Understanding food structure and function in developing food for appetite control

Dietary triacylglycerols (TAGs) are the major lipid components in the human diet and they are carriers of energy as well as important fatty acids. Many factors affect the digestion and absorption of TAGs. Evidence is accumulating that, in addition to the overall fatty acid profile, the TAG structure and the species composition are of importance when considering the nutritional effects of a dietary fat. There is good evidence that in addition to its short-term effects in the intestine on absorption of fatty acids the TAG structure also has long-term effects resulting from differences in the profile of absorbed fatty acids. Observations on the different atherogenic potential of dietary fats have given us a clear indication of the importance of the TAG structure for absorption of saturated fatty acids. In this context, one may focus on the effects of the structure of dietary fats as such, or one may speculate additionally on the possibilities of modifying the structure of fats to affect their absorption and the distribution of the fatty acids in the body after digestion and uptake. In this review we will summarize diverse aspects of TAG digestion and absorption, as well as the influences of the fatty acid composition and the intramolecular structure of dietary TAGs on their digestion and absorption.

The influence of dietary fiber on energy regulation remains controversial. This review summarizes published studies on the effects of dietary fiber on hunger, satiety, energy intake, and body composition in healthy individuals. Under conditions of fixed energy intake, the majority of studies indicate that an increase in either soluble or insoluble fiber intake increases postmeal satiety and decreases subsequent hunger. When energy intake is ad libitum, mean values for published studies indicate that consumption of an additional 14 g/day fiber for >2 days is associated with a 10% decrease in energy intake and body weight loss of 1.9 kg over 3.8 months. Furthermore, obese individuals may exhibit a greater suppression of energy intake and body weight loss (mean energy intake in all studies was reduced to 82% by higher fiber intake in overweight/obese people versus 94% in lean people; body weight loss was 2.4 kg versus 0.8 kg). These amounts are very similar to the mean changes in energy intake and body weight changes observed when dietary fat content is lowered from 38% to 24% of energy intake in controlled studies of nonobese and obese subjects. The observed changes in energy intake and body weight occur both when the fiber is from naturally high-fiber foods and when it is from a fiber supplement. In view of the fact that mean dietary fiber intake in the United States is currently only 15 g/day (i.e., approximately half the American Heart Association recommendation of 25-30 g/day), efforts to increase dietary fiber in individuals consuming <25 g/day may help to decrease the currently high national prevalence of obesity.

Dietary fiber has many functions in diet, one of which may be to aid in energy intake control and reduced risk for development of obesity. The role of dietary fiber in energy intake regulation and obesity development is related to its unique physical and chemical properties that aid in early signals of satiation and enhanced or prolonged signals of satiety. Early signals of satiation may be induced through cephalic- and gastric-phase responses related to the bulking effects of dietary fiber on energy density and palatability, whereas the viscosity-producing effects of certain fibers may enhance satiety through intestinal-phase events related to modified gastrointestinal function and subsequent delay in fat absorption. The goal of this paper is to provide a brief overview of the role of dietary fiber in energy intake regulation, highlighting the relationship between fiber properties and physiologic action.