It may be hard to believe, but Rachel Khong’s novel, “Goodbye, Vitamin” (Henry Holt) is a heartwarming book about Alzheimer’s. It’s narrated by Ruth Young, a willful 30-year-old sonographer who, after being jilted by her erstwhile fiancé, moves back home to a Los Angeles suburb to help care for her father. He’s a university professor who is beginning to “forget things” and, even though this could be material for a difficult exploration of loss, it isn’t. The novelist, an ex-editor of the now defunct cult cooking magazine Lucky Peach, has produced a book that’s original, quirky, bittersweet and often very funny.

We first meet Ruth when she goes home for Christmas after Joel — for whom she dropped out of college in her last year to accompany him to medical school in San Francisco — leaves her unceremoniously for another woman. Ruth hasn’t been home in years but her father, Howard, has been diagnosed with dementia, and her exasperated mother asks her to stay home and help for at least a year. When a stranger calls to say he’s found her father’s pants and shirts — all labeled — hanging from trees up and down the road, Ruth realizes she “can’t not stay.” Ruth then re-enters life in her childhood home and becomes half daughter, half caretaker.

The novel depicts the painful confusion that can follow a tumultuous breakup, as Ruth frets over the waste of so many of her younger years. Her training as a maternity ultrasound sonographer provided no help in analyzing their relationship, and she’s depressed with her own cluelessness. As she strives to move on, upsetting memories creep up “out of nowhere — like an ancient candlestick from some wrecked ship.” She adds “You know what else is unfair, about Joel? That I loosened the jar lid, so somebody else could open him.”

Meanwhile, Ruth’s father slips in and out of reason — leaving an avocado skin in the dish rack as if it were a freshly washed plate, other times lecturing lucidly on California history to a loyal group of graduate students who have come up with a convoluted, whacky deception to “keep his mind off, well, losing it,” by pretending he’s been reinstated to his academic position.

The story is presented as a series of vignettes, which when taken together build up a picture of a family in crisis, doing their best. Howard — in saner moments — shares a notebook in which he recorded Ruth’s pearls of wisdom when she was little. “Today we went over to your mother’s friend’s house for dinner. We’d asked you to be polite, so you said, ‘No more, please, it’s horrible thank you,’” reads one entry. And another: “Today, while I was changing your brother’s diaper and putting baby powder on him, you burst into tears and begged me not to put too much salt on him.”

During the course of Ruth’s homecoming year, their roles switch and she starts cataloguing her father’s erratic days. “Today I cooked salmon and you said it was esculent,” she writes. “Today you disappeared again, and scared the () — out of us.” As she details their family pulling together in moments of stress, hilarity and tenderness, she comments, “Here I am, in lieu of you, collecting the moments.” Ruth fills her diary with whimsical observations and oddball facts. For instance, you learn the title comes from Ruth’s mother’s new faith in vitamins, and her father’s habit of bidding them farewell before swallowing. Ruth also spends a lot of time reading message boards on caregiver forums, inventing new yoga poses, and preparing meals that feature brain food like jellyfish, bok choy and cruciferous vegetables, which her father is loath to eat: “No more crucified vegetables,” he begs. “But they died for you, Dad,” Ruth responds.

The story involves getting over a bad breakup and reconnecting with family, but it’s also about a loving father who went a bit crazy — with booze and women — when his adored firstborn left home, a situation that was worsened when Ruth stayed away after hearing her younger brother’s stressful reports. Most of all, though, “Goodbye, Vitamin” is about memory and forgiveness, and the author displays a profound understanding of the way in which they make us more humane, connecting us individually and jointly — and without which all becomes chaos.