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Mark Pereira
Epidemiology and Community Health
PHOTO BY PAUL BERNHARDT
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The obesity epidemic can be attributed to environmental factors
affecting diet or physical activity level. One potentially important
dietary factor may be consumption of "fast food," which
can be defined as "convenience food purchased in self-service
or carry-out eating places without wait service." From its
origins in the 1950s, fast food has grown into a dominant dietary
pattern, with a quarter-million fast food restaurants in the United
States. Consumption of fast food by children has increased from
two percent of total energy in the late 1970s to 10 percent of energy
in the 1990s.
Surprisingly few studies have examined the effects of fast food
consumption on energy balance or body weight. Mark Pereira, an assistant
professor in the School of Public Health's Division of Epidemiology
and Community Health, has performed what appears to be the first
scientific, comprehensive, long-term study of the effects of fast
food on weight gain and the risk of diabetes. With colleagues at
four other institutions, Pereira examined the association between
reported fast-food habits and changes in body weight and a pre-diabetes
condition known as insulin resistance over a 15-year period.
The following is a summary of the results of their study recently
published in the British medical journal The Lancet.
The fast-food habits of approximately 3000 healthy young black and
white adults living in American four cities --Birmingham, AL, Chicago,
IL, Minneapolis, MN, and Oakland, CA-- were followed for 15 years
as part of a long-term study on heart-disease risks. Participants
had routine medical check-ups and answered questions about diet,
physical exercise, and other lifestyle factors. Among the questions
they were asked was: "How often do you eat breakfast, lunch,
or dinner at places such as McDonald's, Burger King, Wendy's, Arby's,
Pizza Hut, or Kentucky Fried Chicken?" The investigators examined
the associations of the frequency of fast-food restaurant visits,
as reported at baseline and at follow-up, with 15-year changes in
body weight.
Pereira's team found fast-food frequency to be lowest for white
women compared to the other race-sex groups. After adjustment for
many other lifestyle factors, baseline fast-food frequency was found
to be directly associated with changes in body weight. Change in
fast-food frequency over 15 years was found to be directly associated
with changes in body weight and in insulin resistance. In comparison
to the average 15-year weight gain among participants with infrequent
(<1 time per week) fast-food restaurant use at baseline and follow-up,
those with frequent (>2 times per week) fast-food restaurant
use at both baseline and follow-up had gained an extra 10 pounds
of body weight and had a doubled increase in insulin resistance.
These associations appeared to be largely independent of other potentially
influential lifestyle factors, such as physical activity and television
viewing habits.
In their report, Pereira and his colleagues noted that the associations
between fast food and insulin resistance were not fully explained
by adjustment for a large number of other lifestyle factors, energy
intake, nutrients, and food groups. The single most obvious aspect
of fast food that might lead to weight gain is the large portion
size, with certain single-meal calorie levels approaching total
daily energy-intake requirements. Independent of energy intake,
many other aspects of fast food may also predispose to insulin resistance.
For example, certain fast foods contain large amounts of partially
hydrogenated oils, highly refined starchy food, and added sugar,
all of which may cause insulin resistance and increase risk of type
2 diabetes.
Pereira and his colleagues concluded that fast-food habits have
strong, positive associations with adverse health outcomes, in particular
weight gain and insulin resistance, suggesting that fast food increases
the risk of obesity and type 2 diabetes. They also concluded that
the link between fast-food habits and weight gain and insulin resistance
were largely independent of other bad habits like a sedentary lifestyle,
alcohol consumption, or smoking. In view of the high and increasing
rates of fast-food consumption, they recommend that further research
into the effects of this dietary pattern on public health be given
priority.
Mark Pereira's home page: www.epi.umn.edu/people/people.asp?ID=195
Reprinted with permission (in an edited form) from the June 2005
edition of Research
Brief, a publication of the School of Public Health.
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