"We need a more active federal government in setting guidance for public schools," he said.
"Currently, under 30 year-old USDA standards, it's just fine for schools to sell ice cream, Oreos, Snickers candy bars, donuts, and all kinds of other junk foods.
"Obviously, it's time to update USDA standards based on all that we have learned about nutrition and obesity over the last three decades."
Harkin was speaking at this week's Healthy Schools Summit 2005 in Washington D.C. to lobby support for his Child Nutrition Promotion and School Lunch Protection Act. The summit, attended by government, business and non-profit groups, involves two days of discussion on how to improve the health of children.
The Iowa senator has been central in forcing the issues of obesity and nutrition onto the national agenda, and is trenchant in his opinions on what must be done.
"We've got our work cut out for us," he told the Summit.
"According to the Government Accountability Office, the vast majority of our schools - including 83 percent of elementary schools, 97 percent of middle schools, and 99 percent of high schools - allow so-called 'competitive food sources,' mostly vending machines selling sugary sodas, candy, and junk food."
"Think about a child purchasing a 20-ounce Coca-Cola during the school day," said Harkin. "That's equivalent to 15 teaspoons of sugar. Would any parent in their right mind send their child to school with a snack of 15 teaspoons of sugar?"
Harkin's bill would close the loophole that allows the USDA to set standards for foods sold in the lunchroom, but forbids it from setting standards for foods sold elsewhere on campus.
"This loophole is a disaster," he said. "It means USDA spends nearly $9 billion a year on nutritious breakfasts and lunches, but this is undermined by the pervasive sale of junk food and sugary sodas elsewhere on campus."
Harkin nonetheless identified some positive steps that have already been taken. The Fresh Fruit and Vegetable Program, which was included in the 2002 farm bill, was expanded in 2004 to involve at least ten states in the project.
"This is modest progress, but we're heading in the right direction," he said.
"Meanwhile, under terms of the Child Nutrition and WIC Act reauthorization, by July 1, 2006 every school that participates in the school lunch or school breakfast program must have a local wellness policy in place.
"Schools will have to set targets for nutrition education and physical activity. And they'll be required to set nutrition standards for all foods sold in school, including in vending machines, a la carte lines, and school stores."
The proliferation of junk food in US schools has rarely been out of the headlines recently, with the result that the food industry is increasingly taking the flak for making children fat. In 2002, the Center for Disease Control (CDC) cited that 16 percent of children aged 6-11 were overweight, with the same percentage holding true for 12-19 year olds.
Approximately 42 percent of Mintel's respondents surveyed identified someone in their households as being overweight. And despite high profile voluntary bans from industry, schools remain pretty much saturated with junk food.