Monkeys do best on perfectly ripe and fresh tropical fruits. Is that what they were eating? I really doubt it.
The idea that anything processed in a factory is full of "toxins" and anything from nature is "healthy" is an irritating and pervasive fallacy.
Were you referring to a specific toxin that is in their foods, or were you using it in the more vague and hand-wavy "woo woo homeopathic" sense?
Specific toxins that accumulate in tissues over time and are known to contribute to premature aging in mammals include certain fatty acids and excess iron intake, for examples. In excessive amounts they are "toxic."
I don't see what is remotely "woo" about this. The whole calorie restriction idea has been pretty well debunked as far as I'm concerned. Whenever it's looked at more closely it's a matter of food quality. Animals with the highest metabolisms among their peers are actually healthiest and longest lived.