HN user
Less effective in what sense? If one included drinking water, bathing/cleaning, or sexual relations it wouldn't be a proper religious fast, unless one is excepted from it, e.g. due to health issues. There are no degrees of effectiveness so to say.
Coincidentally, Yom Kippur [1] begins tomorrow, when observant Jews fast for approximately 25 hours.
Krypton is relatively cheap because, while it is produced by atmospheric distillation, it is a by-product of oxygen/nitrogen production. The boiling point of oxygen is -183 °C, and the boiling point of krypton is -153 °C. This means that when you distill air and obtain liquid oxygen, krypton will necessarily also be obtained as a liquid.
Helium, however, has the very low boiling point of -267 °C. Commercial, high-scale production of oxygen doesn't even approach this temperature, so helium will never be distilled and instead be vented as a gas along with a residual air stream.
The point is that the price of krypton is actually the marginal cost of producing it from an existing process, while the price of helium will approach the cost of energy required to extract it, which can be calculated and is quite high.