Prime Minister Shinzo Abe may sacrifice barriers protecting Japan's beef and wheat farmers to join the Trans-Pacific Partnership free-trade accord, a former government adviser on farm policy said.

Still, Abe's administration will fight to maintain tariffs on rice, sugar and dairy products, said Shinichi Shogenji, an agricultural science professor at Nagoya University who chaired the Cabinet's food security advisory panel in 2007 during Abe's first term as leader.

"Japan may be able to protect about 5 percent of its total goods in the TPP negotiations," Shogenji said Tuesday. "Rice is the national staple, sugar is vital to Okinawa and milk is what our kids drink."