Good question. I suspect there are scales on this topic in various disciplines, e.g., psychology, sociology, nutrition, medicine, etc.

I am not sure what you mean by "healthism" since that is a term I have never heard before. There are several tools that you can use to assess health behaviors and other constructs such as self-efficacy, patient activation measure, readiness to change, locus of control, etc. If you can be more specific with your question, I am sure we can point you in the right direction.

It is difficult to define, and has been used in several different ways, but I think of it as equating healthy living behaviors with morality, or as one's highest value. 

Greenhalgh and Wessely (2004) describe it this way..."Healthism is a well-recognized socio-cultural phenomenon in the western (and westernized) middle classes, characterized by high health awareness and expectations, information-seeking, self-reflection, high expectations, distrust of doctors and scientists, healthy and often ‘alternative’ lifestyle choices, and a tendency to explain illness in terms of folk models of invisible germ-like agents and malevolent science. The healthism phenomenon probably arises from a number of different demographic, economic, technological, scientific and ideological forces—including what has been aptly termed ‘the post-modern condition’."

Greenhalgh T and Wessely S. ‘Health for me’: a sociocultural analysis of healthism in the middle classes. Br Med Bull (2004) 69 (1): 197-213.

You may find these papers helpful. I wrote them a long time ago, so I suppose I should consider writing an updated version as well.

I hope this helps

Ariel

Article Disease Management Interventions: What's in the Black Box?

Article Disease Management Interventions II: What Else Is in the Black Box?