Secular care as well as nutrition. With


increase in intelligence is one of the most intriguing issues in the
psychological field.

nutrition theory suggested that economically developed countries have
demonstrated an increase of 3 IQ points for children per decade due to
improvement of nutrition. (Lynn and Hampson, 1986). It has been proposed that
nutrition and cognitive stimulation are two main factors for the generational
intelligence gains, which is termed as the Flynn effect. This represented that
the upward trend in intelligence is caused by the benefits of a particular
nurturing environment on the physical development of individual, meaning there
is a general trend of enhancement in health care as well as nutrition. With
reference to the nutrition hypothesis proposed by Lynn (1990), there is a
larger IQ rises among the lower half of the distribution within the population
along with a disproportionation of intelligent gains at relatively low
intelligent level (Lynn, 1990). A number of studies have displayed that
malnourished infants exhibited a lower mean of IQs, which is able to support
that stance that nutrition has affect intelligence to a certain extend.

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empirical findings have put emphasis on the positive correlation between
nutrition and intelligence. In a study of Winick et al. (1975) on investigating
the impact of infant malnutrition on subsequent intelligence, 112 Korean
malnourished infants were adopted by American families. 111 babies were
separated into three groups of severely malnourished, moderately nourished and
adequately nourished according to height and weight. The IQ of the three groups
were measured at the age of 10. The result demonstrated that the severely
malnourished group obtained a mean IQ of 102, the moderately nourished group
obtained a mean IQ of 106, and for those who were well- nourished obtained a
mean IQ of 112. Although there are other possible factors that may lead to
lower intelligence levels (for example the transmission of genetic
differences), the findings still presented a permanently adverse effect of poor
nutrition on later intelligence. One of a very similar research is that of Crovioto,
Delicardie and Birch (1966) of children in the lower and upper class. They
adopted height as an indication of nutritional status, with a “control group”
of children in the middle class of similar age. The children from the upper
class performed better than those of the lower class in terms of inter-sensory
integrative competence. The result revealed that nutritional status was
significantly associated with intelligence.


of the most powerful evidence of contribution of nutrition on intelligence is
the study of identical twins with different birth weights (Willerman &
Churchill, 1967). Birth weight differences are due to inadequate supply of
nutrition from the placenta to one foetus, leading to restricted growth and low
birthweight. This research is to investigate the impact of light birthweight of
a twin on future intellectual performances. Such condition enabled genetic
differences and environmental factors to be controlled as to validly
investigate whether sub- optimal nutrition at early childhood can demonstrate
adverse effect on intelliegent gain. The study involved 27 monozygotic twin
pairs with differences in birth weights and were tested with the WISC at the
mean age of 9.6 years old. The result showed that the lighter twins exhibited a
lower verbal IQ of 0.4 points than that of the heavier twin and a lower
performance IQ of 5.3 points. A study from Hendrichsen et al. (1986) also
report a similar result for 14 monozygotic twins at the mean age of 13 years.

They were tested with WISC as well and the performance IQ of the twin with
lighter weight was 7.1 points lower than that of the heavier twin.


During the
post- World War II decades, people are able to buy more nutritious food due to
the rise of living conditions. Therefore, resulting in increased in height of
children and young adults by around 8 cm, particularly in economically
developed countries. Such effect alludes to the fact that similar amount of
increase has taken place in terms of intelligence. (Whitehead and Paul,
1988). The increase in nutrition level has also increased head size of the
general public. The nutrition theory of the secular increases in intelligence
suggested that increase in head size also positively correlated with
intelligence. therefore, there is a positive correlation between these 3
variables. Although some recent writers had wrote against such theory of
association, such as Engsner (1974, P.37) “there is little or no correlation
between brain size and mental performance” and “there is really no evidence to
show that brain size is positively correlated with higher intelligence”
(Latham. 1974, P.549), there were several studies which in fact evident such
hypothesis. In 1906, Pearson suggested a correlation of +0.11 between the
circumference of heads and the ability of children, and Pearl suggested a
correlation of +0.14 between the circumference of heads and the ability of


interesting phenomenon could be explained by 2 mechanisms. First, a larger head
stored a larger brain, and there is a tendency of people with larger brains to
be more intelligent (Jerison, 1982; Mackintosh et al, 1985). Secondly, the
enhancement of nutrition in the living condition have the possibility in carrying
out the influence on intelligence through impacting the neurological
development of the brain, which can encourage the growth of the number of glia
cells, neurons’ myelination, dendrites’ growth and synaptic connections
formations. In the studies of Winick et al. (1970) and Dobbing (1984) on
animals and autopsies humans has evident that malnutrition is an important
sector in adversely affecting these internal neurological developments. Therefore,
the influence of increase in nutrition can encourage the internal neurological
development of the brain thus create an upward trend on intelligence, while the
effect of such development is correlated to the increase in intelligence.


positive correlations between nutrition level and intelligent gain confirmed
the nutrition theory of the secular increase in intelligence (Lynn, 1989),
showcasing that nutrition level is an important stator for the intellectual
performances among children. To further explain the extend that impact of
nutritional level to intelligence, various tests have been adopted to investigate
which component of intelligence does nutrition determinate. Studies have
discovered that the visuospatial abilities have presented a greater upward
trend that that of the verbal- educational abilities. The result of the
Wechsler tests from various countries such as the US, Japan, Austria and France
shown that there is greater increase on the performance scale of visuospatial
component than that on the verbal component. The result of non- verbal test
with visuospatial scale of CCF test and Coloured Progressive Matrices have
shown a general increase of 2.5 IQ per decade, which is in contrast with the
increase of 0.4 IQ per decade on the verbal component of the Mill Hill
Vocabulary Test (Lynn and Hampson, 1986; Lynn et al., 1988). This
phenomenon is explained by the nutrition theory of the secular rise of
intelligence. The studies of the intelligence of monozygotic twins with
differential birth weights displayed that the visuospatial abilities are more
impaired in the low birth weight twin, but the verbal abilities are not
affected that much. This explains that the adverse effects of sub- optimal
nutrition have more effect on the visuospatial scale of the individuals. Therefore,
when nutrition is more improved nowadays, visuospatial abilities – as a
component of intelligence, displayed a greater improvement. 


nutrition theory of the secular increase in intelligence contained certain
significance for cognitive and developmental psychology. A lot of efforts have
already been put in raising the intelligence of the deprived children, such as the
Head Start Program, mainly focused on increasing cognitive stimulation for
young people as such stimulation is the main determinant of intelligence. Although
the result in raising intelligence were not very effective (Bronfenbrenner,
1974), intelligence has been increasing over the years. Nutrition theory
explained that it is nutrition instead of cognitive stimulation that determinate
the intelligence level. To summarize, proper nutrition should be provided to
children as to increase the intelligence among deprived children.


there is a study by Crnic (1976) refuted such conclusion. Although most of the
studies used randomized experiments, there is still other factors existing to
affect the learning performance other than malnutrition. Crnic claimed that it
is unclear whether malnutrition or the manipulations related with its outcome
was the cause for the effect on intelligent, which is a problem that afflicted
researches with only observation methods rather than non- experimental methods.

As a large number of children are under malnutrition, their subsequent
performance is relatively inferior than those who are well- nourished. Thus, the
study should not be focusing on whether malnutrition causes a drop in
intelligent performances, but on would improving nutrition level improves
performances simultaneously.


Cali study by Bejar (1981) is an example of a multi – treatment research,
showing the effect of administering post- natal supplemental nutrition
constantly and for a very long respectively. This study stated that treatment
that is implemented is an assumption to what people think is the causation for
any inferior intellectual performances. As malnutrition would not occurs in
isolated situation, studying other environmental factors of the children can allow
revelation of other factors.


result of Cali study find that the supplemental nutrition did not cause enhancement
in cognitive development. Meaning that the children who participated did not
suffered from malnutrition that restricted cognitive development, or just the
effect of supplemental nutrition have not taken place before the experiment
started. Such vagueness might cause a null result with such compensatory
approach. Therefore, it is important to note the direct measure to tackle the
problem of environment factors on cognitive development. The Cali study proclaimed
that the educational treatment is the key cause instead of the nutritional
supplementation. It means providing proper nutrition is only part of the factor
cognitive development, as to reach intelligent gain eventually. In short, the
Cali study evident that although intelligent level is somehow inherited,
environmental factors like educational treatment also has a remarkable effect
for intelligence.