"Fed Up" examines why, while there is a boom in gym membership and a surge in shoppers seeking low-fat alternatives on supermarket shelves, two out of three Americans are overweight.
"Obesity has been a problem for the last 30 years and I think we are reaching the breaking point," director Stephanie Soechtig said in an interview ahead of the film's US release.
"At the end of the day, I think it comes down to money. I think there's a lot of money in the food industry and it influences politics, unfortunately."
The film, which opened on limited release in US cinemas Friday, shows how the food industry has managed to persuade US authorities to recommend that 25 percent of calories come from sugar.
The World Health Organization says the figure should be 2.5 times less.
"I think we can say that the government is right now more interested in making money than taking care of its society," Soechtig said.
- Resist the temptation -
The problem is not unique to the United States.
The WHO has also sounded the alarm in Jordan, Mexico, Saudi Arabia, South Africa and Venezuela, among other countries where more than 30 percent of the population is obese or overweight.
In the movie, three children recount their efforts to combine diet and exercise to fight the flab.
Despite their best efforts, they continue to gain weight as processed, sugar-rich foods are all around them.
At school, the lunchtime cafeteria offers a menu of pizzas, nachos and hot dogs.
The documentary criticized the fact that in 2006, 80 percent of high schools had contracts with soft drink companies and in 2012, half of all schools served fast food.
First Lady Michelle Obama has weighed in on the issue with her "Let's Move!" campaign, and politicians have put pressure on food companies to reduce sugar levels.
But brands like Coca Cola, Pizza Hut and Pepsi have not disappeared from school refectories and corridors.
- 'We can change food industry' -
Nutritionists have been warning about the problem of obesity for decades. The issues are well known by experts: sedentary lifestyles, high-calorie diets and poor policy choices among them.
"There are a lot of good people in the government trying to do really good things," said the filmmaker.
"But there are a lot of people that have financial interests. So I think once people hear what's been going on, it will galvanize people to get involved and make changes in their own lives and make bigger changes."
The data is striking: in 1980, there were no cases of type 2 diabetes in children and teens aged eight to 19 in the United States.
Two decades later, there were 57,638 cases recorded.
"Fed Up," which Soechtig first presented at the Sundance Film Festival in January, insists that parents can help reverse the trend.
"We can change the food industry, to change its way by not buying its products and we can pressure our politicians by voting for politicians that support the same needs and desires that will make us a better society," Soechtig said.
"Parents are incredibly powerful. They also need to create a safer environmental at home and make sure the food is available for their kids."
And she said: "This is the kind of fight parents and kids need to do. Kids are future voters. I think anyone needs to get involved."