Giles Yeo tests the extraordinary claim that eating less can boost your memory. Alain Gregoire discovers the body's secret built-in stress-buster. Zoe Williams reveals how to spot a hidden illness that can cause stillbirth. Michael Mosley uncovers how a simple magnet can save the sight of people with glaucoma. And in a special report, Dr Javid Abdelmoneim investigates what is really in the cannabis-based health products you can buy over the counter.