Actually, topic is much more complex. Yes, sugar is the poison, I recommend watching this excellent speech of Dr. Lustig: Sugar, the bitter truth (1.5 hour long but well worth watching)

But too much we are focusing only on sugar. Carbohydrates is what we should be looking at as a whole group. We should be consuming much less carbohydrates than we do. That's where the problem is.

Body can get needed energy from three sources:

• carbohydrates
• proteins
• fats

Many thousands of years our main source of energy were fats and proteins. Lately they are carbohydrates. It is that simple.