What happens to the body when you lose weight rapidly?

ASK A RESEARCHER: Along with health benefits, there are also quite a few challenges.

Losing weight can change the body in many ways that are not visible.
Published

According to Helsenorge, weight loss in cases of obesity reduces the risk of conditions such as cardiovascular diseases, diabetes, and joint wear and tear.

It also becomes easier to move, and you may experience increased energy levels.

However, weight loss can also put strain on the body, especially if it happens quickly.

Along with fat mass, both muscle and bone mass are also lost.

Dietician Hanne Rosendahl-Riise explains that when you lose weight quickly, you may struggle to keep the weight off.

Increased risk of osteoporosis

"Bone density peaks around the age of 25. After that, many factors come into play. Some are genetic, while others can be influenced by lifestyle choices," says Hanne Rosendahl-Riise.

She is an associate professor at the University of Bergen's Nutrition Section and has experience as both a dietitian and researcher.

Rosendahl-Riise explains that carrying a few extra kilos is not necessarily bad for the skeleton. Extra weight can make bones stronger, but when weight is lost, it can lead to problems.

"Bone mass decreases when weight disappears," she says.

In the worst case, this can lead to osteoporosis, which increases the risk of fractures.

If weight loss happens very quickly, it also affects the muscles in the body.

"It's easier to maintain muscle mass with slow weight loss, especially if you stay physically active during the process," explains Rosendahl-Riise.

Benefits of gradual weight loss

In a study conducted at Cambridge University in 2020, researchers examined the differences between gradual and rapid weight loss.

Researchers performed a systematic analysis of studies from various medical databases.

Their results showed that the total weight loss was nearly the same between the two groups.

There were also no significant differences in terms of waist and hip measurements between the groups.

However, the researchers found that gradual weight loss led to greater reductions in fat mass and body fat percentage compared to rapid weight loss.

Additionally, the resting metabolic rate – the body's energy expenditure during rest and fasting – was less well preserved when people lost weight rapidly.

A 2020 study from Cambridge University examined the differences in outcomes between gradual and rapid weight loss.

Hard to keep the weight off

Rosendahl-Riise explains that a poorer resting metabolic rate can make it challenging for people to maintain weight loss over time.

"The body wants to restore its previous weight. Metabolism slows down to conserve energy during weight loss, meaning the body burns less energy overall," she says.

She further explains that hormonal changes also occur. Satiety hormones decrease, while hunger hormones increase after weight loss.

This can create a persistent feeling of hunger even after you have lost weight. 

"Hormone levels may never fully return to their pre-dieting state," says Rosendahl-Riise.

The body wants to restore its previous weight, says Rosendahl-Rise.

Mental health problems

Rosendahl-Riise notes that rapid weight loss can also increase the risk of gallstones and, over time, nutrient deficiencies that weaken the immune system.

However, it's not just the body that is affected by such rapid changes.

Rosendal-Riise believes that rapid weight loss can also negatively impact mental health.

"Rapid weight loss can lead to disordered eating habits and an unhealthy focus on food," she explains, adding:

"If someone regains the weight, they may experience negative emotions that contribute to poor body image."

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Translated by Alette Bjordal Gjellesvik

Read the Norwegian version of this article on forskning.no

Reference:

Ashtary-Larky et al. Effects of gradual weight loss v. rapid weight loss on body composition and RMR: a systematic review and meta-analysis, British Journal of Nutrition, 2020. DOI: 10.1017/S000711452000224X

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