Wednesday, May 10, 2017

Studies: Saturated fats don't impair vascular endothelial function, but starch and sugar do

Many people will think first that this study was funded by the meat and dairy industry.  Nice try, but it wasn't.  The authors are from the Diabetes and Nutritional Sciences Division and British Heart Foundation Centre of King's College London. 

They simply "tested the effects of replacing SFAs with monounsaturated fatty acids (MUFAs) or carbohydrates on endothelial function and arterial stiffness."

The subjects were moderately insulin resistant but not diabetic.  This would characterize a large portion of the general population.  

The authors wrote: "We set out to test the hypothesis that decreasing SFA intake would improve vascular function. Our hypothesis was based on the belief that decreasing SFA intake would improve insulin sensitivity, which the main report (17) showed not to be the case."

Put otherwise: Before doing this study, they believed that reducing saturated fat would improve insulin sensitivity and improve vascular function.   If they had a bias, it was against saturated fat.  They fully expected that removing saturated fat from the diet would improve vascular function. 

They measured vascular function after 1 month of consumption of a high-SFA (HS) diet and after 24 week after random assignment to the high saturated (HS) fat diet or diets that contained  less than 10% saturated fatty acids and were high in either monounsaturated fatty acids (HM) or carbohydrates (HC). The primary outcome was a change in flow-mediated dilation (FMD), and secondary outcomes were changes in carotid to femoral pulse wave velocity (PWV) and plasma 8-isoprostane F-III concentrations.

The HS reference diet used full-fat milk (3.8 g/100 mL) and cheese (35 g/100 g), whereas these were replaced with skimmed milk (0.1 g fat/100 g) and half-fat cheese (18 g/100 g) in HM and HC diets.  Those on the HS diet also consumed palm oil. 

On the HM diet, the MUFA was provided by refined high oleic sunflower oil and nuts.

With the HC diet, participants were advised to consume additional portions of bread, potatoes, and rice to compensate for the energy reduction that resulted from decreased fat intake, thus it was a high starch diet, not a high sugar diet. 

They found the opposite of what they expected to find.  To their credit, they reported results contrary to their expectations: 
"In the current study, we were unable to show any benefit on vascular function from replacing SFAs with MUFAs or carbohydrates."

Replacing saturated fats with either MUFAs or starch was not beneficial to mildly hyperinsulinemic, prediabetic subjects.


In contrast, another research team tested the effects of starch and sugar on endothelial function:
'Using 56 healthy volunteers, the researchers looked at four groups. One group ate a cornflake mush mixed with milk, a second a pure sugar mixture, the third bran flakes, while the last group was given a placebo (water). Over four weeks, Dr. Shechter applied his method of "brachial reactive testing" to each group. The test uses a cuff on the arm, like those used to measure blood pressure, which can visualize arterial function in real time."

"The results were dramatic. Before any of the patients ate, arterial function was essentially the same. After eating, except for the placebo group, all had reduced functioning."
 The lead author commented:
"We knew high glycemic foods were bad for the heart. Now we have a mechanism that shows how," says Dr. Shechter. "Foods like cornflakes, white bread, french fries, and sweetened soda all put undue stress on our arteries. We've explained for the first time how high glycemic carbs can affect the progression of heart disease." 
 The article continues:
Endothelial health can be traced back to almost every disorder and disease in the body. It is "the riskiest of the risk factors," says Dr. Shechter, who practices at the Chaim Sheba Medical Center — Tel Hashomer Hospital... 
The take-away message? Dr. Shechter says to stick to foods like oatmeal, fruits and vegetables, legumes and nuts, which have a low glycemic index. Exercising every day for at least 30 minutes, he adds, is an extra heart-smart action to take.
 Schecter neglects to mention that greens, nuts, fats and meats are the foods with the lowest glycemic index: 0. Zero. Zip.

Look at the glycemic indices listed by the Harvard School of Public Health for the foods Schecter tested or mentions as harmful:

cornflakes, 81
milk, 31
All Bran, 44

white bread, 70-75
french fries, 80-114

And, again from Harvard, sweetened soda, 60-70:

Now the foods he recommends:

oatmeal,  55
whole grain wheat breads, 51-69 
whole grain pasta, 42
100% whole rye bread, 65
brown rice, 50
quinoa, 53
fruits, 22-72
roots and tubers, 51-111 (baked potato is 111, sweet potato is 70)
legumes (excluding peanuts), 10-40
nuts (except cashews), 0

Schecter's experiment revealed that bran flakes, with a GI of only 44, impaired endothelial function. 

White potatoes (80-111), sweet potatoes (70), whole rye bread (65), whole grain wheat bread (51), oatmeal (55), quinoa (53), and brown rice (50) all have glycemic impact slightly or markedly GREATER than the bran flakes.

Therefore it can be expected that eating these foods would have a negative effect on the endothelium similar to eating bran flakes.

These whole plant foods all have an impact on blood sugar of the same order of magnitude as white bread, Coca Cola and Fanta soft drinks. 

Note that the glycemic indices of many low sugar fruits are actually lower than those of starches.

Thus, it is not true that restricting fruits and increasing whole plant food starches in their stead (recommended by some advocates of plant-based diets) reduces your exposure to sugar or blood sugar variations. 

However, it is also true the most of the listed fruits have a glycemic index about the same as bran flakes.  Therefore, if the glycemic effect is the driver of the phenomenon observed by Schecter, it can be expected that eating any of these fruits in sufficient quantity would have a negative impact on vascular function similar to the bran flakes. 

Compare the whole foods to snacks and candy bars:

The only snack foods listed that have a higher glycemic index than sweet potato are pretzels and fruit roll ups.  Corn chips, M&Ms, popcorn, potato chips, and Snickers Bar all have similar or less impact on blood sugar than oatmeal, brown rice, whole wheat bread, whole rye bread, and quinoa.  Corn chips have a GI similar to bran flakes.

Thus, according to Harvard School of Public Health, many so-called "low glycemic" whole grains, roots, tubers, and legumes release sugar into the blood at a rate similar to or greater than these junk foods.

The glycemic impact of the recommended whole plant foods is  at a minimum 10 and a maximum a little more than 100 times that of greens, nuts, fats and meats, if we assign those a false value of 1.  However, since greens, nuts, fats and meats actually have zero impact on blood sugar, there is no comparison.  Items that have no effect on blood sugar can't have even 0.00000000000001 percent of the effects down stream from post-meal blood sugar elevation, such as the impairment of vascular endothelial function observed by Schecter. 


Schecter's findings are not surprising to any serious student of basic biochemistry. It is well known from studies of diabetics that glucose – abundantly provided by starchy foods – does a lot of damage. 

After meals, the liver converts excess dietary carbohydrate into saturated and monounsaturated fats, which enter the bloodstream as triglycerides and LDL.[1] (This is why high carbohydrate diets typically produce high triglyceride levels compared to low fat diets.)  LDL then delivers the fats to cells where they will be stored or burned. (This is why LDL is not "bad;" without it cells would not get the fuel they need.)

The liver does this because high blood sugar (hyperglycemia) is very toxic:
"It's important to treat hyperglycemia, because if left untreated, hyperglycemia can become severe and lead to serious complications requiring emergency care, such as a diabetic coma. In the long term, persistent hyperglycemia, even if not severe, can lead to complications affecting your eyes, kidneys, nerves and heart."[2]
Prolonged hyperglycemia causes kidney damage, neurological damage, cardiovascular damage, damage to the retina or damage to feet and legs.  Thus, the liver turns any unnecessary dietary glucose into the much safer saturated fats.  Remember, there is no dietary requirement for glucose.  Thus, all dietary glucose is unnecessary dietary glucose.

In contrast,  SFA and MUFA are essential to health. They are used to make cell walls resistant to penetration by parasites, viruses, and bacteria. The fat pads that protect bony surfaces (palms, soles, sitting bones) and fat deposits that cushion the internal organs are made up largely of saturated fat.
Saturated fats are also very important in the nervous system and brain. The gray matter of the nervous system is made up largely of sphingomyelin, a compound that incorporates 1 fatty acid, most commonly saturated stearic acid or palmitic acid (the same as in palm oil).(3, 4) The white matter of the brain is composed largely of phospholipids incorporating palmitic or stearic acids.(5) All told, about a third of the brain’s fat is saturated.

Am I to believe that Nature chose to construct my brain of a substance that causes heart disease?

Human body fat has a saturated fat composition similar to beef tallow and lard,  about 43% SFA, 47% MUFA, and 10% PUFA:

When you fast – between meals, overnight, or longer – your body releases saturated and monounsaturated fats from fat stores into the blood stream to satisfy ongoing energy demands.  On an ongoing basis, these body fats supply about 60-70% of total body energy expenditure (6). 

Fatty acids are the main fuels for muscles at rest; muscles prefer glucose only during very high intensity activities (such as middle distance sprinting):
"The major fuels for muscle are glucose, fatty acids, and ketone bodies....muscle retains glucose, its preferred fuel for bursts of activity...The metabolic pattern of resting muscle is quite different. In resting muscle, fatty acids are the major fuel, meeting 85% of the energy needs."[1]
Muscles get about 70% of their energy from fats during aerobic activities.  As stated, they only rely on glycolysis when the activity incurs an oxygen-debt.

Thus, contrary to oft-made claim, fats – saturated and monounsaturated – are the body's predominant, hence preferred fuel source. 

More importantly, saturated and monounsaturated fats are the principle fuel source for the cardiac muscle, and the heart muscle actually prefers the ketone body acetoacetate to glucose.
"Unlike skeletal muscle, heart muscle functions almost exclusively aerobically, as evidenced by the density of mitochondria in heart muscle. Moreover, the heart has virtually no glycogen reserves. Fatty acids are the heart's main source of fuel, although ketone bodies as well as lactate can serve as fuel for heart muscle. In fact, heart muscle consumes acetoacetate in preference to glucose."(1)
So the heart is primarily fueled by saturated and monounsaturated fats on an ongoing basis, and yes, it prefers ketones to glucose.  So, if you want your heart to function well, why would you try to force it to run on glucose?

Since glucose suppresses ketosis, this basic biochemistry knowledge indicates that the heart prefers a high fat, ketogenic diet to a glucose-based diet, because glucose-rich foods – starches and fruits – suppress fat metabolism and ketosis through raising insulin level.

The hypothesis that fats are harmful to health can't provide a cogent explanation for why not only humans but all mammals use saturated fats as one of the primary fuel sources at all times and also store large amounts of this supposedly toxic stuff all over the body to serve as a reserve between meals.  (Even a lean individual stores minimally 30 times as much fat as glucose in the form of glycogen, 15 kg vs a maximum of 0.5 kg).

The hypothesis that dietary saturated fats harm and dietary starches (glucose) benefit the heart can not accommodate the well-proven fact that fat and ketones are the preferred fuels of the heart.   

To support the hypothesis that fat is harmful to the heart, you would have to produce a refutation of facts well-established by basic biochemistry research.


In conclusion, saturated fats are intrinsic to the human body, unavoidable because our own liver produces them on an ongoing basis.  Since the liver converts excess dietary glucose into either saturated or monounsaturated fats as quickly as possible, to prevent hyperglycemia, which "can produce noticeable organ damage over time," it seems clear that the body treats glucose as a more toxic substance than saturated fat, to be controlled and eliminated as rapidly as possible.

Based on these basic biochemistry facts, it would appear that the most scientific, rational approach to diet would regulate glucose intake to keep it at the very minimum required to support one's typical type and level of physical activity, liberalize intake of fats having a fatty acid profile similar to our own body fat, and stay near or in ketosis to provide the heart with its preferred fuels on an ongoing basis.


1.  Berg JM, Tymoczko JL, Stryer L. Biochemistry. 5th edition. New York: W H Freeman; 2002. Section 30.2, Each Organ Has a Unique Metabolic Profile. Available from:
2. Mayo Clinic, "Hyperglycemica in diabetes."
3.  Bettelheim FA, Brown WH, March J. Introduction to General, Organic, & Biochemistry, sixth edition. Brooks/Cole, 2001:482.
4.  Enig M. Know Your Fats. Silver Spring, MD: Bethesda Press, 2000:270.
5.  IBID., 60.
6.  Whitney and Rolfes, Understanding Nutrition 11th Edition (Cengage Learning, Apr 30, 2007), p. 156.

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