Sample #1: From Samaha et al.'s Introduction
The differences in health benefits between a carbohydrate-restricted diet and a calorie- and fat-restricted diet
are of considerable public interest. However, there is concern that a carbohydrate-restricted diet will adversely
affect serum lipid concentrations. Previous studies demonstrating that healthy volunteers following a lowcarbohydrate diet can lose weight have involved few subjects, and few used a comparison group that followed
consensus guidelines for weight loss. The reported effects of a carbohydrate- restricted diet on risk factors for
atherosclerosis have varied. We performed a study designed to test the hypothesis that severely obese subjects
with a high prevalence of diabetes or the metabolic syndrome would have a greater weight loss, without
detrimental effects on risk factors for atherosclerosis, while on a carbohydrate-restricted (low-carbohydrate)
diet than on a calorie- and fat-restricted (low-fat) diet.
Sample #2: From Samaha et al.'s Discussion
We found that severely obese subjects with a high prevalence of diabetes and the metabolic syndrome lost
more weight in a six-month period on a carbohydrate-restricted diet than on a fat- and calorie-restricted diet.
The greater weight loss in the low-carbohydrate group suggests a greater reduction in overall caloric intake,
rather than a direct effect of macronutrient composition. However, the explanation for this difference is not
clear. Subjects in this group may have experienced greater satiety on a diet with liberal proportions of protein
and fat. However, other potential explanations include the simplicity of the diet and improved compliance
related to the novelty of the diet.
Sample #3: From Rabast et al.'s Discussion
The dietary study described was performed on 21 selected obese persons who could be classified into three
groups with virtually identical somatic data.
Earlier studies have shown that, in reducing diets involving isocaloric exchange of carbohydrate and fat, the
reduction in body weight was more marked during the diet restricted in carbohydrate and relatively rich in fat.
The finding outlined in the present paper are in confirmation of these results, in that the mean weight
reduction on the high-carbohydrate diet 1 was 9.5 kg, as compared to 11.4 and 12.5 kg, respectively, on the
low-carbohydrate diets 2 (corn oil) and 3 (butter fat). The methodological design of the present study varied
from the conditions previously described in the literature. It is felt that the conflicting results reported in the
literature are causally related to the fact that the individual studies were performed over short periods and in
small heterogeneous groups receiving inaccurately defined diets [for references, see Rabast et al. 25]. . . .
The nitrogen excretion measured at weekly intervals was significantly higher on the low-carbohydrate diet
after the 3rd and 4th week. Also the cumulatively calculated excretion of urinary potassium was found to be
significantly higher on the low-carbohydrate diet during the 1st and 2nd week. Therefore the greater loss of
lean tissue, especially on the corn oil diet, is to be discussed as an explanation for the more pronounced
weight loss on the low-carbohydrate diet. But there were no significant differences for potassium excretion
after 21 and 28 days, so the differences were not sufficiently conspicuous to afford a full explanation for the
observed weight differences.
Sample #4: From Johnston et al.'s Discussion
The absence of a thermic response to the HC diet at 2.5 hours after the breakfast meal seems contradicted, but
this phenomenon has been noted by others [18]. The metabolic cost of glycogen synthesis and lipogenesis is
believed to account for 55% to 65% of the thermic effect of carbohydrate ingestion [22], but only for 10% to
30% of the thermic effect of protein ingestion. The breakfast meal was consumed after an overnight, 12-hour
fast; hence, it is conceivable that the ingested glucose was readily utilized by body tissues and not available
for glycogen synthesis. At the lunch and dinner meals, nutrient storage would be enhanced as nutrient
availability increased with repeated food ingestion.
Sample #5: From Halton & Hu's Review Paper
In addition, Johnston [9] found that a diet with 30% from protein had a thermic effect of 34 kj/hour higher
than a diet consisting of 15% protein. Mikkelson [14] found that a 29% pork diet increased 24-hour energy
expenditure by 3.9% compared to a high carbohydrate diet with 11% protein. Leblanc [11] found that a 97%
protein diet caused an oxygen consumption of 31 mL O2/kg/min while a 1% protein feeding resulted in an
oxygen consumption of 17 mL O2/kg/min. However, this level of protein is unrealistic. Zed [18] found
significantly increased oxygen consumption for a high protein meal compared to a high carbohydrate meal. In
both normal and obese subjects, Swaminathan [5] found significantly higher mean metabolic rates for a high
protein preload compared to high fat and high carbohydrate preloads. This evidence suggests that diets higher
in protein exert a larger effect on energy expenditure than diets lower in protein. A logical question is whether
or not this difference is enough to affect body weight. In the Johnston investigation [9], it was estimated that
the average difference between the high and low protein diet for their subjects was 126 kj a day. For Crovetti
[7], this number was 168 kj after 7 hours, and for Robinson [15] it was 251 kj after 9 hours.
Sample #6: Student Draft
A study on the effects of carbohydrate-restricted diets on exercise in obese persons is necessary for assessing
the value of low carbohydrate restricted diets. Exercise is associated with proven health benefits, such as
improved cardiovascular health, improved utilization of fatty acids, and increased insulin sensitivity, which
are all important for obese individuals who are at greater risk of heart disease and diabetes (5). But, if the
mechanisms that cause weight loss in low carbohydrate diets impede exercise or even make exercise a
potentially dangerous activity, then the value of such diets would need to be reevaluated. Present research
provides a very unclear idea of how studies on obesity and exercise would turn out. Helge's (4) study on
untrained individuals indicated that a high fat diet would not be as effective as a high carbohydrate diet at
improving endurance performance. Though performance may be a measure of diet and exercise success, it
isn't necessarily important to the issue of weight loss in obese individuals. If the diet and exercise regime
reduced overall body fat composition and decreased disease risk factors then such a diet might be of some
value. Helge's (4) study showed that subjects on a high fat diet had significantly lower insulin levels than
those on the carbohydrate based diet. Subjects on the high fat diets also had higher free fatty acid profiles (4).
Depending on the interpretation this could be seen as a positive or detriment to the high fat diets. Some
interpret higher free fatty acids as a risk factor. Others see it as a result of increased fatty acid metabolism.
Lambert's study involved cyclists on the more standard high fat diets. With highly trained athletes and a diet
that conformed more to the standard high fat diet, Lambert found improved endurance among the cyclists on
the high fat diet, further encouraging the idea that the high fat diet could potentially improve exercise capacity
in obese individuals (6). Because Lambert used trained individuals, the value to exercise among the obese is
limited. Highly trained individuals not only have superior basal metabolic rates but they metabolize fats better
as well (5).
Sample #7: Student Draft
One limitation to our study is that women were not used as subjects. The main reason that women were not
used is the fact that women tend to have a higher body fat percentage than men. Along with a higher body fat
percentage, the distribution of fat between men and women is different. Men usually accumulate fat in the
abdominal region while women accumulate fat in the gluteal-femoral region. Blaak (2001) discusses the
theory that adipose tissue free fatty acids release in higher amounts in upper body fat rather than lower body
fat in both men and women. With a higher percent of fat located in the gluteal-femoral region for women,
women have less of chance to lose weight when taking this theory into mind.
Blaak (2001) also discusses the fact that lower basal fat oxidation may contribute to an increase in fat storage
in women. If lower basal fat oxidation contributes to an increase in fat storage for women, then if women
were used the results would most likely be affected. To fix this limitation, the study could be performed in all
the same ways as in accordance with the methods but instead separate women and men thus performing two
different tests, one on a group of women on the low-carbohydrate diet and one on a group of men on the lowcarbohydrate diet. For this experiment to work, two groups, one of women and the other of men, must be used
as the control thus placing them on the conventional diet. If performed properly, comparable results should
occur for the men, as happened in our study, but for women, the results would most likely vary when
compared to men.
From Luscombe et al.'s Discussion
We found a small (4.2%) but not statistically significant decrease in TEE after weight loss. Our study had
enough power (80%, a 0.05) to detect an overall fall in TEE of 8%. In all, 15 of the 36 subjects had a decrease
in TEE of 8% or more, but in the remaining 21 subjects there was a large degree of variance in the change in
TEE; seven individuals experienced a decrease of less than 8% and 14 experienced an increase in TEE. This
is the first time we have examined the effect of HP diets on TEE. Our findings are in contrast to those of
Whitehead et al, the only study to have shown that an increased protein intake during energy restriction blunts
both the fall in TEE as well as the sleeping metabolic rate. However, since the fall in sleeping metabolic was
significantly less in Whitehead et al’s HP group than in their LP group, it is not surprising that the fall in TEE
was also significantly blunted. Discrepant findings between Whitehead et al and the present study may also be
the result of a larger difference in the protein content between the HP and LP diets (21% difference in their
study vs 12% difference in this study), or they may be because of the larger variability observed in the change
in TEE in our subjects as compared to theirs. We used the [14C]-bicarbonate–urea method to measure TEE
whereas Whitehead et al used whole-body indirect calorimetry. The [14C]-bicarbonate–urea method, which
does not restrict subjects to an artificial living environment, has been shown to measure TEE within 2– 5% of
the value derived from whole-body indirect calorimetry. Our observation that TEE was not significantly
decreased after weight loss is consistent with the findings reported by others. Both Rumpler et al and
Amatruda et al measured TEE after their subjects’ body weights had been stabilized at the reduced level for a
period of time. Therefore, the timing of the energy expenditure measurements (ie during dynamic weight loss
vs after stabilization at reduced weight) may have also impacted on the disparity in outcomes between the
study of Whitehead et al and our study.
We conclude that total energy intake and not the protein-to- carbohydrate ratio of the diet is the major
determinant of weight loss in insulin-resistant subjects. The HP diet did not blunt the decrease in energy
expenditure that may be associated with weight loss. It remains to be determined whether increased protein
diets are of benefit in the maintenance of weight loss, or associated with better compliance with energy
restriction in the long term.
From de Graaf et al. (1992)
The differences between the results of various studies may be explained by methodological differences in
experimental setup. One issue is the time between preload and test meal or ad libitum food intake. In the
present study the subjects were not allowed to eat after consumption of the breakfast preload until lunch time.
Two hours after the preload consumption there were differences in motivational ratings; for instance, subjects
had a greater appetite for a meal after a low-energy preload than after a high-energy preload. The significant
correlations between motivational ratings before lunch and energy intake at lunch suggests that, if subjects
had been allowed to eat after 2 h, the result of the present study might have been different. In the experiments
of Rolls et al (10) and Hill and Blundell (9), the protein preload was more satiating than were carbohydrate or
fat preloads. The higher satiating efficiency of protein was apparent from both the motivational ratings and
the subsequent energy intake in a test meal. In these experiments the test meals were given 2-3 h after the
preload. The time between preload and ad libitum food intake in the present study was almost 4 h. As Figures
1 and 2 show, this is an important difference. Apparently the time between the preload and test meal is a
crucial variable in determining whether or not caloric compensation occurs.