What do the World Health Organization, the European Food Safety Authority, the American Food and Drug Administration, and the British National Health Service have in common? this is not the first line of a riddle, by the way.

They all give incorrect dietary advice, many contemporary experts believe.

A large review of dozens of studies, just published in the British Medical Journal, concluded that one type of fat, long thought to be unhealthy, was actually not so.

When a different team of researchers proposed this conclusion after a similar-sized literature review in 2014, sparks flew in the medical community. It is now becoming one of the most fiercely debated issues around.

In August 2015, a group of Canadian academics published a massive review of previous studies on the heart health of saturated fat.

Altogether, the studies they surveyed had over 300,000 participants. They found that the majority of studies demonstrated no association between saturated fat and all of coronary heart disease, cardiovascular disease, ischemic stroke, and type 2 diabetes.

The review also concluded that people who consumed a lot of saturated fats were not more likely to die early than those who consumed little of it.

In other words, it seems as if consuming saturated fat from red meat, milk, cheese, egg yolks, coconut oil, and palm oil may not be harmful after all.

This is very different from the dietary guidelines with which most of us grew up. The food pyramid used by many governmental health authorities prescribes that we consume saturated fat in extremely small amounts, as it causes such serious cardiovascular consequences that can lead to death.

The Canadian researchers were cautious, however, noting that the studies they surveyed did differ, and that their scientific controls were not always appropriate to warrant strong conclusions.

In 2014, the Annals of Internal Medicine published an article that reached a similar conclusion, though. It was an even bigger literature review of studies with a total of almost 600,000 participants. It also concluded that most studies found no association between saturated fat and a range of cardiovascular diseases.

This study was strongly criticized by prominent academics at Harvard and Yale, among others, but its conclusion seems to have been confirmed now.

Scientists will still not be happy, however, as large reviews of dozens of scientific studies performed in 2011 and 2010 reached exactly the opposite conclusion than the 2014 and 2015 literature reviews.

So what is going on here? Why can scientists not agree?

There could be several reasons:

1. It is quite possible that different sources of saturated fat have different health profiles. For example, many studies show that milk is heart-healthier than red meat, and it seems to be the case that plant-sourced saturated fat like coconut oil are healthier than animal sources. As studies on the heart health of saturated fat normally group all these different sources together, their results will come out muddled, and different studies will reach different conclusions, depending on what sources of saturated fat they use. Organic grass-fed meat could also be healthier than antibiotic-filled, corn-fed meat.

2. It is genuinely a difficult subject to study. Researchers must trust that their study participants eat what they say they eat; they cannot exactly lock them up in a lab for years to ensure that they refrain from cheating.

3. If study participants are followed over a period of years to see whether cardiovascular diseases develop later, any of their other lifestyle habits can affect the study’s results; for example, the drugs they take, the amount of exercise they do, and so forth.

Everyone obviously has a major stake in the outcome. Meat eaters want saturated fat to be heart healthy, while vegans want it to be heart unhealthy. Ironically enough, many vegans with their high consumption of coconut oil also want saturated fat to be healthy, while governmental authorities who stand behind their dietary guidelines want it to be unhealthy.

As a result, this debate is likely to continue.

It is indisputable, however, that the latest studies are more positive about saturated fat than the earlier ones. So while you should certainly not rush out to replace your nuts, seeds, and vegetable oils with red meat and milk, it appears as if the massive crusade against saturated fat is, for the moment, over.

The best strategy is probably to maintain a balance between saturated and unsaturated fat, but until scientists settle the issue, we are on our own.

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