Dietary intake
Dietary intake contributes directly to
energy consumed. Dietary intake in children may have changed over time,
possibly contributing to the rise in childhood obesity.
A number of factors may have influenced
the financial and time cost of food consumption, leading to a change over time.
First, agricultural and food processing
innovation may have led to reductions in both the financial cost of food, and
the time cost for preparing food.
Second, rising incomes increase the
opportunity cost of the time spent preparing food. Third, increasing working
hours also increases the time cost of preparing food.
The quantity of food consumed is not the
only important consideration. The energy density of food is also important as
different macronutrients (such as fat, protein and carbohydrates) contribute
different amounts to energy intake. Also, fat, in particular, is stored more
readily as fat in the body than other macronutrients (Davison and Birch 2001).
Different macronutrients have different satiety effects that will promote or
suppress additional dietary intake:
• Energy density influences the
palatability of food, which will influence consumption.
• Different macronutrients have different
thermic effects, which will influence energy expenditure.
• Energy storage in the body will be
influenced by food composition and the metabolic efficiency of fat (Rodriguez
and Moreno 2006).
Overall energy intake increased with age
and the difference between males and females became wider as they got older.
Just under half of total energy consumed came from carbohydrates for all age
groups. Of this, sugars contributed more to energy intake in younger children,
while starch contributed more to energy intake in older children. Dietary fat
contributed just under a third to energy intake, with saturated fat
contributing more than monounsaturated and polyunsaturated fat. Protein contributed
about 17 per cent.
Cook, Rutishauser and Seelig (2001) found
that 10–15 year olds in 1995 consumed significantly more energy than 10–15
years olds in 1985. In particular, they consumed significantly more protein,
carbohydrates, starch, sugars, and dietary fibre. There was no significant
change in intake of fat and cholesterol.
However, they were not related to BMI or
triceps skinfolds. The authors concluded that macronutrient intake when young
did not predict body fatness when older.
Another study, Sanigorski, Bell and
Swinburn (2007), found significant positive relationships between daily
servings of fruit juice/drinks and soft drinks and the probability of being overweight/obese.
Surprisingly, children who consumed the highest amount of fruit and vegetables
were also more likely to be overweight/obese than children who had consumed no
fruit and vegetables the previous day.
This result could be due to a number of
factors, including overweight/obese children eating a higher overall volume of
food, overweight/obese children positively changing their diet in response to
their weight, or reporting bias being stronger in parents of overweight/obese
children. There were no significant relationships between the proportion of
overweight and obese and daily consumption of fast foods and packaged snacks.
An international review (Newby 2007) found
that, overall; there is no consistent association between childhood obesity and
most dietary factors. The evidence on the relationship between total energy
intake and obesity was the most inconsistent, but there was some evidence to
support positive relationships between fat intake and consumption of
sugar-sweetened drinks and obesity.
However, several methodological weaknesses
in the studies covered by the review could at least partly explain the
inconsistent findings, including interaction effects with other factors not
taken into accounted, underreporting of dietary intake, genetic influences,
different growth stages and generalisability of studies.
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