Cardiovascular Journal of Africa: Vol 30 No 4 (August 2019)

CARDIOVASCULAR JOURNAL OF AFRICA • Volume 30, No 4, July/August 2019

AFRICA

235

the study in the USA, lower intakes of n-3 PUFA compared to

the FAO/WHO recommendation of 0.25–2 g/day were found.

Under-reporting of dietary intake may significantly influence

nutrient pattern investigation and association with disease,

however, in the PURE study, over- and under-reporters of

dietary intake (subjects with reported energy intakes

≥

30 000

≤

3 000 KJ) were excluded prior to analyses.

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.

In a study in Japan,

serum VLC-SFAs were also inversely associated with the MetS

and positively associated with HDL-C.

The authors concluded

that these VLC-SFAs may be indicative of healthier metabolic

health.

15,16

Li and colleagues

derived a cluster that consisted

of the same VLC-SFAs mentioned above. This cluster was also

associated with the healthier metabolic profile,

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.

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 C18:1n-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 C20:5n-3, C22:5n-3 and C22:6n-3, as well as the n-6

PUFA arachidonic acid (C20:4n-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

C20:5n-3, and estimated delta 5 desaturase activity and negative

loading of C20:3n-6) in the study by Warensjo

et al.

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

is that they included estimated

desaturase activity in their patterns and measured FAs in serum.

Omega-3 PUFAs, especially C22:6n-3 and C20:5n-3, have

multiple beneficial effects and are generally inversely associated

with obesity and related risk factors, as detailed in a recent

review.

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.

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 C18:3n-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 C20:4n-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.

The eicosanoid metabolic products

from C20:4n-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.

The fourth plasma phospholipid pattern, n-6 VLC-PUFA,

had positive loadings of n-6 VLC-PUFAS, C20:3n-6, C22:4n-6

and osbond acid (C22:5n-6) and was positively associated with

the MetS. Mayneris-Perxachs

et al

also reported a positive

association between plasma phospholipid C20:3n-6 PUFAs and

the MetS among older adults in Spain.

Higher concentrations of plasma phospholipid C20:3n-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 C20:3n-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,

indicating that different n-6 FAs showed opposite

associations with the MetS. The association of C20:3n-6 with the

MetS requires further investigation.

The fifth pattern, n-9 LC-MUFA, loaded positively with

C20:1n-9 and C24:1n-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 C20:1n-9 were significantly higher in lean men and

women compared to their overweight counterparts, whereas

C24:1n-9 was higher in overweight compared to lean women

only. Nervonic acid (C24:1n-9) and C20:1n-9 are both products

of endogenous metabolism by elongation from oleic acid,

but

plasma C24:1n-9 may also be related to fish intake.

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

C18:3n-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 C18:3n-3 in serum cholesteryl