Ruthlessly and riotously, “A Matter of Size” (“Sipur Gadol”) proves once and for all that Israel is the world capital of tough love.

Four seriously overweight friends, each with his own insecurity, mishegass or secret, might be expected to form a rock-solid, mutually dependent support network. The characters that form the rotund quartet in Erez Tadmor and Sharon Maymon’s winningly oddball movie, however, hardly ever cut each other slack, to both hilarious and wrenching effect.

 “A Matter of Size” is a comedy, a romance, a sports movie and an underdog story all wrapped up in one. But its slicing depiction of male friendship, Israeli style, adds a wholly unexpected layer of astringency that undercuts the film’s occasional lurches into sentimentality.

A highly entertaining picture that covers the waterfront from audacious humor to easy emotion, “A Matter of Size” is the centerpiece film in the S.F. Jewish Film Festival. It is co-sponsored by the Israel Center of the Jewish Community Federation and the Oshman Family Jewish Community Center.

The Hebrew title translates as “A Big Story,” which is not what we expect when we meet Herzl (played by Itzik Cohen, who resembles Liev Schreiber with a much bigger waistline). A 35-year-old who lives with his widowed mother in the centrally located city of Ramla, he’s big, all right, and getting bigger, despite (or because of) the insulting attitude of his diet-group leader.

An Israeli sumo team made up of four former diet-group friends weighs in for its coach in the film “A Matter of Size.”

But Herzl is a shlub, and not the type we expect big things from — until he’s had enough of the abuse and walks out of his weight-loss circle, followed by the pretty and equally zaftig Mona (Levana Finkelstein) and his three buddies.

“A Matter of Size” is a story of self-awareness, self-confidence and self-acceptance, complicated by the reality that being fat is not socially accepted in many cultures.

The exception is sumo, the Japanese style of wrestling, as Herzl discovers when he takes a menial job at a Japanese restaurant. These athletes aren’t embarrassed by their girth; to the contrary, bigger is better. Herzl bugs his boss to coach him, and our unlikely hero eagerly embraces the sport, along with the training-table regimen.

Meanwhile, Herzl’s romance with Mona picks up speed. His mother emerges as the villain for a while, thanks to her repeated bad-mouthing of the younger woman. But we should have empathy for the frustration of a Jewish mother who doesn’t know whether to say “Eat!” or “Don’t eat!”

Tadmor (co-director of last year’s opening night film, “Strangers”) and Maymon shift tones with dexterity and the occasional, intentional whiplash effect. Blending the eccentric with the formulaic, they keep the audience feeling a bit like a sumo novice — slightly off-balance. But we’re always right there with Herzl, a sad sack who deserves happiness just as much, if not more, than the next guy.

Herzl’s Japanese boss/coach and co-workers are good for a few solid laughs, but it would have been nice to see them play bigger roles. The filmmakers largely choose not to explore the culture clash between East and Mideast, foregoing an opportunity to shed some light on another unlikely minority group that has settled in Israel.

One of the pleasures of “A Matter of Size” is watching good actors who don’t fit the leading-man model and likely aren’t offered such meaty roles very often. For viewers fed a steady diet of Hollywood movies, it’s downright bracing to hang out with characters who aren’t drop-dead, blow-dry gorgeous.  

In fact, it’s both amusing and painful to contemplate how “A Matter of Size” would be remade for American audiences. It would certainly be more timid and pandering, and somehow simultaneously more insulting and more politically correct.

And it would star Seth Rogen or Jack Black — or Matt Damon, if we stretch the point — in a fat suit.

“A Matter of Size” screens at 7:30 p.m. July 29 at the Castro Theatre, S.F.; 6:45 p.m. Aug. 1 at the CineArts at Palo Alto Square; and 7:30 p.m. Aug. 8 at the Roda Theatre in Berkeley.