Limitations of the ‘simple’ vs.
‘complex’ classification of CHO foods
Traditionally, foods containing significant
amounts of CHOs have been categorized accord-
ing to the structural classification of the princi-
pally occurring CHO. This has led to a simplistic
division of CHO-containing foods into ‘simple’
CHOs (containing mono-, di- and oligo-
saccharides) or ‘complex’ CHOs (containing
polysaccharides). A variety of beliefs about the
metabolic and nutritional characteristics of CHO
foods have been apportioned to these categories:
1 ‘Simple’ CHO foods cause large and rapid
excursions of blood glucose levels on ingestion (a
rapid rise followed by a rapid and often greater
fall). They are prized for their sweetness but are
generally not nutritious. ‘Simple’ CHOs are com-
pletely digested and are a cause of dental caries.
2 ‘Complex’ CHO foods are nutritious foods
which contain significant amounts of other nutri-
ents, including dietary fibre. The digestion and
absorption of complex CHO foods are complete
but slower, producing a flatter and more sus-
tained blood glucose and insulin response to
their ingestion.
3 Dietary fibre is an inert substance found in
nutritious or complex CHO foods. It is undi-
gested, and plays a major role in maintaining
bowel function and regularity.
While this classification system may have been
developed as a simple nutrition education tool
for the lay person, it encompasses many erro-
neous beliefs which have, in fact, confused both
nutrition science and practice. Such misconcep-
tions have spilled over into the area of sports
nutrition.
An oversimplification which underpins many
of these misconceptions is the labelling of foods
according to a significant nutrient in their com-
position. To describe bananas, bread or lasagne
as ‘CHO foods’ is to undervalue the complex
nature of foods and the cocktail of chemicals of
which each is composed. Most naturally occur-
ring foods contain a mixture of CHO types, often
of both simple and complex structure, as well as
other macro- and micronutrients, and a large
array of non-nutrient chemicals. This mixture is
even more intricate in the case of processed
foods, and composite foods and dishes (e.g.
lasagne, pizza). Therefore it is preferable to
use a description such as ‘CHO-rich’ or ‘CHO-
containing’, which better recognizes the hetero-
geneity of characteristics of each food, and the
presence of other nutrients. As shown in Table
5.2, many CHO-rich foods containing mostly
simple CHOs are also good sources of protein,
fibre and micronutrients, and conform to dietary
guidelines that promote moderation of the intake
of fats and oils. On the other hand, there are a
number of examples of CHO-rich foods contain-
ing mostly complex CHOs which have low nutri-
ent density and/or a high fat content, and might
be considered less ‘nutritious’. Clearly, a judge-
ment of the nutritional value of a food based on
the structural nature of its CHOs is invalid, and is
further confused by the occurrence of foods that
contain significant amounts of both simple and
complex CHO types (Table 5.2).
Notwithstanding this difficulty of dividing
foods cleanly into two categories, there is little
correlation between the structural type of CHOs
in foods and their actual effect on blood glucose
and insulin levels. Data collected since the 1970s
have shown overwhelmingly that postprandial
responses to various CHO-rich foods vary from
that predicted by the simple vs. complex CHO
model. Several CHO-rich foods containing pre-
dominantly sugars (e.g. fruit and sweetened
dairy products) produce a flattened blood
glucose curve when ingested, while other foods
high in complex carbohydrates (e.g. bread and
potatoes) produce a high blood glucose
response, similar to that following the ingestion
of glucose itself. Furthermore, the presence of
dietary fibre in foods does not always seem to
delay absorption and flatten the postprandial
blood glucose curve; blood glucose responses to
wholemeal bread are similar to those following
the consumption of white bread.
The availability of carbohydrate types must
also be readdressed. A number of simple CHOs
are not well digested and absorbed by all people;
lactose is poorly digested by a small percentage