A Functional Perspective on Diet and Cholesterol

For nearly 50 years, cholesterol and saturated fat have been maligned by the medical community for their purported role in heart disease. However, a large body of scientific research indicates that dietary cholesterol and saturated fat are not the driving forces behind heart disease. Despite this evidence, much of the medical community continues to promote outdated dietary guidelines for patients with high cholesterol and heart disease, including low-fat and low-cholesterol diets. As it turns out, this outdated advice may actually be harmful to the heart! Read on to learn why dietary cholesterol and saturated fat are not to blame for high cholesterol and heart disease and why a reduced-carbohydrate, nutrient-dense diet is the healthiest approach for treating high cholesterol and heart disease.

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Heart Disease in the United States

The prevalence of heart disease in the United States is a rapidly growing problem. Heart disease affects approximately 85.6 million Americans and is a leading cause of death in the United States. The detrimental impacts of heart disease are not limited to physical effects; heart disease also has an enormous effect on our pocketbooks. In 2015, the American Heart Association estimated the total cost of heart disease to be $320 billion!

While this is a shockingly large sum of money, research indicates that this may not be a necessary expenditure. In fact, it has been found that up to 90 percent of heart disease is preventable. (1) When we consider this finding in conjunction with the latest research on diet and heart disease, it becomes clear that nutritional interventions should be at the forefront of our approach to preventing and treating heart disease. However, much confusion and misinformation surrounds the topic of diet and heart disease; this has led to the promotion of dietary recommendations for high cholesterol and heart disease that are not founded on solid science and may actually be harmful to our health. The confusion is due in large part to an obsolete idea called the “diet–heart hypothesis.”

The Diet–Heart Hypothesis

The diet–heart hypothesis promotes the idea that the consumption of saturated fat and cholesterol raises cholesterol in the blood, thus increasing the risk of heart disease. Based on this hypothesis, dietary saturated fat and cholesterol are to be strictly avoided, and saturated fat should be replaced with vegetable oil rich in linoleic acid, a food purported to reduce the risk of atherogenesis and heart disease. (2) The diet–heart hypothesis has been the backbone of conventional dietary treatment for heart disease for over 50 years and has led the medical community to promote low-fat, low-cholesterol, high-carbohydrate diets with great fervor. Despite the popularity of the diet–heart hypothesis, the reality is that rigorous scientific research does not support this theory! (3, 4)

The ideas promoted by the diet–heart hypothesis originated with animal studies and epidemiological studies back in the 1940s and 1950s that seemed to suggest that dietary saturated fat and cholesterol could raise cholesterol levels in the blood. (5) However, further research quickly disproved this theory, but not before the media and general populace had hopped on board the anti-cholesterol, anti-saturated-fat train! Many of the original proponents of the diet–heart hypothesis have reversed their own stances on dietary cholesterol and saturated fat and their role in heart disease over the years and have attempted to change the medical community and public’s views of this topic. Ancel Keys, the founder of the diet–heart hypothesis, attempted to do just this when he wrote a letter to The New England Journal of Medicine in 1991, stating:

Dietary cholesterol has an important effect on the cholesterol level in the blood of chickens and rabbits, but many controlled experiments have shown that dietary cholesterol has a limited effect in humans. Adding cholesterol to a cholesterol-free diet raises the blood level in humans, but when added to an unrestricted diet, it has a minimal effect. (6)

Keys’s admission of the lack of evidence supporting a relationship between dietary cholesterol and heart disease in humans was a big deal and has initiated a change in thought among many health professionals. However, the ideas of the diet–heart hypothesis have been extremely difficult to kill, as they have become so deeply ingrained in the collective consciousness. Low-fat, low-cholesterol diets have continued to be promoted as “heart healthy” when in fact, research indicates that they are anything but healthy. This persistent misunderstanding about how diet relates to heart disease may actually be causing further damage to people’s health. In 2004, Sylvan Lee Weinberg, the former president of the American College of Cardiology, stated that:

The low-fat, high-carbohydrate diet … may well have played an unintended role in the current epidemics of obesity, lipid abnormalities, type 2 diabetes, and metabolic syndromes. This diet can no longer be defended by appeal to the authority of prestigious medical organizations. (7)

Thus, continued acceptance of the outdated low-fat, high-carbohydrate dietary approach may in fact be worsening our collective health, rather than preventing high cholesterol and heart disease.

Dietary Cholesterol and Saturated Fat Do Not Cause Heart Disease

High-quality scientific evidence indicates that, contrary to what the diet–heart hypothesis has led us to believe, dietary cholesterol has little to no impact on blood cholesterol levels. (8, 9) It appears that dietary cholesterol has very little impact on blood cholesterol levels in approximately 75 percent of the population. The minimal impact of dietary cholesterol on blood cholesterol occurs because most cholesterol in food is not well absorbed in the body. The remaining 25 percent of the population does experience a slight increase in blood cholesterol in response to dietary cholesterol intake; these people are referred to in the medical literature as “hyper-responders.” In these people, dietary cholesterol moderately increases both LDL and HDL but does not affect the LDL-to-HDL ratio or the total cholesterol-to-HDL ratio and thus does not increase the risk of heart disease. Therefore, the increase in blood cholesterol levels is not clinically significant. (10)

Dietary cholesterol and saturated fat are not the driving forces in heart disease. #heartdisease

In addition to letting dietary cholesterol off the hook, it appears that we can also release saturated fat from the heaps of blame we have placed on it for its purported role in heart disease. Long-term studies have failed to show an association between saturated fat intake and serum cholesterol levels. In addition, a large meta-analysis of previous studies has concluded that there is no significant evidence indicating that dietary saturated fat increases the risk of heart disease. (11) Furthermore, a scientific panel consisting of experts on dietary lipids and heart disease determined that increased saturated fat intake does not raise the risk of heart disease or stroke. (12) Finally, a very recent article published in the British Journal of Sports Medicine has put another nail in the coffin of the diet–heart hypothesis, stating that coronary heart disease is not caused by saturated fat intake, but rather is a chronic inflammatory condition that can be reduced using lifestyle intervention such as a healthy diet. (13)

Past studies suggesting that saturated fat raises blood cholesterol, thus contributing to heart disease risk, were almost exclusively short-term studies, lasting only a few weeks, and were therefore not appropriate reflections of the long-term effects of saturated fat on blood cholesterol levels. (14) Out of all the long-term studies examining saturated fat and its potential influence on blood cholesterol levels, only one study has shown an association between saturated fat and cholesterol, and the association was weak. (15)

Refined Carbohydrate Intake Contributes to Heart Disease

Now that dietary cholesterol and saturated fat have been let off the hook, what dietary factors really contribute to high cholesterol and heart disease? As the former president of the American College of Cardiology made clear in his statement, the high intake of refined carbohydrate that has invariably accompanied low-fat diet recommendations has had the unintended consequence of worsening atherogenic dyslipidemia, rather than preventing it.

A comprehensive review of the research on carbohydrate intake and cardiovascular disease has concluded that a diet high in refined carbohydrate aggravates atherogenic dyslipidemia and is associated with increased triglycerides and small LDL particles, decreased HDL, insulin resistance, and obesity. (16) When the amount of triglycerides and LDL particles rises in the blood, this increases the chance that these particles will become oxidized and damage the walls of blood vessels, ultimately leading to plaque formation and heart disease.

Low-Carbohydrate, High-Fat Diets May Improve Heart Health (For Most People)

If saturated fat caused heart disease, we’d expect to see an increase in cardiovascular risk factors with low-carb diets, since they are typically high in saturated fat. However, a meta-analysis of 17 low-carb diet trials including more than 1,000 patients found that low-carb diets improved CVD risk factors, including decreases in triglycerides, blood glucose, BMI, abdominal circumference, plasma insulin, C-reactive protein, and HDL cholesterol. (17)

A low-carb Paleo diet can be a healthy choice for people struggling with concurrent heart disease risk factors and insulin resistance. The goal with this diet is to reduce LDL and triglycerides by decreasing carbohydrate intake and replacing carbs with saturated fat. Carbs should generally be restricted to 10 to 15 percent a day, not counting non-starchy vegetables.

While low-carbohydrate diets may be beneficial for many people struggling with high cholesterol and heart disease, it is important to note that this approach may not be appropriate for those who have elevated cholesterol due to genetics, such as familial hypercholesterolemia or the ApoE4 gene. A better dietary approach for these individuals would be a “Mediterranean Paleo diet” that emphasizes the consumption of more whole foods-based carbs and leaner cuts of meat, while reducing intake of added fats and saturated fat.

Replacing Saturated Fat with Vegetable Oil Does Not Reduce Risk of Heart Disease

A key component of the diet–heart hypothesis has been its recommendation to replace saturated fat with vegetable oils high in linoleic acid. This recommendation was based on some questionable scientific evidence suggesting that the replacement of saturated fat with vegetable oils could reduce cholesterol. While this dietary switch may modestly reduce cholesterol, not a single randomized controlled trial has demonstrated that replacing saturated fat with vegetable oil reduces incidence of heart disease, the outcome of interest. (18)

Despite the dearth of evidence, vegetable oils such as soybean oil and canola oil have been promoted as “heart healthy” by food manufacturers and misinformed medical professionals for decades. In reality, consumption of these highly processed oils may actually contribute to lipid imbalances and heart disease. In a large meta-analysis of studies examining the diet–heart hypothesis, there was no indication of any benefit to heart health from the replacement of saturated fat with vegetable oils rich in linoleic acid. (19)

In addition to vegetable oils not offering any heart health benefits, they also tend to displace healthier fats in the diet such as omega-3 fatty acids. Linoleic acid, the primary fatty acid in vegetable oils, is an omega-6 fatty acid and is inflammatory when consumed in large quantities. (20) Inflammation is a driving force behind heart disease and must be minimized if one intends to prevent or reverse this condition. Excessive consumption of omega-6 fats, combined with a general lack of omega-3 fats in the diet, also can lead to a fatty acid imbalance that has been found to contribute to the development of high cholesterol and heart disease (21). Thus, removing vegetable oils high in omega-6 fatty acids from the diet while simultaneously increasing intake of omega-3 fatty acids from sources such as cold water fish and grass-fed meats can help reduce inflammation and balance out an undesirable omega-6-to-omega-3 ratio and thus reduce one’s risk of heart disease.

Overall, the research indicates that dietary saturated fat and cholesterol no longer need to be avoided as part of a “heart healthy” diet. Rather, the foods that should be avoided in order to promote heart health are vegetable oils and refined carbohydrates. A diet that avoids vegetable oils and refined carbohydrates while emphasizing nutrient-dense whole foods and an optimal balance of fats is an optimal choice for lowering high cholesterol and promoting heart health.