According to Mr. Nick Gammon, thats not the case (or I`m missing something):
Running from a 9V battery through the "power in" plug, it draws about 50 mA.
Running on 5V through the +5V pin, it draws about 49 mA.
(Note: around 68 mA on a Mega 2560 board)
Now we'll try putting it to sleep:
Sketch B
#include <avr/sleep.h>
void setup ()
{
set_sleep_mode (SLEEP_MODE_PWR_DOWN);
sleep_enable();
sleep_cpu ();
} // end of setup
void loop () { }
Now the Uno draws 34.5 mA. A saving, but not a lot.
(Note: around 24 mA on a Mega 2560 board)
http://www.gammon.com.au/power
Also see:
https://forum.arduino.cc/index.php?topic=76724.0
