I think the report he's talking about is this one? I haven't looked at the numbers myself - though I believe the key is 34% of the biomass
due to obesity (not 34% of all biomass).
http://www.biomedcentral.com/1471-2458/12/439/abstract
http://www.biomedcentral.com/content...458-12-439.pdf
North America has the highest average body mass of any continent (80.7 kg). In North America one tonne of human biomass corresponds to 12 adults. More than 70% of the North American population is overweight and biomass due to obesity is 1.2 million tonnes. North America has 6% of the world’s population but 34% of world biomass due to obesity. Asia has the lowest average body mass of any continent (57.7 kg). In Asia, one tonne of human biomass corresponds to 17 adults. Asia has 61% of the world’s population but 13% of world biomass due to obesity (449 thousand tonnes).