Food Lipids: Chemistry, Nutrition, and Biotechnology

II. DIETARY FAT AND BODY WEIGHT
An effect of dietary fat on body weight has been well documented, especially in
experimental animals. Warwick and Schiffman (9), in a thorough examination of the
literature, reviewed the effects of diet type (fat vs. carbohydrate) and caloric density
on caloric intake and weight gain reported in animal studies. They suggested that
the caloric density of the diet plays a major role in promoting weight gain. If the
density is 4.5 kcal/g or more, excess weight gain is more likely to occur. In several
instances, an increase in body weight occurs without an increase in food intake.
Human studies, because they are more difficult to control, are less prevalent
than studies with animals. However, human studies also demonstrate that dietary fat
promotes weight gain. Lissner et al. (10) demonstrated that subjects consuming a
high-fat diet gained weight whereas those eating a low-fat diet lost weight. Others
(11,12) have reported that switching from a high-fat to a low-fat diet promotes relative
weight loss. Finally, indirect evidence provided from epidemiologic studies
shows positive correlations between body weight and fat intake (13).
III. DIETARY FAT AND FOOD INTAKE
A. Does Dietary Fat Affect Food Intake?
Dietary fat can have a profound effect on energy balance and, ultimately, body
weight. Studies designed to investigate the effect of dietary fat on food intake generally
employ one of two approaches: short-term studies examining the influence of
dietary fat on meal size or frequency, and longer term investigations of the effects
of dietary fat on energy intake over days or weeks. Short-term effects are typically
examined in one of two ways: (a) fat is given as a ‘‘preload’’ and subsequent feelings
of hunger or food intake is reported; or (b) fat is given as part of a mixed diet and
concurrent food intake is measured. In the first instance, ‘‘satiety,’’ i.e., the ability
of a substance to suppress further eating, is measured by the time elapsed, or amount
of food eaten at the next meal. In the second case, ‘‘satiation’’ is assessed and is
defined as the size of the current meal (14).
Many studies have been carried out examining the effect of a ‘‘preload,’’ often
in the form of a liquid, on subsequent intake, typically over a short time period.
Others have investigated the effect of high- or low-fat meals or snacks, or meals
supplemented with fat or carbohydrate, on subsequent feelings of fullness and food
intake. The results of these studies have been quite variable [for review, see Blundell
et al. (15)]. Many reports indicate that with a preload, individuals do not fully compensate
for the calories ingested, i.e., they do not reduce their intake in accurate
proportion to the calories previously consumed (16–19). This seems to be truer for
fat versus carbohydrate preloads (18–24), though some studies have indicated that
fat has satiety value equal to carbohydrate (25,26) or even greater than carbohydrate
(27,28). In addition, compensation seems to occur initially but then decreases over
time (25–27).
It is important that the volume, sensory characteristics, and protein content of
the preloads be similar when investigating the satiety effect of fat. A number of
studies have not controlled for all of these factors (17,24,29,30). However, when
preloads are similar, investigators have found that individuals vary substantially in
their response to preloads and that body weight may play a role in these responses.
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