The Skinny on Fat
Humans have never eaten less animal meat and fat, yet we're more metabolically deranged than ever.
The four (alleged) dietary villains:
salt,
cholesterol,
saturated fat, and
animal protein
... all essential for high functioning human health and development.  Increasingly "The Science" (TM) is subject to non-disclosed funding sources that influence publishing bodies.  Those publishing bodies, in their infinite wisdom, over the past 100 years have tripled the rate of heart disease – purportedly because they have outwitted evolution.
Since "a picture is worth a thousand words", let's dig in to some graphs and literature surrounding the lipid hypothesis and it's fallacies (1).
Eating More Saturated Fat is Correlated with Less Heart Disease:
"Based on these data, SFA intake in 1998 was inversely correlated to CHD mortality in 1998 among males for all countries with available data for this year (n 41)..."
In this study of 41 countries found a significant inverse correlation (-0.58, p < 0.01) – meaning that as one variable goes up, the other goes down – between saturated fat intake and risk of heart disease.  The same study found no correlation between serum cholesterol and heart disease (2).
Obesity Rates Have Doubled Since Low Fat Guidelines Were Introduced:
"WTF happened in 1971?" Â The low fat dietary recommendations began in 1977 and clearly did not aide in combating obesity (3, 4). Â So, either people are too stupid to follow these brilliant recommendations, or the recommendations are baseless and ineffective. Â The former is a topic for another day, but there is ample evidence that:
When we tell people to "eat less meat" they don't eat more fruits and veggies, they eat more bread and candy.
Overall, people generally do follow dietary recommendations (5, 6, 7).
High Fat Diets Yield More Weight Loss Than Low Fat Diets:
Here, the low-carb group lost almost twice much weight as the low-fat group (8).  What's amazing is that "low carb" here is still 15% - 30% of total calories – hardly ketogenic for most folks.  "In addition, despite eating a high percentage of calories as fat and having relatively high intakes of saturated fat and cholesterol, the women in the very low carbohydrate group maintained normal levels of blood pressure, plasma lipids, glucose, and insulin."
Americans Are Getting More Obese, More Diseased Hearts, and Eating More Oil and Less Butter
Suffice to say that butter consumption is 1/4 of what it was 100 years ago while shortening consumption has tripled, and (vegetable) oil consumption tripled in the last 50 years (9, 10, 11). Â Again, correlation is not causation, but there can never be causation without correlation. Â So, if there is a 300% delta in something I'd be pointing a lot more fingers there; lest we fall back to the competing null hypothesis: is it the removal of butter, or the addition of oils causing the surge in obesity and heart disease?
We Get Sicker With Less Fat and Less Red Meat
This may throw you off a bit since heart disease actually went down a bit during the time period graphed here. Â However, we can layer together the previous data about low-fat vs. low-carb diets and see that obesity doubled during the time period identified here (12).
What's that about confounding factors? Â Ah, only about half as many people smoked in 1990 as in 1980. Â So, perhaps it was not the reduction in red meat, but reduction in smoking that lead to improved heart outcomes whilst the increase in oils and "low-fat" products increased obesity.
Margarine Amplifies Heart Disease
This is astounding. Â For about every teaspoon / day of margarine you consume above 1.8 for 10-20 years; you add 0.1x to your odds ratio for heart disease. Â In other words, adding 10 tsp of margarine (12 total) doubles your risk for heart disease.
"Adjustment for total fat intake and for cigarette smoking, glucose intolerance, left ventricular hypertrophy, body mass index, blood pressure, physical activity, and alcohol intake did not materially change the results." (13)
Conclusion:
Your body needs fat, specifically animal fat – a topic for another day, but look into DHA / EPA and cholesterol's role in myleination and structural components of the brain.
We must always remember that correlation does not equal causation. Â We must also not fall prey to appeals to emotion or reason (i.e. "it makes sense."). Â So, the facts are:
Americans are being told to eat less animal fat and animal protein.
Generally Americans are following that advice and eating more grains and seed oils.
Americans are rapidly becoming more obese and diabetic.
We must also look for co-morbid factors. Â Is it the salt and "milk" in the Halloween candies that are really driving obesity and heart disease? Â Many "experts" would say so. Â They would also say that:
Frosted Mini Wheats are healthier than steak and eggs, and that the
"Meat" on pepperoni pizza and nachos are to blame for heart disease (14).
I used to tell people to "eat like your grandmother."  However, my own grandmother is still under the low-fat hypnotic propaganda; my aunt is a nurse and constantly chastises my dietary choices.  "The Science" (TM) – i.e. propaganda – is seemingly so strong that my grandmother has forgotten to eat like her grandmother.
At a minimum, this article should be a good jumping off and reference point to get others curious. Â For a little extra credit you can read "12 Graphs that Show Why People Get Fat."