Weight gained after a vacation or indulgent weekend doesn't mean you've put on fat. It's probably just water retention, experts say.

• Rebel Wilson said she gained almost seven pounds while on vacation at an all-inclusive resort.
• Eating more salt and carbs can make us gain water weight, not fat, a dietitian said.

Weight gained after a vacation or indulgent weekend is likely caused by water retention not fat, experts told Insider after actor Rebel Wilson said she put on three kilograms (almost seven pounds) while at an all-inclusive resort.

The Australian actor previously said she lost 77 pounds since the start of 2020, after declaring it her "year of health." Personal trainer Jono Castano said he trained Wilson, and she told Today she did lots of walking to maintain her weight. Wilson has also been open about her relationship with food, saying she used to overeat to numb her emotions.

In an Instagram post shared on July 2, she wrote in the caption, "I've lost all self control. But you know what? I can get up tomorrow and go to the gym, and hydrate and eat healthy and love myself."

Wilson went on to write that she knows what it's like to experience food guilt or feel bad after overeating, but being hard on herself doesn't help.

"If you're like me just know YOU are more than just your weight, your weight doesn't define you, just try your best to be healthy and don't be so hard on yourself," she wrote. "Be the best version of you."

Experts told Insider that weight gained after an indulgent few days is unlikely to be fat, and usually falls away when a person's normal diet is resumed. Taking a break from a diet while on vacation can even be beneficial in the long run, according to research.

Vacation weight gain is often largely water

After an indulgent weekend or a vacation, it's normal to see a higher number on the scale. This can be worrying if you're trying to lose weight, but it's normal after eating more and isn't anything to stress about, Kara Mockler, registered dietitian and coach at RP Strength, told Insider.

Celebrations and vacations can involve eating foods higher in carbs and salt than your normal diet, and both of these lead to water retention, she said.

"We store carbs as glycogen in our body, and for each gram of glycogen we retain several grams of water right along with it," Mockler said. "Same with salt."

This is why some people feel more bloated or swollen after a salty meal.

"So the uptick on the scale after a short period of higher calorie intake is mostly water," Mockler said.

Personal trainer and fat-loss coach Jordan Syatt estimated that not even one pound of Wilson's holiday weight gain is actually fat, telling Insider that as well as water weight, the physical weight of the extra food in her stomach likely plays a role.

"When you go on vacation for a weekend, a week, or even two weeks, it's physiologically impossible to gain that much fat," he said.

A diet break can be beneficial

Eating more food for a short period can give your metabolism a temporary boost due to the energy required to digest it, which is known as the thermic effect of food, according to research.

Taking a diet break can also relieve the mental and physical fatigue that can come with prolonged periods in a calorie deficit and lead to greater weight loss.

The key is to get back on track afterwards, Mockler said, and this will see the scale go back down.

"There's no need to restrict your food or over-exercise, just get back to normal and drink some extra water," she said. "The excess fluid will come off over the next few days and you'll be right back on track."

By getting back to healthy eating afterwards, Wilson has exactly the right approach, Syatt said.