There’s an idea, and it’s a little crude, that being depressed makes you fat – and being fat makes you depressed.

Does the relationship really go both ways? Intuitively, it feels true.

But fascinating new research from Cambridge University suggests it isn’t.

How depression affects your weight

The study explores “how changes in an individual’s mental health influence their bodyweight over time”.

What they found was that “increases in symptoms of depression are associated with a subsequent increase in bodyweight when measured one month later.”

In other words, each specific episode of a depressive symptom is linked to an instance of specific weight gain four weeks down the track.

The more symptoms, the greater the weight gain

Specifically, the researchers found that “for every increment increase in an individual’s usual score for depressive symptoms”, their subsequent weight one month later increased by 45 grams.

Not a lot? Maybe not in isolation. But depressive symptoms tend not to happen singly.

In someone whose symptoms pushed their depression from mild to moderate, it would relate to an average weight gain of 225 grams or about a quarter of a kilo.

Curiously , this increase “was only seen among people with overweight or obesity”.

Otherwise, the researchers found “no link between generally having greater symptoms of depression and higher bodyweight”.

What led to these findings

The researchers were from Cambridge’s Medical Research Council (MRC) Epidemiology Unit. They examined data from more 2000 adults living in Cambridgeshire, UK, who’d been recruited to the Fenland COVID-19 Study.

The Fenland study, also conducted by the MRC Epidemiology Unit, in part sought to investigate how social distancing and the easing of restrictions impacted on other health-related outcomes such as diet and physical activity.

In the new study, participants completed digital questionnaires on mental wellbeing and bodyweight every month for up to nine months during the COVID-19 pandemic (August 2020 – April 2021) using a mobile app developed by Huma Therapeutics Limited.

Questions assessed an individual’s symptoms of depression, anxiety and perceived stress.

A higher score indicated greater severity, with the maximum possible scores being 24 for depression, 21 for anxiety and 40 for stress.

The team then used statistical modelling to explore whether having poorer mental wellbeing than usual was related to changes in bodyweight one month later.

The effect was only observed in those individuals with overweight (defined as BMI 25-29.9kg/m2) or with obesity (BMI of over 30kg/m2).

Individuals with overweight had on average an increase of 52 grams for each increment point increase from their usual depressive symptoms score.

For those with obesity the comparable weight gain was 71 grams. The effect was not seen in those individuals with a healthy weight.

What the researcher says

First author Dr Julia Mueller from the MRC Epidemiology Unit said:

“Overall, this suggests that individuals with overweight or obesity are more vulnerable to weight gain in response to feeling more depressed.

“Although the weight gain was relatively small, even small weight changes occurring over short periods of time can lead to larger weight changes in the long-term, particularly among those with overweight and obesity”.

She said people with a high BMI are already at greater risk from other health conditions.

“So this could potentially lead to a further deterioration in their health,” said Dr Mueller.

Monitoring and addressing depressive symptoms in individuals with overweight or obesity “could help prevent further weight gain and be beneficial to both their mental and physical health”.

The researchers found no evidence that perceived stress or anxiety were related to changes in weight.

Previous studies have suggested that poor mental health is both a cause and consequence of obesity. But this research found no evidence that weight predicted subsequent symptoms of depression.

Ten symptoms of depression

Depression is a lot more than just feeling sad or down.

• Feelings of helplessness and hopelessness.
• Loss of interest in daily activities.
• Appetite or weight changes. Significant weight loss or weight gain of more than five per cent of body weight in a month.
• Sleep changes. Either insomnia or oversleeping.
• Anger, irritability, even violent behaviour.
• Loss of energy.
• Self-loathing.
• Reckless behavior.
• Concentration problems.
• Unexplained aches and pains.