Submitted to: International Journal of Obesity
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/10/2004
Publication Date: 5/1/2006
Citation: Rumpler, W.V., Rhodes, D.G., Paul, D.R. 2006. Covert manipulation of macronutrient intake has little impact on long term voluntary food intake and macronutrient selection in men. International Journal of Obesity. 30(5):774-781. Interpretive Summary: Approximately 300,000 deaths occur yearly due to obesity-related causes, and the economic cost to the United States is approximately $70 billion per year. A sedentary lifestyle and the abundance and diversity of food in western societies have been identified as principal factors contributing to an increase in excess body fat of the American population. Regardless of the causative factor, or factors, the fundamental defect is the inability of the individual to match energy intake with energy expenditure over the long term. The amount of fat in the diet is suspected to be a principle cause of "over eating". However, no long term studies have been conducted to determine if it is the fat in the diet that causes people to over eat or some other factor. As a means to investigate the effect of fat intake on calorie intake, twelve healthy normal weight men were fed, cafeteria-style, at the Beltsville Human Nutrition Research Center for 4 months. In order to accurately monitor food intake, every item consumed by the subjects was recorded at each meal. To ensure a higher fat intake by some volunteers each participant consumed a 166 calorie drink with each meal that was high in either fat, protein or carbohydrate. High fat intake induced overeating and low fat intake decreased calorie intake for only the first few weeks. By the end of the study calorie consumption was the same regardless of the fat content in the diet. This study suggests that fat content in the diet is not the principle cause of weight gain and that other factors must be influencing individuals to over consume calories. This work will benefit health care providers and government agencies who will be able to utilize the data collected to formulate improved dietary recommendations for the public. The food industry can used this work to provide foods to help individuals maintain a more healthy weight. Scientists can use data collected on the time course of food intake regulation and the extent to which diet and physical activity influence total calorie intake and food selection to design future research.
Technical Abstract: As a means to investigate the effect of daily macronutrient composition on food intake, twelve healthy normal weight men (79.9 ± 8.3 kg, 39 ± 9 yrs, 24.1 ± 1.4 kg/m2) were fed continuously for two 8-week periods. They were allowed cafeteria-style ad libitum access to a variety of foods of varying macronutrient composition that were provided by the Beltsville Human Nutrition Research Center (BHNRC). In order to accurately monitor food intake, every item consumed by the subjects was recorded at each meal. As a means to covertly alter macronutrient intake, subjects consumed a 698 kJ (2093 kJ/d) drink with each meal that was predominately carbohydrate (CHO), fat (FAT) or a combination of protein and carbohydrate (PRO). Each subject received 2 of 3 treatments over the course of the study. There were no significant changes in body weight or fatness related to treatment or duration of feeding. Average energy intake (EI) during week 1 - 2 was 6% lower on CHO than either FAT or PRO, but this effect disappeared by week 7 - 8. EI during CHO increased by 8% from week 1 - 8 through the increased selection of fat and protein-containing foods, but not carbohydrate foods. It appears as though EI is regulated by macronutrient composition in the short-term, but the effect disappears when feeding is continued past a few weeks. These data suggest the presence of macronutrient-specific regulatory mechanisms in the body, but do not support the notion that a high intake of any of the three macronutrients suppresses EI over a prolonged period of time.