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Whenever we have good, positive, or meaningful experiences, our brains provide a reward signal that triggers feelings of happiness, enjoyment, well-being, pleasure, or feeling content. This is done through neurotransmitters through dopamine or opioid systems in the brain.
This study (using pigs) found that sugar triggers similar reward feelings. The opioid system was activated with the first sugar intake. After 12 days of sugar intake, major changes were observed in the brain's dopamine and opioid reward systems.
Added sugar adds unnecessary calories and addresses zero nutritional needs. It appears to be an addictive substance that we, as a culture, have become dependant on.
Read the study here: Sucrose intake lowers μ-opioid and dopamine D2/3 receptor availability in porcine brain