In 1988 he achieved a Doctoral Degree, focusing on fat cells for newly born children.
He was subsequently granted a postdoctoral research position (Docent) in pediatrics at the Karolinska Institute.
His primary research area related to the regulating of fat cell metabolism as well as clinical obesity and diabetes.
[4] Marcus regularly appears in various media outlets in debates relating to childhood obesity.
In particular, he has propagated the introduction of a so-called "sugar changeover tax"[5] in, which would increase the price of unhealthy, sugary products such as confectioneries and soda and in turn subsidise a decrease of the Value Added Tax (VAT) on fresh fruit and vegetables.