Sugar, beliefs and biology.
I came across this fascinating study recently, where they took two groups of people and gave them both a sugary drink with 15g of sugar in it. In the first group, they knew they were consuming a drink with high sugar content and the other group were told the drink had zero sugar in it. The results showed the group who knew they were consuming the sugary drink had a greater increase in blood sugar levels than those in the other group. Our mind and beliefs have such enormous ca