The Cake Boss star's mother, 66, was diagnosed in 2012 with the neurodegenerative disease that affects nerves in the brain and spinal cord.
As for how his mother's doing now, "She's got good days; she's got bad days," Valastro tells PEOPLE, adding that while it's difficult watching her weaken, there is a silver lining.
"You've gotta look at it [glass] half-full – we've been blessed," he says of his mother's condition, noting she's now in a wheelchair permanently. "The form of ALS my mom has, it's not really attacking her breathing or her speech. It's more of her limbs, so she can't really walk or move too much."
Valastro, who began the Mama Mary Foundation upon his mother's diagnosis, says he was "gung-ho" when he found out about the Challenge because he's seen the debilitating disease's effects firsthand and wants to raise more money and awareness. (He did the Challenge himself last week and nominated his Carlo's Bakery staff, as well as all of his social media followers.)
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"The worst part about ALS is that one day you're able to brush your teeth, then you'll never be able to brush your teeth again. One day you're able to walk – you're never going to walk again," he says. "The basic functionalities of life are stricken from you day by day."
While Mary has her ups and downs, "She's still my mom," Valastro, 37, says. "She still yells at me. She still calls me. She still drives me a little crazy. She'll never stop being my mom."
Still, the hardest part is watching her suffer.
"I've seen the most independent, lively person that I've ever met in my life – I mean, she was just like a ball of energy – reduced to not being able to do anything for herself," Valastro says. "And I think that's the part that kills her the most because she was the matriarch. Se did so many things for everyone.
"And now everyone has to do for her, which nobody minds doing – it's just a big pill to swallow."