I do not believe eating a healthy Diet is a vice. However, have you noticed that some people tend to become arrogant, self-righteous and holier-than-thou after beginning a health program or successfully losing a great deal of weight. To me, this is a vice, and I prefer to distance myself from such people.
Katie, I don't believe you are that way based on the way you post here, but some of your co-workers may feel a sting of conscience when you talk about your efforts. Healthy eating is a very personal thing. Even in this thread there has been no definition of what a healthy Diet is. Is the ultimate diet the correct ratio of meat, dairy and plant foods?, or is it vegetarian, or vegan, or fruit only, is eat anything really healthy or is man meant to live on air and sunshine? There are no easy answers.
I believe the important thing is to practice what we preach and not worry about the opinions and judgments of others; but at the same time we must avoid feeling superior and judging others. Healthy eating may keep the physical body healthy, but if we have the wrong attitude when dealing with others, then our virtue may indeed seem like a vice to others. We need to adopt a humble attitude as we strive to heal and become healthier.
Read First Corinthians 6:12 and apply this principle to diet. Everything is lawful, but not all things are going to be good for you (expedient). The real key is not becoming a slave to our diet, our appetite, or our opinions on what is the only healthy way to eat.