Health professionals should be involved in creating a system, such as traffic light colours, where a red light labels on foods attracted the highest tax, Dr Morgan said.
Kevin Hague, Green Party spokesperson on health and wellbeing, said he would be interested to read Mr Morgan's new book as it sounded similar to party policy on combating obesity.
Clear front labelling of unhealthy ingredients and a traffic-light type classification system is a "no-brainer", said Mr Hague.
But while the Greens would endorse increased taxes on unhealthy products such as alcohol, cigarettes and sugary drinks, it may be too difficult to police a wide range of food, he said.
"In a broader sense a tax on unhealthy foods is more complex and would require a more technical process. There is some dispute among academics about how exactly to design a tax to do that."
In 2011, Denmark introduced a tax on butter, meat, cheese, pizza, oil and processed food that contained more than 2.3 per cent saturated fat, but withdrew it a year later due to difficulty in implementing it.
However, the Greens would support an investigation into how to design an effective processed food tax.
"The urgency to combat obesity is so great, we should be exploring all these avenues," said Mr Hague.
"Spending on prevention of obesity should be the absolute priority for any health minister."
However the government said processed food was unlikely to be taxed anytime soon.
"Families don't need a special tax on food and the Government has no plans to introduce one," said Health Minister Tony Ryall.
"Such a tax would add to the burden of many families in tight economic times."
The Labour Party has suggested in the past GST be removed from fruit and vegetables, which Dr Morgan dismissed.