Before answering this question we should answer what health is. The World Health Organization (WHO) defines health as a “State of complete physical, mental, and social well being, and not merely the absence of disease or infirmity.” Expanding from there you can see that health encompasses more than just how your body directly (I use the term direct or forms of it throughout this article as all three of these areas interconnect and can influence each other) reacts to food (physical), but instead how your quality of life is as a whole.
First, I would like to point out that this article is not attempting to treat any condition with a particular diet. It is instead meant to address some of the many facets that encompass physical, mental, and social well being regarding food and how that can affect what is more healthy for a particular individual. So, how does this affect how we define I personally would determine if a diet is healthy for me? It means that beyond the simple question of “does my diet fulfill my bodily needs without causing physical damage,” I also need to take into account the mental and social ramifications of the diet I choose. Scientifically speaking there are possibly many diets that would simply fulfill bodily needs (high carb, low carb, vegetarian, pescatarian, Mediterranean, and so on) given they have adequate bio-availability of required nutrients. However, as you take into account mental and social well being there are other things to consider. A diet will be healthier for an individual if it promotes peace of mind and healthy social atmosphere in addition to it’s direct impact on the physical body.
Let’s say that an animal product heavy diet meets all of an individuals physical needs, but personally they feel that current animal husbandry is unkind to animals. In this case choosing to limit consumption may be better for the mental well being of this individual even though the direct physical well being difference is the same. In a similar situation where it is not the individual, but their peer group that is against current animal husbandry practices it may be their social well being (and mental as a result) in regards to their position in a community that would take a blow if they continued to eat large amounts of animal products. These examples are not meant to condone giving in to peer pressure or ideology, but to address issues that some may not have thought about before. Depending on the peer group leaving the group may be better in the long run, but that is a whole other topic I would rather not dig into right now.
You may notice that I write a lot on the ketogenic diet and do strange personal diet challenges. I do this because I enjoy expanding my knowledge and personal experiences in nutrition and challenging convention is one of the fastest ways to learn something new. This is not to say that conventional wisdom is always wrong, but by taking things for granted it is easy to find oneself developing strong biases and new information is going to cause cognitive dissonance instead of greater understanding. The ketogenic diet for example is not for everyone or for all situations, but neither is any other diet currently. Where I differ from many in the wellness field is that I believe that the purely physical needs of the body is often second to other measures of well being for deciding things like what is the “best” diet for someone. A great example is that as more and more science on fasting and health comes out it seems to point to many great things, but suggesting fasting to an individual that has struggled with disordered eating such as anorexia or binge eating is likely not a great idea. At the same time, I would not suggest that someone continue to binge drink for the sake of their social environment as I can not imagine a scenario where the impact on physical and mental well being would not greatly outweigh the social impact in the long run.
In short, pick a diet that you can live with if you want it to be a healthy long-term choice.