Soaring obesity levels are contributing to a decline in organ transplants because people's organs are unusable.
The proportion of clinically obese donors has increased from 24 per cent to 29 per cent in deceased donors in the last 10 years, figures show.
For every 10 donors, there was one fewer transplantable organ last year than the previous year for a variety of reasons.
In total, 849 organs - more than one in six of those retrieved - were rejected, almost double the 460 from 10 years ago.
Almost one in three adults in the UK are obese, as well as one in five children aged 10 to 11 years old.
Even if a person is eligible to donate and their family also approves, the final decision comes down to doctors who assess the health of an organ.
Soaring obesity levels are contributing to a decline in organ transplants because the organs are unusable, a report said (stock image)
During 2018-2019, 408 patients died while on the transplant waiting list or within one year of being removed from it, according to NHS Blood and Transplant (NHSBT).
The overall number of transplants fell by two per cent last year, from 5,104 to 4,990,
Currently more than 6,000 people are still waiting for a transplant.
There were 87 fewer organ transplants taking place last year compared to the previous year - 3,951 in 2018/19 compared to 4,038 in 2017/18.
Fewer organs are being approved for use for complex reasons, an NHSBT report said, including donors being more obese, reflecting the worsening obesity levels in Britain, medical problems and an ageing population.
The total number of patients whose lives were potentially saved by organ transplants fell by two per cent to 4,990, while more people were added to the waiting list.
There was no change in the number of kidney transplants, but pancreas, liver, heart, lung and heart-lung transplants all fell. Every person is able to donate nine organs in theory.
A spokesperson for NHS Blood and Transplant said: 'There are multiple factors which could have led to the drop in transplants this year, and we are working hard to fully understand these.
'It is true that in recent years, we have seen an increase in older donors and more donors who are overweight or obese.
'However we have also seen a reduction in the proportion of donors who have died from traumatic injuries and other changes which could also play a part.
'We assess every donor individually, in order to confirm that their organs are healthy and suitable for transplant. The most important thing is for people to register their decision and tell their families what they want, and that way we can ensure that more lives can be saved.'
There have been improvements, however, with the number or people who donate after death slowly rising, hitting a record high of 1,600 people in the year to March 2019.
The NHBT said this is because hard work to raise awareness has led to more families are agreeing to support their loved ones' wishes to donate, which they are entitled to overrule.
This is despite fewer people being eligible to donate, meaning they died in intensive care or similar circumstances.
Over the last 10 years there