For the last decades, we have been told to reduce our saturated fat and cholesterol intake to prevent heart diseases and while we followed the recommendations, heart diseases kept his spot as the number one killer worldwide. The problem is that these dietary recommendations were never backed-up by science but unfortunately, it is still in the head of most people that cholesterol equals heart diseases.
The fear of saturated fat really took off when Dwight D. Eisenhower suffered from his first heart attack and Ancel Keys published his famous “7-country study”, showing that heart disease rates are higher in countries that eat more saturated fat. However, besides being observational data (causation doesn’t mean causation), Ancel Keys left out data from 15 more countries in his analysis to strengthen his personal hypothesis.
Cholesterol and heart diseases
By now, there are many studies that examine the connection between cholesterol and heart diseases in regard to heart diseases and we can be quite confident about the accuracy of the data.
A meta-analysis (which is considered as gold-standard for scientific research) looked at 40 different, individual studies that analyzed the risk of high dietary cholesterol on heart diseases but found that: “Dietary cholesterol was not statistically significantly associated with any coronary artery disease or ischemic stroke or hemorrhagic stroke.” In other words, cholesterol has nothing to do with heart diseass and this despite the fact that so many people tried to prove it. 
The same analysis also found that high cholesterol diet barely lead to an increase in blood cholesterol levels. By looking at 17 trials using dietary interventions as a way to study the effect of ingested cholesterol on blood cholesterol levels.
Most trials compared diets in which the cholesterol intake was around 800 mg/day, which is almost three times the amount of the daily recommendation, to a low cholesterol diet of 200 mg/day. Not entirely surprisingly, there was an increase in the groups on the high cholesterol diets. But despite the 4 times higher intake of cholesterol, the average increase on blood cholesterol levels were meager 11.2mg/dL.
The body tightly regulates the amount of cholesterol in the blood by controlling its production. When your dietary intake of cholesterol goes down, your body simply produces more and vice versa.
Cholesterol is essential for life as it is a major component of each of our cells - It contributes to the membrane structure and is also needed to make hormones like testosterone and vitamin D.
By now, we know that total cholesterol is somewhat outdated and most people know about the “good” HDL cholesterol and the “bad” LDL cholesterol. Well, even here it seems to be more complex.
A study that looked at 136,000 people that were admitted to the hospital because of a coronary artery event found that only half of the patients had what we consider high LDL cholesterol levels of above 100 mg/dL. 
For those of you that eat a diet relatively high in fat might see an increase in total cholesterol or LDL cholesterol but that shouldn’t get you worried as there are more important factors to look at.
LDL particle size
The actual size of the LDL particles rather than the total concentration has been connected to an increased risk for heart diseases. There are several mechanisms by which small dense LDL is likely to play a causal role in promoting atherosclerosis, including a higher susceptibility to oxidation and reduced uptake efficiency. 
Surprisingly (or not), a low-carb diet, which is extremely high in fat and low in carbohydrates has been shown to actually increase size and volume of LDL cholesterol particles and thereby, reducing the risk for heart diseases. [4, 5]
Another factor you see on a normal blood work, and which is probably worth watching, are your triglyceride levels. Liver triglycerides are packaged into very low-density lipoproteins, or VLDLs, which are then exported into your blood. [6-8]
Elevated VLDL cholesterol levels were found to increase CHD risk by 2.2- to 3.3-fold in people with LDL cholesterol within the normal range and this effect was exacerbated in those with elevated LDL cholesterol levels.
How to reduce Triglyceride levels?
A trial published in 2007, divided people into four groups ranging from the Ornish diet, which is high in carbohydrates and low in fat to the low-carb Atkins diet. As you can see in the figure below, the group that followed the Atkins diet was more successful in losing weight and by far most successful in lowering triglyceride levels. 
Another factor that is strongly associated with an increased risk of heart diseases is sugar. The consumption of 23% of calories from added sugars doubled the risk for heart diseases compared to a daily intake of 10%. If the intake of added sugar surpasses 28% the risk was even triplet. 
This is almost ironic, as the sugar replaced the fat in many food products to keep the food tasty.
“Heart Healthy” Vegetable Oils
Talking about irony, the other thing that helped to replace “unhealthy” saturated fats are the “heart healthy” vegetable oils.
In another blog, I already explained why cooking with vegetable oils is probably not a good idea as they oxidize very rapidly and thereby, create toxic molecules such as aldehydes.
A study published in the British Medical Journal analyzed the effect of vegetable oil supplementation on heart diseases. Therefore, patients who already had heart diseases were divided into two groups. One group received advice to reduce saturated fat intake and were given a daily supplement containing corn oil. No advice was given to the control group. The group that received the dietary advice and the corn oil supplementation lowered their cholesterol significantly BUT after a 3 years follow-up, almost 50% of people with the low-fat + corn oil diet suffered either from a heart attack or died whereas only 25% of the people that received no treatment diet. 
“Dying with "corrected" cholesterol is not a successful outcome”
John Abramson, M.D
One potential mechanism on how vegetable oils lead to heart diseases might be that they increase inflammation and inflammation is in fact at the root of all heart disease as the plaques that eventually clog the arteries are filled with so-called exhausted immune cells.
A study from 2006 found that people who had high levels of inflammation were 2.6 times more likely to develop heart failure than people who had low inflammatory levels. 
Generally, losing some body fat and eating real, unprocessed food will lower overall inflammation but a study from 2008 found that especially low-carbohydrate diets are very effective for lowering inflammatory proteins. 
Another factor for heart diseases is blood pressure. One study found that when obese participants followed a ketogenic diet for 48 weeks they reduced their blood pressure to a greater extent than a group following a low-fat diet supplemented orlistat. Orlistat is a drug that is used to treat obesity by its function as a lipase inhibitor and also is supposed to lower blood pressure and still the low-carb diet was more successful in this study.  In fact, evidence is accumulating showing show that refined-carbohydrates and sugar are major drivers of hypertension. 
There are certainly other factors contributing to heart diseases like a healthy gut microbiome or an adequate intake of vitamins and minerals like vitamin K2. 
However, this video is by no means a medical advice but simply states the scientific research on heart diseases.
Berger et al., Dietary cholesterol and cardiovascular disease: a systematic review and meta-analysis., Am J Clin Nutr. 2015
Sachdeva et al., Lipid levels in patients hospitalized with coronary artery disease: An analysis of 136,905 hospitalizations in Get With The Guidelines, American Heart Journal, 2009
Rajman et al., LDL particle size: an important drug target, Br J Clin Pharmacol, 1999
Volek, J.S.; Sharman, M.J.; Forsythe, C.E. Modification of lipoproteins by very low-carbohydrate diets. J. Nutr. 2005
Sharman et al., A ketogenic diet favorably affects serum biomarkers for cardiovascular disease in normal-weight men. J Nutr. 2002
Castelli, Epidemiology of triglycerides: a view from Framingham. Am J Cariol, 1992
Ren et al., Long-term coronary heart disease risk associated with very-low-density lipoprotein cholesterol in Chinese: the results of a 15-Year Chinese Multi-Provincial Cohort Study (CMCS)., Atherosclerosis, 2010
Nordestgaard and Varbo, Triglycerides and cardiovascular disease, The Lancet, 2014
Garnder et al., Comparison of the Atkins, Zone, Ornish, and LEARN Diets for Change in Weight and Related Risk Factors Among Overweight Premenopausal Women, JAMA, 2007
Yang et al., Added sugar intake and cardiovascular diseases mortality among US adults., JAMA Intern Med., 2014
Rose et al., Corn Oil in Treatment of Ischaemic Heart Diseases, Brit med J, 1965
Kardys et al., C-reactive protein and risk of heart failure. The Rotterdam Study, American Heart Journal 2006
Fortsythe et al., Comparison of Low Fat and Low Carbohydrate Diets on Circulating Fatty Acid Composition and Markers of Inflammation, Lipids, 2008
Mayer, S.B.; Jeffreys, A.S.; Olsen, M.K.; McDuffie, J.R.; Feinglos, M.N.; Yancy, W.S. Two diets with different haemoglobin A1c and antiglycaemic medication effects despite similar weight loss in type 2 diabetes. Diabetes Obes. Metab. 2014
DiNicolantonia and Lucan, The wrong white crystals: not salt but sugar as aetiological in hypertension and cardiometabolic disease, Open Heart, 2014
Geleijnse et al., Dietary intake of menaquinone is associated with a reduced risk of coronary heart diseases: the Rotterdam Study, J Nutr, 2004