Look: Phil Mickelson Shows off Physique in Photo Posted by Sister Tina

Golfer Phil Mickelson has never been known as a "body guy," but photo evidence suggests that may be changing.

Mickelson's sister, Tina Mickelson, snapped a picture of a lean-looking Lefty during a family beach day Tuesday:

The quick-witted Mickelson offered a humorous response:

Mickelson, 49, has gotten serious about his health this year. Most notably, he revealed in July ahead of the Open Championship that he fasted for six days and lost 15 pounds over a 10-day period:

While the five-time major champion looks better than ever physically, the on-course production has lagged behind, as he hasn't recorded a finish better than 18th since winning the Pebble Beach Pro-Am in February.

He is down to 38th in the world golf rankings, and his 47th-place spot in the FedEx Cup standings means he will not take part in the Tour Championship.

Although Lefty needs to find his game again, getting in shape could potentially help prolong his career moving forward.