(CNN) -- San Francisco, California, Mayor Gavin Newsom vetoed Friday the city's ban on most McDonald's Happy Meals with toys.

In making the veto, the mayor released a new report on how a public-private partnership is combating childhood obesity and how San Francisco's more than 55,000 public school students are now eating fresher and healthier foods.

"Parents, not politicians, should decide what their children eat, especially when it comes to spending their own money," said Newsom. "Despite its good intentions, I cannot support this unwise and unprecedented governmental intrusion into parental responsibilities and private choices."

Under a partnership with the private sector, the local government has been remedying the root causes of obesity, Newsom said.

Since the city launched its "Shape Up San Francisco" program in 2006, the city has received state funds to expand physical exercise for schoolchildren, put gardens in schools, delineate safe school routes to walk and bike to school, and educate kids about making healthy choices, Newsom said.

His spokesman added the mayor is looking for the Board of Supervisors not to override his veto, even though eight of its 11 members had voted for the ban.

"He hopes some members will reconsider should it be put up for an override," said spokesman Tony Winnicker. "One of the eight is not entirely comfortable with it and some of them are getting heat as this thing is being mocked around the world."

The mayor, he said, is "doing what he thinks is the right thing."

Supervisor Eric Mar, who sponsored the legislation, predicted an override.

"I am surprised that Mayor Newsom plans to veto the Healthy Meal Legislation, given his consistent support of healthy eating and active living through his sponsorship of programs like Shape Up San Francisco, Sunday Streets, and Soda Free Summers," Mar said before the veto.

He said he applauds the mayor's work to combat childhood obesity "through increasing access to healthy food and promoting physical activity. However, as a city, we need to do more."

"The dollars spent by the fast-food industry far outnumber any resources that we as a city could spend on outreach and education. Southeast San Francisco is a food desert, where fast-food restaurants are abundant and fresh produce is

scarce. No amount of physical activity can undo the harms of unhealthy eating," Mar said.

"From the Institutes of Medicine to the World Health Organization, we know that reducing the consumption of junk food by kids could spare the health of millions and save billions of dollars to our overstrapped public health system. That's why pediatricians, educators, parents, community health advocates, and thousands of individuals lined up to support this ordinance," he added.

The Board of Supervisors approved the ban on Tuesday. The ordinance requires McDonald's Happy Meals and other fast-food servings that come with toys to meet new nutritional standards.

Newsom, elected last week to be the state's lieutenant governor, had indicated he would veto the proposal before leaving for his new job.

The bill, which San Francisco officials hope other cities will adopt in battling a child obesity epidemic, was a defeat for McDonald's, which led the fight against the measure.

"As previously stated, we are extremely disappointed with this decision. It's not what our customers want, nor is it something they asked for," said McDonald's spokeswoman Danya Proud after the board voted.

The proposal addresses how toys and other marketing freebies entice children to buy fast-food meals that are high in fat and calories, Mar said. He initiated the proposal because his fifth-grade daughter is in the 6-to-11 age group that has seen obesity rates quadruple over the past 30 years, the same time that the Happy Meal has been on the market.

"This is a simple and modest policy that holds fast-food accountable," he said.

Before Tuesday's vote, Mar cited a study released this week by Yale University's Rudd Center for Food Policy and Obesity, which examined 12 popular restaurant chains and found only 12 out of more than 3,000 kids' meal combinations met the nutritional guidelines for preschool-age children.

The study said that the fast-food industry spent $4.2 billion on advertising in 2009, that 40 percent of preschool-age children ask to go to McDonald's on a weekly basis, and that 15 percent ask on a daily basis. Also, 84 percent of parents say they've taken their children to eat fast food at least once in the past week.

Under the law, McDonald's and other restaurants would have until December 2011 to improve their meals' nutrition by adding fruits and vegetables -- if the chains want to keep offering toys, including those promoting the latest films.

The food and beverages would have to contain fewer than 600 calories, and less than 35 percent of the total calories would be allowed to come from fat. The meal would have to contain half a cup of fruit and three-fourths a cup of vegetables, and offer less than 640 milligrams of sodium and less than 0.5 milligrams of trans fat. Breakfast would have the option of offering half cups of fruit or vegetables.

City officials said they expect a legal challenge from McDonald's, which declined to comment on possible legal action.