As we find ourselves in the middle of a diet guideline flurry - sugar is bad, fat is good - it's worth remembering that dietary recommendations evolve all the time. Or in some cases, are based on zero scientific evidence.
Recent research has revealed that guidelines warning people to avoid eating fatty foods such as butter and cheese "should not have been introduced".
Dietary advice issued to tens of millions warned that fat consumption should be strictly limited to cut the risk of heart disease and death.
But experts say the recommendations, which have been followed for the past 30 years, were not backed up by scientific evidence and should never have been issued.
The guidelines, introduced in the UK in 1983 and in the US six years earlier, recommended reducing overall dietary fat consumption to 30% of total energy intake and saturated fat to 10%.
But researchers say the guidelines "lacked any solid trial evidence to back it".
Experts warned that in characterising saturated fat as the "main dietary villain" public health teams have not paid enough attention to other risks - especially carbohydrates which are believed to be helping to fuel the obesity crisis.
The research paper, which reviewed data available at the time the guidelines were issued, sates: "It seems incomprehensible that dietary advice was introduced for 220 million Americans and 56 million UK citizens, given the contrary results from a small number of unhealthy men.
"The results of the present meta-analysis support the hypothesis that the available (randomised controlled trials) did not support the introduction of dietary fat recommendations in order to reduce (coronary heart disease) risk or related mortality."
The paper, published in the online journal Open Heart, added: "Dietary advice not merely needs review; it should not have been introduced."
But in a linked editorial, Rahul Bahl, of the Royal Berkshire NHS Foundation Trust, sounded a note of caution.
He wrote: "There is certainly a strong argument that an overreliance in public health on saturated fat as the main dietary villain for cardiovascular disease has distracted from the risks posed by other nutrients, such as carbohydrates.
"Yet replacing one caricature with another does not feel like a solution."
Dr Alison Tedstone, chief nutritionist at Public Health England, said: "This paper is not critical of current advice on saturated fats but suggests that the advice was introduced prematurely in the 1980s before there was the extensive evidence base that exists today.
"The advice issued by Coma (Committee on Medical Aspects of Food Policy) in 1991 confirmed that eating too much saturated fat can raise cholesterol levels, which increases the risk of heart disease."