Michael conducts an ambitious study on the health benefits of omega-3 fish oils, while Dr Chris van Tulleken puts omega-3 supplements to the test. Dr Zoe Williams goes on a high fat diet and discovers why eating a lot of fat affects men and women differently. Gabriel Weston seeks out an innovative new brain treatment for PTSD, and Dr Saleyha Ahsan reveals how to spot the symptoms of a little-known condition that can cause sudden and irreversible sight loss.