Lex - to be fair to Ancel Keys, his work didn't suggest that ALL fat made people fat, only animal and saturated fats, which (to be fair) the heart disease industry still believe. Apart from his K-rations for US ww2 soldiers, his greatest contribution to the diet world was his promotion of the Mediterranean diet. However, his message was somewhat lost/twisted for a long while and general "low fat diets" were promoted as being beneficial for healthy hearts (still are in some places).
And, what is also rarely recognised, he also believed that exercise was a necessary component in the avoidance of obesity.
In that he was correct - because (getting sciencey) cholesterol is produced in the body on the same pathway that produces coenzyme Q10, a molecule which is used in producing mitochondrial energy, specifically in muscles that work all the time, even more specifically heart muscle. The cholesterol-inhibiting drugs mostly block that pathway before the divergence to produce cholesterol or coQ10, which means that most cholesterol inhibitors ALSO inhibit coQ10, which is a lot of an arse (more so for some than others). Things that drive the pathway away from cholesterol = things that require more coQ10, i.e. harder working muscles, i.e. exercise.
But again that part of his message was lost - the official line was "eat low fat to reduce cholesterol and the risk of heart disease" - but the Med diet is far from low fat, and that was his favourite way of eating.
I'm not a great fan of his (especially as he was part of the gang who trashed Prof Yudkin, the first person who truly warned us of the dangers of sugar) but I do like to be fair! 
I'm still not doing well. I'm STS because during the day I'm mostly eating LC, and being good - no starches etc. - but the evenings are ruining me because of my perceived "need" for a drink (just one, usually) and then the sugar cravings have been extremely difficult to ignore. I KNOW I'm not helping myself, I KNOW I'm sabotaging and I KNOW I'm not in the right zone - but every day I start again, trying to do the right thing.