Cardiovascular Journal of Africa: Vol 25 No 6 (November/December 2014)

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CARDIOVASCULAR JOURNAL OF AFRICA • Volume 25, No 6, November/December 2014 302 AFRICA
Comment
The cardioprotective diet: carbohydrates versus fat
FJ Raal
The global burdens of cardiovascular disease, obesity and type 2
diabetes mellitus continue to rise in both developed and developing
countries.1 Much of these burdens are preventable as they are the
result of sub-optimal lifestyle, which includes poor diet, excess
calorie intake, physical inactivity and cigarette smoking.2
As discussed by Lionel Opie, several diets, such as the
new Adkins diet, the Noakes diet and the Dukan diet, which
encourage the restriction of carbohydrates rather that the
restriction of fat, has recently been introduced and many more
are likely to follow.3 Each claim to be better that the next at
addressing this global health burden. However one has to
consider what these diets are trying to achieve. Are they trying
to achieve weight loss and prevention of the onset of type 2
diabetes, or are they trying to achieve cardiovascular protection?
It is correct that excessive carbohydrate intake, particularly
refined carbohydrate as found in sugary drinks and energy
snacks, is contributing to the global epidemic of obesity and
type 2 diabetes mellitus but it is wrong to conclude that a
high-carbohydrate intake is the major cause of atherosclerosis,
the leading cause of cardiovascular disease worldwide.
Atherosclerosis, particularly coronary artery disease, is not a
disease of carbohydrate metabolism and there is little evidence
to show that a low-carbohydrate diet will prevent atherosclerosis.
Restriction of refined carbohydrates, being our major
energy source, will assist with weight reduction in the short
term. However in terms of prevention of atherosclerosis and
cardiovascular disease in the longer term, restriction of saturated
fat is more important. It is therefore incorrect, and in fact it may
be harmful, to advocate the substitution of refined carbohydrates
with saturated fats.
Increasing the intake of saturated fats raises serum
low-density lipoprotein (LDL) cholesterol levels.4 Innumerable
epidemiological studies have shown a positive relationship
between serum LDL cholesterol levels and risk for cardiovascular
disease, particularly coronary artery disease. In fact the link
between LDL cholesterol and coronary artery disease is one of
the most thoroughly researched in all of medicine.5
There is overwhelming evidence, accumulated over more than
three decades, to show that the more you lower LDL cholesterol
the lower your cardiovascular risk. For every 1 mmol/l reduction
in LDL cholesterol using statins, there is approximately a 12%
reduction in total mortality and a 21% reduction in major vascular
events.6 We have not yet identified a threshold below which LDL
cholesterol reduction is no longer beneficial but harmful.7
So what should we be advising our patients at risk for
cardiovascular disease? Obesity is not so much about diet
but about energy balance – calories consumed versus those
expended. Appropriate restriction of calorie intake whether it be
carbohydrate, protein or fat is important for weight maintenance
and prevention of obesity and type 2 diabetes. However in terms
of achieving cardiovascular protection or maintaining a low
LDL level, cholesterol is pivotal.
As Lionel Opie emphasises, we need to encourage and
promote a healthy lifestyle with regular exercise, non-smoking
and a healthy diet consisting of moderate portions of all three of
the major components of our diet, namely carbohydrate, protein
and fat.3 If LDL cholesterol levels remain elevated or if the
individual has established cardiovascular disease or diabetes, or
is considered at high cardiovascular risk, international guidelines
worldwide recommend that statin therapy should be initiated.8,9
This will be much more beneficial for long-term cardiovascular
protection than the short-term benefit of weight reduction
achieved with marked carbohydrate restriction.
FJ Raal, FCP (SA), FRCP, FRCPC, Cert Endo, MMed (WITS),
PhD,
Division of Endocrinology and Metabolism, Department of
Medicine, Johannesburg Hospital, Parktown, Johannesburg,
South Africa
References
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380 : 2197–2223.
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Artery Disease. Cambridge, Ma: Harvard University Press, 1980.
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