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Institutions and saturated fats part 2

6/18/2012

In Los Angeles in the 1960s, the Veteran's hospital would be the place of arguably the most rigorous clinical trial ever done, testing the potential benefits of a low saturated fat diet. Only three such trials took place in controlled hospital environments, enabling investigators to feed study subjects meals in which saturated fats were replaced with polyunsaturated fats while keeping the rest of the diet relatively unchanged, and this Veterans study was particularly well done. It was a double blind, randomized trial involving 846 subjects for up to 8 years. The subjects were former veterans, living in a domilicary unit. Half ate a control diet, similar to the American diet, and half ate the experimental diet. All meals were served in the cafeteria.

Dietary Intervention
Subjects were given meal tickets of a certain color, corresponding to a particular diet unknown to them. The control diet was 40% calories from fat, “mostly of animal origin,” and the experimental diet involved substitution of vegetable oils for 2/3 of the animal fat, incorporated into the diet in the form of milk, ice cream, margarine, and cheeses. In this trial the low saturated fat experimental diet produced a 13% reduction in serum cholesterol compared to the control group throughout the trial, objectively confirming the experimental group’s adherence to the low saturated fat diet.

Outcome
After eight years of participation, there was no significant difference in heart disease rates, the primary endpoint, manifested as sudden cardiac death or heart attacks (78 events in 65 men in the control group vs. 60 events in 52 men in the experimental). However, when pooled with the data for cerebral infarction and "other secondary end points," the difference in total cardiovascular disease reached statistical significance, with 119 major events occurring in 96 subjects in the control group and 85 events in 66 subjects in the experimental group (p=0.01).

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This clinical trial is all too often cited as supporting the diet-heart hypothesis. By reading the abstract, it seems reasonable, until you track down what these "secondary endpoints" happen to be. Which turned out to be quite difficult. After requesting an interlibrary loan from Pittsburgh, I eventually tracked down the ~80 page tome describing the study in vivid detail. And here are the secondary endpoints:

ruptured aneurysms
limb amputations due to peripheral vascular disease
and “miscellaneous” events, such as occlusion of the mesenteric arteries

To say limb amputation and occlusion of arteries supplying your intestines is related to saturated fat intake would be a bit of a stretch. Extremity amputation was required if the dorsal pedal pulse and the posterior tibial pulse on the affected foot were absent or extremely faint.

In other words, these "secondary endpoints" involved small arteries that supply the muscles on the top and bottom of your foot.

Deaths due to non-atherosclerotic causes were higher in the experimental group (85 vs. 71 in control), resulting in near identical rates of total mortality (177 in control vs. 174 in experimental group). This study also raised an interesting question as to whether or not a diet high in unsaturated fat may contribute to death by other causes, since the experimental group had more non-cardiac deaths (specifically from cancer: 7 deaths in experimental, and 2 in control). However, these numbers are much too small to determine if this result was significant or not. Other such clinical trials have not supported this phenomenon.

This study is another perfect example of how profoundly misleading an abstract can be, and how important it is to read each study in its entirety before making bold claims that this study supports the idea that eating a low saturated fat diet prevents heart disease.

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Mental Institutions & Saturated Fats Part 1

6/12/2012

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In the 1960s and 70s, mental institutions offered dietary researchers an excellent opportunity to test various diets in a highly controlled setting for a long duration. At the time, long term mental hospital stays were common, and researchers used this to their advantage. This opportunity was famously utilized three separate times, in Los Angeles, Helsinki, and Minnesota. In each city, researchers tested the long term effects of eating a low saturated fat diet, and how it may be related to developing cardiovascular disease. The last post discussed the pitfalls involved in blinding a diet study, and the Minnesota Coronary Survey is an example of quite the contrary.

This was a double-blind randomized control trial lasting 4.5 years in 6 Minnesota state mental hospitals and one nursing home involving 4,393 men and 4,664 women. It examined effects of a lipid lowering diet on heart disease. This was the largest study by far that tested the diet heart hypothesis, and they did so with arguably the most rigorous study design to date.

Each patient was randomly assigned to consume either the low saturated fat intervention diet (38% fat diet; 9% Saturated fat, 15% polyunsaturated fat, 14% monounsaturated, 166 mg cholesterol), or the control diet (39% fat diet; 18% saturated fat, 5% polyunsaturated fat, 16% monounsaturated fat, 446mg cholesterol). The difficult part then, is to create two different diets containing these macronutrient compositions that are not discernable by taste or smell. The next challenge is serving over 9,000 people their correct diet for years, based on which group they were randomly assigned to. Here is how they did it:

"Both diets were served in a single line. As a participant entered the line, he or she was handed a label bearing his or her name and a code number that was incomprehensible to the uninitiated but easily interpreted by the foodservers to determine which diet was to be served...The label also enabled the food service worker to serve the proper tray without compromising the blind design, and the labels remaining on the sheet provided the basis for the daily tally of missed meals. Each month the hospital technicians transferred the missing meals data to a "Port-o-Punch card." These cards were read by the computer and at the end provided a correlation between adherence and cholesterol response"

To compliment the rigorous study design, the cholesterol levels of the patients can be used as an objective marker throughout the study to make sure everything is going as planned. Since we know from feeding studies that when you replace saturated fats with polyunsaturated fats, total cholesterol levels decrease, researchers can use this phenomenon to measure adherence. Here is a graph of the cholesterol levels of the study subjects over the course of 4+ years on their respective diets:

Intervention group cholesterol levels decreased 14.5% and were stable for the entire study. The stability of these graphs is spectacular, offering an excellent test of the diet heart hypothesis. Those who kept their cholesterol levels 14.5% lower for 1-4 years should have less heart disease. However this was not the case.
After 4.5 years, no reduction in cardiovascular events or total deaths from the treatment diet. In fact there was a non-significant trend towards a benefit to a high saturated fat diet:

Although the trial laster 4.5 years, not everyone consumed the diet that long. The main criticism of this study was the average length of time on the diet, which was 384 days. However, the number of person years observed was 9,538, with 5,903 of these years continuously for more than 2 years and 2,495 for more than 4 years.

The authors waited about 16 years before publishing this data. According to Gary Taubes in Good Calories, Bad Calories, when he asked Dr. Frantz, the principal investigator, why they waited so long to publish the study, he explained in an interview: "We were just disappointed in the way it came out."

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A calorie is a calorie, unless of course they derive from an Atkins diet

4/3/2012

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Consumer Reports compared various popular diets based on how they match up to the the USDA dietary guidelines, as well as how successful they are. Coming as a surprise to many, the Atkins diet seemed to perform the best. Here is their chart (red means good, black is bad. Whole circles are better than half circles):

If a calorie is a calorie, regardless of what macronutrient it comes from, then how is it possible that the Atkins diet allows the most calories, yet they boast the best short term and long term weight loss results? Consumer reports took an average of meal plans for two weeks on each diet (taken from the published books) and found that on average, an Atkins diet suggests eating over 1900 calories per day, while the Zone and Ornish suggest eating 1260 and 1525 respectively.

According to traditional logic, if you want to lose weight, there must be a calorie deficit. In other words, you should find out how many calories your body uses each day, then eat 500 calories less each day and you will lose 1 pound per week. According to PhotoCalorie.com (which employs the widely used mifflin-St Jeor basal metabolic rate equations), for a 5'3" 160 pound woman to lose one pound per week she should eat about 1,480 calories a day. If this person went on the Atkins diet summarized in Consumer Reports, they would be predicted to GAIN a pound each week! And those consuming the Zone diet would be predicted to lose the most weight since they allow the least calories per day.

Yet this doesn't seem to be the case. In this review of diets and the scientific literature supporting them, calories don't predict weight loss.

This seems to be an unspoken consistent finding in the scientific literature. I have summarized this exact topic, with a link to all the recent studies in the Related Science section.

If calories don't predict weight loss, then what else could?

To try to explain these findings, or any other weight loss questions, as Gary Taubes points out, we should figure out three things:

What does "getting fat" mean?
What regulates our fat cells?
Is there anything we eat that modifies or enhances the effects of these regulators?

Of course getting fat means having more fat in your fat cells. The more fat that is stored in your fat cells located under your skin, the fatter you become. Next, we would want to find out if there is anything that causes the calories we eat to be diverted into our fat cells for storage as opposed to used by the body for energy? And the answer is yes. It is a hormone called Insulin. When insulin is high, calories are stored as fat. If it is low, calories are released from fat cells for energy.

This is uncontroversial. Any biochemistry textbook can explain this in depth. The million dollar, controversial question then becomes: If insulin causes us to store fat in our fat cells, then does anything we eat cause insulin to spike?

Without a doubt, sugar or refined carbohydrates tend to spike insulin the most. Carbohydrates in general spike insulin levels. Protein does too, but too a lesser degree, and fat has hardly any effect. So assuming this theory is true, then a net reduction in sugar and carbohydrates in your diet should result in more weight loss secondary to how many calories you are eating. It is also possible those consuming the Atkins diet are also more satiated and spontaneously eat less, despite the lenient calorie allowance in their diet.

This does seem to be true in the report above, since the Atkins group offers the most calories and the least carbohydrates. This also is suggested in dietary clinical trials, in which the various diets report eating the same amount of calories, yet the Atkins group seems to lose the most weight.

The next counter argument tends to be that a diet so high in saturated fats is bad for your heart. Here is how Consumer Reports explains this concept:

"Isn't it dangerous to eat so much fat? That's still a subject of vigorous scientific debate, but it's clear that fat is not the all-round villain we've been taught it is. Several epidemiology studies have found that saturated fat doesn't seem to increase people's risk of cardiovascular disease or stroke. Other studies suggest that you might be even better off if you replace saturated fat with unsaturated fat instead of with certain carbs, the ones that turn to blood sugar quickly after you eat them, such as white bread and potatoes.

A nutrition researcher, Frank B. Hu, M.D., of the Harvard School of Public Health, recently wrote that he believes "refined carbohydrates are likely to cause even greater metabolic damage than saturated fat in a predominantly sedentary and overweight population." Moreover, clinical studies have found that an Atkins or Atkins-like diet not only doesn't increase heart-disease risk factors but also actually reduces them as much as or more than low-fat, higher-carb diets that produce equivalent weight loss."

There does not seem to be any strong evidence that saturated fats cause heart disease. You can read more about this here and here.

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Tried a paleo or carb restricted diet? Join the registry today and contribute to a better understanding of this way of eating.

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