to understand the significance of , and reason for balancing the proportion of saturated and polyunsaturated fatty acids in the fat - containing foods mentioned above such as cooking fats , prepared baked foods , dietary foods , and the like , one must understand some of the important parameters governing lipoprotein and cholesterol synthesis and catabolism . the ldl / hdl ratio , and changes in this ratio depend upon a number of metabolic variables such as hormonal , metabolic , environmental and nutritional perturbations including changing dietary fat compositions which affect lipoprotein levels . as detailed in fig1 it can be seen that both ldl and hdl are derived , in part , by the catabolic events resulting in the breakdown of vldl ( very low density lipoprotein ), the tg ( triglyceride )- rich lipoprotein secreted by the liver for the purpose of delivering tg to muscle for energy generation or to adipose tissue for storage . in humans , the breakdown of vldl is a major source of hdl as well as the primary origin of ldl as described by grundy et al ., 31 j . lipid res . 1149 , 1990 . thus , the potential mass for both hdl and ldl generation is dependent , in part , upon the production rate ( mass per unit time ) of vldl secreted by the liver . on the other hand , reduction in the final pool of circulating ldl depends both upon the proportion of the vldl remnants which are retained and cleared by the liver directly ( reducing diversion to ldl ) as well as the rate of ldl removal by the liver once ldl is formed . both vldl remnants and ldl are cleared via liver receptors ( ldl r ), and both represent a &# 34 ; sink &# 34 ; for receiving hdl cholesterol esters ( ce ) via cetp ( cholesterol ester transfer protein , see below ), thereby reducing the hdl pool once it has been formed . the main function of hdl in this cholesterol - shuttle pathway is to &# 34 ; clean - up &# 34 ; the cholesterol excess &# 34 ; spilled &# 34 ; during vldl catabolism and then deliver it ( as indicated above ) as ce either to vldl remnants or to ldl . these lipoproteins can then carry cholesterol back to the liver for excretion as bile acids ( or biliary free cholesterol ). both the catabolism of vldl involving release of tg , and the ce shuttle from hdl to vldl - ldl are controlled by proteins that are affected by dietary fat . the former process is modulated by lipoprotein lipase ( lpl ) and the latter by the transfer protein cetp . these proteins are affected oppositely by the presence of saturated ( sat ) and trans ( elaidic acid - containing ) fats on the one hand , versus polyunsaturated ( poly ) fat on the other hand . sat and trans fats induce increased cetp activity which is associated with increased ldl , and trans fats can even decrease hdl . however polys reduce the activity of cetp and enhance lpl activity and favor formation of hdl from vldl as shown by demacker et al ., 21 eur . j . of clin . invest . 197 , 1991 . applicant and other investigators have found that dietary fatty acids consumed in the form of natural fats or fat blends affect different lipoproteins and their concentrations in a number of ways . for example , for more than 30 years it has been appreciated that saturated fat increases total cholesterol ( tc ), whereas polyunsaturates decrease it , and monounsaturates were thought to be neutral ( see hegsted et al ., 17 am . j . of clin . nutr . 281 , 1965 , hegsted et al ., 57 am . j . of clin . nutr . 875 , 1993 , and heyden , 38 ann . nutr . metab . 117 , 1994 ). more recently , investigators have focused on nutritional variables by which the different species of lipoproteins , as opposed to tc , are affected . the consensus is that most saturated fatty acids consumed as fats , i . e ., twelve to fourteen carbon saturated fatty acids including lauric , myristic , and palmitic acids ( 12 : 0 , 14 : 0 , and 16 : 0 respectively ), have the potential for elevating both ldl and hdl , although the relative increase in ldl tends to be greater than that for hdl ( see grundy et al ., 31 j . lipid res . 1149 , 1990 , pronczuk et al ., 8 faseb j ., 1191 , 1994 , katan et al ., 60 suppl . am . j . clin . nutr . 1017s , 1994 and mensink et al ., 12 arteriosclerosis and thrombosis 911 , 1992 ). adding to the complexity , 14 : 0 - rich tgs are more cholesterolemic than 16 : 0 - rich tgs ( see hegsted et al ., 17 am . j . clin . nutr . 281 , 1965 , sundram et al ., 59 am . j . clin . nutr . 841 1994 , hayes et al ., 53 am . j . clin . nutr . 491 , 1991 , and hayes et al ., 6 faseb j . 2600 , 1992 ), and the impact of 16 : 0 is highly dependent on the host &# 34 ; metabolic setpoint &# 34 ; for tc in the serum at the time of intervention . thus in people with high tc , 16 : 0 acts as a cholesterol - raising fatty acid , but at tc & lt ; 200 mg / dl 16 : 0 typically appears neutral , neither raising nor lowering tc ( see heyden , 38 ann . nutr . metab . 117 , 1994 , and hayes et al ., 53 am . j . clin . nutr . 491 , 1991 ). on the other hand , 14 : 0 - rich tgs are always cholesterol - raising , suggesting a different regulatory role for 14 : 0 and 16 : 0 . natural tgs , i . e . fats containing the 12 : 0 fatty acid also contain 14 : 0 , so for all practical purposes they can be considered together ( 12 : 0 + 14 : 0 ) and separate from 16 : 0 , which is generally the most prevalent saturated fatty acid in fats derived from plant and animal sources , often without any 12 : 0 + 14 : 0 . surprisingly , stearic acid ( 18 : 0 ) seems to be neutral in its regulatory behavior over tc ( see hegsted et al ., 57 am . j . clin . nutr . 875 , 1993 and katan et al ., 60 suppl . am . j . clin . nutr . 1017s , 1994 ) only one fatty acid , linoleic acid ( 18 : 2n6 or 18 : 2 ), is generally acknowledged to be cholesterol - lowering . as an essential or required dietary polyunsaturated fatty acid , it alone among all of the polys [ including linolenic or 18 : 3n3 , eicosapentenoic ( epa ) or 20 : 5n3 , and docosahexenoic acid ( dha ) or 22 : 6n3 ] consistently lowers tc , especially lowering ldl - c but also decreasing hdl - c at high dietary intake of polys ( grundy et al ., 31 j . lipid res . 1149 , 1990 , hegsted et al ., 17 am . j . clin . nutr . 281 , 1965 , and hegsted et al ., 57 am . j . clin . nutr . 875 , 1993 ). in fact , this tendency for 18 : 2 to lower hdl has even led to warnings against recommending polys as a means for lowering tc . rather , the recommendation has been offered that monunsaturated fats ( monos ) containing oleic acid ( 18 : 1 ) should replace saturated fat as much as possible because monos do not lower hdl like polys do , and replacing saturates with monos will primarily lower ldl as suggested by grundy et al ., 31 j . lipid res . 1149 , 1990 . as applicant will describe below , the later statement is true , but it ignores the critical role of polys , and the fact that it is a critical balance between dietary intake of sats and polys ( both at moderate intake ) which actually allows hdl to increase to yield the highest serum hdl / ldl ratio , at least in humans with normal cholesterol metabolism . over the past few years a number of nutritional experiments using animal models and humans are relevant to applicant &# 39 ; s finding of fatty acid proportions required for generating the highest hdl / ldl ratio . the first relevant study was in monkeys ( hayes et al ., 53 am . j . clin . nutr . 491 , 1991 ). in that report it was found that for sats , 16 : 0 increased tc less than 12 : 0 + 14 : 0 , but quite surprisingly 16 : 0 had an effect on tc very similar to polys ( 18 : 2 ) when 5 % of the daily dietary calorie intake ( abbreviated 5 % en ) was exchanged between these 2 fatty acids ( between 5 - 10 % en as 18 : 2 , ie . diets 4 vs . 5 in the cited study ). at the time of the study , the authors failed to appreciate the significance of the fact that once 5 % en as 18 : 2 in the daily diet has been achieved , additional dietary 18 : 2 does not really exert much effect on tc and can be exchanged for other &# 34 ; neutral &# 34 ; fatty acids without altering tc appreciably . this relationship has been described as the &# 34 ; threshold effect &# 34 ; for 18 : 2 ( hayes et al ., 6 faseb j . 2600 , 1992 and pronczuk et al ., 8 faseb j . 1191 , 1994 ). in a second study in rhesus monkeys ( khosla et al ., 1083 biochem . et biophys . acta 46 , 1991 ), the authors explored possible metabolic reasons for differences observed in tc during the exchange of ( 16 : 0 + 18 : 1 ) for ( 12 : 0 + 14 : 0 ) [ diet 4 versus diet 2 in the cited study ]. it was found that the former fatty acids ( 16 : 0 + 18 : 1 ) led to 3 - fold more vldl output than the ( 12 : 0 + 14 : 0 ) diet , and that the ( 12 : 0 + 14 : 0 ) diet produced a larger ldl pool and a poorer ( lower ) hdl / ldl ratio . the authors interpreted this to mean that dietary ( 12 : 0 + 14 : 0 ) fatty acids were worse than 16 : 0 ( and 18 : 1 ) in terms of raising ldl , presumably because ( 12 : 0 + 14 : 0 ) down - regulate the ldl r making it difficult for vldl remnants and ldl particles to be cleared by the liver . this ultimately causes ldl to accumulate . in a third monkey study ( khosla et al ., 55 am . j . clin . nutr . 51 , 1992 ) the effect of high dietary intake of sat 16 : 0 in the form of palm oil , versus high dietary intake of mono 18 : 1 in the form of high oleic safflower oil , and also versus high dietary intake of poly 18 : 2 in the form of high linoleic safflower oil was examined . here the tc response was animal species specific , with all three fats causing an equal tc response in rhesus . however the high dietary 18 : 2 ( at 30 % en ) produced lower tc in the cebus species by virtue of an undesirable depressed hdl - c level while the ldl - c was unaffected by all three diets in both species . these data indicated that genetic differences can affect the sensitivity to 18 : 2 in the diet , but that 16 : 0 , 18 : 1 , and 18 : 2 can appear to exert similar effects when lipoprotein metabolism is unimpaired and when essentially no dietary cholesterol is present to interfere with lp metabolism ( especially by decreasing ldl receptor number and ldl clearance rate ). an interesting observation and measurement recorded in the above cited study and unexplained until now was a favorable hdl / ldl ratio which was greater in monkeys fed the 16 : 0 - containing sat diet than the mono or poly diet . this observation contradicted the generally held belief that dietary sats should be avoided in favor of polys and monos . however , this early measurement taken together with the more extensive new data provided in appendix i now indicate that saturated fatty acids are a necessary dietary component for increasing hdl and increasing the hdl / ldl ratio in the serum . in other previous experiments using saturated animal fats blended with polys described in perlman and hayes , supra , it is noted that rodents ( gerbils and hamsters ) and monkeys ( cebus ) exhibited unexpectedly increased hdl / ldl lipoprotein ratios when corn oil ( rich in 18 : 2 ) was blended into animal fats stripped of cholesterol . these data are also consistent with the model now proposed in which a balanced ratio of sats and polys in the diet may be the most important consideration in modulating lipoproteins to increase hdl and maximize the hdl / ldl ratio . the discovery confirming and validating applicant &# 39 ; s new model appears in the human nutritional study involving three different diets described in appendix i ( hereby incorporated by reference in totality , nutrional biochemistry vol 6 : 179 - 187 1995 . the most critical results from this study are summarized in table iii . table iii__________________________________________________________________________hdl concentration in human serum varies with ratio of saturated topolyunsaturated fatty acids in dietary fatdietarydietary fat composition percent dietary energy serum cholesterolfat ( weight percentage ) ( percentage of daily calories ) ( mg / dl concentration )( code ) sat mono poly 16 : 0 sat 18 : 1 mono 18 : 2 poly hdl - c ldl - c tc__________________________________________________________________________can 7 57 36 4 17 6 49 97 177pol 44 45 11 11 13 3 . 5 49 102 181aha 30 37 33 8 12 7 57 96 179__________________________________________________________________________ these diets included one containing low dietary sats combined with moderate polys and high monos ( canola oil diet - abbreviated can ), a second containing high dietary sats combined with low polys and moderate monos ( palm olein - abbreviated pol ), and a third containing moderate dietary sats combined with moderate polys and moderate monos ( soybean oil - palm olein - canola oil blend - abbreviated aha ). indeed , all three fat - containing diets produced equal tc and similar ldl - c , but the aha fat blend increased hdl - c by 20 % ( see table iii ) relative to the other two diets . thus , applicant unexpectedly discovered that normolipemic people ( i . e ., people with normal lipoprotein metabolism and exhibiting serum tc values of & lt ; 200 mg / dl ) appear to require moderate levels of both sats and polys which , in appropriate total dietary amounts , produce an increased hdl concentration and increased hdl / ldl ratio in the serum . in order to provide a general method for maximizing the hdl / ldl ratio in human serum it is useful to understand the physiological basis by which the hdl / ldl ratio may be altered . returning to fig1 and the experimental observations reported on herein , it appears that sats ( 16 : 0 in the above diet ) drive vldl output , maximizing the potential for hdl production ( i . e ., increasing the hdl precursor pool of vldl ). since high dietary levels of monos did not increase hdl while moderate levels of sats did increase hdl , it would appear that 16 : 0 ( not 18 : 1 ) may have been responsible for the greatest vldl output in the previous rhesus study ( khosla et al ., 55 am . j . clin . nutr . 51 , 1992 ). secondly , it seems that an adequate intake of polys [ which must exceed the 3 . 3 % en shown to be sub - optimal in the low - poly diet in the appendix ] is needed to assure up - regulated or stimulated ldl = activity . this level of polys is estimated to be at least 5 - 6 % en and has been described elsewhere as &# 34 ; assuring the 18 : 2 threshold requirement &# 34 ; ( hayes et al ., 6 faseb j . 2600 , 1992 and pronczuk et al ., 8 faseb j . 1191 , 1994 ). this intake of polys also assures that vldl catabolism and ldl clearance proceeds efficiently and rapidly ( decreasing plasma ldl ) while sparing the need for hdl &# 34 ; clean - up &# 34 ; ( ultimately increasing available hdl ). viewed as a balancing process , adequate sats are needed to enhance hdl precursor output ( as vldl ) and adequate polys are needed to keep ldlr up - regulated to enhance ldl and vldl remnant clearance by the liver . together this combination results in the highest hdl and lowest ldl levels in the serum . to applicant &# 39 ; s knowledge neither this combination of fatty acids nor this rationale for metabolic function has ever been recognized , let alone demonstrated in humans prior to this time . the importance of diversifying the dietary intake of polyunsaturated fatty acids to include one or more of the omega3 polyunsaturates [ i . e ., α - linolenic acid ( 18 : 3 , omega3 ), eicosapentenoic acid ( epa ) and docosahexenoic acid ( dha )], in addition to linoleic acid ( 18 : 2 , w6 ), has recently been pointed out by charnock et al . ( 3 rd int . symp . on lipid metabolism in the normal and ischemic heart , sep . 1991 ) and by mclennan et al . ( 19 aust . nz j . med . 1 , 1989 ). according to these investigators , adding the above - mentioned omega3 polyunsaturated fatty acids to the diet improved the mechanical performance and the electrical stability of the marmoset heart . in this animal model the incidence of ventricular fibrillation was reduced while ventricular ejection , peak filling rate and end diastolic volume increased when compared to animals fed similar diets containing only polyunsaturates of the w6 type , e . g ., linoleic acid . in marmosets fed saturated animal fats in place of comparable amounts of sunflower oil ( linoleic acid - rich oil ) or fish oil ( omega3 - rich oil ), cardiac performance deteriorated significantly with respect to both mechanical and electrical parameters . as taught in the present invention , there are several straightforward means of providing a mix , and controlling the balance of saturated and polyunsaturated fatty acids in ones daily dietary fat . in the extreme case , the strictly controlled use of liquid and / or solid dietary formulations which provide all of the dietary fat can be used to insure this balance . in a moderately controlled setting , institutional preparation of food for resident populations allows the monitored use of fats , e . g ., hospital , university , and military kitchens , in which appropriately balanced fat blends can be used throughout the food preparation scheme . in addition , manufacturers of prepared food such as commercial bakers can use appropriately balanced blends of fats and oils . two parts palm oil ( 44 % palmitic acid , 9 % linoleic acid ) are blended with one part corn oil ( 11 % palmitic acid , 58 % linoleic acid ) to provide a balanced fat blend containing approximately 33 % palmitic acid ( 16 : 0 ) and 25 % linoleic acid ( 18 : 2 ). when consumed as the principal and essentially the sole source of dietary fat in the daily diet , and representing approximately 30 % of the dietary energy this fat blend will increase the level of hdl cholesterol in human serum and the hdl / ldl ratio compared to a similar diet in which the proportion of either palmitic acid or linoleic acid is 3 - fold lower . one part palm oil ( 44 % palmitic acid , 9 % linoleic acid ) is blended with one part cottonseed oil ( 23 % palmitic acid , 52 % linoleic acid ) to provide a fat blend containing approximately 34 % palmitic acid and 31 % linoleic acid . one part palm oil is blended with one part soybean oil ( 10 % palmitic acid , 51 % linoleic acid and 7 % linolenic acid ) to provide a fat blend containing approximately 27 % palmitic acid , 30 % linoleic acid and 3 % linolenic acid . alternatively , one part coconut oil ( approximately 70 % lauric , myristic , and palmitic acids , and 2 % linoleic acid ) is blended with one part sunflower oil ( 6 % palmitic acid , 66 % linoleic acid ) to provide a different balanced fat blend containing approximately 38 % c12 - c16 mixed saturated fatty acids and 34 % linoleic acid . alternatively , in a three component system , one part palm kernel oil ( 47 % lauric acid , 16 % myristic acid , 8 % palmitic acid , and 2 % linoleic acid ) is blended with one part corn oil ( 11 % palmitic acid and 58 % linoleic acid ) and one part canola oil ( 4 % palmitic , 20 % linoleic acid and 9 % linolenic acid ) to provide a fat blend containing 29 % c12 - c16 mixed saturated fatty acids , 27 % linoleic acid , and 3 % linolenic acid . in another three component system termed the aha blend ( see table i ), four parts palm oil are blended with five parts soybean oil and one part canola oil to provide a fat blend containing 26 % palmitic acid , 29 % linoleic acid , and 3 % linolenic acid . in still another three component system , three parts palm olein ( 39 % palmitic acid , 11 % linoleic acid ) are blended with one part cottonseed oil ( 23 % palmitic acid , 52 % linoleic acid ) and one part safflower oil ( 6 % palmitic acid , linoleic acid ) to provide a fat blend containing 29 % palmitic acid and 32 % linoleic acid . oxidation - resistant fat blends for food preparation as well as for increasing the hdl concentration and the hdl / ldl ratio consistent with examples 1 and 2 , blends useful for increasing the hdl level and the hdl / ldl ratio in human serum include four to nine parts palm olein ( 39 % palmitic acid , 11 % linoleic acid ) blended with one part of corn oil ( 11 % palmitic acid , 58 % linoleic acid ) to provide a dietary fat blend containing approximately 33 % to 36 % palmitic acid and 20 % to 16 % linoleic acid . similarly , two parts palm olein are blended with one part of corn oil to provide a fat blend containing approximately 30 % palmitic acid and 27 % linoleic acid . likewise , as illustrated in example 1 , two parts palm oil are blended with one part corn oil for use as a dietary fat . these and other blends of vegetable fats and oils have been found to be valuable as ingredients in baked , fried , and other prepared foods , e . g ., salad dressings , desserts , etc . because of the increased oxidative stabilities of these blends in combination with their metabolic benefits already described . the increase in oxidative stability for the polyunsaturated vegetable oil component in these blends is reflected in a longer shelf life for foods prepared using these blends , and a longer cooking ( i . e ., frying ) lifetime for these blends when they are maintained at an elevated temperature ( approximately 350 ° f .) for many hours . by way of specific example , when blended with palm oil or palm olein , the oxidation - resistance of certain polyunsaturated vegetable oils is increased relative to that of the same oil when heated separately from the blended composition . in this example and in table iv , the stability of various oils and blends was measured by the rancimat method in which the oxidative stability is directly proportional to the rancimat number provided . a fat blend in which the oxidative stability of the blend is at least 25 % greater than that of the polyunsaturated vegetable oil component in the blend is considered an oxidation - resistant blend for the purposes of this invention . the extent of oxidation - resistance in such blends has been found to vary widely depending upon the type of vegetable oil ( e . g ., corn versus soybean oil ) and the extent of its dilution into the saturated fat such as palm fat . accordingly , it is apparent from table iv that at higher dilutions of polyunsaturated vegetable oils ( e . g ., 5 - fold and 10 - fold dilutions of soybean oil into the palm fats ), the fat blends maintains good stability . however , when diluted only 3 . 3 - fold ( see 2 . 3 : 1 column in table iv ), and within the composition range nutritionally useful in the present invention , the oxidative stability of the soybean oil - palm fat blends can fall to approximately the same level as the unblended vegetable oil ( cf . 7 . 6 and 5 . 6 for the blends versus 6 . 3 for the soybean oil alone ). surprisingly however , table iv reveals that corn oil can be stabilized against oxidation at both lower ( 3 . 3 - fold ) and higher ( 5 and 10 - fold ) dilutions with palm fat . thus , the oxidative stability of the corn oil - palm blends is at least two - fold greater than the corn oil alone ( cf . 11 . 2 and 9 . 9 for the lower dilution blends versus 4 . 8 for the corn oil alone ). the results from this table and from previous unpublished experiments of applicant have shown that the oxidative stability of fat and oil blends is unpredictable and can only be determined by experimentation . it is significant that the proportions of a number of fats and oils in such blends which are useful in the diet for controlling cholesterol levels as taught herein , are also useful owing to their oxidative stabilities . table iv______________________________________oxidative stability of fat blends ( rancimat method *) ______________________________________polyunsaturated ratio ( palm olien : polyunsaturated oil ) oil 9 : 1 4 : 1 2 . 3 : 1______________________________________soybean 16 14 . 4 7 . 6corn 16 . 7 13 . 5 11 . 2soybean 14 . 4 10 . 2 5 . 6corn 15 . 3 12 . 2 9 . 9______________________________________oxidative stability of pure fats and oils______________________________________ palm olein 20 palm oil 21 . 2 soybean oil 6 . 3 corn oil 4 . 8______________________________________ * the rancimat method determines the oxidative and thermal stability towards oxidative decomposition in oils and fats . the oil sample is exposed to a stream of atmospheric oxygen at elevated temperatures giving rise to organic acids in the oil / fat . these volatile products are trapped in a measuring vessel filled with distilled water and continuously detected with a conductivity cell . the measurements are then evaluated by a control unit which records the induction time of the sample . the progress of the oxidation curve determined in this manner virtually parallels the development of the peroxide values in the oils being tested
a method of increasing the hdl concentration and the hdl / ldl concentration ratio in human serum by providing a balance between a sufficient and required proportion of cholesterol - free saturated fatty acids in the daily dietary fat of the human and a sufficient and required , but not excessive , proportion of polyunsaturated fatty acids comprising linoleic acid in dietary fat , while the remaining proportion of fatty acids and energy from the dietary fat is provided by monounsaturated fatty acids comprising oleic acid . the saturated fatty acids must constitute between 20 % and 40 % by weight of the daily dietary fat based upon dietary fat accounting for 30 % of the total dietary energy consumption , and linoleic acid must constitute between 15 % and 40 % by weight of dietary fat . in this way , the required proportional intake of polyunsaturated fatty acids enhances the formation of hdl from vldl and / or decreases the clearance of hdl , while an excessive proportional intake of polyunsaturated fatty acids and monounsaturated fatty acids is avoided to assure a sufficient dietary availability of saturated fatty acids which are required for sufficient vldl synthesis and hdl production .