Nearly half of adults in England have put on weight since the beginning of the pandemic.
The average amount of weight gained since last March was half a stone, according to the survey of 5,000 adults by Public Health England.
Restrictions imposed under the first lockdown last March encouraged people to stay at home, apart from essential reasons like exercising once a day.
Vulnerable people were told to isolate for the best part of the pandemic and gyms were also repeatedly shut through various waves of the crisis.
PHE said lockdowns had caused a rise in unhealthy habits such as snacking and comfort eating, likely through boredom or worry.
Overall, those who put on weight gained an average of 9lbs (4.1kg), but one in five picked up a stone or more in weight.
And in those aged between 35 and 65, the average weight gain jumped to 10lbs (4.6kg).
While the lockdowns curbed the spread of Covid, PHE said they took a toll on the nations' wider health.
A study by Public Health England found 41 per cent of Brits put on weight during lockdown, with the average gain being half a stone. But 21 per cent of those who put on weight gained a stone or more since last March
PHE are encouraging people to eat better and get active in a bid to shed some pounds
England's third national lockdown has caused an 'unprecedented' mental health crisis, experts warn
England's third lockdown has sparked an 'unprecedented crisis' in mental health, top experts warned.
Charities and politicians urged No10 to provide much-needed funding to prop up services, and ensure all patients receive treatment.
Mind warned during the second wave that its pandemic support page has seen its highest number of visitors since April — when the country was in the grips of the first wave.
And former Health Secretary Jeremy Hunt warned there is a 'real risk' self-isolation becomes a 'tipping point leading to an epidemic of severe mental illness'.
Experts claim the mental health crisis has been fuelled by the UK's huge death toll, mass unemployment caused by the lockdowns and the social effects of stay at home orders.
Leading psychiatrist Dr Adrian James warned in December that Covid could deliver the biggest hit to Briton's mental well-being since the Second World War.
And the Office for National Statistics (ONS) revealed in August around one in five Britons suffered either moderate or severe depressive symptoms in June 2020, almost double the level recorded the same time last year.
The findings prompted PHE to re-launch a campaign for supporting people to reach a healthier weight called Better Health.
Jo Churchill, the public health minister, said: ‘The pandemic has been hugely challenging for everyone and it has upended our daily routines.
‘As we build back better in the months ahead, we want to make it easier for people to adopt a healthier lifestyle that works for them.
‘The brilliant Better Health campaign returns today and provides a wide range of tools – including an easy to use phone app – to support people, whether that’s losing weight, sharing healthier recipes or motivating people to be more active.’
People in the study who used the NHS Weight Loss Plan app over 12 weeks lost an average of just under one stone (5.8kg).
Researchers found around six in 10 people want more advice on eating better, as well as ideas for exercise routines.
Dr Alison Tedstone, chief nutritionist at PHE, said it is not surprising that people have reported weight gain, because the pandemic has forced people to change their routine.
She said: ‘We know how hard it can be to lose weight and keep it off – so, we are providing a range of support options to help motivate people and help them maintain a healthy weight. It’s never too late to make changes to help improve your health.
‘Visit the Better Health website for ideas and support that is right for you and you can seek support from your local weight management service.’
A study by Weight Watchers last summer found half of Brits put on weight during the first lockdown, with chocolate and biscuits the go-to snack.
Linda Robson, a TV presenter and actress said: ‘I can definitely relate to having slipped a bit during lockdowns – in fact I actually gained over a stone myself!
‘People shouldn’t feel guilty for having put on weight, especially after the year we’ve had – we’ve all had to just try and get through it the best we can.
‘However, this summer I want to get my health on track and look to lose some weight. I know it can feel hard, but the Better Health apps are a great place to start, I’ve started eating some of the Better Health recipes – they are dead easy to do and taste great!’
An earlier study found that the body mass index (BMI) of 80,000 women in January 2020 was 27.1. BMI shows whether someone is a healthy size, based on their height and weight.
But a second study of 163,000 women by the same researchers a year later found the average BMI jumped to 28.4 - the equivalent of gaining more than half a stone.
Additionally, researchers earlier this year found 64 per cent of Brits were trying to lose weight ahead of the original ‘Freedom Day’ deadline on June 21.
Being overweight has also been linked to a higher risk of experiencing more severe Covid.
A study by Oxford scientists found for every BMI point above 23, a person is 5 per cent more likely to be hospitalised.
Boris Johnson urged overweight Brits to shed the pounds last year after he spent a week in intensive care with the virus in May 2020.
The Prime Minister said last summer he had lost over a stone since coming out of hospital by eating less and exercising more.