Late 1980's era film about thick white paste controlling people

Question

When I was much younger (1980's), my brother and I recall watching a movie at a sci-fi convention. The premise of the movie is that there's some white paste, resembling marshmallow fluff, that enters the market and everyone eats it and starts acting mysteriously, and becomes addicted to eating it and forcing others to eat it.

There are two very distinct scenes I can remember:

1. The protagonist, a kid, was being sat down at the table and forced by his (very 80s looking) family to eat the paste. The boy runs to the bathroom and grabs some toothpaste, and replaces his dinner plate with that in order to convince his fanatic family that he has indulged in the stuff.

2. Later on, possibly after a chase scene, they get to a manufacturing plant which actually turns out to be some machines that were actually just harvesting the stuff out of the ground (possibly via mining) but had been collected into a giant pool.

I seem to remember the name of the product being "Stuff", but I am not 100% sure on this.

Answer 1

This is The Stuff (1985)

Several railroad workers discover a yogurt-like white substance bubbling out of the ground. These workers find it to be sweet and addictive. Later, the substance, marketed as "The Stuff," is being sold to the general public in containers like ice cream. It is marketed as having no calories and as being sweet, creamy, and filling. The Stuff quickly becomes a nationwide craze and drastically hurts the sales of ice cream.

Answer 2

The Stuff (1985) is clearly what you are remembering.

Several railroad workers discover a yogurt-like white substance bubbling out of the ground. These workers find it to be sweet and addictive. Later, the substance, marketed as "The Stuff," is being sold to the general public in containers like ice cream. It is marketed as having no calories and as being sweet, creamy, and filling. The Stuff quickly becomes a nationwide craze and drastically hurts the sales of ice cream.

[...]

Under their commissions, Rutherford conducts an investigation into The Stuff. His efforts reveal, to his initial horror, that the craze for the dessert is far deadlier than anyone had believed: The Stuff is actually a living, parasitic, and possibly sentient organism that gradually takes over the brain; it then mutates those who eat it into bizarre zombie-like creatures, before consuming them from the inside and leaving them literal empty shells of their former selves.

A young boy named Jason also discovers The Stuff is alive and sees how it affects his family and how they are adamant towards his beliefs on The Stuff. He gets arrested for vandalizing a supermarket display of The Stuff, attracting the attention of Rutherford, who comes to his aid.