Everyone is Everything (To Varying Degrees) - How Binaries Suck

Yesterday in a journal club at SOCHARA, we were faced with many challenging classification questions.

The paper we were discussing was titled "Metabolic non-communicable disease health report of India: the ICMR-INDIAB national cross-sectional study (ICMR-INDIAB-17)". The second classification question was in the title. What is a "metabolic NCD"? Are there non-metabolic NCDs? The paper was only discussing diabetes and pre-diabetes, hypertension, obesity, and dyslipidaemia. What about things like stroke? MI? Cancer? Does the paper mean that these are not metabolic?

My explanation was that the study started out as a diabetes study, but expanded to others, and, to fit the word restrictions that journal format puts out, they came up with a word called "metabolic NCD" to refer to the subset of NCDs that were studied.

I searched on google scholar for any other reference to metabolic NCD and couldn't find any other place where such a classification was being made. But on the WHO website, they classify the risk factors into two:

Modifiable behaviours, such as tobacco use, unhealthy diets, physical inactivity, and the harmful use of alcohol, all increase the risk of dying from an NCD.

Metabolic risk factors contribute to four key metabolic changes that increase the risk of NCDs: raised blood pressure; overweight/obesity; hyperglycemia (high blood glucose levels); and hyperlipidemia (high levels of fat in the blood). In terms of attributable deaths, the leading metabolic risk factor is elevated blood pressure, followed by raised blood glucose and overweight and obesity.

This language is repeated in Table 2 of the paper too where it refers to the prevalences of diabetes, prediabetes, hypertension, etc as: "Weighted prevalence of cardiometabolic risk factors among the study population"

What becomes clear is that categorizing NCDs into binary categories (like metabolic, not metabolic) is next to impossible. After all, nature doesn't fit into neat categories. Every disease has metabolic risk factors. Every disease has behavioural risk factors. All things contribute to a disease to varying degrees. Rather than categorizing, it is better to think about how much the contribution of each is.