The 2010 Dietary Guidelines suggest lowering our saturated fat intake even more. 

For the past 15 years, Americans have done a tremendous job of nearly achieving the current goal of no more than 10% of their calories coming from saturated fats. However, due to the less than satisfactory reduction in heart disease rates, these guidelines suggest we should eat even less:

"given that in the US population 11-12 percent of energy from SFA [saturated fatty acids] intake has remained unchanged for over 15 years, a reduction of this amount resulting in the goal of less than 7 percent energy from SFA should, if attained, have a significant public health impact"


For a 2,000 calorie diet, this means eating about 15 grams of saturated fat a day, a value that seems unattainable for the omnivore. The equivalent of a glass of milk and two 6 ounce pieces of chicken breast; or one 9 ounce piece of steak:

Given these rather strict limitations on saturated fat, it seems logical to assume that the clinical trials supporting this relationship are clear-cut and abundant. However, this is not the case.

Since the 1950s, there have been a relatively small number of large, long-term clinical trials examining the potential benefits of decreased saturated fats in the diet as a primary focus. All major trials since 1966 are listed here. Some took place in mental institutions, some were not randomized, and some also involved major confounding interventions such as weight loss, exercise, or increased fruit and vegetable consumption. Some show benefits to replacing saturated fats with polyunsaturated fats, while others do not.

If we were to focus on the largest (i.e. > 100 subjects), randomized, most famous trials ever done lasting longer than 1 year, we are left with very few to assess that meet the following 2 criteria:

1) The only significant intervention involved a reduction in fat and saturated fat and an increase in polyunsaturated fats
2) They ask the question: does this diet reduce heart disease? (defined as heart attacks or death from heart disease)

Listed in reverse chronological order:
Women’s Health initiative (2006) – 48,835 women, 8 years, no significant difference between intervention and control.

Diet and Reinfarction trial (1989) – 2,033 men, 2 years, no significant difference between the groups given and not given fat and fiber advice. No significant differences in ischaemic heart disease between intervention and control (intervention was only advice in this trial)

Minnesota Coronary Survey* (1989) – 4,393 men and 4,664 women, double-blind, 4 years, no significant reduction in cardiovascular events or total deaths from the treatment diet
Los Angeles Veteran’s Trial* (1969) –  846 subjects, up to 8 years, non significant difference in primary endpoints –  sudden cardiac death or myocardial infarction. More non-cardiac deaths in experimental group, resulting in near identical rates of total mortality

Oslo Heart Study (1968) – 412 men, 5 year, slight decrease in CHD with intervention. Many dietary interventions accompanied the low saturated fat diet. When stratified by age, the results were significant only in subjects younger than 60.

* Double blind

A full list of all the trials done supporting and refuting the saturated fat-heart-disease relationship, and a more in depth description of each, can be found here. There are many others that did not meet the criteria I defined above. (Note: The finnish Mental Hospital Trial did not make the cut, since it was not randomized.)

Meta-analyses
If we instead focus on the recent meta-analyses of clinical trials testing this relationship, the majority have failed to elucidate a benefit associated with a low saturated fat diet:

• In 2010, Ramsden et al. published a meta-analysis of randomized clinical trials, including trials where polyunsaturated fats (PUFAs) were increased in place of saturated fats (SFAs) and/or trans fatty acids (TFA), and non-fatal heart attacks, Coronary heart disease-related deaths, and/or total deaths were reported.  In the nine studies included, there was a non-significant increased pooled risk of 13% for n-6 PUFA intake (RR=1.13, CI: 0.84, 1.53) and a decreased risk of 22% (RR=0.78, CI: 0.65, 0.93) for mixed n-3/n-6 PUFA diets. In other words, increasing polyunsaturated fats in the diet provides no benefit, and may be harmful according to this study.
  
  
• Also in 2010, Mozaffarian et al published a systematic review and meta-analysis of randomized clinical trials investigating the effects of increasing PUFAs in place of other nutrients.  Among the seven studies included, an overall pooled risk reduction of 19% (RR= 0.81, CI=0.83-0.97) was observed for each 5% of energy of increased PUFA in the diet.  
  
  
• In 2009, Mente et al. published a systematic review of the randomized clinical trial (RCT) evidence that supports a causal link between various dietary factors and coronary heart disease  The pooled analysis from 43 RCTs showed that increased consumption of marine omega-3 fatty acids (RR=0.77; 95% CI: 0.62-0.91) and a Mediterranean diet pattern (RR=0.32, 95% CI: 0.15-0.48) were each associated with a significantly lower risk of CHD. Higher intake of polyunsaturated fatty acids or total fats were not significantly associated with CHD, and the link between saturated fats and CHD received a Bradford Hill score of only 2 (out of a maximum score of 4), signifying weak evidence of a causal relationship.
  
  
• Also in 2009, the Cochrane Collaboration, an international not-for-profit organization, published a meta-analysis of clinical trials that either reduced or modified dietary fat for preventing cardiovascular disease. Twenty-seven studies met the inclusion criteria, and no significant effect on total mortality (RR = 0.98, 95% CI: 0.86-1.12) or cardiovascular mortality (RR = 0.91, 95% CI: 0.77-1.07) was found between the intervention and control groups.  They concluded by saying: “It is not clear whether a low fat diet, a modified fat diet, or a combination of both is most protective of cardiovascular events.”

The only study above showing a benefit to replacing saturated fats with polyunsaturated fats was the Mozaffarian meta-analysis. The authors of the study claim to have only included randomized clinical trials in their meta-analysis. Surprisingly, the non-randomized Finnish Mental Hospital Study was included twice – split into separate analytical pools of male and female subjects. It is unclear why this study was even included to begin with, since it was not randomized and contained a disproportionate number of control subjects who were taking cardio-toxic medications and consuming higher levels of trans fats than the experimental group.

Inclusion of male and female Finnish data separately further raises concern since it clearly exaggerates the apparent cardio-protective effect of PUFAs demonstrated in this meta-analysis. Excluding the Finnish data from their pooled analysis would diminish the observed results and elicit a null finding, since all other included studies apart from the Oslo heart study (RR=0.75, CI 0.57-0.99) were null:    

Extra Weight Loss in High Saturated Fat Group Adds Complexity:
To further complicate things, the diets that are typically characterized by high amounts of saturated fats seem to result in the most weight loss. When researchers compare a calorie unlimited, low-carb, high saturated fat diet to a traditional low calorie, low-fat diet, the low carb group generally -- but not always -- loses more weight. With few exceptions, their good cholesterol levels go up and their triglycerides go down. Despite having an unlimited calorie budget and often consuming 3x the amount recommended saturated fats, the subjects tend to lose more weight and rarely increase their bad cholesterol levels. ( For more on this and a list of all major clinical trials, see carbohydrate-restricted diets.)

Recommending such low levels of saturated fat, primarily found in meats, may have unintended consequences. 

Since saturated fats are mainly found in protein-dense animal products, decreasing saturated fat intake to very low levels  by definition encourages low-protein diets, which seem to be less effective for weight loss and satiety (feeling full).  Such a drastic recommended decrease in one nutrient of our diets (fats) can lead to a large increase in another. This unfortunate story has played out over past 30 years with carbohydrates. Especially the refined ones:

In February of 1977, the USDA released the first ever dietary goals for the United States. Here is what they recommended: 

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We've been hearing the same thing for the past 30 years: Fat is bad. It has more than twice as many calories as protein or carbs AND it shares the same name with the very characteristic so many of us have acquired during this obesity epidemic.

It has been the general consensus because it makes sense on a superficial level. If people are gaining weight by eating too many calories, then eliminating fat (the most potent calorie-contributor) from the diet should ameliorate the problem. The recommendations soon followed: "Choose lean meats; Use low fat salad dressing; Eat fat free potato chips." 

After 30 years of trying, Americans - as well as the rest of the world - have not been very successful.

Inadequate advice or poor compliance are the two obvious explanations for this failure.  The latter has been incriminated thus far: the majority of Americans just aren't listening. Yet much evidence suggests they may have been listening quite well.

Clinical Trial Evidence
The appearance and sudden popularity of the Atkins diet in the 1990s had dieters running to the meat department, leaving carbs in the dust. The apparent success of this diet, mostly ascertained from anecdotal evidence, had the overweight population excited and health experts worried. A diet characterized by high amounts of meat and fat was deemed impossible to be effective and a serious health risk.

At the time, few clinical trials had been done analyzing the efficacy and safety of such a diet, which understandably led to extreme skepticism among dietitians and doctors. Recent years have seen numerous studies comparing a calorie unlimited, low carbohydrate diet to various other low-fat, low calorie diets.In other words, a battle between two notorious opponents: Eat until you are full and limit carbs Vs. Eat until you reach a calorie limit and restrict fat. Since fat has 9 calories per gram and protein or carbs have 4 calories per gram, a high fat diets seem destined to fail.

Yet to the surprise of many, when compared to other diets, the calorie unrestricted, lowest carbohydrate diet group generally — but not always — loses more weight. With few exceptions, their HDL increases and their blood triglyceride levels decrease without having any significant effect on LDL (bad cholesterol). When subjects keep their carbohydrate intake lower than 50-75 grams per day, they seem to be most successful.

Often times the various groups fare the same, both losing approximately the same amount of weight. But NEVER, in dietary clinical trial history, has the low-fat, low-calorie diet group lost more weight (more on this idea).

The High Fat Paradox
The very idea that a diet characterized by high-fat foods and unlimited calories can do as well, or better, than a low-fat, calorie-restricted diet poses a challenge to the current weight-loss recommendations. However, conceding to this evidence, and altering the recommendations would mean the advice from the last 30 years may have been premature. 


Yet it seems that slowly, the anti-carb message is seeping in. 

Here is a recent public service announcement from the New York City Health Department:

Researchers at Harvard Seem To Agree:
"Fat is not the problem. If Americans could eliminate sugary beverages, potatoes, white bread, pasta, white rice and sugary snacks, we would wipe out almost all the problems we have with weight and diabetes and other metabolic diseases."

-Dr. Walter Willett, chairman of the department of nutrition at the Harvard School of Public Health

"The country's big low-fat message backfired. The overemphasis on reducing fat caused the consumption of carbohydrates and sugar in our diets to soar. That shift may be linked to the biggest health problems in America today."

-Dr. Frank Hu, professor of nutrition and epidemiology at the Harvard School of Public Health. 

Compliance to the high-carbohydrate recommendations
According to the center for disease control, since 1975 Americans have eaten less fat and more carbohydrates:

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