I watched the film "Fat Head" over the weekend. See ...
This was done as a riposte to the documentary "Supersize Me" by standup comedian Tom Naughton. He ate fast food for a month to see what effect it had on him. However, he was careful to stick to under 2,000 calories and less than 100g of carbs a day. Basically eating a big mac, but skipping the fries and drinking diet drinks rather than the full sugar versions. His "junk food" diet was over 50% fat. Surprisingly he actually lost weight over the four weeks and his percentage body fat dropped.
Another film called "Cereal Killers" (available on dietdoctor.com) has athlete Donal O'Neill eating a low carb, high fat diet for a months to see the effect. He too lost weight.
You get fat by eating too many carbs which raises blood glucose and triggers the body to create insulin which stores the sugar as fat. Eating fat does not make you fat unless you also eat a lot of carbs as well.