Both of my DSs, one a USNA graduate (currently an aviator) and the youngest who is a candidate for the class of 2021 received the same notice. Both are very athletic (football, basketball and track) and spend a lot of time in the weight room were outside of the guidelines. DS # 2 has about 8% body fat DS # 1 was close that same stat, simply went to their doctors office and a measurement was taken and submitted, within a few weeks their status was updated.
CA_ and MichUSNA, I think the whole body mass index thing is archaic, I think they should use a body fat test from the start. Fortunately they allow you to have follow up test to assess the candidates body fat if they fall out of the BMI scale. The first follow up is the tape measure test, if the candidate does not fall in line by that test then there are other test options.
I believe that there are few types of people who fall out of the required body fat lines. There are those who are really fit and have high muscle content, they have nothing to worry about and just need to get their follow up measurements taken, they will fall right in line. Then there are those who are just slightly overweight who need to make some minor adjustments in their life style. There are those who are a combination of the first two that I mentioned, that need to get their weight down a little, but will still fall out of line because of the muscle content. In that case healthy life style changes and the follow up measurement should take care of that. Then of course there are those who are more than slightly overweight and need to quickly get on a healthy fitness and eating regiment.