Good food and cocktail-fuelled nights are a no-go on most weight-loss plans.
But there's new hope for those who consider sanity more important than slim waistlines.
An Auckland nutritionist has devised a plan based on foods used by high-performance athletes to prepare for big events.
Catherine Sissons, who has a degree in sports medicine and human nutrition, says she cringes at the age-old diet advice to make lifestyle changes. "You have to learn about what your lifestyle is and adjust for it," she says.
One client, Anna Perry, 29, lost 9kg during the Rugby World Cup while socialising three to four times a week. Her friend Paula Martin, 27, lost 5kg in the four weeks leading up to Christmas, a time when people usually get heavier.
Sissons says the secret is eating high-fibre, high-water fruit on the day before an indulgence.
"When you wake up, have something like a pear or an apple and again three times that day," she says.
Regular, well-balanced meals and exercise also keep the brain and metabolism ticking.
Carbohydrates are not the enemy - although Sissons recommends types close to the natural form, such as potato rather than bread, which is highly processed.
Each meal should include protein, too. She advises people to beware of nuts as they are packed with calories and fat. This "pre-toxing" will also lessen the hangover.
"A hangover is a mixture of dehydration and intoxication," Sissons says.
"Keep ahead of both of those before you drink and you can be in a better state the next day, which also means you are less likely to crave the high-fat, quick-fix foods.
"You can have your takeaways the day after drinking. However, it is important to get the fibre/water-based and vitamin C foods in beforehand."
The morning after a blow-out, Sissons suggests having a big glass of water with lemon juice, along with eggs, tomato, spinach and mushrooms for breakfast - and swap the toast for a potato cake.