Study: losing weight does not necessarily improve people’s life satisfaction

Many self-help books and Instagram influencers would have you believe that happiness is just a diet away, but new research suggests that losing weight does not necessarily improve your satisfaction with life.

A new study, published in August in Obesity Facts, analysed extensive survey and health data from more than 15,000 adults in Denmark. The researchers found that, although people considered overweight versus their peers pay a life satisfaction penalty, people who had lost weight in the past five years were no more satisfied with life than those whose weight had stayed stable.

“The cultural perception and idealisation of thinness basically overshadows the evidence” that losing weight improves the quality of life, says co-author Rasmus Køster-Rasmussen, Associate Professor of Public Health at the University of Copenhagen.

Chipping away at an embedded narrative

Køster-Rasmussen, who also treats patients as a general practitioner, says that overstating the stigma against fatness is difficult. People considered overweight face tremendous pressure to slim down from both social sources – their family, friends and even complete strangers – and healthcare providers.

But awareness is growing that some of the foundational dogmas of obesity research, including the body mass index (BMI), are based on shaky science, Køster-Rasmussen says.

Recent studies, including a review by Denmark’s Statens Serum Institut of randomised trials with long follow-up, have called into question what doctors have long assumed: that weight-loss interventions, including lifestyle changes, reduce the chances of developing cardiovascular disease.

As a result, Køster-Rasmussen says that many healthcare providers have turned to arguments about life satisfaction to encourage people to lose weight.

But previous research on the impact of weight loss does not necessarily support this. “Traditional weight-loss studies – without medication but with lifestyle intervention – do not really have any convincing effect on the quality of life,” Køster-Rasmussen says. “When you use a medication for weight loss and weight loss is greater, then you see an effect on quality of life – but this is mostly in the physical domain, such as being easier to get around and climb the stairs.”

Your “best possible life”

Two medium-sized islands in Denmark were recently made a hotspot for health research. From 2016 to 2019, the Lolland-Falster Health Study examined the lives of 19,000 adults in extreme detail, collecting biological samples (blood, urine, saliva and faeces), multiple physical examinations and extensive questionnaires.

The Lolland-Falster Health Study represents a unique opportunity to study how weight loss affects the general population, Køster-Rasmussen says – since studies about weight loss and life satisfaction are often tied to weight-loss programmes or clinical trials, which disproportionately represent people actively trying to lose weight.

The Lolland-Falster Health Study asked 15,213 adult respondents to rate their life satisfaction using the Cantril Ladder score. Participants were instructed: Imagine a ladder with steps numbered from 0 from the bottom to 10 at the top. Step 10 means the “best possible life” for you and step 0 means “the worst possible life” for you. Where on the ladder do you think you are at the present time?

Then, the participants were weighed and their height was measured to calculate their BMI. Although the BMI has flaws, the researchers wanted to examine how weight loss affects the populations that doctors most often encourage to lose weight – and many healthcare practitioners use BMI to assess whether a patient has a “healthy” weight.

Another survey included a question about recent changes to participants’ weight. Participants were asked to estimate their weight in kilograms five years ago, which people are surprisingly good at doing accurately according to previous studies.

What they found

The researchers were particularly interested in respondents who would be categorised as having overweight or obesity based on their BMI – people with a BMI between 25 and 30 are considered to have overweight, and at 30–35 they have obesity. (A person with BMI of 40 or above, or 35–40 if “experiencing obesity-related health conditions,” has class 3 obesity, formerly known as morbid obesity and now sometimes called severe obesity.)

For the Lolland-Falster respondents, higher BMI was strongly associated with lower life satisfaction – that’s no surprise, Køster-Rasmussen says, based on how society treats fat people.

People with a BMI indicating obesity had a 0.47 point lower life satisfaction score than people of the same sex, age and educational attainment level with a “healthy” BMI. And people with a BMI of 45 or higher had life satisfaction scores 1.85 points lower than their “healthy” weight peers.

But did losing weight improve the life satisfaction of people with overweight?

The researchers found that people with overweight who had lost weight in the previous five years were no more satisfied with their lives than similar people with overweight whose weight had stayed the same.

If anything, the people who had lost weight were slightly less satisfied with their lives, rating themselves 0.15 points lower on average than people who had maintained their weight, Køster-Rasmussen says.

Changing the script

Køster-Rasmussen and co-authors think that the results of the study should make doctors more cautious about promising improved life satisfaction to patients who manage to lose weight.

Considering the results in the broader context of studies on weight loss, “you need quite substantial weight loss to get better physical performance,” Køster-Rasmussen says. “That weight loss, perhaps, does not improve mental health very much.”

“We know that lifestyle interventions for weight loss do not result in less cardiovascular morbidity and mortality” long term, Køster-Rasmussen says, “because no one can actually maintain these weight losses.”

If there is a compelling medical reason for weight loss for a specific patient, Køster-Rasmussen says that he favours medication or surgery over lifestyle adjustments. “But for most people, I think it is much better to work with body acceptance – we come in different shapes and sizes” and focus on other metrics of health.

He emphasises that future research should include more qualitative evidence: simply asking people with overweight and obesity how weight loss has affected their quality of life. For decades, doctors have “only been looking at a number on the scale and perhaps the blood sugar count”.

“In the past five years, we have been able to open our eyes to the adverse effects of weight-loss advice. It carries on the stigmatisation and results in poorer body satisfaction for the patients,” Køster-Rasmussen says. “Finding good arguments to ask people to lose weight based on lifestyle intervention gets increasingly difficult.”