Newsgroup: it.salute.alimentazione
Titolo: Dietary Fat

DEPARTMENT OF HEALTH AND HUMAN SERVICES
Centers for Disease Control and Prevention
Nutrition, Physical Activity, and Obesity Prevention Program
Resource Guide for Nutrition and Physical Activity Interventions
to Prevent Obesity and Other Chronic
Dietary Fat
While Americans have decreased the percent of total energy from dietary fat,
on average, they have continued to exceed the recommended < 30 % of total
energy from fat (Norris 1997, Troiano 2000). A comparison of the 1989 and
1995 Continuing Survey of Food Intakes by Individuals (CSFII) revealed a
steady decline in the percent of energy from total fat and saturated fat
over the last 30 years, however the amount of fat in the diets (mean total
fat in grams) increased from 1989 to 1995 (Males age 19-50 consumed a mean
of 93.7 grams of total fat in 1989-1991 and 100.9 grams in 1995; Females age
19-50 consumed a mean of 63.2 grams of total fat in 1989-1991 and 65.5 grams
in 1995) (Kennedy 1999). There is reason to believe that a diet containing
even less than the recommended 30% of total energy from fat could be
beneficial for energy balance, long-term weight maintenance and a reduction
of diet-related chronic disease risk (Astrup 2001, Hill 2000). There is
abundant cross-sectional evidence that supports the premise that dietary fat
is positively associated with obesity. The primary reason for this is that
higher intakes of dietary fat are associated with higher energy intakes.
There are several ways in which dietary fat leads to excess energy intake:
its low satiety value as compared to other macronutrients (Stubbs 2000;
Astrup 2001, Bray 1998, Golay 1997, Stubbs 2001), and its high palatability,
high energy density, efficient storage, and lower oxidative rates (Schrauwen
2000, Hill 2000). It should be noted that not all dietary fats have the same
oxidation rate; some fatty acids, such as medium-chain triglycerides, have
been shown to have higher oxidation rates and these are metabolized
differently. In general, unsaturated fatty acids are oxidized more rapidly
than saturated fats, which lead to greater energy expenditure (St-Onge 2002,
Delany 2000).
In controlled settings, dietary fat independent of caloric intake does not
lead to obesity. In other
11 words, if the caloric amount stays the same, a
higher percent of calories from fat will not lead to obesity. However, in a
free-living situation with individuals eating ad libitum, it appears that
higher fat diets are much more likely to lead to excess caloric intake than
lower fat diets (Schrauwen 2000). There is ample evidence that if the
percentage of fat in the diet is lowered enough, most individuals could eat
ad libitum and not gain weight (Rolls 2000). In other words high fat diets
tend to trump the satiety mechanisms which facilitate energy balance (Astrup
2001).
Of course there are exceptions to this rule. Other diets, such as high
protein, low carbohydrate diets may be high in fat. The ketosis, which is
induced by this type of diet suppresses the appetite and results in low
calorie intakes (St. Jeor 2001). But the percent fat in these diets is not
the reason these diets can be effective - it is the high protein and low
carbohydrates that are inducing the effect. While the comparative safety and
efficiency of weight loss diets are beyond the scope of this review, it is
important to establish that this phenomenon does not refute the hypothesis
that low fat diets facilitate energy balance, but rather demonstrates there
are other types of diets that can have a similar effect, at least
temporarily. Low fat diets, however, have been shown repeatedly to be more
effective for the prevention of overweight and for long-term weight
maintenance (Rolls 2000).

 temporarily. 
Ecco perchè a diversi di noi puzza di bruciato l'atteggiamento del
mondo accademico (di cui faccio parte, pur se in un altro settore) di
fronte alle diete low-carb....
Ciao
Gianni