This is one of those 'the dosage makes the poison' - and there seems to be some variability between individuals, almost certainly some is genetic, but also what simple carbohydrates do to the populations in the microbiome. From the literature, six teaspoons are *probably* OK for *most* of us. But if you come from a population not historically exposed to simple carbs (e.g. Inuit) or your parents were diagnosed with T2DM, particularly before age 60, you might not tolerate them well.
Just my $0.02...