It was thought the body needed time to remove fatty particles from the blood
Patients do not need to fast before having their cholesterol tested, a major report has found.
After analysing data from 300,000 people, Cambridge researchers found results were just as accurate if the patient had eaten before the test.
While a number of studies have pointed to this, the "no need to fast" message has not yet been absorbed, experts say.
It is hoped the review in the Journal of the American Medical Association will inform guidelines everywhere.
Cholesterol tests have long been a key part of assessing a patient's risk of cardiovascular problems.
Fasting was recommended as it had been thought the body needed enough time to digest food in the system and to clear any fatty particles from the blood. This was in order to produce an accurate reading of so-called "bad" cholesterol - or low-density lipoprotein (LDL).
But data from 68 long-term surveys in 21 countries suggests this is not the case.
"For decades, people have been asked to fast overnight before their cholesterol tests," lead researcher Professor John Danesh said.
"These findings indicate that cholesterol measurements are at least as good - and probably somewhat better - when made without fasting."
The study also adds to the ongoing controversy over whether testing for blood proteins called apolipoproteins is a more reliable way of predicting heart risk than cholesterol testing.
The studies showed that analysing "good" cholesterol - or high-density lipoprotein (HDL) in conjunction with LDL was just as informative as testing for apolipoproteins AI and B.
Professor Peter Weissberg, medical director of the British Heart Foundation, which funded the study, said: "Given the financial pressure the NHS is under, it's good news that doctors don't need to spend money on setting up more sophisticated tests based on apolipoproteins.
"But the study underlines the importance of all GPs being able to measure HDL cholesterol as well as total cholesterol, in order to make the best predictions about heart disease risk."
Not all doctors currently use tests which differentiate between the two different forms of cholesterol.
Cardiovascular disease - CVD - is the leading form of death in the UK and many other parts of the world.
Dr Dermot Neely of charity Heart UK said the findings on fasting confirmed what many clinicians already knew.
"But it has been very slow to get through, particularly in primary care. There are still labs that will not take non-fasting specimens, so patients get sent home. Hopefully this analysis, which backs up current guidelines, will drive the message home."