During the making of his documentary “That Sugar Film,” Australian filmmaker Damon Gameau conducted an experiment about sugar — on himself.

He decided to consume 40 teaspoons of sugar each day while maintaining the total numbers of calories he was eating before the experiment began and continuing his exercise routine. He didn’t seek out cakes and doughnuts, but instead consumed “hidden sugars” in foods like barbecue sauce or flavored yogurt.

In the movie, as he starts his ordeal, he fills his cereal bowl with Kellogg’s “Just Right,” racking up 7 ½ teaspoons of sugar. He adds flavored yogurt, giving him 4 more teaspoons. Then, he downs a big glass of apple juice, adding 9 teaspoons.

“I’m looking at 20 teaspoons to start the day,” he tells the camera. “I did all the maths and it just seems ridiculous.”

That’s just the beginning. Twelve days in, Gameau has gained 5 pounds. Just six days later, his doctor tests his blood and sees bad news.

“You’ve got the signs of fatty liver,” his doctor tells him. This is a warning sign for liver disease, which in severe cases, can progress to scarring and cirrhosis.

More than a week into the Star Tribune’s 28-Day Sugar-Free Challenge, we talked to Gameau (who has since founded the nonprofit That Sugar Movement to promote healthful foods) about how he felt during the making of the 2014 movie and what he eats now:

Q: How did you decide to make “That Sugar Film”?

A: I was, like most people, pretty confused about the messaging around diet. There’s so many conflicting theories and stories out there at the moment, and it can be overwhelming sometimes.

So I felt that rather than go back and forth reading between various opinions or scientific studies, I would do an experiment myself and find out my own truth.

I remember being in the supermarket, and just discovering how much sugar is in a bottle of barbecue sauce, and I was quite gobsmacked by that. And thinking, could you make a film and really bring the fact that sugar is found not in our conventional obvious places but it’s hidden in all these foods that often get advertised as being healthy and good for us.

That’s really how the whole journey started.

Q: How did you feel eating this much sugar?

A: I certainly would never have done the experiment if I had known what I know now. I think my naiveté and stupidity probably helped the film to a great degree.

I just felt quite exhausted. It’s the impact on your mood and overall vitality. If you’re constantly giving yourself this quick burst of energy, then you’re going to keep coming down. What goes up must come down. And over time, that can have an effect on your adrenal glands and other parts of your body.

Q: What do you eat now?

A: I have a very good diet and enjoy a whole range of foods and don’t really exclude anything. If you’re just eating real foods, you’re not going to get into trouble. It’s when you start having processed foods, that’s when all the sugars are added into the food.