Food addiction is, quite simply, being addicted to junk food in the same way as drug addicts are addicted to drugs.
It involves the same areas in the brain, the same neurotransmitters and many of the symptoms are identical (1).
Food addiction is a relatively new (and controversial) term and there are no good statistics available on how common it is.
This is very similar to several other eating disorders, including binge eating disorder, bulimia, compulsive overeating and having an “unhealthy” relationship with food.