Positive vs Negative

Positive

• "X" may positively affect the circulatory system.
• Several studies have suggested that eating "X" can help reduce the risk of certain cardiovascular problems and also reduce blood pressure in both overweight and normal adults.
• "X" may boost cognitive abilities.
• "X" may lower cholesterol levels in adults. Although basic research has provided preliminary evidence that polyphenols in "X" might inhibit oxidation of LDL cholesterol, few results from clinical trials are conclusive about such an effect in humans.
• According to one study, "X" consumption correlates with lower Body Mass Index.
• Other possible effects under basic research include anticancer, brain stimulator, cough preventor and antidiarrhoeal activities.

Negative

• "X" is believed to cause heartburn because of one of its constituents, theobromine, relaxes the oesophageal sphincter muscle, hence permitting stomach acidic contents to enter into the oesophagus.Theobromine is also toxic to many animals because they are unable to metabolize it (see theobromine poisoning).
• The unconstrained consumption of large quantities of any energy-rich food, such as "X"  without a corresponding increase in activity, is thought to increase the risk of obesity
• "X" contains moderate to high amounts of oxalate,which can cause some health concerns particularly for individuals at risk for kidney stones.
• "X" absorbs lead from the environment during production, and there is a slight concern of mild lead poisoning for some types of "X" 
• Research on elderly people showed "X" might cause osteoporosis.
• A few studies have documented allergic reactions with "X" in children.
• There is some evidence that "X" may be addictive

Id "X"

Answer (highlight to read) : "X" - Chocolate