Volkow describes how the reward system, of which the dopamine rich mesolimbic pathway is particularly important, is involved in signalling desire and predicting pleasure.
Needless to say, it plays a key role in addiction. But as it’s involved whenever we do anything pleasurable, from taking drugs to eating to laughing, it’s also central to many non-pathological situations.
In fact, we presume it kicks in when we desire anything pleasurable, to any degree.
So it may be crucial to understand what happens in this pathway in people who have difficulties with over-eating.
Volkow mentions that people with obesity tend to have fewer D2 dopamine receptors in the striatum, perhaps suggesting more food is needed for the same pleasurable response, which could promote over-eating.
A similar thing has been found in addicted drug users, which raises the question, is obesity a ‘food addiction’?
Although not without controversy, drug addiction is usually described as having three main components (the ‘three Cs’): Compulsive use (wanting to do it again), loss of Control (feeling you can’t stop yourself), and continued use despite adverse Consequences (even when you know it’s damaging).
The difficulty is, normal eating fulfils all three criteria. We’re compelled to eat, stopping ourselves is incredibly difficult, and we all continue to eat things we know are bad for us, even when our health suffers.
Notably, Volkow is careful not to describe obesity as an addiction in the interview, although the magazine is quite happy to label it a ‘food addiction’.
Increasingly, we’re finding that problems labelled as separate in the diagnostic manuals can actually have some core features in common.
In this case, similar differences in the reward system in addiction and obesity seem to be important.
However, we always have to beware of over-simplifying complex problems.
Obesity, like high-blood pressure, is simple to define, but is caused by many different things acting together.
Highlighting overlaps can be incredibly powerful, but inappropriately lumping problems together often means missing the other factors which may be equally important.
Scientists are usually pretty good at this, typically discussing the similarities or talking about shared factors, but it’s worth looking out for when the message gets simplified when retold in the press.
Link to SciAm interview on obesity and addiction.