With coronary heart disease (CHD) killing more than 370,000 people every year in the United States, a team of researchers from Saint Luke's Mid America Heart Institute and Albert Einstein College of Medicine were interested in seeing what's worse for the heart — saturated fats or refined sugars? Their findings, published in Progress in Cardiovascular Diseases, argues that, after years of believing fat was worse, it could have been sugar all along.

"We now have more than a half century of data as well as increased understanding of how nutrition impacts the body and specifically coronary heart disease," said the study’s co-author James DiNicolantonio, a cardiovascular research scientist at the American Heart Institute, in a press release. "After a thorough analysis of the evidence it seems appropriate to recommend dietary guidelines shift focus away from recommendations to reduce saturated fat and toward recommendations to avoid added sugars. Most importantly recommendations should support the eating of whole foods whenever possible and the avoidance of ultra-processed food."

The research team put its theory to the test and found after just a few weeks of participants consuming a diet high in refined (processed) sugar, those with CHD began to experience several signs of heart abnormalities, like higher levels of total cholesterol, triglycerides, LDL (bad cholesterol), and lower levels of HDL (good cholesterol), all of which increase their risk of heart disease. Meanwhile, saturated fats increased levels of LDL, but in doing so also increased levels of HDL, making their negative impact on the heart less dangerous compared to sugar. Ultimately, this led researchers to conclude in their study that "sugar consumption, particularly in the form of refined added sugars, are a greater contributor to CHD than saturated fats." 

In addition, consuming large quantities of processed sugar, such as high fructose corn syrup and table sugar can lead to leptin resistance — leptin is a hormone responsible for regulating normal body weight. Diets high in processed sugars promote type 2 diabetes, which also lead to a much greater risk for CHD compared to patients maintaining a healthy diet.  

Saturated fats have been demonized for years, subsequently leading many consumers to avoid animal products like red meat, poultry, and dairy. These types of fat were first blamed for causing high rates of heart disease in the 1950s, when scientist Ancel Keys observed those who ate diets high in saturated fats also had higher rates of heart disease. But those same people were also eating a lot of refined sugar. DiNicolantonio pointed out this is the reason why past studies, which the longstanding guidelines have been based on, found saturated fats had a negative impact on heart health. The studies were largely observational, however, and didn’t involve intensive investigation. Had past researchers conducted proper studies to determine the cause of CHD, they would've realized sooner that refined sugar impacts risk more. Today, troves of evidence-based research have overwhelmed the weaker observational studies, revealing Keys was wrong all along.

Most recently, a study published in the journal Circulation, found drinking sugary drinks each day increased dangerous fat in the body and increased risk of heart disease and type 2 diabetes. Another study, published in the journal Heart, found people who drank at least two sugary drinks a day increased their risk of heart failure by 25 percent.

Source: O’Keefe JH, DiNicolantonio JJ, and Lucan SC. The Evidence for Saturated Fat and For Sugar Related to Coronary Heart Disease. Progress in Cardiovascular Diseases. 2016.