Pain, food, and love: The scientific way friends affect your choices

Close friendships are good for us, with countless studies showing they have positive effects on blood pressure and weight, and reduce our chances of cancer and heart disease. But it’s not just our physical health friends influence; they also alter our moods, behaviours and world views – and not always in positive ways.

A study published last month in the Scandinavian Journal of Pain found that men in the same friendship groups tend to have similar pain thresholds as each other, meaning they can withstand the same levels of pain when, for example, getting a tattoo. In the study, this was tested by administering small amounts of pain and heat to participants, and by immersing their hands into ice water.

Similar pain thresholds form partly because men tend to brag about their abilities to withstand pain. The researchers called this ‘social contagion’, which is the theory that ideas and behaviours spread within groups through imitation.

Pain thresholds are invisible, but we don’t even need to know for definite what another person thinks or feels to be influenced by it. Fergus Neville, a researcher at the University of St Andrews, studies crowds, and says many of his findings can be applied to friendship groups. Just like the men in the pain study, he argues we’re all susceptible to changing our behaviour based on our assumptions about those around us.

“Ask students about their alcohol consumption and the consumption of the average student, and they rate themselves as being outside of the group norm, which they think is heavy binge-drinking all the time,” he says. “But that can’t be the group norm because that’s the average of individuals. Our attitudes are driven by what we think the norm is.”

The larger the group we’re with, the more we eat

Friends can therefore have a powerful influence over how much, and what, we eat. Studies show we eat more when we’re with other people than when we eat alone – and the larger the group size, the more we eat. Helen Ruddock, a researcher on eating behaviour at the University of Birmingham, found that we eat 28 per cent more when we eat with one other person, and 41 per cent more when we eat with two people. This applies across weekdays and weekends, regardless of alcohol consumption, and affects us most when we eat with friends.

Ruddock has also found that, while we eat more around friends, we eat less with strangers – possibly because we don’t want to look greedy. We also look to others for cues on what we should eat.

“If people are given information about, say, the normal amount of fruit and vegetables others eat, they tend to copy that. This is affected by factors including the weight status of the person they’re copying,” Ruddock says. In other words, we’re more likely to be influenced by people who have a healthy weight. 

Happy friends make us happy, but happy co-workers don’t

Friends can also pass on their moods. A 2008 study followed 4,739 people between 1983 and 2003, and found that people with happy friends are more likely to become happy in the future, and this extends up to three degrees of separation, i.e. friends of friends of friends. But this effect isn’t as simple as being around just any happy people, because the researchers found that co-workers didn’t have the same influence.

If your friends’ happiness can make you happier, logic dictates it goes the other way too. A study from 2013 looked at data collected from 12,000 people over 32 years, and found that both increases and decreases in depressive symptoms can travel along social networks, and the effect is stronger for friends who are more connected. Surprisingly, spouses were found to be significantly less influential than friends.

Thankfully, researchers from the University of Warwick found that while depressive symptoms, including helplessness and loss of interest, can be contagious, depression itself didn’t spread. 

Why do friends influence us so much? Derek Heim, a professor of psychology at Edge Hill University, says we are all fundamentally driven by the need to identify as part of a group. 

“Humans are fundamentally social animals, which impacts how we think and view the world,” he says. “If you’re part of a group which derives its identity as rule-breakers, and you subscribe to that, you buy into that view of yourself. If the group associates with substance misuse – and there’s a strong link between cannabis use and the quest to be part of a group – then you’ll derive a sense of self from group membership.”

Heim explains that we’re more likely to see our own group as much cooler than the outside world in order to simplify the world around us and feel better about ourselves, which can also lead to the formation of dangerous views.

“The brain can’t process all the information it receives without mental shortcuts, categorising things into in-group and out-group comparison, which can put down others and reinforce behaviours in a group. Unfortunately, this can be a pre-cursor to racism and discrimination.”

“I started smoking. Being part of the group helped me forget my problems”

There’s evidence to suggest we pick friends who are similar to ourselves, therefore we’re more likely to have the same behaviours and views without actually being influenced by each other. But studies suggests that a change in a friend’s behaviour can affect us. For example, a 2007 study by Massachusetts Medical Society found that we have a 57 per cent increased chance of becoming obese if we have a friend who becomes obese, more than if our sibling or spouse (40 per cent and 37 per cent respectively) gained weight.

We’re also more likely to stop smoking if our friends do. A 2008 study found that despite a fall in the number of smokers in the US, the size of “clusters” of smokers remained the same, suggesting that whole groups of people quit together. If a person stops smoking, the chances of their friend smoking decreased by 36 per cent.

Ian Stephenson, 29, was living away from home in France eight years ago and going through a bad break-up when he looked to his group of friends, who all smoked, for support.

“Looking back on it I think I was on the verge of some kind of breakdown, and I was using the fact that I had moved away to change my life,” he says. “The group of people I managed to gravitate into really suited my idea of what I would like to be a part of, so I spent as much time as I could with them.” Ian started to feel excluded when they took smoke breaks without him.

“Whenever we went out for a drink they always said, ‘no no stay here, we’ll be back in a minute.’ I don’t believe they meant anything malicious by it, but I was feeling vulnerable because of the break-up and I took it kind of personally.

“One of my friends from England who was helping me get through it told me, ‘If it’s affecting your self confidence so much then just start smoking and go with them. You’re only 21, there’s loads of time to quit.’ So I started smoking. Being able to be a constant part of the group really helped me forget everything. I’m still in touch with some of them. 

“I still smoke, though.”

The breakdown of a friends’ marriage increases your own chance of divorce by 75 per cent 

Ominously, we can “catch” divorce from friends too, at least according to a 2013 divorce study by Rose McDermott at Brown University. She found that a break up between immediate friends increases your own chances of getting divorced by 75 per cent, and by 33 per cent if the divorce is between friends of a friend.

Heim says, however, groups can influence in a positive way. 

“A group might see peers doing more recycling, so they will do more themselves, or maybe they give blood every month, and you do too because you don’t want to be the one to violate the social norms”. 

This has been the case for 31-year-old Stephanie Barnes from Brighton, whose friends’ drinking habits have led her to cut down.

“I split up with my partner and went into a really weird destructive time, hanging around people who drank a lot. I remember one time I went go and see my mate and I was so drunk he had to take me home at 9pm,” she says. Her drinking – and subsequent three-day hangovers and alcohol-fuelled anxiety – continued for a year until last year, when she decided to cut down. 

MORE: How to tell your best mate they’re drinking too much

“My friend has recently become sober and it’s inspired me to drink less. We were having dinner with another friend who has never really drank, and they both spoke about how they felt better in the morning, and how it was so much cheaper to go out,” Barnes says, adding that instead of having another glass of wine, she opted for water.

“Really great things have been happening since I decided to cut down. I feel a lot more connected and clear.”

Although your friends could make you fatter, drunker, and sadder, then, Heim says that friends can and do influence us to be healthier. 

“No man is an island,” he says. “We need to take more responsibility for each other, and support each other in fostering positive identities and behaviours”. 

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(Pics: Getty)