The experimental question is whether or not sugar can be a substance of abuse and lead to a natural form of addiction. “Food addiction” seems plausible because brain pathways that evolved to respond to natural rewards are also activated by addictive drugs. Sugar is noteworthy as a substance that releases opioids and dopamine and thus might be expected to have addictive potential.
This review summarizes evidence of sugar dependence in an animal model. Four components of addiction are analyzed. “Bingeing”, “withdrawal”, “craving” and cross-sensitization are each given operational definitions and demonstrated behaviorally with sugar bingeing as the reinforcer.
These behaviors are then related to neurochemical changes in the brain that also occur with addictive drugs. Neural adaptations include changes in dopamine and opioid receptor binding, enkephalin mRNA expression and dopamine and acetylcholine release in the nucleus accumbens.
The evidence supports the hypothesis that under certain circumstances rats can become sugar dependent. This may translate to some human conditions as suggested by the literature on eating disorders and obesity.
From an evolutionary perspective, it is in the best interest of humans to have an inherent desire for food for survival. However, this desire may go awry, and certain people, including some obese and bulimic patients in particular, may develop an unhealthy dependence on palatable food that interferes with well-being.
The concept of “food addiction” materialized in the diet industry on the basis of subjective reports, clinical accounts and case studies described in self-help books. The rise in obesity, coupled with the emergence of scientific findings of parallels between drugs of abuse and palatable foods has given credibility to this idea. The reviewed evidence supports the theory that, in some circumstances, intermittent access to sugar can lead to behavior and neurochemical changes that resemble the effects of a substance of abuse.
According to the evidence in rats, intermittent access to sugar and chow is capable of producing a “dependency”. This was operationally defined by tests for bingeing, withdrawal, craving and cross-sensitization to amphetamine and alcohol. The correspondence to some people with binge eating disorder or bulimia is striking, but whether or not it is a good idea to call this a “food addiction” in people is both a scientific and societal question that has yet to be answered.
What this review demonstrates is that rats with intermittent access to food and a sugar solution can show both a constellation of behaviors and parallel brain changes that are characteristic of rats that voluntarily self-administer addictive drugs. In the aggregate, this is evidence that sugar can be addictive.