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AFRICA
esters to be inversely associated with abdominal obesity in a recent
cross-sectional study of 60-year-old men and women.
57
Alpha-
linolenic acid (C18:3n-3) is an essential FA and a precursor from
which n-3 LC-PUFAs are synthesised. Increased consumption
of C18:3n-3-rich foods elevates its tissue levels as well as levels
of C22:6n-3 and C20:5n-3 in the liver lipids.
58
Alpha-linolenic
acid can be beneficial to health. Firstly, C18:3n-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, C18:3n-3 competes for the same
metabolic enzymes, as does C18:2n-6, and increased dietary
intake may be a worthy approach to decrease elongation of n-6
FAs leading to reduced plasma C20:4n-6 levels and increased
plasma levels of C22:6n-3 and C20:5n-3.
58
As C18:3n-3 is an
essential FA, this pattern, identified in our study participants,
is probably related to food intake and therefore indicative of a
higher intake of vegetable oils, legumes, nuts and seeds.
61
Strengths and limitations
A rigorous methodological approach of sequential regression
modelling enabled us to investigate the associations between
dietary FA and plasma phospholipid FA patterns, respectively,
and measures of adiposity and the MetS. Another strength of
our study is the use of both dietary FA and plasma phospholipid
FA patterns,
27
which is a preferred method to investigate the
association between diet and diseases.
27
Our work is not free of limitations. Firstly, inaccuracies
associated with collecting dietary intake data may have
influenced the dietary FA results; however, in our population,
fieldworkers collecting dietary data were intensively trained and
supervised, and both under- and over-reporters of dietary intake
were excluded.
50
In addition, repeatability of the QFFQ was
also demonstrated.
10
Secondly, the cross-sectional design does
not account for possible reverse causation between measures
of adiposity and dietary FA intake or plasma phospholipid
FA concentration, nor can causality be inferred. Thirdly, a
possible limitation of the study is incomplete information on FA
composition in the food composition databases. This limitation
was compensated for by our study design that also considered
plasma phospholipid FAs. Fourthly, we assessed the associations
with indirect measurements of adiposity, including BMI, WHtR
and WC, as secondary markers of total and central adiposity,
whereas imaging methods would better differentiate between
lean and fat mass.
Conclusion
To our knowledge, this is the first study to investigate and
document novel data on dietary FA and plasma phospholipid
FA patterns and their association with measures of adiposity
and the MetS in a selected group of black South African adults.
This study presents evidence that although marginal association
was found with dietary FA patterns, some circulating plasma
phospholipid FA patterns were more strongly and significantly
associated with BMI, WC, WHtR and the MetS. The high-
Satfat and n-3 VLC-PUFA patterns were positively associated
with adiposity and the MetS, whereas the n-9 LC-MUFA and
n-3 EFA patterns were inversely associated with adiposity. These
patterns may suggest possible differences in FA metabolism
between lean and overweight/obese individuals. It should also
be considered that, in a study population with low-fat intakes,
such as the PURE participants, plasma FA levels may reflect
endogenous FA generation rather than dietary intakes, which
could result in different findings than those reported in other
studies from affluent communities.
Our results are not sufficiently conclusive to make
recommendations on dietary FA intakes in this population.
Further prospective cohort studies that explain possible
differences in characteristics of FA metabolism among black
South African men and women are needed. More studies that
apply the use of dietary FA and plasma or tissue FA patterns are
required to determine whether the results from the current study
can be generalised to the black population of African descent.
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