Losing weight can be difficult for a number of reasons, including fad diets that do more harm than good. Dr Charlotte Norton, Chief Medical Officer of The Slimming Clinic, the UK's largest online weight loss clinic, explains how you could be holding yourself back. Buying low-fat products. Reaching for the low-fat products in the supermarket is a "huge mistake", according to Dr Norton. "Whilst many of these products may be low in fat, they're full of sugar to compensate.