Both fat and glugose have more than order of magnitude better energy density (both MJ/kg and MJ/litre). Human metabolic efficiency for mechanical work is abou

Both fat and glugose have more than order of magnitude better energy density (both MJ/kg and MJ/litre). Human metabolic efficiency for mechanical work is about 22-25% (measured on a bike) and about 80% efficient in intake (food -> fat). If you take that into account human energy storage is still several times better.