Atherosclerotic Coronary Heart Disease (CHD) is responsible for one in every six deaths in the United States as well as being the leading cause of death throughout the developed world.
The theory of dietary saturated fats as the principal promoter of elevated serum cholesterol and heart disease stems from research beginning in the 1950's by an American scientist Ancel Keys. It was this hypothesis which was embraced by the American Heart Association and the US federal government in the 1960s and until recently. However, at the same time of Keys research, a British physiologist named John Yudkin argued that sugar intake was more closely related to incidence of and mortality from CHD.
For years the guidance has been to reduce heart disease by limiting saturated fats but studies that showed links were simply asking people to remember what they ate and then compared fats to how many developed heart disease. Sugar is the new scourge and an article in Progress in Cardiovascular Diseases says it has a greater impact on coronary heart disease than saturated fats. But it uses some of the same methodologies that led to the claims about saturated fats, so it suffers from the same weaknesses.
Both Yudkin and Keys were able to support their theories through observational studies in large part because people eat foods, not isolated food constituents. Dietary sources of saturated fat are also often dietary sources of sugar and people who eat lots of sugar often also eat lots of saturated fat. A group of scholars evaluated the evidence to date linking saturated fats and sugars to CHD, considering basic science, epidemiology, and clinical trial data related to CHD risk, CHD events, and CHD mortality. The authors concluded that sugar consumption, particularly in the form of refined added sugars, are a greater contributor to CHD than saturated fats.
The original studies upon which the longstanding guidelines were based were largely observational but there is now more than a half century of data as well as increased understanding of how nutrition impacts the body and specifically coronary heart disease.
The metabolic aspects of saturated fatty acids (SFAs) are complex but existing research suggests that certain SFAs may actually confer measurable benefits for lipid profiles and CHD risk. For instance, some SFAs increase high-density lipoprotein cholesterol (HDL), which is often referred to as the "good cholesterol" as this lipoprotein is associated with a reduced risk of CHD
Replacing saturated fats, or any other component, from one's diet almost inevitably means replacing it with something else. When carbohydrates, particularly refined carbohydrates like sugar, replace saturated fats, which can have a negative impact on lipid profiles (HDL tends to fall and triglycerides tend to rise).
As stated earlier, people don't eat isolated fatty acids - they eat foods that are a mix of various fatty acids and other food constituents. While high intakes from processed meats may increase risk of CHD, higher intakes from dairy sources of saturated fat may not only pose no risk but actually decrease risk.
Consuming a diet high in sugar for just a few weeks has been shown to cause numerous abnormalities found in patients with CHD, such as high total cholesterol, triglycerides, LDL, oxidized LDL, uric acid, insulin resistance and abnormal glucose tolerance, low HDL, and altered platelet function. The overall effect of consuming a diet high in sugar on these numerous health markers is likely more detrimental to overall health compared to increased consumption of saturated fat, which can increase LDL but at the same time raise HDL.
In their analysis, added fructose - generally in the form of sucrose (table sugar) or high fructose corn syrup (HFCS) in processed foods and beverages seems especially potent for producing harm. Consuming these sugars can lead to resistance in leptin, which is a key hormone in the maintenance of normal body weight. The overconsumption of added fructose undoubtedly increases the risk for obesity, which is also a risk factor for CHD. Excess fructose also markedly increases the risk for non-alcoholic fatty liver disease (NAFLD) - the most common liver disease in the US and a strong independent risk factor for CHD. The association between NAFLD and CHD is stronger than the link between CHD and smoking, hypertension, diabetes, male gender, high cholesterol or metabolic syndrome.
This defies belief a little. The same sugars occurring naturally in fruits and vegetables pose no increased risk for CHD, which means the participants under review had other lifestyle choices that impact heart disease. Nonetheless, the scholars do a little bandwagon jump and claim the problem must refined sugars - with ultraprocessed foods being of greatest concern. That's the same confirmation bias that led to beliefs about saturated fats.
Ultra-processed foods also tend to be sources of saturated fats but the harms associated with eating these products may have nothing to do with the fat and everything to do with processed foods themselves. Therefore, best advice is to avoid processed foods rather than to simply avoid SFAs as avoiding SFAs might direct people away from foods that are not only completely benign but actually beneficial (such as dairy foods) but also steer people towards foods that may be harmful - i.e. low-fat, ultra-processed, with huge amounts of hidden added sugars.