Canon has been doing this with the +1/3 and -1/3 stop ISO settings since at least the original 5D back in late 2005. The last EOS DSLR that did not appear to do it was the APS-H EOS 1D Mark IIN introduced in mid-2005. The next 1-series cameras, the APS-H EOS 1D Mark III as well as the FF EOS 1Ds Mark III that were introduced in 2007 both demonstrated this as well.

There's an extended answer regarding how all of this works out in the accepted answer and the comments following it at:

Is it really better to shoot at full-stop ISOs?

Rather than copy/paste that entire answer here, I'm voting to close this question as a duplicate. Although the questions aren't exactly the same, the answer to both is.

The only additional information that might be relevant is about ISO 50. It is a "virtual" ISO that uses the sensor amplification set at ISO 100 and then "pulls" the exposure one full stop when the raw file is converted, just like ISO 160, ISO 320, ISO 640, etc. "pull" exposure by one-third (1/3) stop from the sensor amplified for ISO 200, ISO 400, ISO 800, etc. Even if you use a third party raw conversion application, the EXIF info attached to the raw file will let the app know to apply the exposure adjustments.

With ISO 50, the effect of the "pull" in development is to reduce the brightness of the entire picture, including the shadows where noise tends to be most noticeable, by one full stop. It also reduces the highlights by one full stop. So any areas that are right at the clipping point in the raw file (which is probably a stop or two brighter than what could fit into a jpeg with typical gamma and contrast curves applied) are also reduced by one full stop.