Losing weight together: why a partner or friend helps

What the research shows

In 1999, the American researchers Rena Wing and Robert Jeffery recruited 166 people for a weight loss programme. Half signed up on their own. The other half signed up with three friends or family members. They were then randomly given either the standard programme or the standard programme with extra focus on social support¹.

Those who came with others lost more weight, both at the end of four months and at the ten month follow up¹. But the big difference showed up afterwards, the stretch when most people start to regain.

Among those who started alone on the standard programme, 76% finished and 24% kept their full weight loss from month four to ten. Among those who started with friends and had extra support, 95% finished and 66% kept all of it off¹. That is almost three times as many.

The ripple effect: your partner loses weight too

In a 2018 trial, 130 couples took part. One partner in each couple got a weight loss programme, either Weight Watchers or a simple self guided handout. The other got nothing at all².

The partners who weren't on any programme still lost weight. After six months it was around 2 kg on average in both groups, and roughly a third (32%) had lost at least 3% of their body weight². The couples' weight curves also moved together².

This had been seen before. In the large American Look AHEAD study, the spouses of people on the intensive lifestyle programme lost 2.2 kg over a year, against 0.2 kg for spouses in the comparison group, and 26% against 9% lost at least 5% of their weight⁴. The researchers also saw the food and habits at home change⁴.

When one changes, the other follows

A British study followed 3,722 couples aged over 50³. When one partner lost weight, the other was around three times as likely to lose at least 5% as well: 36% against 15% for women, and 26% against 10% for men³.

One detail stands out. A partner who changed mattered more than a partner who had always been healthy³. Watching someone you love make the change seems to pull you along. It is an observational study, so it shows a link rather than proof of cause.

Why it works

• You turn up. When someone is counting on you, it is easier to see it through, as the completion rates above show¹.
• Your home changes. When one person in a household changes how they eat, the food in the cupboards and on the table changes for everyone⁴.
• You see that it can be done. A partner who changes pulls harder than one who was always healthy³.
• Bad days pass sooner. Support from people around you was part of what helped people keep the weight off¹.

What the studies don't say

The effect on the partner who isn't taking part is modest. A couple of kilos on average is not a plan in itself². And the British study can't separate cause from link³. Taken together, though, they point the same way: it is easier to start, and easier to keep going, when you are not on your own.

How to do it together

You don't need the same goal or the same pace. How much energy you burn depends on sex, height, weight and age⁵, so you each need your own daily target. Keep the shared part simple:

• Eat the same dinner, just in different portions.
• Agree on one small thing you both do every day, such as logging every meal.
• Cheer the day, not the scales. A well logged day counts.
• Talk about the week once a week, not at every meal.

Try not to turn it into a contest over who loses most. The point is to pull in the same direction, including the weeks when only one of you has the energy. You might also like our guides on keeping a photo food diary and working out your daily calories.