The increasing prevalence of weight-related diseases have led health organisations world-wide to advise overweight and obese people to lose weight.  Indeed, the notion that weight loss is generally ‘a Good Thing’ for people who are overweight (BMI 25-30) or obese (BMI ≥30) seems to have been taken on board by the wider society.  Rightly or wrongly, magazines are full of stories, tips and tricks on how to achieve the ‘perfect’ weight, and the diet industry’s worth is estimated to be several billion pounds.   In a recent study of over 9000 overweight and obese adults, over 60% reported that they were ‘trying to lose weight’.

Undoubtedly, even losing relatively small amounts of weight (5% of body weight) will reduce the risk of many obesity-related conditions and diseases, most notably, diabetes, heart disease and stroke.  There are also many reports that weight loss has psychological benefits.  Most commonly, people said that they had improved energy levels, and felt less depressed after losing weight.

However, when researchers from our department looked more closely at the evidence for improvements in depression, it became clear that most of these reports came from people in weight loss trials.  Interestingly, mood improvements often occurred before any weight was lost in these studies, and were not related to the actual amount of weight lost.  This suggests that factors other than weight loss per se may have been responsible for the reported mood improvements.  One explanation is that personal contact (which is a central part of most weight loss trials) may have been responsible for people feeling less depressed by providing support during the weight loss process.  Furthermore, it is likely that people who take part in weight loss trials are very different from the ‘average’ weight loser in the population, so we cannot say that findings from trials will also be true for most people in the UK.

When our researchers looked for studies that used big samples that were representative of the population, they found results from only two studies, the Health and Retirement study, and the Health ABC study.  Curiously, both of these reported slight increases in depressive symptoms in people who lost weight.  However, because these studies also included healthy weight people, and did not look at whether people wanted to lose weight, or lost weight because they got ill during the study period or had significant stress in their lives (which is often related to both weight loss and depression) it was difficult to determine what the reason behind this puzzling finding was.

Therefore, our researchers set out to explore the relationship between weight loss and depressed mood in the English Longitudinal Study of Ageing (ELSA), a large cohort, representative of the UK population that has been going on for over 12 years.  The good thing about ELSA is that it includes lots of measures on all sorts of topics, so that it is very unlikely that people take part because they feel strongly about a certain issue, and it weighs and measures all of its participants every four years so does not rely on self-reported data.

For this particular analysis, the researchers decided to only look at overweight and obese people because these are the people who might be advised to lose weight; a sample of 1979 people.  They also used data telling them about participants’ intention to lose weight, their mood (using an established scale for depressive symptoms), any life stressors or illnesses that occurred during the study period, and blood pressure and triglyceride levels (which were used to check that people benefitted physically from weight loss in the expected way).

The results showed that people derived typical physical benefits from weight loss, with blood pressure and blood test results improving over a period of four years.  However, just like in the other two studies, our researchers found that overweight and obese people who lost at least 5% of their body weight (which is recommended) over four years were nearly twice as likely to be depressed than people who were weight stable, even when taking life stress and onset of illness into account.

However, this study was not able to determine cause and effect, so it is impossible to say whether weight loss caused depressed mood, or whether depressed mood caused weight loss or a third factor that was not measured caused both weight loss and depression.  It is important to investigate these findings further in order to establish why these results were observed, and why they differ so greatly from those reported in weight loss trials; especially since there are so few other studies out there at the moment that could hint at an explanation.

People often think that losing weight will make them happier, but these findings suggest that weight loss may not always be a positive experience.  In fact, the psychological ‘costs’ of weight loss might explain why many who do successfully lose weight struggle to keep the weight off in the long term.  However, this is not to say that people should not attempt to lose weight – after all, people in the study got physically healthier.  Rather, it seems important that service providers are mindful of the possibility that weight loss may worsen mood, and to perhaps include an assessment of mood in their weight loss programmes.  It may also be sensible for anyone trying to lose weight to be aware of any on-going mood changes and to seek psychological support from health professionals or even friends and family if they begin to struggle.

Article reference:

Psychological Changes following Weight Loss in Overweight and Obese Adults: A Prospective Cohort Study

Jackson SE, Steptoe A, Beeken RJ, Kivimaki M, Wardle J (2014) Psychological Changes following Weight Loss in Overweight and Obese Adults: A Prospective Cohort Study. PLoS ONE 9(8): e104552. doi: 10.1371/journal.pone.0104552