Factors that moderate energy intake: Investigating protein, energy density, and pre-portioned entrees
Open Access
- Author:
- Blatt, Alexandria D
- Graduate Program:
- Nutrition
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- April 20, 2011
- Committee Members:
- Barbara Jean Rolls, Dissertation Advisor/Co-Advisor
Barbara Jean Rolls, Committee Chair/Co-Chair
Terryl Johnson Hartman, Committee Member
Sharon Nickols Richardson, Committee Member
Penny Margaret Kris Etherton, Committee Member
Mary Jane De Souza, Committee Member - Keywords:
- pre-portioned entrees
energy density
protein
intake
obesity - Abstract:
- The rates of overweight and obesity in America continue to increase along with the need for effective dietary strategies that can help people to reduce energy intake, enhance satiety, and facilitate weight management. Research has suggested strategies such as consuming a high protein diet, reducing dietary energy density, or consuming pre-portioned meals to help lower energy intake. The literature testing these strategies, however, is either inconsistent or incomplete. A series of studies have been conducted that examine the effects of these strategies on energy intake in order to provide better recommendations for controlling energy intake. The purpose of Study 1 was to determine whether increasing the protein content of meals reduced daily energy intake and enhanced satiety. The satiating effects of protein were investigated by varying the protein content of meals consumed ad libitum across a range of commonly consumed amounts over a day. In this crossover experiment, 18 normal-weight women consumed ad libitum lunch and dinner entrées one day a week that were covertly varied in protein content (10, 15, 20, 25, or 30% energy). Entrées were manipulated by substituting animal protein for starchy ingredients and were matched for energy density, fat content, palatability, and appearance. Unmanipulated breakfasts and evening snacks were consumed ad libitum. Participants rated their hunger and fullness before and after meals as well as the taste and appearance of entrées. Results showed that mean 24-hour protein intake increased significantly across conditions, from 44±2 g/d in the 10% protein condition to 82±6 g/d in the 30% condition. Daily energy intake, however, did not differ significantly across the 10% to 30% protein conditions (means 1870±93, 1887±93, 1848±111, 1876±100, and 1807±98 kcal). There were no significant differences in hunger and fullness ratings across conditions or in taste and appearance ratings of the manipulated entrées. Study 2 tested the recommendation of substituting low-energy-dense foods (vegetables) for foods higher in energy density to reduce energy intake. Puréed vegetables were incorporated into entrées at multiple meals to decrease the energy density and the effects on daily energy and vegetable intakes were investigated. In this crossover study, 20 men and 21 women ate ad libitum breakfast, lunch, and dinner in the laboratory once a week for three weeks. Across conditions, entrées at meals were varied in energy density (100%, 85%, or 75%) by covertly incorporating 3 or 4.5 times the amount of puréed vegetables. Entrées were accompanied by unmanipulated side dishes. Participants rated their hunger and fullness before and after meals. The results showed that subjects consumed a consistent weight of food across conditions of energy density; thus, daily energy intake significantly decreased by 202±60 kcal in the 85% condition (p<0.001) and 357±47 kcal in the 75% condition (p<0.0001). Daily vegetable consumption significantly increased from 270±17 g in the 100% condition to 487±25 g in the 75% condition (p<0.0001). Despite differences in energy intake, ratings of hunger and fullness did not differ significantly across conditions. Entrées were rated similar in palatability across conditions. Study 3 determined how the effects of energy density and energy content of pre-portioned entrées combine to influence daily energy intake. In a crossover design, 28 men and 40 women were provided with breakfast, lunch, and dinner on one day a week for 4 weeks. Each meal included a compulsory, manipulated pre-portioned entrée and a variety of unmanipulated discretionary foods that were consumed ad libitum. Across the 4 weeks, the entrées were varied in both energy density and energy content between a standard level (100%) and a reduced level (64%). In men, reducing both the energy density and the energy content of the pre-portioned entrées led to independent decreases in total meal energy intake (both p<0.01). A 36% decrease in energy density led to a 6% decrease in energy intake (154±46 kcal), and a 36% decrease in energy content led to an 11% decrease in energy intake (291±75 kcal). Thus, decreases in the energy density and energy content of pre-portioned entrées acted independently and added together to reduce total meal energy intake. Women showed similar effects on daily energy intake as men, however, this outcome was influenced by the interaction of energy density and energy content to reduce total meal energy intake (p<0.01). The findings from these studies suggest that energy density plays a major role in the regulation of energy intake. When energy density is held constant, variations in the protein content of entrées consumed ad libitum are not likely to influence daily energy intake or affect ratings of satiety. On the other hand, variations in energy density lead to changes in energy intake and may influence satiety. One way to reduce energy density is by increasing the amount of vegetables or fruits in foods. Puréed vegetables can be incorporated into various sweet and savory foods in large amounts; a strategy that can not only reduce energy intake, but can also increase vegetable intake without increasing hunger. A reduction in energy intake can also be found when the fruit and vegetable content of pre-portioned entrées is increased. Furthermore, reducing the energy density in addition to reducing the energy content leads to further decreases energy intake while maintaining satiety. In summary, the results of these studies support the recommendation of decreasing energy density, but not increasing protein content, to reduce energy intake and make an impact on the growing rates of obesity.