Many (most?) animals cannot digest straight glucose, e.g. cats, which are obligate carnivores. I suspect most animals would have to be able to digest starches to be able to process sugars (though a good exception is the bee, so my surmise could be bogus).
I believe that cats don't even have sweet taste receptors. I've done "experiments" over the years, offering my own food to various of our household (terrestrial) pets. Cats and rodents are the most picky; dogs will eat a proper superset of what cats do, except that I have never had a dog that liked drinking milk (eating cheese, though, sure, and ice cream). Dogs seem OK with sugar (not crazy about it) cats are utterly uninterested.
An ancestor of all cat species lost a gene required for sweet taste, so none of them could taste sugar which could be why they became obligate carnivores.
I was curious, so I just mixed a teaspoon of sugar and water into a paste and put it in my dogs’ bowls. Two completely different breeds. Both went crazy for it.
Both love
Milk too. Neither dog will eat raw fruit
I had a dog which was absolutely crazy for cucumbers. He was typically sneaking into garden, sniffing for cucumbers among leaves, took it out and eat it. When I was peeling cucumber, he was salivating and whimpering to eat peelings, he would get angry if I didn't share at least some of of them. My current dog eats almost anything (he didn't like raw lemon), including most fabrics, but he's only a year old. Had to electrify the garden though because he digged and tried to eat compost.
I believe that cats don't even have sweet taste receptors. I've done "experiments" over the years, offering my own food to various of our household (terrestrial) pets. Cats and rodents are the most picky; dogs will eat a proper superset of what cats do, except that I have never had a dog that liked drinking milk (eating cheese, though, sure, and ice cream). Dogs seem OK with sugar (not crazy about it) cats are utterly uninterested.