New series. Doctors Chris and Xand van Tulleken put health theories to the test with the help of pairs of identical twins, revealing ways we can live a healthier life. Thanks to their matching DNA, identical twins are the perfect candidates for scientific comparison, so Chris and Xand use this principle to put contrasting health theories to the test. In the first episode, the doctors pit diet against exercise, and analyse the results as they challenge twins to go head-to-head with contrasting regimes to see who loses the most weight.