Could strong teenage friendships be a route to healthier weight in later life?

Obesity is a major concern for policymakers and society more widely. In the United Kingdom rates of obesity have doubled since 1990, the House of Commons heard recently, with two thirds of adults carrying excess weight and a quarter classified as obese. In the United States, rates have trebled in three decades. We know that adolescence is a key time in setting patterns relating to both weight gain and social relationships, but is there a link between the two? Katie Taylor and colleagues from UCL used data on US adolescents to examine this question – and found strong peer relationships in early life could be a key to slower weight gain in adulthood.

Adolescence is a risky time for weight gain, and there are several reasons for that. Physical and behavioural factors are at play, with both puberty and a decline in physical activity playing a part. The US Growing Up Healthy Study found increased consumption of fast food was linked to increased weight gain between the ages of 9 and 14. So strategies to tackle obesity in adults need to informed by what happens during this important phase.

Our new study set out to investigate whether adolescents’ social relationships influenced changes in their body mass index (BMI) during their adult lives, and whether such effects might also be moderated by gender, ethnicity or age.

Using data from the US National Longitudinal Study of Adolescent to Adult Health(Add Health), we were able to track more than 17,000 participants who were adolescents in the mid-1990s through their next two decades. We placed information on their social contacts and the relative amounts of support – or lack of support – they felt they received from friends and from family alongside measures of how their BMI changed over time.

Support strategies

We used adolescents’ responses from at-home interviews to gain a picture of whether they felt lonely, to whom they tended to turn for support and whether they often argued with family members.

Five hypotheses were tested:

• Strong social relationships would be linked to lower increases in BMI over time, while weaker ones would be linked to greater increases

• These associations would be stronger for peer relationships than for familial relationships – in line with earlier research.

• The associations would be stronger among females than males.

• Associations would differ by ethnic group.

• Associations for peer relationships would be stronger among older adolescents than younger.

Effects over time

The results showed the rate of BMI increase over time was slower for those with higher contact or support from peers compared to those with low contact or support. For example, the BMI of those who had high social contact with friends was almost four fifths of a kilogramme per square metre lower after two decades when compared to those with low social contact.

Meanwhile, BMI increase among those with high family support was almost a kilogramme per square metre more after two decades than among those who received lower levels of family support.

We concluded that while strong friendships were associated with a flatter trajectory of weight gain, the opposite was the case for those with high family contact. Differences were not observed by gender, ethnicity or age.

Strong friendships

So what does this mean for those looking for policy interventions that might help reduce levels of obesity among adults? First, a note of caution: there may be factors at play which we could not fully examine.

For example, a young person who turns to parents for support may do so because there are problems – and those problems could include weight gain. So, the obesity link might not be caused by the parental support – it might instead be the reason why it was needed.

Also, it is possible strong family relationships could run alongside more indulgent parenting styles – which might lead to more lenient attitudes to unhealthy eating, for instance. So the behavioural and psychological mechanisms of family relationships – including the family food environment – need more research.

And our finding that strong peer relationships in adolescence can be linked to lower weight gain later in life is particularly worthy of further consideration: for example, promotion of peer-based interventions could be explored as a strategy to promote healthy weight trajectories. All those involved in trying to improve health outcomes among adults should take into account the complex nature of social relationships in adolescence.

Social connections with family and friends in adolescence: Shaping body mass index trajectories into adulthood is by Katie S Taylor, Harry Tattan-Birch, Martin N Danka, Liam Wright, Eleonora Iob, Daisy Fancourt and Yvonne Kelly. It is published in SSM – Population Health Volume 29, dated March 2025, 101756.