US president George W Bush suffered a stomach upset on Friday and missed morning sessions at the G8 talks.
Mr Bush was keen to keep to his schedule, aides said
White House counsellor Dan Bartlett said Mr Bush woke up feeling "under the weather". But he was rejoining other leaders, though still not feeling 100%.
Mr Bush met French President Nicolas Sarkozy in his hotel suite on Friday, and was keen to keep his schedule.
Last night, Mr Bush - a teetotaller - was seen sipping beer, but his advisers insisted it was non-alcoholic.
Doctors are not sure if it is "a stomach virus or something like that", Mr Bartlett said.
"[I] guess he didn't want to follow in the footsteps of his father in Asia," his aide said.
In January 1992, the father of the current leader, vomited and collapsed during a state dinner at Japanese Prime Minister Kiichi Miyazawa's residence.
The US leader is due to fly to Poland after the summit ends on Friday afternoon, and to Italy on Saturday.