Last book by Gary Taubes takes a difficult way, how to demonstrate sugar as a toxic substance for our health. Although he tries to show evidence for his words, he finally concedes the following conclusion:
Ultimately and obviously, the question of how much is too much becomes a personal decision, just as we all decide as adults what level of alcohol, caffeine, or cigarettes we’ll ingest. I’ve argued here that enough evidence exists for us to consider sugar very likely to be a toxic substance, and to make an informed decision about how best to balance the likely risks with the benefits. To know what those benefits are, though, it helps to see how life feels without sugar.The "very likely" expression is crucial. Unfortunately we don't have a explicit causal explanation of the impact of sugar on metabolic syndrome, for example. I think that epigenetics will provide neew perspectives on the issue, however we will have to wait. Meanwhile reducing exposure is the best advice.
PS. On the sugar sweetened beverage taxes. And in this blog