Public Health Nutrition: 12(4), 525–530 doi:10.1017/S1368980008002814
Linolenic acid and folate in wild-growing African dark leafy
vegetables (morogo)
Anna M van der Walt1,*, Mohamed IM Ibrahim1, Cornelius C Bezuidenhout1 and
Du Toit Loots2
1School of Environmental Sciences and Development, North-West University (Potchefstroom Campus), Private
Bag X6001, Potchefstroom 2531, South Africa: 2School of Physiology, Nutrition and Consumer Sciences,
North-West University (Potchefstroom Campus), Potchefstroom, South Africa
Submitted 12 April 2007: Accepted 12 March 2008: First published online 27 May 2008
Abstract
Background: Transition from a low-fat vegetable-rich rural diet to a high-fat
Westernised diet is considered a factor in the escalating occurrence of vascular-
related diseases and type 2 diabetes in urban black South Africans. Consumption
of morogo is a distinguishing feature of rural African diets.
Objective: To determine fatty acid profiles and folate contents of three widely
consumed, wild-growing, African dark green leafy vegetables (morogo).
Design: GC–MS was applied for analysis of fatty acid composition and a validated
microbiological assay conducted to determine folic acid contents of wild-growing
morogo sampled from deep rural villages in three different geographical regions
of South Africa.
Results: Measured fatty acids ranged from 1610?2 to 2941?6mg/100 g dry mass,
with PUFA concentrations 1?4 to 2?8 times those of SFA. Calculated from the
relative percentages of linoleic acid (18 : 2n-6) and linolenic acid (18 : 3n-3), the
ratio of 18 : 2n-6 to 18 : 3n-3 PUFA was 1?0:3?4 to 1?0:8?9. The only MUFA was
palmitoleic acid (16 : 1), measured at 34?7 (SD 0?3) to 79?0 (SD 9?3) mg/100 g dry
mass, and the predominant SFA was palmitic acid (16 : 0), measured at 420?6
(SD 83?3) to 662?0 (SD 21?2) mg/100 g dry mass. Folic acid concentration varied
from 72 to 217mg/100 g fresh sample.
Conclusion: Morogo is low-fat food item high in folate and with 18 : 3n-3 in excess
of 18 : 2n-6, the proposed anti-inflammatory effects of which may lower risks of
vascular-related chronic diseases and type 2 diabetes.
Keywords
African diet
Traditional vegetables
Morogo
Polyunsaturated fatty acids
Folate
Chronic lifestyle-related cardio- and cerebrovascular dis-
eases (CVD) and type 2 diabetes are becoming more pro-
nounced in urbanised black South Africans(1). Levitt and
Mollentze(2) predicted that type 2 diabetes could affect over
3 million South Africans by 2010. The occurrence of these
lifestyle-related chronic diseases apparently does not dis-
criminate on a socio-economic basis(1,3,4). Currently, dietary
transition from a traditional low-fat, plant protein-rich rural
diet towards a high-fat, animal protein-rich Westernised diet
receives much attention as a factor contributing to the
increased occurrence of chronic diseases of lifestyle in
urbanised black South Africans(5,6). In rural diets, a variety of
cultivated and/or wild-growing African dark green leafy
vegetables (morogo) supplement traditional maize-based
staples(7). Concerning micronutrient levels, morogo vege-
tables compare well with spinach, Swiss chard and cab-
bage(8–10). Dark green leafy vegetables (DGLV) are also
indicated as rich sources of folate(11,12) and linolenic acid
(18 : 3n-3)(13–15). Nutritional data on cultivated varieties of
traditional African vegetables are fragmentary and almost
non-existent for wild-growing morogo species. The present
study reports on the fatty acid profiles and folate contents of
three wild-growing morogo species: cowpea (munawa),
vegetable amaranth (thepe) and spider flower (lerotho; also
known as African cabbage or cat’s whiskers).
Materials and methods
Sample collection and preparation
Sampling sites were situated in three geographically
separated and climatically distinct areas of South Africa.
One fresh field sample of each morogo type, i.e. amar-
anth, spider flower and leafy cowpea, were collected
from rural villages respectively in the Rustenburg District
(North-West Province), as well as Vhembe and Capricorn
Districts (Limpopo Province). One traditionally sun-dried,
household sample of spider flower was obtained from
*Corresponding author: Email Retha.VanDerWalt@nwu.ac.za r The Authors 2008
a rural family in Capricorn District. Samples were trans-
ported to the laboratory in Ziploc
R plastic bags on ice.
Upon arrival at the laboratory, the fresh samples were
freeze-dried and stored at 2208C until analysis. Finely
ground, freeze-dried sample material and the traditionally
sun-dried material were subsequently used for fatty
acid analysis. Samples for folic acid determinations were
weighed accurately before oven-drying at 1058C for approx-
imately 1h until oven-dried weight remained constant.
Moisture loss was recorded for use as a dry to wet mass
conversion factor in calculations of folate concentrations
in fresh leaves.
Chemicals
All organic solvents used were of GC grade and, together
with fatty acid standards, were purchased from Sigma-
Aldrich Corp. (St. Louis, MO, USA).
Folic acid analysis
Freeze-dried morogo samples were sent to the South
African Bureau of Standards (Pretoria, South Africa) for
folic acid analysis. A standard method for the micro-
biological assay of folic acid in foods and pharmaceutical
products was employed(16,17). Streptococcus faecalis
(ATCC 8043; American Type Culture Collection, Manassas,
VA, USA) was the test organism. Materials included USP
folic acid standard (Merck, Darmstadt, Germany), Difco
Bacto-folic AOAC medium (code 0967; Becton Dickinson
Microbiology Systems, Sparks, NV, USA) and Oxoid MRS
agar (code CM 361; Oxoid Ltd, Basingstoke, UK) as culture
media; and Oxoid MRS agar (code CM 359; Oxoid Ltd)
to prepare the inoculum. Folic acid detection limit was
0?0005mg/ml. Dry mass concentrations were converted
for expression as mg/100 g wet mass.
Fatty acid determinations
Heptadecanoic acid (72 mM), as an internal standard, was
added to 25mg of lyophilised sample followed by 100ml
of a 45mM solution of butylated hydroxytoluene and 2ml
of methanolic HCl (3 M). The mixture was subsequently
vortexed before incubation at 908C for 4 h. Following
cooling to room temperature, the sample was extracted
twice with 2ml of hexane, dried under an N2 stream and
finally re-suspended in 100ml of hexane, 1ml of which
was injected into the GC–MS system via split-less injec-
tion. An Agilent 6890 gas chromatograph ported to a 5973
mass selective detector (CA, USA) was used for identifi-
cation and quantification of individual fatty acids. For the
acquisition of an electron ionisation mass spectrum, an
ion source temperature of 2008C and electron energy of
70 eV were used. The gas chromatograph was equipped
with a SE-30 capillary column (Agilent, Palo Alto, CA,
USA), a split/split-less injection piece (2508C) and a direct
GC–MS coupling (2608C). Helium (1ml/min) was used as
the carrier gas. An initial oven temperature of 508C was
maintained for 1?5min and then allowed to increase to
1908C at a rate of 308C/min. The oven temperature was
maintained at 1908C for 5min and then allowed to
increase at a rate of 88C/min to 2208C, this temperature
being maintained for 2min. Finally, ramped at a rate of
38C/min, the oven temperature was maintained at 2308C
for 24min. All samples were analysed in triplicate and
reported as the mean and standard deviation of con-
centration in mg/100 g.
Statistical analyses
Data of fatty acid analyses were processed using the
STATISTICA Data Analysis Software System version 7?1
(StatSoft, Inc., Tulsa, OK, USA). Statistical evaluation of
measured folic acid concentrations employed statistical
techniques included in a computerised data processing
program of the South African Bureau of Standards.
Results
Botanical species identification
Amaranth (thepe) samples were identified as Amaranthus
hybridus L. subsp. cruentus (L.) Thell. (Rustenburg),
Amaranthus hybridus L. subsp. hybridus var hybridus
(Vhembe) and Amaranthus thunbergii Moq. (Capricorn).
Spider flower (lerotho) from Rustenburg and Capricorn
were in both instances identified as Cleome gynandra L.
and cowpea (munawa) as Vigna unguiculata (L.) Walp.
subsp. unguiculata (Table 1).
Folate contents
Results of the folic acid determinations (Table 1) indicated
considerable variation in folic acid concentrations in
Table 1 Folic acid contents and botanical species identification of wild-growing amaranth, spider flower and cowpea: sampling sites were
situated in three geographically separated and climatically distinct areas of South Africa (Rustenburg District, North-West Province;
Vhembe and Capricorn Districts, Limpopo Province)
Plant species Study area
Folic acid content
(mg/100g fresh sample)
Amaranthus hybridus L. subsp. cruentus (L.) Thell. (amaranth/thepe) Rustenburg 72
Amaranthus hybridus L. subsp. hybridus var hybridus (amaranth/thepe) Vhembe 122
Amaranthus thunbergii Moq. (amaranth/thepe) Capricorn 130
Cleome gynandra L. (spider flower/lerotho) Capricorn 217
Vigna unguiculata (L.) Walp. subsp. unguiculata (cowpea/munawa/dinawa) Vhembe 154
526 AM van der Walt et al.
morogo: 217mg/100 g fresh weight (spider flower, Capri-
corn), 154mg/100g fresh weight (leafy cowpea, Vhembe),
122mg/100 g fresh weight (amaranth, Vhembe), 130mg/
100 g fresh weight (amaranth, Capricorn) and 72mg/100 g
fresh weight (amaranth, Rustenburg).
Fatty acid profiles
Total measured fatty acid concentrations (Table 2) ranged
from 1610?2mg/100 g dry mass in Capricorn amaranth to
as high as 2941?6mg/100 g dry mass in spider flower of
Rustenburg. The major PUFA detected in all samples
included linolenic acid (18 : 3n-3), ranging from 753?8
(SD 48?6) to 1629?7 (SD 77?1) mg/100 g dry mass, and
linoleic acid (18 : 2n-6), ranging from 110?8 (SD 7?1) to
506?3 (SD 47?2) mg/100 g dry mass. Palmitic acid (16 : 0),
the predominant SFA, varied between 420?6 (SD 83?2) and
662?0 (SD 21?2) mg/100 g dry mass and the only MUFA,
palmitoleic acid (16 : 1), ranged between 34?7 (SD 0?3) and
79?0 (SD 9?3) mg/100g dry mass. Table 3 indicates the
relative percentages of SFA and PUFA in terms of the total
measured fatty acid concentrations. The ratio of SFA
to PUFA ranged from 1?0:1?4 to as high as 1?0:2?8, and PUFA
contents from 51?5% (Vhembe amaranth) to 73?5%
(Vhembe cowpea leaves). Notable variations were observed
in measured concentrations of both 18 : 2n-6 and 18 : 3n-3
in samples of the same plant genus but from different
species or different localities. The highest dry mass con-
centrations of PUFA (Table 2) were found for Rustenburg
samples of amaranth and spider flower, with values for
18 : 2n-6 of 506?3 (SD 47?2) and 385?7 (SD 9?7) mg/100g dry
mass, respectively and for 18 : 3n-3 of 1183?9 (SD 114?9)
and 1554?3 (SD 59?4) mg/100g dry mass, respectively.
Expressed in percentages of total measured fatty acids
(Table 3), ratios of 18 : 2n-6 to 18 : 3n-3 PUFA in Vhembe
amaranth (1:9), spider flower (1:4?5) and Rustenburg
amaranth and Vhembe cowpea leaves (1:3?4) were in
favour of 18 : 3n-3 PUFA.
Discussion
Steyn(6) describes the low-fat, plant protein-rich diet of
rural black South Africans as most prudent. Wild-growing
DGLV, such as amaranth, spider flower and cowpea,
feature prominently in this type of diet(7,18). DGLV are
important sources of food folate(11,12). Table 1 shows that
folic acid concentrations of amaranth varied between 72
and 130mg/100 g fresh weight, while its concentration
was 217mg/100 g fresh weight in spider flower and
154mg/100 g fresh weight in cowpea. South African food
composition data (SAFCOD) tables(10) report the folic
acid concentrations in raw samples of these vegetables
respectively as 64, 346 and 141mg/100 g fresh weight. The
folic acid concentrations in raw leaves of other morogo
vegetables such as amadumbe, black jack and night-
shade(7) are respectively 126, 351 and 404mg/100 g fresh T
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Linolenic acid and folate in morogo 527
weight and that of raw commercial Swiss chard, 52mg/100g
fresh weight(10). Boiled amaranth contains 5mg folic acid/
100 g fresh weight, cowpea leaves 60mg/100 g, sweet
potato leaves (also consumed as morogo) 124mg/100 g
and commercial spinach 146mg/100 g(10). Values reported
from the National Food Consumption Survey for the
percentage of energy derived from plant and animal
sources(19) indicate that rural populations in South Africa
consume a larger amount of plant foods than their urban
contemporaries. Families in the Mopani District of Lim-
popo Province indicated that, when available, morogo is
eaten on a daily basis(20). Results from the present study
and information provided by the SAFCOD tables(10)
suggest that, if consumed on a regular basis in normal
amounts, morogo vegetables could be an important
source of dietary folate.
In addition, DGLV generally contain small amounts of fat
predominantly in the form of PUFA(10). In the present
study, six SFA, one MUFA and two PUFA (18 : 2n-6 and
18 : 3n-3) featured in differing ratios in the fatty acid
profiles of the three types of morogo (Table 2). In all
samples, 16 : 0 was the predominant SFA measured in
concentrations higher than 18 : 2n-6 but lower than 27% of
18 : 3n-3. The ratio of SFA to PUFA in wild-growing mor-
ogo vegetables ranged from 1?0:1?4 to 1?0:2?8 (Table 3).
Calculated from the SAFCOD tables(10) the ratios of SFA to
PUFA in other morogo and commercial vegetables are of
the same order (between 1?0:1?1 and 1?0:2?5).
The following percentages of energy from total fat
are indicated for various groups of adult black South
African males(6,21): rural areas 22?9%; informal settle-
ments 24?3%; urban middle class 26?0%; urban upper
class 30?6%. Steyn et al.(22) found that a rural black
population derived 3?7–4?4% of energy from SFA com-
pared with 8?5–9?2% for an urban black population.
The following consumption pattern is indicated for black
South Africans in terms of the percentage of the popula-
tion consuming a food item respectively in rural and
urban settings(6): meat 46 and 74%; full cream milk and
products 10 and 60%; vegetable fats and oils 26 and 62%.
The adoption of a Westernised diet due to urbanisa-
tion(5,21) appears to be linked with a propensity among
black South Africans to consume greater amounts of fat.
Moreover, the fat content of their diet seems to increase
with the degree of affluence. Simopoulos(23) describes the
Western diet as ‘deficient’ in 18 : 3n-3 mainly because of
the high intakes of cereals and vegetable oils rich in
18 : 2n-6 and the low intakes of fruits, nuts and DGLV
containing large amounts of 18 : 3n-3. Sanders(24) main-
tains that, consumed in normal amounts, DGLV would
contribute little to the dietary intake of 18 : 3n-3 because
of the overall low fat content. In rural settings, morogo
vegetables are prepared mixed with other plant foods,
including groundnuts and traditional legumes such as
cowpeas, which are expected to contribute to the overall
18 : 3n-3 intake(7,10,20,23,25).T
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528 AM van der Walt et al.
Adequacy in dietary 18 : 3n-3 is essential for the bio-
synthesis of DHA, the long-chain PUFA derivative with
vital membrane, brain and cardiac functions(14,24). In all
the morogo vegetables 18 : 3n-3 was the predominant PUFA
with ratios of 18 : 2n-6 to 18 : 3n-3 ranging between 1?0:2?3
to 1?0:8?9 (Table 3). EPA, an intermediate in the synthesis of
DHA, and DHA are both absent from plant foods and very
low in ruminant fats such as milk and dairy products(14).
Since the synthesis of DHA from 18 : 3n-3 via EPA occurs at
a slow rate in man, EPA and DHA sufficiency is dependent
on dietary intake from sources such as oily fish and
seafood(14). With limited access to oily fish and seafood,
poultry and eggs would serve as an alternative, though less
efficient, source of EPA and DHA, provided animals are not
fed on grain concentrates high in 18 : 2n-6 which compe-
titively inhibits the conversion of EPA to DHA(14). Dietary
studies in South Africa indicate the following relevant
consumption pattern in rural and urban black South
Africans, respectively(6): grain-based food (maize porridge,
sorghum and bread) 98?6 and 98?5%; fish (canned) 3?2 and
10?6%; eggs and egg products 7?4 and 16?2%; vegetables
48?1 and 42?8%. Rural and urban black South Africans thus
have equally high 18 : 2n-6 intakes from grain staples, and
seem to derive EPA and DHA primarily from poultry, eggs
and canned fish. However, raised on commercial corn
mixtures, poultry and eggs purchased from urban retail
outlets are expected to have a higher 18 : 2n-6 content(23,24)
than similar items consumed by rural farm-based families.
Furthermore, the percentage of urban black South Africans
consuming vegetable fats and oils is 2?4 times the rural
subjects(6), implying a higher overall 18 : 2n-6 intake by
urban populations. Rural populations furthermore con-
sume a wider range of vegetables, including DGLV
(morogo) which is absent from the vegetable list of their
urban contemporaries(6).
By comparison, urban black South Africans seem more
likely to consume a diet high in SFA and 18 : 2n-6 and
lower in folate than rural families in subsistence settings.
This dietary trend could relate to findings of epidemio-
logical studies suggesting that the high fat content of their
Westernised diet might be a prominent factor in the rise
of Western lifestyle diseases in urbanised black South
Africans(1,2,26,27). Notwithstanding underlying genetic
factors, obesity in black populations is attributed to
overnutrition and linked with the consumption of a
Westernised diet(26,28). In conjunction with other negative
factors (e.g. excessive alcohol use, cigarette smoking and
a sedentary lifestyle) obesity enhances risks of chronic
diseases among adults(6,21,27,29). Biological functions of
long-chain fatty acids respectively derived from 18 : 2n-6
and 18 : 3n-3 differentially modulate risks of CVD(12,15,23),
degenerative and inflammatory diseases(14,30) as well
as type 2 diabetes(31). Proposed antioxidant and anti-
inflammatory actions of folate(12) may further enhance the
health protective value of morogo consumption. In
combination with tetrahydrobiopterin and insulin, folate
suppresses superoxide anion generation and increases
endothelial nitric oxide and prostacyclin production, both
of which are potent platelet anti-aggregators and vasodi-
lators(30). The inhibiting effect exerted by dietary 18 : 3n-3
intake on the clotting activity of platelets(32) appears to act
complementary to mechanisms by which folate lowers
risks of CVD. Mandatory folic acid fortification of various
food items, and national strategies aimed at increasing fruit
and vegetable intake and reducing saturated fat con-
sumption in Western countries, emphasise the importance
of folate and 18 : 3n-3 in disease prevention(12,33).
The present study underscores the value of morogo
vegetables as low-fat food items that could contribute
notable amounts of folate and provide 18 : 3n-3 in excess
of 18 : 2n-6. Lowering fat intakes and including morogo
vegetables could adjust the diet of urbanised black South
Africans to a more prudent one. Reporting the health
beneficial qualities of morogo could improve the image
of these valuable vegetables and enhance their market-
ability in wider society and urban centres. Future research
should focus on expanding the nutritional database,
including possible anti-nutritional properties. Epidemio-
logical studies could accurately assess the role of morogo
vegetables in health and disease.
Acknowledgements
The Morogo Research Programme (MRP) gratefully
acknowledges the National Research Foundation of South
Africa (NRF) for financial support of this study (Focus
Area Grant FA2004050600064), the South African National
Botanical Institute for botanical species identification, and
Mrs Mary Blythe (South African Bureau of Standards,
Pretoria) for folic acid analysis of morogo samples and
statistical evaluation of results. The MRP is most grateful
to the communities in Vhembe, Capricorn and Phokeng
for allowing sampling of their morogo.
Conflict of interest: The corresponding author hereby
states that there is no ‘conflict of interest’ concerning the
data published in the present paper. The study was
carried out as a part of the corresponding author’s PhD
research. Analysis was funded by the NRF Focus Area
Grant (FA2004050600064) to the corresponding author.
The present article is included as a chapter in the PhD
thesis entitled ‘Fusarium in rural subsistence agro-environ-
ments of traditional African green leafy vegetables and
consumer health aspects – an ecological approach’. The
thesis clearly indicates Public Health Nutrition as the
scientific journal publishing this article.
Author contributions: A.M.v.d.W. was the grant
holder of the NRF Focus Area Grant (FA2004050600064)
funding the present research; and contributed to project
design and coordination, interpretation of the results and
writing of the article. M.I.M.I. carried out sample extrac-
tion and execution of analytical procedures. C.C.B.
Linolenic acid and folate in morogo 529
supervised the PhD project and contributed to inter-
pretation of the results. D.T.L. supervised the analytical
procedures and data processing.
References
1. Vorster HH (2002) The emergence of cardiovascular
disease during urbanisation of Africans. Public Health Nutr
5, 239–243.
2. Levitt N & Mollentze WF (1995) Diabetes and impaired
glucose tolerance: a review of South African studies. In
Chronic Diseases of Lifestyle in South Africa, pp. 109–121
[J Fourie and K Steyn, editors]. MRC Technical Report.
Tygerberg: Medical Research Council.
3. Panz VR & Joffe BI (1999) Impact of HIV infection and
AIDS on prevalence of type 2 diabetes in South Africa in
2010. BMJ 318, 1351–1352.
4. Van der Merwe M-T, Crowther NJ, Schlaphoff GP, Gray IP,
Joffe BI & Lo¨nnroth PN (2000) Evidence for insulin
resistance in black women from South Africa. Int J Obes
Relat Metab Disord 24, 1340–1346.
5. Bourne LT, Lambert E & Steyn K (2002) Where does the
black population of South Africa stand on the nutrition
transition? Public Health Nutr 5, 157–162.
6. Steyn N (2006) Nutrition and chronic diseases of lifestyle in
South Africa. In Nutrition and Chronic Diseases of Lifestyle
in South Africa: 1995–2005, pp. 33–47 [K Steyn, J Fourie
and N Temple, editors]. MRC Technical Report. Tygerberg:
Medical Research Council.
7. Jansen van Rensburg WS, Van Averbeke W, Slabbert R,
Faber M, Van Jaarsveld P, Van Heerden I, Wenhold F &
Oelofse A (2007) African leafy vegetables in South Africa.
Water SA 33, 317–326.
8. Odhav B, Beekrum S, Akula U & Baijnat H (2006)
Preliminary assessment of nutritional value of traditional
leafy vegetables in KwaZulu-Natal, South Africa. J Food
Compost Anal 20, 430–435.
9. Mnkeni AP, Masika P & Maphaha M (2007) Nutritional
quality of vegetable and seed from different accessions of
Amaranthus in South Africa. Water SA 33, 377–380.
10. Kruger M, Sayed N, Langenhoven M & Holing F (1998)
Composition of South African Foods. Vegetables and Fruit.
Tygerberg: Medical Research Council.
11. Kalter H (2000) Folic acid and human malformation: a
summary and evaluation. Reprod Toxicol 14, 463–476.
12. Das UN (2003) Folic acid says NO to vascular disease.
Nutrition 19, 686–692.
13. Singh RB, Pella D, Mechirova V & Otsuka K (2004) Can
brain dysfunction be a predisposing factor for metabolic
syndrome? Biomed Pharmacother 58, S56–S68.
14. Innis SM (2007) Dietary (n-3) fatty acids in brain develop-
ment. J Nutr 137, 855–859.
15. Simopoulos AP (1991) Omega-3 fatty acids in health and
disease and in growth and development. Am J Clin Nutr
54, 438–463.
16. Association of Official Analytical Chemists (1999) Folic
acid. In Official Methods of Analysis, 16th ed. Washington,
DC: Association of Official Analytical Chemists.
17. Barton-Wright EC (1961) Practical Methods for the Micro-
biological Assay of the Vitamin B-complex and Amino
Acids. London: United Trade Press.
18. Schippers RR (2002) African Indigenous Vegetables: An
Overview of the Cultivated Species, revised ed. Chatham,
UK: Natural Sources Institute.
19. Labadarios D, Steyn NP, Maunder E et al. (2005) The
National Food Consumption Survey (NFCS): South Africa,
1999. Public Health Nutr 8, 533–543.
20. Van der Walt AM, Mossanda KSA, Jivan SD, Swart WJ &
Bezuidenhout CC (2005) Indigenous African food plants:
vehicles of disease or sources of protection? Indilinga 4,
279–279.
21. Bourne L & Steyn K (2000) Rural/urban nutrition-related
differentials among adult ethnic groups in South Africa,
with special emphasis on the black population. S Afr J Clin
Nutr 13, S23–S28.
22. Steyn NP, Burger S, Monyeki KD, Alberts M & Nthangeni G
(2001) Seasonal variation in dietary intake of the adult
population of Dikgale. S Afr J Clin Nutr 14, 140–145.
23. Simopoulos AP (2001) Evolutionary aspects of diet,
essential fatty acids and cardiovascular disease. Eur Heart
J 3, Suppl. D, D8–D21.
24. Sanders TAB (1999) Essential fatty acid requirements of
vegetarians in pregnancy, lactation, and infancy. Am J Clin
Nutr 70, Suppl. 3, 555S–559S.
25. Faber M, Van Jaarsveld PJ & Laubscher R (2007) The
contribution of dark-green leafy vegetables to total micro-
nutrient intake of two- to five-year-old children in a rural
setting. Water SA 33, 407–412.
26. Van Rooyen JM, Kruger HS, Huisamen HW, Wissing MP,
Margetts BM, Venter CS & Vorster HH (2000) An
epidemiological study of hypertension and its determinants
in a population in transition: the THUSA study. J Hum
Hypertens 14, 779–787.
27. Vorster HH, Wissing MP, Venter CS et al. (2000) The
impact of urbanisation on physical, physiological
and mental health on Africans in the North West Province
of South Africa: the THUSA study. S Afr J Sci 96,
505–513.
28. Joffe BI & Seftel HC (1994) Diabetes mellitus in the black
communities of Southern Africa. J Intern Med 235,
137–142.
29. Puoane T, Steyn K, Bradshaw D, Laubscher R, Fourie J,
Lambert V & Mbananga N (2002) Obesity in South Africa:
the South African demographic and health survey. Obes Res
10, 1038–1048.
30. Lombardo YB & Chicco AG (2006) Effects of dietary
polyunsaturated n-3 fatty acids on dyslipidemia and insulin
resistance in rodents and humans. A review. J Nutr
Biochem 17, 1–13.
31. Suresh Y & Das UN (2003) Long-chain polyunsaturated
fatty acids and chemically-induced diabetes mellitus: effect
of v-3 fatty acids. Nutrition 19, 213–228.
32. Renaud S, Godsey F, Dumont E, Thevenon C, Ortchanian E
& Martin JL (1986) Influence of long-term diet modification
on platelet function and composition in Moselle farmers.
Am J Clin Nutr 43, 136–150.
33. Mills JL (2000) Fortification of foods with folic acid – how
much is enough? New Engl J Med 342, 1442–1445.
530 AM van der Walt et al.