If you ask the average person what causes heart disease, he or she would probably say dietary fat. Though fat has been vindicated through many studies, it is still a common belief that dietary fat is unhealthy. A new research review titled Saturated Fat, Carbohydrates and Cardiovascular Disease from The Netherlands Journal of Medicine, sheds more light on the confusion surrounding dietary fat. Europe tends to be more progressive around nutrition, supplementation and drug therapy and a review such as this one, will pave the way for similar messages here in the United States in the near future.
Historically, high LDL cholesterol was seen as one of the most significant risk factors for heart disease. In recent years, LDL by itself, has been shown to be less significant than once thought. In fact, LDL cholesterol by itself is not a cause of atherosclerosis. Rather, it is a sign something else is going on in the body which may lead to atherosclerotic plaque. LDL cholesterol can be found in different sizes. Large-particle LDL does not affect heart disease risk, whereas, high levels of small-particle LDL does. When you add high levels of small-particle LDL cholesterol to elevated triglycerides and low HDL cholesterol, the combination is called the “deadly lipid triad.”
Fat and cholesterol misconceptions.
Eating saturated fat has little to do with the cardiovascular disease so common in Western culture. However, today a common recommendation for those with a poor lipid profile is to cut saturated fat intake and replace it with carbohydrate in the form of “healthy” whole grains. As the authors of this review showed, people who replace dietary saturated fat with carbohydrate end up with decreased LDL, decreased HDL, increased triglyceride and no change to the ratio of total cholesterol to HDL cholesterol. In fact, they end up with more of their LDL cholesterol being the smaller, dense type of LDL cholesterol. The overall result is more small-particle LDL cholesterol, higher triglycerides and lower HDL cholesterol – the “deadly lipid triad.”[i]
What if saturated is replaced with other fats? When 5% of energy from saturated fat is replaced with polyunsaturated fat, like olive oil, the result is a meager 7.5% decrease in heart disease risk.[i] Overall, there appears to be little benefit in these changes to diet. More recently, omega-3 and omega-6 fats have been recommended to reduce heart disease risk. As the authors point out, the benefits of omega-6 fatty acids have been misinterpreted in research. In studies where both omega-3 and omega-6 are consumed, the health benefits actually come from the omega-3 fatty acids.[ii] When the two fats are reviewed separately, omega-3 fatty acids have a significant effect on reducing heart disease while replacing saturated fat intake with omega-6 actually increases heart disease risk. Next time you see vegetable oil, which is an omega-6 fat, being promoted as healthy, remember this fact.
If saturated fat doesn't cause cardiovascular disease, what does?
The authors reiterate two potential causes of CVD which are becoming more accepted. First, they discuss the effect chronic, low-grade inflammation has on heart disease risk. Chronic inflammation is a symptom of virtually every disease process, including coronary artery disease, hypertension and stroke. The other potential cause of cardiovascular disease is carbohydrate consumption. Consuming carbohydrates, even when total calorie intake is kept below maintenance levels, stimulates the production of triglycerides in the blood, along with decreasing the particle size of LDL cholesterol. Studies show eating less carbohydrate and more saturated fat results in lower fatty acid levels in the blood than diets equal in calories, with less saturated fat and more carbohydrate. The lower saturated-fat and higher carbohydrate levels also increase the risk of developing non-alcoholic fatty liver disease, which impacts over a quarter of adults living in Western cultures.
Does this mean people should be unconcerned about their saturated fat intake? Not necessarily. When people eat saturated fat AND too much carbohydrate, the two together can put the body in more of an atherogenic state than when reducing one or the other. The consumption of carbohydrate prevents the body from using the saturated fat, or really any fat, for energy, since it stimulates insulin. Carbohydrates also stimulate the production of other fatty acids from the carbohydrates themselves. The evidence suggests dietary carbohydrate has far more of an impact on cardiovascular disease than saturated fat.
The tide is changing in how development of cardiovascular disease is seen in relation to diet, though not fast enough. Consumers must become more educated about the truth around heart health as food companies and large organizations will be much slower to change their messaging. To summarize what the evidence suggests about cardiovascular disease:
- Saturated fat in the diet is not associated with an increased risk of developing heart disease and has little impact on lipid levels in the blood.
- Carbohydrate consumption beyond what's needed to keep glycogen levels full, stimulates the production of triglycerides in the blood.
- Replacing saturated fat with carbohydrate increases cardiovascular disease risk.
- Replacing saturated fat with omega-6 fatty acids increases cardiovascular disease risk.
[i] Kuipers RS, de Graaf DJ, Luxwolda MF, et al. Saturated fat, carbohydrates and cardiovascular disease. Net J Med. 2011;69(9)372-378
[ii] Ramsden CE, Hibbeln JR, Majchrzak SF, et al. n-6 fatty acid-specific and mixed polyunsaturated dietary interventions have different effects on CHD risk: a meta-analysis of randomized controlled trials. Br J Nutr.2010;104:1586-600
This post was co-authored by my handsome husband.