If you are lean and healthy, a low carb plan can still be of benefit health-wise. Nobody needs the highly processed, sugar-filled crap full of hydrogenated oils that passes for healthy food these days, including those that are already lean and healthy. Thin people get heart disease and have strokes, too. However...there's also no need to go on an ultra low carb plan such as Atkins induction if you are already lean and healthy; maintainance levels of carbs would be appropriate there. What level is maintainance level? That depends on your age, gender, level of activity and a host of other factors. Some who are excercising strenuously can eat up to 100 grams of carb per day or even a bit more and still maintain. Others find that something in the range of 50-80 grams suits them better.
I'm sure you can agree that eating less processed food and more veggies, nuts, lower glycemic fruits, whole grains, adequate amounts of protein and healthy fats while avoiding sugar and transfats couldn't be considered unhealthy? That's what maintainance on low carb is.