AND WEIGHT LOSS
A, and Pawan, GLS. (1958) Metabolic study in human obesity with
isocaloric diets high in fat, protein, or carbohydrate.
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.
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
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.
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
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.
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
levels were not monitored in any of the studies on the effect
of dietary protein level and weight loss.