I did my own 18-month study on fat adaptation.
I did a lab test after coming off a couple of years of alpine climbing frequently. My lab test showed that I was pretty bad at burning fat despite feeling fairly strong(on one AK trip we did summit Denali three times from 14k, and in Kyrgyzstan it wasn’t hard to get up my first 7000m peak).
Coming off the alpine climbing binge, I got my first real office job, 50-60 hours a week when you consider the commute. My activity level went way down, but I decided to eat mostly fat with minimal carbs. After 18 months, on a trip to Chamonix my fitness felt like garbage. On a powder day at Mont Blanc, my lack of fitness is what ultimately shut us down. Other mistakes happened, but during a different year I would have happily broken trail to the summit. Instead I was struggling hard just to keep up in my friend’s skin track. I got another lab test anyway, and the verdict: I had completely ruined my fat burning capacity.
That office job sucked, but at the time I had to take it, and at least it also allowed me to collect my own personal data that definitively says that physical activity level is dramatically more important than nutrition for the sake of fat adaptation. You cannot just eat fats and expect something amazing to happen. This doesn’t mean “eat garbage,” but hopefully it may help someone focus on what’s important, which is actually getting out.
That being said, yes, whole milk is great. I’m also struck by the fact that 90% of high protein yogurts at grocery stores are fat-free. This seems sad, like they are stuck on the false pretense that fat is bad for you.