Doubling saturated fat in the diet does not increase saturated fat in blood, study finds

Study: Doubling saturated fat in the diet does not increase saturated fat in blood
Sampling of foods provided to research participants during the three weeks that they were eating a very-low-carb diet. Credit: Ohio State University

Doubling or even nearly tripling saturated fat in the diet does not drive up total levels of saturated fat in the blood, according to a controlled diet study.

However, increasing levels of carbohydrates in the diet during the study promoted a steady increase in the of a fatty acid linked to an elevated risk for diabetes and .

The finding "challenges the conventional wisdom that has demonized saturated and extends our knowledge of why dietary doesn't correlate with disease," said senior author Jeff Volek, a professor of human sciences at The Ohio State University.

In the study, participants were fed six three-week diets that progressively increased while simultaneously reducing total fat and saturated fat, keeping calories and protein the same.

The researchers found that total saturated fat in the blood did not increase - and went down in most people - despite being increased in the diet when carbs were reduced. Palmitoleic acid, a fatty acid associated with unhealthy metabolism of carbohydrates that can promote disease, went down with low-carb intake and gradually increased as carbs were re-introduced to the study diet.

"It's unusual for a marker to track so closely with carbohydrate intake, making this a unique and clinically significant finding. As you increase carbs, this marker predictably goes up," Volek said.

When that marker increases, he said, it is a signal that an increasing proportion of carbs are being converted to fat instead of being burned as fuel. Reducing carbs and adding fat to the diet in a well-formulated way, on the other hand, ensures the body will promptly burn the saturated fat as fuel - so it won't be stored.

"When you consume a very low-carb diet your body preferentially burns saturated fat," Volek said. "We had people eat 2 times more saturated fat than they had been eating before entering the study, yet when we measured saturated fat in their blood, it went down in the majority of people. Other traditional risk markers improved, as well."

The research is published in the Nov. 21, 2014, issue of the journal PLOS ONE.

Volek and colleagues recruited 16 adults for the study, all of whom had metabolic syndrome, defined as the presence of at least three of five factors that increase the risk for heart disease and diabetes (excess belly fat, elevated blood pressure, low "good" cholesterol, insulin resistance or glucose intolerance, and high triglycerides).

After getting them to a baseline reduced-carb diet for three weeks, researchers fed the participants the exact same diets, which changed every three weeks, for 18 weeks. The diets started with 47 grams of carbs and 84 grams of saturated fat each day, and ended with 346 carb grams per day and 32 grams daily of saturated fat.

Each day's meals added up to 2,500 calories and included about 130 grams of protein. The highest-carb level represented 55 percent of daily calories, which roughly matches the estimated daily percentage of energy provided by carbs in the American diet.

Compared to baseline, there were significant improvements in blood glucose, insulin and blood pressure that were similar across diets. Participants, on average, lost almost 22 pounds by the end of the trial.

When looking at palmitoleic acid, however, the scientists found that it consistently decreased on the high-fat/low-carb diet in all participants. The fatty acid then showed a step-wise increase in concentration in the blood as carbs were progressively added to the diet. Elevated levels of palmitoleic acid in the blood have been linked to obesity and higher risk for inflammation, insulin resistance, impaired glucose tolerance, metabolic syndrome, type-2 diabetes, heart disease and prostate cancer.

The study does not address what happens to palmitoleic acid levels when high carbs are combined with a diet high in saturated fat. Instead, Volek hoped to identify the carb-intake point at which participants began to store fat.

"That turned out to be highly variable," he said. "Everyone showed increased palmitoleic acid levels as carbs increased, but values varied widely between individuals, especially at the highest carb intake. This is consistent with the idea that people vary widely in their tolerance to carbohydrates."

Participants' existing health risks were not a factor in the study because everyone ate the exact same diet for 18 weeks. Their bodies' responses to the food were the focus of the work.

"There is widespread misunderstanding about saturated fat. In population studies, there's clearly no association of dietary saturated fat and heart disease, yet dietary guidelines continue to advocate restriction of saturated fat. That's not scientific and not smart," Volek said. "But studies measuring saturated fat in the blood and risk for heart disease show there is an association. Having a lot of saturated fat in your body is not a good thing. The question is, what causes people to store more saturated fat in their blood, or membranes, or tissues?

"People believe 'you are what you eat,' but in reality, you are what you save from what you eat," he said. "The point is you don't necessarily save the saturated fat that you eat. And the primary regulator of what you save in terms of fat is the carbohydrate in your diet. Since more than half of Americans show some signs of carb intolerance, it makes more sense to focus on carb restriction than fat restriction."

Volek sees this palmitoleic acid as a potential biomarker to signal when the body is converting carbs to fat, an early event that contributes to what he calls "metabolic mayhem."

"There is no magical carb level, no cookie-cutter approach to , that works for everyone," he said. "There's a lot of interest in personalized nutrition, and using a dynamically changing biomarker could provide some index as to how the body is processing carbohydrates."


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Journal information: PLoS ONE

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Nov 22, 2014
Some day we will know how to eat properly. Today is not the day!

Nov 22, 2014
A useful next step would be to work out a test of this sensitivity to carbs. Armed with such knowledge, individuals who are susceptible could take more care of what they eat.

Nov 22, 2014
For years the governments of the world have been giving people bad diet advice, killing them and making big pharma rich. The so called "food pyramid" has to be rotated 180 degrees to make any sense at all. All of the bad information was due to one bad study in the 50s I think and it has been killing people ever since. It is the easy to digest carbs like processed wheat, corn, rice and potatoes that makes people crave food and become obese. Fats are not the enemy here.

Nov 22, 2014
Three weeks doesn't sound like a long enough time. What if they just measured a temporary effect? Doesn't sound reasonable to me. A broader look at diet is heart disease by region, where a pronounced effect was found for increased heart disease in the south, home to ribs and chicken fried steak. That sounds reasonable.

Nov 22, 2014
And the sponsor od this study... palm oil producers ?

Nov 24, 2014
All the participants of the study had metabolic syndrome already, meaning that the conclusions are only representative for those people who are prone to metabolic syndrome. It has been suggested before that while some people (perhaps the majority of people) burn fats more easily than carbs, others may burn carbs more easily than fats, and that specific diets might some day be tailored to ones own genetics. (Yes, they tried similar with the blood type diet, which is very popular, but unfortunately fad science that was never able to be duplicated.)

It's a failure to believe there is a "one size fits all" diet anyway.

Nov 24, 2014
@MR166

So Southpark was right all along with the reverse pyramid!

Nov 24, 2014
The result of this study make sense.

In country which regular diet is high-carb, everyone did suspect the high-carb is the contributor to diabetes.

The important question is, whether theres way to fix this without eliminating carb? (since only meat diet is nonsensical: it is environmentally unfriendly & unsustainable. Meat must remain in low fraction)

Dug
Nov 24, 2014
The big weakness in the study review above (and perhaps the study - haven't read it) is that the type of carbs are not specified. Are they simple carbs or complex carbs - or what the ratio of the two used were? There are very significant differences in how simple and complex carbs are metabolized and probably more significant health-wise than how much saturated fats you intake. We already know diets high in simple carbs (sugars particularly) are problematic. If carbs were not defined in the study - they lost their chance of making its results far more significant.

Nov 25, 2014
Dug simple carbs, starches and sugars, are the real enemy. The newest research points to the fact that you can have high total cholesterol levels with a poor HLD/LDL ratio just as long as your triglyceride levels are very low. Starches and sugars are the foods that raise triglycerides.

Nov 26, 2014
It's true. If you have extremely low cholesterol <70mg/dL nothing will cause arterial sclerosis. It's only your cholesterol that matters. Consuming saturated fat is deadly and well understood. Publishing studies like this that appear to give people license to eat all the bacon and cheese they want is a tremendous disservice to the world's health. Heed the advice from Dr. William Clifford Roberts. He has a pretty good idea of what he is talking about. As probably the most renowned Cardiovascular Pathologist in the world, he is the head of Baylor's Cardiovascular Institute, author of almost 1400 scientific papers on the subject of cardiovascular disease, author of over a dozen text books on that subject, and he has been the Editor in Chief of the American Journal of Cardiology for 25 years. He states: "Cardiovascular disease is caused by cholesterol. A vegan diet consisting of no saturated fats or refined grains is the only safe diet". Sad but true...

Nov 28, 2014
OK, I will grant you that a diet consisting of bacon grease and lard might not be the best that you can do. But simple carbs are just as dangerous!

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