Snacking and super sizing are two of the dieters worst enemies, research suggests. The average daily calorie intake in the US has increased by almost a third in 30 years, reaching 2,374 kilocalories. The influence of bigger portion sizes and excessive snacking outweighs the shift towards high-calorie foods, say experts. Focusing on reducing how much and how often people eat could help tackle obesity, they report in PLoS Medicine. Obesity levels have risen sharply in many Western countries since the 1970s. In the US, where the study was carried out, a third of all adults - more than 72 million people - are now categorised as obese. BBC