Food Lipids: Chemistry, Nutrition, and Biotechnology

processes. Numerous studies provide evidence that variations in the level and type
of fat included in the diet can lead to alterations in adipose cell size and/or number.
As quantification of total adipose tissue cell number in human subjects is not readily
obtainable, these studies have been primarily conducted in experimental animals.
The major investigations concerning the influence of dietary fat level and type on
adipose tissue cellularity are presented below.
A. Level of Dietary Fat
Many animal studies confirm that high-fat feeding leads to an expansion of adipose
tissue mass through an increase in fat cell size and/or number and to the subsequent
development of obesity. Studies of adipose tissue development in rodents indicate
that increases in fat pad weight are typically associated with increases in both fat
cell size and number until approximately 10–18 weeks of age (252–254). Body and
fat pad weight and fat cell size and number then plateau and remain fairly constant
in the adult animal. High-fat feeding influences both the dynamic stage of adipose
tissue development early in life (252,255,256) and also the more static phase associated
with adulthood (252,257,258). In mice fed high-fat diets from birth, increased
fat pad weights are associated with a greater fat cell size through 18 weeks of age;
this is followed by an increase in fat cell number through 52 weeks of age (252).
At that time fat pad weight is sixfold greater in the high-fat compared with the
control-fed mice, while fat cell size and number are increased 2.3- and 2.5-fold,
respectively. An even greater effect of high-fat diets on adipose tissue cellularity is
observed in young Osborne–Mendel rats (255), a strain susceptible to high-fat feeding
(50). In these rats, a 4- to 16-fold increase in adipocyte number (dependent on
the specific fat pad studied) is observed between 24 and 105 days of age when the
animals are fed a high-fat diet (255).
Dramatic alterations in adipose tissue cellularity are also observed in adult rats
subjected to high-fat feeding (252,257,258). In adult rats, high-fat diet–induced obesity
is associated with increases in both fat cell size and fat cell number, with increases
in cell size preceding changes in cell number. In 5-month-old rats, a significant
increase in fat cell size is detected as early as 1 week after the introduction of
a high-fat diet (257). This response is followed by increases in cell number in the
perirenal fat pad after 2 weeks of diet treatment and in the epididymal fat pad after
8 weeks on the high-fat diet. Likewise, Faust et al. (258) report increases in cell size
in several fat pad depots after 3 weeks of high-fat feeding in adult rats but an increase
in cell number only after 9 weeks of dietary treatment. Fat cell hyperplasia in response
to high-fat feeding is also observed in adult genetically obese rodents, with
the magnitude of response being depot-dependent (259).
B. Type of Dietary Fat
It is generally accepted that a high level of fat in the diet may induce adipose cell
hypertrophy and/or hyperplasia. However, the influence of dietary fat type on adipose
tissue cellularity and the development of obesity is less definitive, particularly with
respect to diet-induced alterations in fat cell hyperplasia. Several studies reported a
greater effect of unsaturated as compared with saturated fat diets on increasing fat
cell number (260–262). Specifically, an increase in the DNA content of the epididymal
fat pad (indicative of an increased cell number) is observed in growing rats
Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.