Even deep in the US's healthy eating heartland, it is clear how decades of farm subsidies have affected what America eats.

Last year at Google's brand-new California headquarters, a wave of media interest surrounded the opening of Cafe 150, a restaurant offering fresh, healthy, high-quality food sourced from within a 150-mile radius. But just across Highway 101 in the affluent college town of Palo Alto is the Driftwood Deli, a roadside grocery and fresh-made sandwich store. Its $4 (€2.81, £1.96) lattes may come with a wrapper advertising The Economist magazine, but the displays of fresh fruit and nuts in the store are massively outweighed by racks of corn chips and popcorn, not to mention snack foods stuffed with the high-fructose corn syrup that is the sweetener of choice for America's processed food.

As the rewriting of the "farm bill" - the five-year agricultural subsidy programme - nears its endgame in the US Senate, proponents of reform have tried to highlight the effect of the subsidies on American health. Their efforts seem likely to have little impact.

Nutritionists critical of US farm programmes say they support large-scale production of simple carbohydrates - corn syrup, sugar, white rice - rather than fruit and vegetables. Adam Drew­nowski, a nutritional scientist at the University of Washington, foundcookies cost 20 cents a megajoule of energy (equal to 238 kilocalories, commonly called calories) while carrots cost 95 cents a megajoule. A soft drink megajoule cost 30 cents; the equivalent in orange juice is $1.43.

Subsidies also have knock-on effects such as encouraging mass-production, grain-fed cattle farming with heavy use of antibiotics, instead of the more natural and traditional grass-grazed variety. Environmentalists add the subsidies are designed to encourage farmers to pump out ever higher volumes of food at lower cost, increasing the incentive to use artificial fertilisers and pesticides.

The demand rather than the supply-based parts of the bill also do little to help. The largest part of the programme, $178bn of the $271bn spent over 2002-07, is given in "food stamps" - now distributed as credits on an ATM-style card - to 26m poorer Americans. But anti-poverty groups that campaign for the food stamp programme have always resis­ted tying those credits to the purchase of healthier food.

Lorelei DiSogra, vice-president for nutrition and health at United Fresh, which represents fruit and vegetable growers, says rising concern about childhood obesity has got them into many lawmakers' offices on Capitol Hill to lobby for federal support for fruit and vegetable purchases in schools. But she adds: "It is very hard to shift nutrition programmes even towards following federal nutritional guidelines. It would be a two-year campaign, not a two-week one."

The Senate is increasing somewhat the small allocation for buying fruit and vegetables in the House of Representatives' proposed farm bill, which covers just 35 schools per state, but it is not clear which will prevail when the two are reconciled.

Organic growers and others aiming at consumers concerned about healthy eating and the environment do not want a corn-style mass subsidy programme, which they say would risk a glut and a collapse in prices.

But some argue more help would be useful. Brian Gardiner, a retired farmer from San Jose, south-east of San Francisco, started an organic smallholding 20 years ago which grew to 18 acres of peppers, tomatoes, squash, watermelons, broccoli and herbs. He sold to chefs at high-end restaurants and ended up running an organic food distribution business.

"I would like to see a significant amount of help given to farmers who decide to switch from chemical to organic farming," he says. Currently, it takes three years for land to make the transition from conventional to organic, and he says it takes another couple for the nutrients in the soil to adjust properly. "In the farm bill there is a small bit of money set aside for research into organics," he says. "But we need more than that."

But those in charge of farm policy largely disagree, and their view is almost certain to prevail. Collin Peterson, chairman of the House of Representatives agricultural committee, says the farm sector that raises organic produce and grass-fed beef for local consumers needs little federal help. "It is growing, and it has nothing to do with the government, and that is good," he told the FT. "For whatever reason, people are willing to pay two or three times as much for something that says 'organic' or 'local'. Far be it from me to understand what that's about, but that's reality. And if people are dumb enough to pay that much then hallelujah."