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Old Wed, Jul-31-02, 10:04
Voyajer's Avatar
Voyajer Voyajer is offline
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Default A fatty acid in beef and chocolate may not raise cholesterol

From the Nutrition Newsletter at Pennsylvania State Univ:

A fatty acid in beef and chocolate may not raise cholesterol

A new Nutrition department study suggests that current guidelines on saturated fats might be oversimplified. The findings from the study of rat-liver cells may help explain why stearic acid--a saturated fat found in red meat and chocolate--does not raise cholesterol levels, compared to other saturated fats.
"Understanding how stearic acid works will help consumers make informed decisions about the type of saturated fats included in their diet," says Yu-Yan Yeh, professor of nutrition. He oversaw the study, which was led by T.K. Pai, a doctoral student.

High blood cholesterol is linked to coronoary heart disease, the number one cause of death in the United States. Nutritional guidelines currently don't distinguish stearic acid from the cholesterol-raising effect of other saturated fats.

In a study two years ago, nutrition professor Penny Kris-Etherton found that young men who ate diets high in cocoa butter (which contains stearic acid) showed no change in blood cholesterol, compared to those whose diets were high in olive oil or butter. Yeh's study may help explain why.

In Yeh's study, liver cells from adult rats were treated with three types of fatty acids. Yeh and Pai found that the cells treated with stearic acid, which are normally found in beef and chocolate appear to cut the liver's output of fat and work to help the liver pull "bad" cholesterol out of the blood.

The findings don't suggest that people can eat unlimited amounts of beef and chocolate. "We can eat some red meat and some chocolate, but I would limit the consumption," Yeh says.


Notes : The first study shows that stearic acid has a favorable effect on blood cholesterol when compared to other saturated fatty acids and oleic and linoleic acids. The second study showed stearic acid makes fluffy VLDL. LDL and VLDL are the "bad cholesterol" [which we still need in our bodies--it is only bad in the sense of if you have too much it's bad], but there are two sub-categories. There is the small bullet type of LDL and VLDL which are the really bad type and the big fluffy LDL and VLDL which are a good type of bad cholesterol [confusing?]. Well stearic acid makes the good fluffy type of bad cholesterol. The third study must be because someone attacked stearic acid on the basis that it's cholesterol lowering effect may be offset by it's conversion to oleic acid which proved to be untrue.

Lipids 1996 Feb;31(2):159-64

Stearic acid unlike shorter-chain saturated fatty acids is poorly utilized for triacylglycerol synthesis and beta-oxidation in cultured rat hepatocytes.
Pai T, Yeh YY.

Department of Nutrition, Pennsylvania State University, University Park, 16802, USA.

Utilization of stearate as compared to various saturated fatty acids for cholesterol and lipid synthesis and beta-oxidation was determined in primary culture of rat hepatocytes. At 0.5 mmol/L in the medium, stearate (18:0) adequately solubilized by albumin was less inhibitory to cholesterol synthesis from [2-14C] acetate than myristate (14:0) and palmitate (16:0) (68% vs. 91 and 88% inhibition, respectively). The rate of incorporation into cholesterol from [1-14C] stearate (3.0 +/- 0.6 nmol/mg protein/4 h) was 37-, 1.8-, and 7.8-fold of that from myristate, palmitate, and oleate, respectively. Conversely, the rate of [1-14C] stearate incorporation into total glycerolipids was 88-90% lower than that of labeled palmitate, myristate, and oleate. The rate of [1-14C] stearate incorporation into triacylglycerol (3.6 +/- 0.4 nmol/mg protein/4 h) was 6-8% of that from myristate, palmitate, oleate, and linoleate. The rate of stearate incorporation into phospholipids was the lowest among tested fatty acids , whereas the rate of mono- and diacylglycerol synthesis was the highest with stearate treatment. The rate of beta-oxidation as measured by CO2 and acid soluble metabolite production was also the lowest with [1-14C] stearate treatment at 22.7 nmol/mg protein/4 h, which was 35-40% of those from other [1-14C] labeled fatty acids. A greater proportion of stearate than other fatty acids taken up by the hepatocytes remained free and was not metabolized. Clearly, stearate as compared to shorter-chain saturated fatty acids was less efficiently oxidized and esterified to triacylglycerol in cultured rat hepatocytes.


Lipids 1997 Feb;32(2):143-9

Stearic acid modifies very low density lipoprotein lipid composition and particle size differently from shorter-chain saturated fatty acids in cultured rat hepatocytes.
Pai T, Yeh YY.

Department of Nutrition, Pennsylvania State University, University Park 16802, USA.

Stearic acid as compared to myristate, palmitate, or oleate is poorly incorporated into triacylglycerol, a major lipid component of very low density lipoprotein (VLDL). The present study investigated the effects of these fatty acids on VLDL metabolism in cultured rat hepatocytes. All fatty acids stimulated [2-3H] glycerol incorporation into VLDL lipids and secretion of [3H]-labeled VLDL by hepatocytes. However, the rate of [3H]-labeled VLDL secretion in the presence of nonlabeled stearate (12.8 +/- 0.7 pmol/mg protein/4 h) was 46, 59, and 22% of that observed for those treated with myristate, palmitate, and oleate, respectively. [1-14C]Stearate as a substrate was also less effective than other labeled fatty acids to be incorporated into VLDL lipids. Of total VLDL lipids synthesized from [1-14C] stearate, triacylglycerol accounted for 78% as compared to 88-97% of that derived from palmitate, myristate, and oleate. The amounts of apoB100 and apoB48 were the same in hepatocytes treated with or without exogenous fatty acids. Similarly, the rate of apoB synthesis from [35S] methionine was not affected by exogenous fatty acids. The treatment of cells with various saturated fatty acids increased the particle size of VLDL to different extents. The largest particles of VLDL, with a mean diameter of 79.3 +/- 11.9 nm, were seen in the cells treated with stearate, followed by those treated with palmitate and myristate (45.5 +/- 9.8 and 38.6 +/- 6.8 nm, diameter, respectively). Clearly, hepatocytes treated with stearate secrete less VLDL and produce larger VLDL particles than those treated with shorter-chain saturated fatty acids.


J Nutr 1997 May;127(5):753-7

Desaturation of stearate is insufficient to increase the concentrations of oleate in cultured rat hepatocytes.
Pai T, Yeh YY.

Nutrition Department, The Pennsylvania State University, University Park 16802, USA.

Desaturation of stearate and palmitate and its effect on cellular accumulation of oleate were determined in primary culture of rat hepatocytes. The rate of oleate synthesis as measured by the formation of monounsaturated fatty acids from stearate was significantly higher than that from palmitate. The rate of [1-(14)C]stearate incorporation into oleate [1208 +/- 195 pmol/(mg protein x 4 h)] was 80% higher than that of [1-(14)C]palmitate [(672 +/- 82 pmol/(mg protein x 4 h)]. Despite the different rates of desaturation, the cellular oleate concentrations did not differ in the cells treated with stearate and palmitate (i.e., 42.5 +/- 4.5 vs. 40.8 +/- 5.2 nmol/mg protein). On the other hand, oleate concentration in the cells incubated with exogenous oleate was 198.1 +/- 9.5 nmol/mg protein. There was a dose-dependent increase in cellular stearate concentration by increasing stearate concentrations from 0.5 mmol/L to 4.0 mmol/L in culture medium. A linear increase in cellular stearate concentration was also achieved by increasing the duration of incubation with 1.0 mmol/L stearate from 2 to 24 h. Despite the marked increases in stearate concentrations under these conditions, oleate concentrations remained unchanged in the cells. These results do not support the contention that the hypocholesterolemic effect of stearate may be mediated by its conversion to oleate, although stearate is a more favorable substrate for desaturation than palmitate.
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