Overweight and obesity is perhaps the biggest risk factor for some of the UK’s biggest killers – heart disease, dementia and many types of cancer.
Then there’s the impact of excess weight on the joints, bones and respiratory system, increasing the risk of debilitating conditions like arthritis and asthma.
Now, with the advent of highly effective slimming injections, Britain is seeing more weight loss transformations than ever before. But does a sudden shifting of several stone reverse the damage of years of obesity?
The impact of extra weight is, after all, significant.
‘Obesity generally leads to higher blood glucose levels, and this extra circulating sugar causes body-wide damage,’ says Stuart Gray, a professor of muscle and metabolic health at the University of Glasgow.
‘Much of this damage affects the heart and blood vessels. If it progresses to diabetes, you could face damage to your kidneys as well as nerves in the feet and eyes.
‘Excess body weight also tends to mean you have higher blood fat levels, which can lead to plaques in the blood vessels, narrowing the blood vessels and putting even more strain on your heart.’
So at what point in life is this damage set in stone – regardless of a change in lifestyle – and when is a healthy weight most crucial? Here, experts reveal the ‘sweet spot’ in life when it’s most beneficial to be slim.
In the UK, nearly two-thirds of adults are overweight, and more than a quarter are obese
Keep a larger frame for less than a decade
The damage done by carrying excess weight begins roughly five years into obesity, according to a 2020 UK study.
However after a decade, the risk of heart disease as well as heart-related death climbs significantly.
A US study following 5,036 people found those who spent between five and 14 years with obesity had roughly a 94 per cent higher risk of early death compared to those who’d never been obese.
However, Prof Gray says the danger applies to those who are overweight for long periods of time, too.
‘It’s the cumulative exposure to excess weight that’s the problem,’ he says. ‘If you’ve had 10 or 15 years of being overweight or living with obesity, then the inflammation, vascular dysfunction [blood vessel damage] and high glucose levels will have caused some damage that you can’t get rid of.’
However he adds that being overweight for a long period of time, for instance 10 or 20 years or more, is perhaps more dangerous than a shorter period of time with obesity.
‘Someone with obesity for five years may not have accumulated the same heart risk as a person in their 40s who has spent most of their life overweight,’ he says.
Although joints and bones may be vulnerable to a short burst of extreme excess weight, he adds.
‘Really high levels of excess weight might accelerate things like joint damage, which is hard to recover from.’
Most critical decades for weight loss: Your 20s, 40s and 50s
Experts agree that there are two points in life that are the most crucial for getting into the best shape of your life – but for very different reasons.
While the body has ‘considerable capacity to recover’ from metabolic problems in your 20s, compared to other decades, it’s the best time to set up healthful habits for life.
Dr Mayoni Gooneratne, Executive Medical Director at Personalised Health Clinics, says your 20s is the time in life when most people have very little reason not to pursue a healthy routine.
Age-related wear and tear is at a minimum, and time-consuming stressors like caring for children and managerial job roles are less common.
Studies show that the earlier in life individuals begin a healthy eating pattern, the more likely they are to stick to it through mid-life and beyond.
‘If you’re in your twenties, build a way of eating and moving that you’ll happily repeat for decades,’ advises Dr Gooneratne.
‘It’s the time to prevent years of gradual weight gain and inactivity from becoming normal.’
Your forties and fifties, aka midlife, are a key time to make changes, experts say.
A UK study published in the journal PLOS Medicine found that those who were obese for 20-30 years – mostly beginning around aged 10 – had double the risk of type 2 diabetes compared to those with just a decade of obesity.
‘When you get to the forties and fifties, you see a much more dramatic increase in risk to your health associated with being overweight or obese,’ says Professor Gray.
‘Although people should be thinking about their health earlier, if you haven’t already, once you get to that age group, that’s when you definitely want to start thinking about it.’
The Framingham Heart Study – an ongoing study into the cardiovascular health of Americans – found that the risk of obesity-related heart disease was 62 per cent higher than average in those aged 50-74, compared to 37 per cent higher in 25 to 49 year-olds.
A big reason for this is the hormonal changes that occur at this stage of life.
For women aged between 45 and 55, the decline in the sex hormones oestrogen and progesterone, triggered by menopause, can lead to weight gain, particularly around the middle.
Visceral fat, which is fat stored around organs, is strongly associated with insulin resistance, making it harder for the body to stabilise blood sugar.
‘Women start to lose muscle and bone at this age and the hormone change starts to affect blood vessel health too,’ says Professor Gray.
‘These hormonal changes happen differently in men but the downstream effects are broadly similar.’
Midlife can also be a hectic phase.
‘Your work life might peak and it’s really stressful, you become less active, you’ve got more responsibility looking after older parents and kids, you’ve just got a lot of life demands,’ says Prof Gray.
‘All those things again contribute to metabolic risk; you start to gain a little bit of weight, you become less active, so on and so on, and you start that vicious cycle.’
The benefits of losing weight at this stage of life are perhaps more considerable than in younger years, experts say.
Research published in the journal JAMA Network Open found that people in midlife who lost excess weight had a 48 per cent lower risk of developing chronic disease, than those who stayed overweight.
This means they developed chronic disease at about half the rate of those who didn’t lose weight during the 23-year follow up period.
This period is so critical that the NHS offers a free health check to those over the age of 40 every five years, which includes waist measurement, blood pressure, cholesterol and sometimes blood glucose testing.
Promisingly, experts say there’s not a point of no return when it comes to weight loss.
A 2010 US study found that a weight loss intervention for adults aged 69 to 75 halved the number of deaths in the group, said to be a result of the average of 10 pound fat loss.
However, research has consistently shown that elderly adults who lose weight – those aged above 75 – are more likely to suffer an early death.
A 2024 analysis found that a 10 per cent reduction in body mass index, or BMI, in adults over 65 was linked to a significantly higher risk of death over the next seven years.
Experts say this is likely because extra weight in your 70s and 80s protects against frailty and falls, which are a major cause of hospitalisation in old age.
What’s more, extreme weight loss at this stage of life is often a sign of an underlying deadly disease, such as cancer.
Even in those who don’t go on to develop deadly conditions, the benefit of weight loss in the over 75s is far less significant than in younger individuals, according to a 2014 meta-analysis of 20 studies.
So, if you’re about to embark on a weight loss journey, where should you start?
According to Prof Gray, portion control is key. ‘ While diet quality should of course be considered, most of the evidence is that quantity is the biggest issue when it comes to excess weight,’ he says. ‘Compliment that with physical activity.’
Dr Gooneratne adds: ‘Make most meals from vegetables, fruit, pulses, wholegrains, nuts/seeds where appropriate and protein.
‘Reduce your reliance on sugary drinks, snack foods, takeaways and ultra-processed meals.
‘Build regular walking or other movement into daily life, alongside progressive resistance training while placing emphasis on good sleep and less stress will go a long way.’
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