Doctor Ranj Singh is issuing a stark warning to people trying to lose weight - especially with summer on the horizon. Stressing how dangerous it can be the doctor took to BBC Morning Live’s to discuss diets, specially crash diets. Despite them may helping you to "lose weight quickly" he noted that they work "because they severely restrict calories and you lose a lot of fluid and water weight. But, and it’s a big but, because they’re so restrictive they can lead to nutritional deficiencies