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SA JOURNAL OF DIABETES & VASCULAR DISEASE
RESEARCH ARTICLE
VOLUME 16 NUMBER 2 • NOVEMBER 2019
69
study, over- and under-reporters of dietary intake (subjects with
reported energy intakes ≥ 30 000 or ≤ 3 000 KJ) were excluded
prior to analyses.
50
Apart from the marine FA pattern, we did not
derive other clear dietary FA patterns, likely due to the homogenous
nature of food intake in this group of adults. Therefore, factor
analysis may not be the most appropriate method to investigate
dietary FAs in this population and the associations observed should
be interpreted with caution.
The first plasma phospholipid FA pattern, high-Satfat, was
positively associated with all measures of adiposity and the MetS.
This pattern had high positive loadings of SFAs C18:0, C20:0, C22:0
and C24:0, as well as negative loadings of MUFAs. In our study,
the plasma phospholipid levels of these saturated FAs were also
higher in overweight men and women compared to their leaner
counterparts, although effect sizes tended to be small.
Plasma phospholipid VLC-SFAs, such as C20:0, C22:0 and C24:0
have previously been reported to be inversely associated with the
MetS among adults in Taiwan.
15
In a study in Japan, serum VLC-
SFAs were also inversely associated with the MetS and positively
associated with HDL-C.
16
The authors concluded that these VLC-
SFAs may be indicative of healthier metabolic health.
15,16
Li and
colleagues
22
derived a cluster that consisted of the same VLC-SFAs
mentioned above. This cluster was also associated with the healthier
metabolic profile,
22
but was not identical to the high-Satfat pattern
identified in this current study, as it did not have negative loadings
of MUFAs.
High intakes of MUFAs are generally considered the driving
force behind the protective effect of the Mediterranean diet on
cardiovascular diseases.
51
The combined presence of high loadings
of some SFAs, particularly C18:0 and low loadings on MUFAs may
therefore explain the association with obesity and the MetS found
in our study. Plasma C18:0 levels were higher and plasma C18:1
n-
9
levels were lower in the overweight/obese groups than among
their leaner counterparts in the current study, and the same FAs
had positive and negative loadings, respectively, in the high-Satfat
pattern. These two FAs made up a considerable proportion of the
FAs in the plasma phospholipid profile and may be the driving force
behind the positive association of the high-Satfat pattern with all
measures of adiposity and the MetS in the current study.
The second pattern,
n-
3 VLC-PUFA, had high positive loadings
of C20:5
n-
3, C22:5
n-
3 and C22:6
n-
3, as well as the
n-
6 PUFA
arachidonic acid (C20:4
n-
6). This pattern was positively associated
with all measures of adiposity and the MetS. In line with our findings,
an
n-
3 FA pattern (with positive loading of C20:5
n-
3, and estimated
delta 5 desaturase activity and negative loading of C20:3
n-
6) in the
study by Warensjo
et al
.
30
predicted the development of the MetS in
Swedish men, independent of lifestyle factors. The main difference
between our study and that of Warensjo and colleagues
30
is that
they included estimated desaturase activity in their patterns and
measured FAs in serum.
Omega-3 PUFAs, especially C22:6
n-
3 and C20:5
n-
3, have
multiple beneficial effects and are generally inversely associated
with obesity and related risk factors, as detailed in a recent
review.
52
Other studies have also reported the inverse association of
circulating
n-
3 PUFAs with measures of adiposity and the MetS.
20,21
It
should be kept in mind that the PURE-SA study population reported
very low intakes of
n-
3 FAs; however, despite these low intakes,
their plasma levels were considered sufficient.
43
Continuous low
intake of
n-
3 LC-PUFAs, as reported in the present study, can result
in up-regulation of the endogenous synthesis of
n-
3 LC-PUFAs from
C18:3
n-
3. The possibility therefore exists that this upregulated
conversion is a response to the cardiovascular risk milieu, reflecting
reverse causality, rather than being the other way around. Further
research is needed to elucidate the endogenous conversion of
dietary
n-
3 PUFAs in black African populations.
It is also possible that the positive association of this pattern
with adiposity and the MetS could have been driven by the
C20:4
n-
6, which formed part of this pattern. Omega-3 and
n-
6
FAs compete for incorporation into target tissues and metabolism
by common enzymes, which may lead to opposing health effects.
53
The eicosanoid metabolic products from C20:4
n-
6 promote
inflammatory responses. There is some evidence that a higher ratio
of
n-
6 PUFAs to
n-
3 PUFAs is associated with a higher prevalence of
obesity and the MetS.
54
The fourth plasma phospholipid pattern,
n-
6 VLC-PUFA,
had positive loadings of
n-
6 VLC-PUFAS, C20:3
n-
6, C22:4
n-
6
and osbond acid (C22:5
n-
6) and was positively associated with
the MetS. Mayneris-Perxachs
et al
.18 also reported a positive
association between plasma phospholipid C20:3
n-
6 PUFAs and the
MetS among older adults in Spain. Higher concentrations of plasma
phospholipid C20:3
n-
6 were observed in both overweight men
and women compared to their leaner counterparts in our study,
but the
n-
6 VLC-PUFA pattern was not associated with BMI in the
fully adjusted model. Plasma phospholipid levels of C20:3
n-
6 were
also positively associated with BMI in participants from the USA
and Mexico.
13,17
There was, however, also a longitudinal study that
found higher total circulating
n-
6 PUFAs, in particular linoleic acid
and arachidonic acid, to be protective of risk factors for the MetS,
including both systolic and diastolic BP and plasma triglycerides
in men,
24
indicating that different
n-
6 FAs showed opposite
associations with the MetS. The association of C20:3
n-
6 with the
MetS requires further investigation.
18
The fifth pattern,
n-
9 LC-MUFA, loaded positively with C20:1
n-
9
and C24:1
n-
9, and negatively with myristic acid (C14:0). This
pattern showed an inverse association with WC and WHtR, but
lost association when adjusted for lifestyle variables and energy
intake. However, lower odds for having the MetS remained
after adjustment for covariates. In our study, levels of C20:1
n-
9
were significantly higher in lean men and women compared to
their overweight counterparts, whereas C24:1
n-
9 was higher in
overweight compared to lean women only. Nervonic acid (C24:1
n-
9) and C20:1
n-
9 are both products of endogenous metabolism
by elongation from oleic acid,55 but plasma C24:1
n-
9 may also
be related to fish intake.
56
Since fish consumption was very low
in our study population, this pattern could therefore reflect an
upregulated metabolism of oleic acid in our lean study participants.
The sixth pattern,
n-
3 EFA, was positively loaded with C18:3
n-
3
and tended to be inversely associated with all measures of adiposity
and showed lower odds for the MetS. This is in agreement with a
study that found C18:3
n-
3 in serum cholesteryl esters to be inversely
associated with abdominal obesity in a recent cross-sectional study
of 60-year-old men and women.
57
Alphalinolenic acid (C18:3
n-
3)
is an essential FA and a precursor from which
n-
3 LC-PUFAs are
synthesised. Increased consumption of C18:3
n-
3-rich foods elevates
its tissue levels as well as levels of C22:6
n-
3 and C20:5
n-
3 in the
liver lipids.
58
Alpha-linolenic acid can be beneficial to health. Firstly,
C18:3
n-
3 intake was associated with a moderately lower risk of
cardiovascular disease in randomised, controlled studies as outlined
in reviews.
59,60
Secondly, as explained above, C18:3
n-
3 competes
for the same metabolic enzymes, as does C18:2
n-
6, and increased