The United States Center for Disease Control and Prevention (CDC), one of the most prominent nutritional advisors in the mainstream media, preaches the following dietary fat intake guidelines :
- 20-35% of your total caloric intake should come from fats.
- < 10% of your total calories intake should come from saturated fats.
- You should replace solid fats with oils when possible.
- You should limit foods that contain synthetic sources of trans fatty acids and minimize total trans fatty acid intake as much as possible.
- You should eat < 300 mg of dietary cholesterol per day.
- You should reduce your intake of solid fats.
The purpose of this article is to challenge the commonly recommended fat guidelines provided by these government-regulated nutrition organizations. At the end of the article you should have additional insight on the importance of saturated fats, trans fats, and cholesterol the so called "off-limits" nutrients.
"The diet-heart hypothesiswhich holds that eating cholesterol and saturated fat raises cholesterol in our bloodoriginated with studies in both animals and humans more than half a century ago. However, more recent (and higher quality) evidence doesn't support it." - Chris Kesser
Are Saturated Fats the Enemy?Saturated fat is subgroup of fat that is often solid at room temperature. It does not have double bonds between carbon molecules, but is instead bonded with hydrogen molecules. According to the American Heart Association, eating foods with saturated fat will increase your cholesterol and as a result increase your risk of heart disease and stroke. 
Common sources of unprocessed saturated fat include:
- Fatty cuts of beef, lamb, pork, and poultry (with the skin intact)
- Butter and Ghee
- Brazil nuts
- Baking chocolate
- Coconut oil
Despite the CDC's, USDA's, AHA's, and USDHHS's best intentions, let's examine a few studies challenging their stance on saturated fat.
Can Saturated Fats Decrease Mortality Rates?In a 14.1 year study of 58,453 Japanese men and women between the ages of 40 and 79, increased saturated fat intake led to decreased mortality rates due primarily to a reduction in strokes.  This study found an inverse relationship between saturated fat intake and mortality rates! Furthermore, saturated fat intake did not affect mortality rates due to hemorrhage and heart disease.
Saturated Fats Won't Give You a Stroke?A meta-analysis of 21 studies, 5-23 years in length and following 347,747 subjects, found that saturated fat intake did not increase risk of coronary heart disease, stroke, or cardiovascular disease.  I don't know about you, but this is reason enough to keep delicious solid fats in my diet.
Saturated Fats Combat Drinking-Related Health IssuesIncreasing saturated fat intake reversed inflammation, increased blood supply to bones (necrosis), and diminished excessive formation of fibrous connective tissue (fibrosis) due to chronic alcohol intake.  Instead of exacerbating chronic drinking-related side effects, saturated fats actually improve health markers! Furthermore, these markers improved despite continued alcohol consumption.
Saturated Fats Raise Good Cholesterol LevelsThe Mayo clinic suggests keeping high-density lipoprotein (HDL) cholesterol (a.k.a. good cholesterol) as high as possible. One study of 13 subjects showed that HDL levels decreased by 29% when switching from high saturated fat and cholesterol intake to low saturated fat and cholesterol intake.  This research suggests that saturated fat is not the enemy and consuming insufficient amounts may negatively impact key health markers.
The macronutrient breakdowns for the high fat diet was 42% fat (24% saturated, 16% monounsaturated, 2% polyunsaturated), 43% carbohydrates, 15% protein, 215mg cholesterol per 1,000 calories. The breakdown for the low fat diet was 9% fat (2% saturated, 4% monounsaturated, 2% polyunsaturated), 76% carbohydrates, 15% protein, and 40mg cholesterol per 1,000 calories. 
Saturated Fat Intake Lowers Bad Cholesterol Levels?Finally, one study of 1,036 individuals found that increased saturated fat intake, when controlling for carbohydrate intake, decreased very low density lipoprotein (VLDL) cholesterol (a.k.a. bad cholesterol) and fasting triglycerides. 
Bottom Line: Don't be scared of saturated fat it can improve your health. Eating more than 10% of your calories from saturated fat is fine. In fact, it may be healthier than consuming a higher percentage of your calories from carbohydrates. With this in mind, ensure that the majority of your saturated fat intake comes from unprocessed sources.
"If you see trans fat in dairy products, it is not new or just added. It has been around since we have been milking cows and there doesn't seem to be, at typical levels of intake, a negative impact on risk factors." - David J. Baer, PhD
Natural Trans Fats and Health MarkersTrans fats are a type of unsaturated fats found in nature, but only in trace amounts. Trans fats are most commonly created artificially. In concentrated amounts it has been shown to increase the shelf life and prevent structural breakdown of popular snack, desserts, and frozen meals. Artificial trans fats are created by adding hydrogen to liquid vegetable oils (a.k.a. partially hydrogenated oil) to increase their solidity. 
The CDC recommends consuming as few trans fats as possible (both natural and artificial). The AHA says that trans fats increase LDL cholesterol, decrease HDL cholesterol, increase the risk of developing type 2 diabetes, and increase the risk of developing heart disease and stroke. 
Common sources of unprocessed trans fats include:
- The meat and dairy products from ruminant animals (e.g. cattle, goats, sheep, deer).
Let's examine a few studies challenging the conventional notion that all trans fats are bad.
CLA: A Good Trans Fat?When 38 male subjects were provided with 5.5 grams of CLA per day for 5 weeks, oxidative degeneration (re: lipid peroxidation) increased but did not negatively affect inflammation, cardiovascular disease risk factors, fasting insulin levels, and fasting glucose concentrations.  Further research is needed to determine how and if this lipid peroxidation affects key health markers past the 5 week study period.
Natural Trans Fats Have No Negative Impact on Health Markers?A comprehensive review on trans fats from ruminant animals shows that vaccenic acid intake does not negatively affect cardiovascular disease (CVD) health markers and may actually lower circulating triglycerides and cholesterol. 
During a 3-week study of rats dosed with 1.5% bodyweight of vaccenic acid their lipid and lipoprotein levels decreased.  This study suggests that supplementing with VA will not harm the user but actually improve health markers.
"Vaccenic acid is a naturally occurring trans-fatty acid found in the fat of ruminants and in dairy products such as milk, butter, and yogurt. It is also the predominant fatty acid comprising trans fat in human milk." - Wikipedia
CLA Improves the Rate of Fat LossDuring a 12 week study of 47 human subjects, those supplementing with 3.4-6.8 grams of CLA per day lost a statistically significant larger amount of body fat mass compared to the placebo group which consumed 9 grams of olive oil per day. 
This study indicates that CLA is a potentially effective fat loss supplement for overweight or obese individuals. However, the law of diminishing returns appeared to kick-in during this study with regards to CLA supplementation; subjects who consumed 6.8 grams of CLA per day did not lose any more fat mass than subjects who consumed 3.4 grams per day.
CLA Improves Lean Body Mass and Your Bench Press?During a 12 week study in 48 healthy obese humans found that 6.4 grams of CLA per day increased lean body mass by 0.64kg compared to placebo which consumed 8 grams of safflower oil per day. 
During a 7 week study of 76 human subjects, those ingesting 5 grams of CLA per day experienced a statistically significant increase in lean body mass, loss in body fat mass, and increase in bench press strength. 
During a 1 year study of 180 human subjects, those supplementing with CLA experienced a statistically significant greater loss of body fat mass compared to individuals who consumed the placebo (olive oil). 
Bottom Line: Minimize your processed trans-fat intake as much as possible, but don't be scared of naturally occurring trans fats in food products. Furthermore, supplementing with vaccenic acid or CLA, trans fats found naturally in ruminant animals, may actually improve your health via decreased fat mass, increased muscle mass, and improved health markers.
"Your body produces three to four times more cholesterol than you eat. The production of cholesterol increases when you eat little cholesterol and decreases when you eat much. This explains why the "prudent" diet cannot lower cholesterol more than on average a few per cent." - Uffe Ravnskov, MD, PhD
Cholesterol and Heart DiseaseCholesterol is a waxy lipid molecule found in all human body cells. It is naturally produced by the body, and also found naturally in food sources. Cholesterol moves throughout the human body via lipoproteins (fat on the inside and protein on the outside) in two different forms low density lipoproteins (LDL) and high density lipoproteins (HDL). 
According to the AHA, eating more than 300mg of cholesterol per day, particularly in individuals with diabetes, can significantly increase the risk of heart disease. Common unprocessed sources of cholesterol are listed below. 
Let's examine a few studies challenging the conventional notion that a daily cholesterol intake above 300mg is dangerous to your health.
Cholesterol Decreases Risk of StrokeDuring a 17 year study following 3,731 Japanese mean and woman between the ages of 35 and 89, a high intake of animal fat and cholesterol led to a decreased risk of death due to stroke (cerebral infarction).  Unfortunately, the diet was self-reported via a 24-hour diary recall and the "high cholesterol" intake marker was relative to the other study participants as opposed to classifying a high cholesterol intake as Xmg per 1,000 calories.
Dietary Cholesterol Does Not Increase Blood or Total Cholsterol LevelsOne extensive study review found that 70% of the general population experiences no changes, or only mild increases in blood cholesterol levels after consuming large amounts of dietary cholesterol.  These mild increases quickly return to baseline in otherwise healthy individuals. Furthermore, this increased consumption of dietary cholesterol did not negatively impact coronary heart disease markers.
A study of 65 healthy postmenopausal women found that consuming dietary cholesterol quantities up to 800mg per day had little effect on total cholesterol and LDL levels.  One can infer that little effect indicates that these impacts were either not statistically significant or did not negatively impact health and quality of life.
Bottom Line: For otherwise healthy individuals eating more than 300mg of cholesterol per day is fine. Ensure the majority of your cholesterol intake comes from unprocessed sources and don't be afraid of eggs!