisms as urban myths. There are some reports that Coca-Cola is addictive, although the veracity of these reports has yet to be established.
For more, see phosphoric acid in food.
Since the late 1980s in the US, Coke has been made with high fructose corn syrup instead of sugar glucose/fructose. This was done largely due the prices of sugar increasing during these times. There are some groups who criticize this move to use high fructose corn syrup over sugar due to the fact that the corn in which the corn syrup is maintained may come from genetically altered plants.
In India, the Centre for Science and Environment, a non-governmental organisation, in 2003 said aerated waters produced by soft drinks manufacturers, including multinational giants Pepsico and Coca-Cola, contain pesticides and insecticides. Coke, Pepsi, Seven Up, Mirinda, Fanta, Thums Up, Limca, Sprite and many others carry "deadly" insecticides like lindane, DDT, malathion and chlorpyrifos.
They conducted tests which showed that Pepsi's soft drink products had 36 times the level of pesticide residues permitted under European Union regulations; Coca Cola's 30 times.
The CSE said in all 12 of the soft drinks it tested it found toxins including lindane, DDT, malathion and chlorpyrifos — pesticides that can contribute to cancer and a breakdown of the immune system. CSE said it had tested the same products in the US and found no such residues. Coca Cola and PepsiCo, the US soft drinks companies, angrily denied allegations that their products manufactured in India contained toxin levels far above the norms permitted in the developed world.
Coca-Cola had registered a 15 percent drop in sales after the allegations were made.