MACRONUTRIENT COMPOSITION
AND WEIGHT LOSS

Kerwick, A, and Pawan, GLS. (1958) Metabolic study in human obesity with isocaloric diets high in fat, protein, or carbohydrate.

The classic study by Keckwick et al included 14 hospitalized participants including non-obese controls and those more than 35% above the standard weight for height. During the entire 12-23 days of the study, participants were allowed a moderate amount of exercise. In this extreme design, participants were given a diet of either 90% fat, protein, or carbohydrate (mean of 5-9 days on each diet) with measured amounts of water and electrolytes. If calories alone accounted for weight loss, the composition of the diet should be of no consequence. Study results indicated that weight was lost rapidly when 90% of calories were obtained from fat or protein. The content of fecal fat indicated 95-97% absorption during the high fat diet and seemingly indicated that weight loss on the high fat diet was not due to inadequate fat absorption. The resistance of the obese participants to hypoglycemia, severe ketosis, and acidosis was very different from the response of the non-obese. No abnormal responses were found in obese participants during the trial periods. Non-obese participants on the 90% fat diet developed marked hypoglycemia, ketosis, and acidosis at the end of three days and had to be taken off the diet. No marked negative nitrogen balance was observed on protein intakes as low as 10% nor was there evidence of greater protein sparing on a high carbohydrate, as opposed to a high fat diet. Water balance was consistent among the dietary regimens. Measurements of oxygen consumption indicated a higher metabolic rate with the high fat diet. The investigators reported, however, that the major limitation of the study was the "inadequate personalities" of their participants, who lied and cheated on the diet or refused to consume prescribed meals. The article reports "a considerable number of known failures…" The authors concluded that certain alterations in metabolism were present in the obese as compared to the non-obese. Whether these alterations represent an inborn metabolic abnormality and were the cause or result of the obese state was not clear.

Alford, BB, Blankenship, AC, Hagen, RD. The effects of variations in carbohydrate, protein, and fat content of the dit upon weight loss, blood values, and nutrient intake of adult obese women. (1990) J Am Diet Assoc 90:534-540.

 

Alford et al examined the effect of diets containing 25%, 45% or 75% carbohydrate with some variation in fat and protein content on weight reduction. Each of the 1,200 kcal/d diets produced weight loss in the 35 female participants. Participants were assigned to one of the three diets and remained on that diet for the full 10 weeks of the study. Compliance with the diets as determined by a dietary compliance score was found to be acceptable. Participants in all three groups lost weight, with no significant differences between the groups. Underwater weighing at the beginning and end of the study showed no significant differences in body fat lost during the study among the three groups, nor was there a significant difference in the change in lean body mass, serum triglycerides or serum cholesterol. Participants participated in weekly classes on nutrition education, behavior modification, and individual nutrition counseling. The authors reported that sufficient personnel were not available to evaluate activity patterns of the study participants but fel this was an important factor for further investigation. They conduced that no statistically significant effect resulted from manipulation of the percentage of carbohydrate in a 1,200 kcal/d diet. Weight loss appeared to be the result of a reduction of caloric intake in proportion to caloric requirements.

Golay, A, Allaz, AF, Morel, Y, de Tonnac, N, Tankova, S, Reaven, G. 1996 Similar weight loss with low-or high-carbohydrate diets. Am J Clin Nutr 63:174-178.

Golay et al evaluated the effect of diets that were equally low in energy but widely different in relative amounts of fat and carbohydrate. Participants included 43 obese persons who were randomly assigned to one of two experimental diets and remained hospitalized during the study to increase compliance. The diets were similar in protein content (32% and29%) but varied in carbohydrate (15 and 45%) and fat (53 and 26%) content. In addition to the low-calorie diet, participants participated in a structured, multidisciplinary program that included physical exercise, nutrition education, and standard behavioral techniques. Exercise consisted of one hour of aerobic exercise per day and one hour of underwater physical activity per day. At the end of the six week study period, there was no significant difference in the amount of weight loss by participants consuming either of the two diets. There were significant decreases in body fat and waist-to-hip circumference at the end of the study, but no differences between the two study groups. The protein-sparing effect of both diets was equal. Fasting plasma glucose, insulin, cholesterol, and triglyceride levels were significantly decreased in patients on the 15% carbohydrate diet. A similar trend was seen in the participants on the 45% carbohydrate diet but these differences were not significant. The authors concluded that energy intake, no nutrient composition, determined the extent of weight loss in response to a low-energy diet over a short period of time. Because of the reported differences in serum lipid levels on the higher fat diet of this study, the authors questioned the current belief that low-fat diets had better long-term benefits for weight maintenance.

Skov, AR, Toubro, s, Ronn, B, Holm, L, Astrup, A. 1999 Randomized trial on protein vs carbohydrate in ad libitum fat reduced diet for the treatment of obesity. Int J Obesity 23:528-536.

65 overweight and obese subjects (18-55 years old) were randomly assigned to a high carbohydrate diet, high protein diet or a control diet. All food was provided by the investigators, and compliance was evaluated by urine analysis. Energy intake, weight loss and fat loss was greater in the high protein groups. The greater weight loss in the high protein diet was attributed to the lower energy intake.

Note: Insulin levels were not monitored in any of the studies on the effect of dietary protein level and weight loss.