According to basic dogma, eating saturated fats increases the level of bad cholesterol (LDL) in the blood, and that high levels of LDL lead to atherosclerosis and CHD. Conversely it is thought monounsaturated and polyunsaturated fat decrease the level LDL and increase the level of good cholesterol (HDL). Yet recent data have argued against this dogma suggesting that saturated fats may not be so harmful especially when compared to diets high in carbohydrates which often substitute for fats.
In the new study,
"Researchers looked at 72 published studies on fats and heart disease. The studies involved more than 600,000 people from 18 countries. Some people already had heart disease, while others did not. [...] They looked at whether different fats helped or hurt your heart. The different fats included: Saturated fats (found in meats, whole-fat dairy products, and baked goods) Polyunsaturated fats, such as omega-3 and omega-6 (found in fish, nuts, seeds, and vegetable oils) Monounsaturated fats (found in olive and canola oils) Trans fats (found in fried foods and baked goods, and being phased out of the food supply).
The surprise? Saturated fats, long thought to raise heart disease risks, had no effect. Neither did monounsaturated fats, which are thought to help the heart. [...] Which fats did have an effect? Trans fats, known to raise bad cholesterol and lower good cholesterol, were linked with a higher risk of heart disease, as expected. Omega-3s from food helped. Omega-6s appeared to help."
In summary, saturated fats were not bad (unexpected), monounsaturated fats were not good (unexpected), trans fats were bad (expected), polyunsaturated fats were good (expected).
Yet not everyone agrees with these conclusions:
“It is a flawed study,” Marvin M. Lipman, M.D. chief medical adviser for Consumer Reports, said. “And a flawed study should not supplant a well-substantiated theory of the mechanism of coronary atherosclerosis. To take one finding and throw out many other studies isn’t warranted.”
One big criticism is with the design of the study. The researchers looked at 72 previously published studies and combined the results. That kind of research, called a meta-analysis, can be tricky. Findings can be influenced by the studies included, and important ones can be left out. That was the case with this analysis. “There were gross errors in the extraction of data from the original studies,” said Willett, principal investigator of the Nurses Health Study II. “Also, important studies were excluded and not acknowledged in the discussion.”
So who is right? Others weigh in that the issue is complicated:
"Where the nutrition experts do agree: Getting a clear picture on how the body handles dietary fats is very complex. For example, studies haven’t demonstrated that the LDL-raising effects of consuming saturated fats leads to more heart attacks and strokes. “Saturated fat in the diet makes LDL particles bigger, but it doesn’t increase the number of LDL particles, which we now think is responsible for the increased heart risk,” Mozaffarian said. Complicating matters further, the body manufactures its own artery-clogging fats in the liver, often from excess carbohydrates that we eat."
In a nutshell, the relationship between LDL increase (caused by saturated fats) and heart attacks is complicated; furthermore, removing saturated fat from your diet doesn't help much if you replace them with trans fat or junk food (i.e. excess carbohydrates).
For now it makes sense to heed the recommendations of the American Heart Association (AHA):
"Guidelines issued by the American Heart Association and American College of Cardiology last November recommended limiting saturated fat intake to no more than 5 to 6 percent of the total calories consumed to prevent heart disease. The average American currently eats about 11 percent of calories from saturated fat, less than the average consumed a few decades ago."
In other words, if you do eat saturated fat don't eat too much (link):
'Nestle’s advice: eat all things in moderation. “We should be enjoying the pleasure of food, but in very small portions.” Eating a quarter-pound burger once or twice a month is a far cry from eating the 22-ounce ribeye at Morton’s once or twice a week.'
TL;DR saturated fats may not be as harmful to your heart as previously suspected. However, eating a lot of a saturated fat is definitely not good for your cardiovascular system. Moderation is always good advice.
Figure 1. Saturated fats may not be harmful as previously thought but just in case do not overindulge.
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