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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Tried a paleo or carbohydrate restricted diet? Join the registry today!

I recently came across a criticism of the AWLR from the carbsanity blog, criticizing the scientific method and overall veracity of this website. She describes it as a "JOKE", condemning the fact that I describe it as an "international assembly" or that I am interested in hearing from those who have gained or maintained their weight while eating a carb-restricted diet as well: 

"They want to hear if you've gained weight! Yeah ... right ... LOL."

This registry is then compared to the National Weight Control Registry (NWCR), describing how inferior our data is, praising the fact that the NWCR only accepts registrants who have lost weight and kept it off for at least a year.

Strength of the data
Speaking specifically to the fact that the data created from this site is of poor quality, I say you are absolutely correct.  This is conspicuously explained on the about page. The Ancestral Weight Loss Registry is self-selected, self reported data and should not be interpreted as a scientific study. Of course, people can "pad their stats", saying they've lost more weight than they actually did. They can lie, or they may enter false data. This is a simple fact that plagues all self-reported data. The carbsanity author eloquently describes this fact in her post:

"Feel free to fill out this survey from each email you own or don't own.  Make shit up all you want ... just beware, we have very special double secret statistical methods to catch you if you lie!  Really!!  No ... really really!!  Don't lie or we will send out the fraud patrol to spam your fake email address. What a JOKE. "

I would simply hope that the same criticism be conjured up when describing the NWCR data. The fact that the NWCR require their registry members to mail in a packet of information and provide their home address does not necessarily improve the quality of self-selected, self-reported data. 

The carbsanity author describes the NWCR, saying  "In a word, there's a lot of ACCOUNTABILITY.  You have to give them your mailing address, and as memory serves you must provide some visual verification of your weight loss.  Not a lot of optional there."

In fact, her memory may not be entirely correct.  You can give a visual verification of your weight loss (before and after pictures), as you can with the AWLR, but it is not required. As Dr. Wing explains in their published findings, "19% (145 subjects) were unable to provide any source of documentation" verifying their weight loss. 

Exclusion criteria
Carbsanity criticizes me for allowing anyone, whether they have lost, gained, or maintained their weight to join the registry and share their story, as opposed to only allowing those who were successful to join:

"Let's see what we need to join NWCR.  For one thing, you have to have lost a minimum of 30 lbs and KEPT IT OFF for at least a year.  The criteria for joining the AWLR?  Laughable -- we don't care how much you've lost or gained, we want to hear from you?  This IS a joke ... right?"

No it isn't a joke. Only allowing people who have lost 30 pounds and kept it off for over a year is like Yelp.com only allowing you to review a restaurant if you are going to give it 5-stars. Excluding those who may have been less successful biases the data to immeasurable proportions. Those people who are most successful at losing weight and qualify for the NWCR may be systematically different in ways uncaptured by the registry questionnaire, further confounding the already weak data these questionnaires can provide. 

In contrast, I specifically want to incorporate all people who have tried a carb-restricted or paleo diet, whether they lost weight or gained it. I believe this will provide a deeper insight into the most effective ways to lose weight and improve health.

What I hope for this registry to become is not proof that carb-restricted diets are more or less effective than a low-fat diet, or any other way of eating. It is not meant to belittle the findings of the NWCR. Far from it. What I do hope it can be is a lens by which the clinical data can be viewed. The most rigorous data we have on effective dietary practices is the randomized clinical trial. Since the early 90s the potential benefits of a carb-restricted or low fat diet have been tested, and there have been a few consistent findings:

• The carb-restricted, calorie unlimited diet usually - but not always - results in more weight (and fat) loss, than a low calorie, low-fat diet. This has been demonstrated at least 14 times. Whether they spontaneously eat less calories because of the satiating nature of a high fat, high protein diet, or they lose weight due to the net reduction in insulin levels, they consistently lose more weight. You can see all the clinical trials (both successful and unsuccessful here). Each study is linked to its original source in the medical literature.
• The people consuming a carb-restricted diet consistently report feeling full between meals, often eat less at subsequent meals. 
• A carb-restricted diet consistently reduces triglyceride levels, increases HDL levels, and improves the atherogenicity of LDL-C, by morphing these particles from small and dense - associated with high carbohydrate diets, to the large and buoyant LDL particles associated with a decreased risk of heart disease.

These results are consistent in the clinical data and brought about with one sweeping recommendation: Limit your carbs. 

While I agree with Carbsanity that the strength of data created in the Ancestral Weight loss registry is weak, I don’t think Rose or Jackie or the hundreds of people throughout the world signing up to AWLR each day, many of which have tremendously inspiring stories of weight loss and improved health without calorie counting and devoid of hunger, would agree that carb-restricted eating is a “joke”.

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Tried a carb-restricted or paleo diet? Whether you lost or gained weight, we want to hear about it! Join today.

As mentioned in my previous post, it seems counter-intuitive as to why a calorie unlimited, carb-restricted diet could produce more weight loss than a low-fat low calorie diet.

Two scenarios could potentially explain this paradoxical phenomenon, both of which seem to shed positive light on carbohydrate-restricted diets.It is possible that the simple act of eating high-protein, high-fat foods causes people to spontaneously eat less total calories. It has been tested and proven many times, that subjects who eat a high-protein meal report being more satisfied and often eat less in the following meal (see satiety). With this explanation, it seems that the regulation of calorie intake does not happen consciously, but rather at the cellular level, sending signals perceived consciously as fullness.
Another explanation, championed by many low-carb enthusiasts, is that carbohydrates, especially refined ones, cause weight gain via their stimulatory effects on insulin, the main hormone required for fat storage. Our fat tissue is regulated by multiple hormones circulating in our blood streams, but the most powerful regulator is insulin. The regulation is quite simple: when insulin is high, the body switches to storage mode, and excess calories are stored in your fat cells; when it is low, energy from your fat cells can be mobilized and used as energy throughout the body. 

Many foods spike insulin to varying degrees, but breads, pastas, sugars and refined flours are particularly potent. The USDA-promoted diet, consisting of 65% of one's daily calories  deriving from carbohydrates, stimulates net insulin secretion to a greater degree than a low carbohydrate diet. As the theory goes,  this excess insulin release may be chronically directing more calories into your fat cells as opposed to your body to be burnt for fuel. This, in turn, will cause the person to remain hungry since a certain amount of necessary energy did not reach the cells but rather was stored away as fat, perpetuating a vicious cycle of hunger co-existing with adipose tissue growth.

This hypothesis implies that calories are secondary in relation to how many carbs you eat. Many of the studies listed below which measured calorie intake seem to support this theory, since the subjects consuming the carbohydrate-restricted diet did not report eating less calories, and often lost more weight. However this is still unclear.

The mechanism by which this extra weight loss occurs remains controversial, but the positive effects of losing the weight is not. In general, the weight loss seems to be most dramatic during the first six months and sometimes levels off after a year or two. The subjects become less compliant to the diet as time goes on, making it impossible to tell if the diet doesn’t work after six months, or the subjects are just not following it properly.

Regardless of the mechanism, carbohydrate-restricted diets seem to be the most effective way to lose weight based on the clinical data. From a practical standpoint it seems logical that the majority of calories consumed on a successful diet should come from the most satiating nutrients. The clinical trials suggest that the simple act of placing someone on a carbohydrate-restricted diet is the only intervention required for the patients to lose weight. Their own internal hunger and satiety mechanisms regulate their food intake, which seems to make calorie counting unnecessary.