Jelly Belly

Jelly Belly is a 1981 YA book written by Robert Kimmel Smith. The protagonist is Nathaniel "Ned" Robbins, an 11-year-old boy who loves to eat and weighs over 100 pounds. Sure, he's on a strict diet but he still isn't losing weight due to constant cheating. His parents decide to send him to a summer diet camp, hoping he'll have better luck there than at home.

Ned is horrified by Camp Lean-Too's strict policies, but soon finds he's not alone: Richard Napoli, Darryl "Hog" Hawkins and Max Cohen are veterans of the camp who are more than happy to help Ned through the hard times ahead. Together, the four boys find ways to cheat the system and indulge themselves without getting caught. Somehow they all manage to lose weight despite their candy bar binges and stolen cheese sandwiches from the camp kitchen.

The real trouble starts when Ned realizes he wants to lose weight, but it's not going to be easy with Grandma always cooking up her delicious, fattening meals and confections. But when there's a will, there's a way.

Tropes used in Jelly Belly include:

Ambiguously Jewish: Grandma Rose
Big Brother Mentor: Jamie is literally this to Ned, with his parallel storyline of trying to do better on the track team
Big Eater: Not just Ned, but Richard, Hog, Max and Richard's parents.
Bratty Teenage Daughter: Elizabeth
Calling The Old Lady Out: Ned tries to avoid this when he talks to Grandma about his diet, but she doesn't listen and he ends up yelling and hurting her feelings. Luckily, he apologizes and she agrees to help him lose weight.
Cold Turkeys Are Everywhere: Poor Ned. His family gets to eat a meal of spaghetti and breaded veal with blueberry pie for dessert and he's stuck with broiled veal and veggies. Even after he becomes serious about losing weight, the temptations of junk food are still tough to resist.
Determinator: Once Ned decides he truly wants to lose weight, he goes at it full throttle.
Diet Episode: The first half of the book is this, right down to the boys getting caught sneaking candy and snacks. Subverted when Ned gets serious about losing weight and is better able to withstand temptation.
Embarrassing Nickname: Richard's parents call him "Roly"
Fat Camp: Where half the story takes place
Food Porn: Considering the story's told from the perspective of a kid who loves to eat...
Four-Temperament Ensemble: Ned is Melancholic, Richard is Choleric, Hog is Phlegmatic and Max is Sanguine.
I Am Big Boned: Ned's grandma insists he's not fat, he just has big bones.
If It Tastes Bad, It Must Be Good for You: Almost all of the food at Camp Lean-Too fits the bill, as does Ned's diet dinner shortly before he leaves for camp. Later subverted when Ned realizes how tasty and filling some healthier foods can be.
Little Miss Badass: Ned's friend Libby, afraid of the class bully? Hell no!
Only Known by Their Nickname: Hog is only called "Darryl" twice throughout the book. Ned himself is rarely ever called by his real name, either.
Supreme Chef: Grandma Rose, big time. Also Richard's mother.
Through His Stomach: It's implied that Grandma and her late husband's relationship was built heavily on this trope. A non-romantic example has Ned mentioning how Elizabeth's boyfriends often ignore her in favor of Grandma's freshly baked pies or cakes.
Trademark Favorite Food: Max Cohen's Hershey Bars, Ned's fondness for Milky Way bars.