Ralph T. Holman*, Susan B. Johnson**, Douglas M. Bibus*
Theo C. Okeahialem *** and Peter O. Egwim***
*The Hormel Institute, University of Minnesota
801 16th Ave. NE
Austin, MN 55913
** Present address: The Mayo Clinic
Rochester, MN 55905
***College of Medicine Univeristy of Nigeria
Correspondence should be addressed to: Ralph T. Holman, PhD.
*The Hormel Institute, University of Minnesota
801 16th Ave. NE
Austin, MN 55913
Tel: 507 433 8804
Submitted for publication: September 1996
Keywords: essential fatty acids, polyunsaturated, hydrogenated, ethnic, African, American,
The purpose of this study was to investigate the essential fatty acid status of a population from
Africa who consume low levels of hydrogenated fat and natural sources of fat derived from fish,
meats and vegetables. Plasma samples from 38 healthy adult Nigerians from Enugu, 25 rural
and 13 urban, were analyzed for their essential fatty acid status. Plasma lipids from
phospholipid (PL), non-esterified fatty acids(NEFA), triglyceride (TG) and cholesteryl ester (CE)
were extracted, derivatized and analyzed by capillary gas chromatograph and are expressed as
% composition +/- SEM. The Nigerian data were compared to our standard control group which
consists of 100 normal Minnesotans. Nigerian subjects had markedly higher amounts of total and
individual w3 acids when compared to Minnesotans for all lipid classes tested. Plasma PL total
w3 was 13.4+/-0.70 compared to MN controls, 5.53+/-0.13, p<0.001, or a 2.42 fold increase. Similar
increases in total w3 were observed for TG, NEFA and CE, 2.67, 2.79 and 2.90 times control,
respectively. Plasma PL 20:5w3, 22:5w3 and 22:6w3, 3.80+/-0.45, 1.26+/-0.06, 8.11+/-0.31, were all
significantly elevated versus MN controls, 0.59+/-0.03, 1.13+/-0.03, 3.59+/-0.11. Increased levels of
w3 acids were partially offset by significant decreases in w6 acids. Plasma PL 18:2w6 and
20:4w6, 18.61+/-0.62 and 8.38+/-0.27, were significantly decreased versus control, 23.90+/-0.28 and
12.81+/-0.19. In conclusion, Nigerians have significantly higher amounts of plasma w3 acids than
do Minnesota controls, largely offset by decreased levels of w6 acids that may be related to the
absence of hydrogenated fat in the Nigerian diet.
The essential fatty acids are defined as linoleic (18:2w6) and alpha-linolenic (18:3w3) acids and
their elongation and desaturation products. Essential fatty acids are required for membrane
integrity, visual and neurological function and their deficiency is associated with neurological
and immunological disease (7-11). This study was initiated with the
intent to describe the fatty acid profiles in the four major classes of plasma lipids, the
phospholipids (PL), cholesteryl esters (CE), triglycerides (TG) and non-esterified fatty acids
(NEFA) in a population that does not consume significant levels of hydrogenated vegetable oils. This would allow evaluation of essential fatty acid (EFA) status with
respect to w3 fatty acids (FA) and w6 FA, and would permit comparison to a free-living
American population known to consume partially hydrogenated vegetable
oils as a major dietary source of its dietary fat. The data presented here concern the essential
fatty acid (EFA) status of the Ibo people of eastern Nigeria, who had little access to partially
hydrogenated vegetable oils in 1989 when this study was begun, in comparison to a typical
American group, for which partially hydrogenated vegetable oil is a common source of dietary
Subjects: The subjects were healthy volunteers, aged 19 to 42 years of age. In our previous
studies of EFA content of plasma lipids (1, 2) , we had observed no
significant sex or age differences in the levels of individual fatty acids or of related groups of
fatty acids. The present study was a comparison of adult Nigerians to adult Minnesotans. The
rural subgroup comprised 25 Nigerian rural subjects,10 male and 15 female, with mean age of
33.8 yr from farming towns within 40 km from Enugu. The urban subgroup comprised 13 urban
subjects, 6 male and 7 female, with a mean age of 34.3 years, who were residents of Enugu. The
female subjects were non-pregnant, non-lactating, multiparous mothers, aged 30 to 40 years,
who accompanied their children to the pediatric outpatient clinic at the University of Nigeria
Teaching Hospital in Enugu. The males were members of their families. Only those were
recruited who were found free of serious illness or health abnormalities upon medical
examination by a physician. All subjects were from the Ibo ethnic group. Following informed
consent, they were classified into two subgroups, rural or urban, based on the place of domicile.
Information about their nutritional background and dietary habits and preferences were solicited
The control group of 100 omnivorous healthy adults, volunteers among the students and
staff of the University of Minnesota, were the control group in a study investigating the effects of
vegetarianism upon EFA status, also conducted in 1989 (3).
Comparison of Rural and Urban Nigerian Populations. The plasma PL of the group of 25 rural
subjects and of the group of 13 urban Nigerians were first compared with each other to reveal
differences in fatty acid pattern due to place of residence. The profile of 25 rural Nigerians
compared to 13 urban Nigerians is shown in Figure 1. Of all the
detected fatty acids, only two minor fatty acids, 14:0 and 22:0, were found to differ significantly
between the two groups. Because no significant difference was found for any of the w3 or w6
fatty acids, we considered the two groups as equal, so the entire composite Nigerian population of
38 subjects was grouped together for comparison to our group of 100 Minnesota control subjects.
The Fatty Acid Profile of Plasma Phospholipids (PL), for all 38 Nigerian subjects in comparison
to our 100 Minnesota normal controls (3), is shown graphically in Figure 2 and in tabular form in Table 1. The
levels of all w6 fatty acids in PL were found to be less than in our Minnesota controls, all of
which were significant, except for 18:3w6. In contrast to the w6 EFA, the levels of all the
individual w3 EFA were significantly elevated above the Minnesota control group. The mean
total of w3 FA in the phospholipid FA of the Nigerians was 2.43 times as high as in our
Minnesota control, p < 0.001. In contrast, the mean total w6 EFA in the PL FA of Nigerians
was 0.72 times that of Minnesotans, p < 0.001. Although these major differences in the
proportions of the two families of EFA occurred, they did not cause major changes in total
saturated fatty acids or monounsaturated acids. Total saturated fatty acids were higher in the
Nigerians than in the Minnesotans by the small but significant factor of 1.16, p < 0.001. Total
monoenoic acids were lower in Nigerians, at 98% of the Minnesotans' content, p < 0.05.
The Fatty Acid Profile of Plasma Cholesteryl Esters (CE), for all the Nigerian subjects
compared to Minnesota controls is shown graphically in Figure 3 and
given numerically in Table 2. The graphic profile of the CE indicates
that 18:2w6, 20:3w6 and 20:4w6 were significantly lower in Nigerians than in Minnesotans,
whereas all w3 FA were significantly elevated. The total of w6 FA in the CE of Nigerians was
79% of the level in Minnesotans, whereas the total of w3 FA was 2.9 times the level found in
Minnesotans. Accompanying shifts in the saturated and monounsaturated acids also occurred in
this comparison. Increased 16:0, but decreased 18:0, accompanied the low w6 level and the high
w3 level in the Nigerians.
The Fatty Acid Profile of Plasma Triglycerides (TG), for all the Nigerian subjects
compared to the Minnesota controls is shown graphically in Figure 4
and given numerically in Table 3. The graphic profile of the TG
indicates that the individual w6 acids and the total w6 acids were lower in the Nigerians than in
the Minnesotans. The total of w6 FA in the TG of Nigerians was 73% of the level found in
Minnesotans, whereas the total of w3 FA was 2.67 times the level found in Minnesotans.
Accompanying shifts in the saturated and monounsaturated fatty acids also occurred in this
comparison. In plasma TG, 16:0, 18:0, 20:0 and 22:0 were significantly lower in Nigerians than
in Minnesotans. Among the monoenoic acids, a major acid 16:1 was significantly lower,
whereas a minor acid 22:0, was significantly higher in the Nigerians.
The Fatty Acid Profile of Plasma Non-esterified Acids (NEFA), for all the Nigerian
subjects compared to the Minnesota controls, is shown graphically in Figure
5 and shown numerically in Table 4. The fatty acid profile of the
NEFA indicates a significantly lower 18:2w6 and significantly higher 20:2w6 and 22:4w6 in
Nigerians than in Minnesotans. However, among the w3 EFA, 18:3w3 was not significantly
different in the two populations , but its metabolic products were all dramatically and
significantly higher in the Nigerians. The total of w6 FA was lower in the Nigerians, 86% as
much as in Minnesotans, but the total of w3 EFA was 2.79 times higher in the Nigerians than in
The data from all four lipid classes show that the w3 EFA status of Nigerians is more
than twice as high as is the status of our Minnesota controls. For PL the ratio is 2.43, for CE
2.9, for TG 2.67, and for NEFA 2.79. Increased levels of w3 FA were predominantly offset by
decreased levels of w6 FA, and they were accompanied by increased levels of 16:0, p < 0.001.
Food selection and habits in rural and urban Nigeria: The level of intake and the selection of
local food staples depends upon the seasonal availability of foodstuffs. The caloric intake is
high, but may fail to meet nutritional requirements, due to cost constraints, especially in the rural
communities. The major carbohydrate-rich staples are the starchy tubers such as yams, cocoa-
yams and cassava, the cereals rice and maize, and minor foods such as plantains and bananas.
The major protein staples include legumes such as beans and pulses, seeds, nuts, cereal proteins
and leaf proteins, some of which are rich in 18:3w3. Animal protein sources such as milk and
eggs are virtually nil for rural communities, and are very limited for the urban population.
Meats and fish, good sources of polyunsaturates, are in limited supply. Crayfish and dried fish
are important but cost constraints limit intake.
The major dietary source of fat in the area is fresh palm oil, which is most affordable, is
produced by rural families and is unhydrogenated. Unprocessed groundnut (peanut) oil is
popular but expensive. Imported oils, many of which are hydrogenated, are infrequently
consumed due to cost, especially for rural families. Minor seasonal fat and oil sources include
the oil seeds such as groundnuts, melon, pumpkin, maize, bush mango seed and coconut. The
latter items are more available to the rural population than to the urban population. Breadfruit
and pears are also available to the rural population in greater amount than to the urban
population. Fats and oils from unusual protein sources of animal origin include the snail
Vicapara quadrata , the crayfish Palamonetes varians, grasshoppers, and locusts. Edible leaf- or
stem-larvae are available rurally, whereas only snails and crayfish are available in urban markets.
From these dietary notes it was apparent that the rural and urban Nigerian populations
are similar with respect to major foodstuffs available, their food preferences and habits. Their
major sources of calories, lipoproteins and lipids are relatively similar. Actual intake of calories
may not be significantly different in the two subgroups. Urban subjects were more likely to be
exposed to the processed vegetable oils, especially the imported varieties which would contain
isomerized unsaturated fatty acids, which may explain the slightly lower levels of the w3 EFA
measured in the plasma PL of the urban subjects as compared to rural subjects. Rural subjects
were more likely to ingest a variety of unusual seasonal sources of animal and plant protein
sources such as snails, mushrooms, edible larvae, locusts and grasshoppers. Information on their
constituent fatty acids are not available, but it would seem likely that they include w3 EFA,
derived from fresh leaves, generally known to contain linolenic acid. It would appear that 18:3w3
may be the predominant w3 FA present in the diet of both groups.
It is apparent from the above dietary notes and from the comparison of the rural and
urban groups presented in Figure 1, that the rural and urban
subgroups are not significantly different with respect to their available foodstuffs and that they
are not significantly different with respect to the profiles of their plasma phospholipids.
Therefore for purposes of comparison with Americans from Minnesota, we combined the urban
and rural groups into one group of Nigerians.
EFA Status of Other Ethnic Control Groups Studied in This Laboratory: Our first
attempt at assessing EFA status was a survey of the four major lipid classes from 200 patients
hospitalized for reasons not related to metabolic diseases (1). We found
no significant correlation versus either age or sex for any individual fatty acid or group of fatty
acid, although graphic correlations showed slight trends. In that study, conducted in 1978, we
found that the total w6 acids in plasma PL were 37.47 +/-5.51 % of the total FA, and that total w3
acids were 4.28 +/- 3.49 %. The variation in the individual values was considerable, probably due
to the fact that the subjects were patients, and that disease affects the EFA pattern, as we now
know. The total w3 EFA (Sw3) of this group of hospitalized patients without metabolic diseases
was lower, 77% of the value for our 100 Minnesota healthy controls .
In a study of Sjogren-Larsson Syndrome, a genetic neuropathy occurring in northern Sweden, we
had occasion to measure the EFA status of a normal adult local population as a standard of
comparison ( 3 ). Those healthy controls from the same area, Umea, (were
found to have 12.43 +/-1.70 % total w3 EFA and 35.8 +/-1.06 % total w6 FA. An unpublished study
of the Keralites of the Malabar Coast of India, made in cooperation with Parinandi, Raj and
Ramasarma, revealed that Keralites' plasma PL contained 10.4 +/-0.63 % total w3 EFA. An
unpublished study in cooperation with Malmros and Fex found that a normal population from
Malm (in southern Sweden) had 8.68 +/-0.73 % total w3 EFA in the plasma PL, 1.88 times that of
Minnesotans. Normal Australians ( 4 ) were found to have 7.35
+/-0.33 % total w3 EFA in their plasma PL, 1.33 times that of Minnesotans. We have found, in an
unpublished cooperation with Bussarow and Berberian, that normal Bulgarians have 5.26 +/-0.42
% total w3 EFA in their plasma PL, 95% as much as Minnesotans. In an unpublished study
with Kretchmer and his colleagues, we have observed Australian aborigines to have 4.69 +/- 0.12
% total w3 in their plasma PL, 85 % of the level in Minnesotans.
The above data from our laboratory indicates a range of total w3 EFA , from 13.4
+/-0.70 (Nigerians) down to 3.57 +/- 0.19 (American infants) in presumably normal humans, a range
of 9.83 %. The Minnesota control group value we customarily use as standard, lies at 5.53 %
of total FA of plasma PL, or 1.96 above the lowest "normal" value. Our Minnesota controls lie at
the 20th percentile of the range we have encountered in this laboratory. We question whether the
20th percentile of the current range is truly "normal" or adequate. We also wonder whether we
should continue to use it as a standard for comparison of other populational groups. We know of
no other element or required substance, where the criterion is set at 20% of its known range of
concentration in the human body.
Recently our laboratory has been also studying the EFA status of patients suffering from a variety
of diseases. The progress of that research has been summarized and reviewed periodically
(8-11). The w3 status of patients suffering from a variety of diseases
associated with impairment of the immune system and/or with neuropathy has been found to be
significantly below "normal", in comparison to the level found in our Minnesota "normal"
population. That is to say, neuropathies and impairment of the immune response are associated
with w3 levels which are significantly lower than our Minnesota controls, significantly lower
than the 20th percentile of the observed range of normal groups we have studied, significantly
lower than 5.35% of total fatty acids of plasma PL.
These studies led to the concept of competition between w6 and w3 fatty acids at each level of the
metabolic cascade (14). The fatty acid pool available for synthesis of
structural lipids contains all the fatty acids which occur in the lipids of the diet, and all the
components of the fatty acid pool compete for the same enzymes as do the w3 and w6 EFA (15). The structures of the fatty acids and their relative concentrations
govern their competition.
The conversion of oleic acid to 20:3w9 is inhibited by even low levels of linoleic acid in the diet,
but the conversion of linoleic acid to arachidonic acid can be inhibited only by high ratios of oleic
to linoleic acid in the diet (21). That is, oleic acid is a relatively weak
competitor to linoleic acid.
When oils containing PUFA are subjected to metal-catalyzed hydrogenation, the catalysts cause
movement of the unsaturation up and down the carbon chain. If the hydrogenation is stopped
before it is complete, it leaves a series of positional monoenoic acid isomers with the double bond
located randomly within the fatty acid chain. Two-thirds of each positional isomer is trans, and
one third is cis. Most of these isomers have not been found in nature, and these monoenoic acids
are also competitive with natural fatty acids for enzyme sites (22) and are
precursors of unusual polyunsaturated fatty acids (23).
The American food supply is increasingly turning toward partially hydrogenated fats and toward
oils containing 18:2w6 as sole or dominant polyunsaturated acid, for reasons of economy and
convenience, ignoring the essentiality of the w3 PUFA. This tendency is driven by the
merchandising system which attempts to provide products which are heat stable, incapable of
autooxidation, and have an extended shelf-life. This has been accomplished at the cost of losing
the w3 EFA necessary for protection against disease, notably diseases which adversely affect the
nervous and immune systems (10). The Nigerian population clearly had
a richer w3 supply than did our Minnesota controls 7 years ago. The current states of Nigerians
and of Minnesotans have not been measured.
Analysis of the fatty acid composition of the plasma lipids of a group of healthy adult Nigerians
and a comparable group of healthy Minnesotans has revealed that the Nigerians have more than
twice as much essential w3 EFA in their plasma lipids as do Minnesotans. Minnesotans lie at the
10th percentile of the range encountered in presumably healthy humans. American newborn
infants are the lowest group of healthy humans in our list. We question whether these are
adequate levels for optimum health and development.
This study was supported by the Hormel Foundation, Scotia Pharmaceuticals Ltd. of England
and the Essential Nutrient Research Corporation (ENRECO).