Does gaining weight make people less happy? According to new research published in the International Journal of Applied Positive Psychology, the answer is generally no. Using a decade’s worth of data, a researcher in Germany found that weight gain does not negatively impact life satisfaction. In some cases, individuals who gained weight even reported slight increases in happiness, regardless of their gender or age, suggesting that weight’s psychological impact may be less significant than previously thought.
Overweight and obesity are major public health issues in Western societies, including Germany, where more than half the population is classified as overweight. While the adverse physical health consequences of being overweight are well-documented, its psychological impacts, particularly on happiness and life satisfaction, remain underexplored. Felix Bittmann at the Leibniz Institute for Educational Trajectories sought to determine whether weight gain directly influences happiness over time and to identify any causal mechanisms underlying this relationship.
“Obesity is a significant and growing problem in almost all modern societies,” explained Bittmann, a postdoctoral researcher. “It not only generates considerable costs for the health system, but also shortens life and therefore contributes to a great deal of unhappiness. The question for me was whether it is possible to quantify the effect of obesity on life satisfaction numerically based on high-quality panel data.”
To examine this, Bittmann used data from the German National Educational Panel Study (NEPS), which tracks a cohort of adults through annual surveys. The sample included 8,815 participants between the ages of 25 and 60, with data collected from 2011 to 2021. The study excluded individuals who were underweight or extremely obese to ensure results were not biased by outliers. Body mass index (BMI), calculated from self-reported weight and height, served as the measure of overweight and obesity. Happiness was assessed using a single-item question about life satisfaction, rated on a scale from 0 (completely dissatisfied) to 10 (completely satisfied).
Two statistical models were employed to analyze the data. First, fixed-effects regression models were used to isolate the within-person effects of weight changes on happiness. This method minimizes the influence of unchanging individual traits, such as personality or genetic predispositions, allowing for a clearer view of how BMI fluctuations affect life satisfaction over time. Second, a random-intercept cross-lagged panel model was applied to explore the temporal dynamics between BMI and happiness. This model examines whether changes in one variable (e.g., BMI) predict subsequent changes in the other (e.g., happiness) and vice versa.
Control variables included age, health, employment status, relationship status, and geographic region (East or West Germany). These factors were included to ensure that the observed effects of BMI on happiness were not confounded by other influences.
While descriptive analyses showed a slight negative correlation between BMI and happiness, this relationship disappeared—and in some cases reversed—when causal effects were examined. Specifically, weight gain was not associated with a decrease in happiness. For both men and women, increasing BMI was either unrelated to happiness or showed a slight positive effect. These findings were consistent across all age groups and BMI categories, including overweight and moderately obese individuals.
“Surprisingly, there is no evidence of a negative effect of obesity on life satisfaction,” Bittmann told PsyPost. “This is good insofar as this problem does not appear to directly affect the psyche. The indirect effects are of course still there, as people who are overweight have poorer health and shorter lifespans. In this respect, the study seems to me to be particularly relevant in demonstrating why so many people are overweight: it hardly burdens them psychologically, which is why they have little incentive to lose the excess weight.”
For example, men who moved from a BMI of 22 (high-normal) to 30 (obese) experienced a small but statistically significant increase in happiness. Similarly, women’s happiness levels plateaued after reaching a BMI of 27 and showed no decline with further weight gain.
These conclusions were supported by the random-intercept cross-lagged panel model, which confirmed that changes in BMI did not lead to subsequent decreases in happiness. In fact, the model suggested a small, reciprocal relationship, where increases in happiness were associated with slight increases in BMI and vice versa. Although the effects were minor, they highlight the absence of the expected negative impact of weight gain on well-being.
“Not being able to detect any negative effects of overweight or obesity on happiness was very surprising to me, but the results are very robust and not a single analysis or model could find any negative effect in a longitudinal setting,” Bittmann noted.
One of the study’s primary limitations is its reliance on self-reported height and weight to calculate BMI. BMI is widely used, but it is an imperfect measure of health and weight-related outcomes. It does not account for differences in body composition, such as the ratio of muscle to fat, which could influence both health and happiness. Additionally, life satisfaction was only measured once a year, preventing any analysis of short-term fluctuations.
“Perhaps being overweight has a negative impact on satisfaction, but then possibly only for a short time, until people have become accustomed to the weight,” Bittmann said. “To measure these small and short-term effects, you would have to survey people much more often, which is costly.”
The findings raise questions about the societal and psychological factors that influence the relationship between weight and happiness. For instance, the growing body-positivity movement may play a role in mitigating the negative social stigma associated with being overweight. Alternatively, the slight positive effects observed could reflect the enjoyment of food or the comfort of avoiding restrictive diets. Future research should investigate these potential mechanisms in more detail, as well as explore how cultural and individual attitudes toward weight influence well-being.
“One of my research interests lies generally in what makes people happy or unhappy in the long term for guidance and, maybe, political interventions or advice,” Bittmann said.
The study, “The Scale Goes Up, the Joy Goes Down? Investigating the Causal Effect of Body Weight on Happiness,” was published November 25, 2024.