Nick Heidfeld, already one of the two lightest men on the formula one grid, lost a full 2.5 kilograms ahead of the 2009 season.

Nick Heidfeld, already one of the two lightest men on the formula one grid, lost a full 2.5 kilograms ahead of the 2009 season.

The diminutive BMW-Sauber driver, who topped the timesheets at the end of the first day of Barcelona testing on Monday, now tips the scales at 58 kilos, Germany's Bild newspaper reports.

Ferrari's Felipe Massa is also believed to weigh 58kg, with the pair set to benefit most from the introduction of heavy KERS systems this year.

"Never in my life had I counted calories. I would not have thought I had anything to lose," Heidfeld said.

"But this winter I paid attention to taking in less carbohydrates and fat and I trained harder than I ever have before," the 31-year-old added.