Why are Americans getting fatter, and who's to blame? It's a question members of the US Congress need to be asking. 

Like the war on tobacco decades ago, the US is now fighting a new battle on obesity. On one side are US public health officials advocating for their government to put in place better nutrition policies. But those efforts have met stiff resistance, in part because the $1 trillion US food and beverage industry is fighting regulation with a powerful weapon: its deep pockets. 

It's no secret the standard American diet is relatively inexpensive, convenient and satisfying. Whether it's highly marketed fast food or highly processed, packaged foods in the supermarket, what Americans eat has changed dramatically over decades.

And it shows. The US has the highest rate of obesity in the industrialised world. One-third of Americans over the age of 20 are obese, according to government figures. For children, this figure is 17 percent.

"It's really expensive to get healthy food in the United States," said a shopper at a mall in McLean, Virginia when asked why the number of obese Americans is rising. "Fast food is much too accessible." Another man explained, "The government can stop the advertising, can stop all the bad foods and yet they let it keep going, and then they complain about obesity."

The American diet is strongly influenced by the US Congress: the US food and beverage industry has for the past two decades spent tens of millions of dollars lobbying for government regulations that favour its finances. One unfavourable policy could cost a company millions. 

A former government food policymaker who now lobbies for the US food and beverage industry, John Bode works to ensure Congress limits regulations on behalf of his clients. "Economics are a big part of it, no doubt about it," Bode told Al Jazeera. "Food companies are in the business to make money."

Indeed, since the 1990s, the food and beverage industry has been one of the United States' biggest political campaign donors, spending almost $107m on congressional and presidential campaigns. Last year, the industry gave nearly $24m to politicians running for Congress. Seventy-one percent of that went to Republican candidates, and 29 percent to Democrats.

In turn, many of those politicians have voted for subsidies to keep food industry ingredient costs low. Since the mid-1990s, $17bn has gone to crops like corn and soybeans, mainstay ingredients of the junk food industry. That's a sharp contrast to the $260m in subsidies given to healthier menu options like fruit and vegetables. 

Although mounting data suggests processed food can lead to obesity, lobbyists have also convinced lawmakers to back voluntary guidelines instead of advertising restrictions, soda taxes and even an attempt to ban French fries from school lunches.

Sheila Krumholz, the executive director of the Center for Responsive Politics, told Al Jazeera "we have a very loud voice among the lobbying community. They speak loudly, because they have a lot of money to hire a lot of people to focus on shaping and influencing policy, and shaping the opinions of our lawmakers. There is no voice - or if there is, it's very weak on the other side of the table."

Bode disagrees, arguing that the industry is already heavily regulated. The last thing he believes it needs is more regulation. "If we start regulating in ways that outlaw various foods, what we are really doing is denying consumers choice," he told Al Jazeera.

But others like Krumholz counter that US consumers are making their menu choices based in part on government policies which favour the food industry's wallets, not consumer health. With so much big money backing fast food lobby efforts, she said, those advocating for healthy food choices don't stand a chance.