Unfortunately it is my experience that most people, Christians or otherwise, upwards of around 97%, do not really know what a biologically healing, chemically altering diet is.
The sad part is that the diet is simply stated in the first chapter of the bible.
Would that portion of scripture cover the typical jewish diet that Christ enjoyed? Or the locusts that John the Baptist lived on? If not, we ought to be careful judging those who eat anything other than what we feel is right or natural.
Unless you have a way to purify all the rain water and air and soil from the toxic chemicals mankind has filled them with, nothing is pure as it once was, everything we eat, drink, and breathe in is chemically contaminated. If you do find a way, such as distilling water for example, you will find it then lacks vital elements that "naturally sourced" water should contain.
Our genetics and our environment are affected by many factors out of our control. A friend's mother for example, has several health problems, requiring conflicting diets to manage. It is a no win situation for her no matter how natural or balanced she tries to be in her eating. Many are born with allergies they have no say in, and did nothing to cause. There are people allergic to many natural products such as nuts and some fruits and veg.
Many people in our world starve for lack of calories, never mind nutrition, and they are thankful for whatever morsel comes their way.
They will die of something one day, we all will, even the most healthy of us. The "healthiest" person I ever met was killed by a regular cold virus that affected his heart!
Yes eating rubbish all the time will take its toll, but so will stressing about rules and regulations and being weighed down by the cares and concerns of this life. So will consuming "healthy" foods you have trouble digesting or absorbing or are allergic to, no matter how good they are for someone else.
If it is sin for you to eat it, you mustn't.
If it affects your health in a way that concerns you, again, don't eat it.
But we mustn't make assumptions about those who have no convictions - or choice in some cases - about what they consume.
For the kingdom is not a matter of food and drink.
It is the word of God that nourishes and sustains a man, it is the will of God that determines the date of a man's death, and it is not what goes into a man that defiles him, but what comes out of his heart after all.
In short, live by your convictions, and give thanks for what you eat and drink, don't judge those who have freedom in the area of food and drink that you don't have.
Whatever you do in word or deed, do everything in the name of the Lord Jesus, giving thanks to God the Father through Him.