to compare the effects of weight loss by an energy - restricted low - fat diet versus low - carbohydrate diet on serum peptide yy ( pyy ) levels .
8-week prospective study of 30 obese adults ( mean age : 42.8  2.0 years , mean bmi 35.5  0.6 kg / m ) .
after 8 weeks , subjects on the low - carbohydrate diet lost substantially more weight than those on the low - fat diet ( 5.8 kg vs. 0.99 kg , p<0.001 ) .
weight loss by either diet resulted in a 9% reduction in both mean fasting serum pyy levels ( baseline : 103.5  8.8 pg / ml , after weight loss : 94.1  6.5 pg / ml , p<0.01 ) and postprandial auc pyy ( baseline : ( 20.5  1.5 )  10 pghrml , after weight loss : mean auc pyy ( 18.8  1.4 )  10 pghrml p<0.001 ) .
there was a trend towards lower levels of pyy with greater degrees of weight loss .
reduced pyy levels after weight loss by an energy - restricted low - fat or low - carbohydrate diet likely represents a compensatory response to maintain energy homeostasis and contributes to difficulty in weight loss during energy - restricted diets .
nearly 45% of women and 30% of men in the united states are attempting to lose weight at any given time ( 1 ) .
although energy - restricted diets and low - fat diets are the most commonly recommended diets for weight loss , low - carbohydrate diets are a popular alternative ( 2,3 ) .
a recent meta - analysis reported that low - carbohydrate diets are as effective as low - fat diets in inducing weight loss for up to one year ( 4 ) .
enteroendocrine cells lining the distal small bowel and colon secrete pyy136 and the truncated isoform pyy336 in response to a meal ( 5 ) .
, we reported that one - week of a low - carbohydrate , high - fat diet led to 55% higher levels of postprandial serum pyy levels compared with a low - fat , high - carbohydrate diet ( 6 ) . in this study , we aimed to compare the effects of weight loss by an energy - restricted low - fat versus low - carbohydrate diet on serum pyy levels .
we hypothesized that weight loss by a low - carbohydrate diet would lead to higher pyy levels . to test this hypothesis ,
we compared fasting and postprandial pyy levels in obese individuals at baseline and after 8 weeks of weight loss with a low - fat ( < 30% of total calories derived from fat ) or a low - carbohydrate diet ( < 30gm of carbohydrate / day , with < 10% of total calories derived from carbohydrates ) .
subjects were recruited to this prospective study by advertisement in the richmond , virginia area .
inclusion criteria included body mass index ( bmi ) 30 kg / m  40 kg / m , age 1860 years , and stable weight for 3 months .
exclusion criteria included clinically significant pulmonary , cardiac , renal , hepatic , or infectious disease ; blood pressure > 170/100 mmhg ; diabetes mellitus with hba1c7.9% ; and pregnancy or lactation .
subjects provided informed , signed consent . procedures took place at the general clinical research center ( gcrc ) , and the protocol was approved by the institutional review board of virginia commonwealth university .
after enrollment , subjects presented for a screening visit and instruction on maintenance of a 3-day food diary .
the subjects energy requirements were estimated with the equation : total energy expenditure = fasting metabolic rate ( calculated with the harris - benedict equation )  activity factor ( sedentary = 1.3 , some regular exercise = 1.5 , and regular exercise = 1.7 ) . from these estimates , daily caloric intake needed to achieve an energy deficit of 500 kcal / day was estimated for each individual .
after randomization to an energy - restricted low - fat or low  carbohydrate diet , subjects presented to the gcrc at 0800 after a 10-hour overnight fast .
baseline serum pyy , glucose , insulin , leptin , and adiponectin levels were drawn at 15 min and 0 min .
subjects consumed a low - fat or low - carbohydrate test meal ( mean 540 kcal ) , and serum samples were subsequently drawn at 30-minute intervals over the next 2.5 hours .
subjects received counseling from a study dietitian on maintenance of an energy - restricted low - fat diet or low - carbohydrate diet and were instructed to avoid modifying physical activity .
compliance was assessed by interview and degree of weight loss , with less than 1 kg loss over a 3-week defined as noncompliance .
after 8 weeks , subjects presented again to the gcrc and underwent similar procedures to those performed at baseline .
serum glucose concentrations were measured on a glucose analyzer using oxidative methodology , and serum insulin using a double - antibody ria . for pyy determinations , aprotinin ( sigma - aldrich , inc . , st .
louis , mo ) at a concentration of 1 g / ml and dipeptidyl peptidase iv ( dpp - iv ) inhibitor ( linco , research , inc . , st .
louis , mo ) at a final concentration of 100 m were added to the serum , and the samples were stored at 70 c until assays were performed .
total pyy was measured using a sensitive and specific ria ( linco research , inc . , st .
louis , mo ) . the lower limit of detection was 10 pg / ml , and the coefficients of variation were 9.4% within and 8.5% between assays .
serum leptin and adiponectin were measured with elisa kits ( diagnostic system laboratories , inc . ,
areas under the curve ( auc ) for insulin , glucose , and pyy were calculated with the trapezoidal method .
the primary variable of interest was postprandial auc pyy . in order to detect a 35% difference between the groups with a standard deviation of 154.5 , based on a published study ( 7 ) , 10 subjects per group
were needed to achieve a power of 80% with =0.05 . estimating a potential 20% noncompliance rate , the sample size increased to 16 subjects per group .
baseline measurements were assessed with unpaired t - tests , and comparisons between groups analyzed using repeated - measures anova with time and diet as main effects .
the macronutrient composition of the diets was calculated using the nutrition data system for research ( version 4.04 , nutrition coordinating center , university of minnesota ) .
all statistical analysis were made using jmp version 8.0 ( sas institute inc . , cary , nc ) , with p<0.05 statistically significant .
the mean age was 42.8  2.0 years , and the mean bmi 35.5  0.6 kg / m .
furthermore , analysis with inclusion of the 2 eliminated subjects demonstrated no differences in any baseline variables between groups .
after 8 weeks , weight loss for the entire study group ( n=30 ) was 3.7  0.7 kg ( 95% ci [ 5.2 , 2.3 ] ) .
subjects on the low - carbohydrate diet lost significantly more weight than those on the low - fat diet ( 5.8  0.75 kg , 95% ci [ 7.3 , 4.3 ] vs. 0.99  0.86 , 95% ci [ 2.8 , 0.8 ] respectively , p<0.001 ) .
no difference in weight loss was observed by gender or race , and there were no significant associations between weight loss and baseline weight , bmi , or levels of fasting insulin , glucose , leptin , or adiponectin .
fasting serum pyy levels ( figure 1a ) decreased by 9% over 8 weeks ( 103.5  8.8 pg / ml , 95% ci [ 85.4 , 121.5 ] vs. 94.1  6.5 pg / ml , 95% ci [ 80.8 , 107.4 ] , p<0.01 ) .
similarly , postprandial serum pyy levels ( figure 1b ) decreased by 9% [ ( 20.5  1.5 )  10 pghrml , 95% ci ( 17.5 , 23.5 ) ] and [ ( 18.8  1.4 )  10 pghrml , 95% ci ( 15.9 , 21.7 ) , p<0.001 ) ]
. there was a trend towards an inverse relationship between weight loss and fasting pyy level such that greater extent of weight loss correlated with lower fasting pyy levels ( r=0.32 , p=0.09 ) .
no significant correlations were observed between pyy and glucose , insulin , leptin , or adiponectin .
contrary to our hypothesis that weight loss with a low - carbohydrate diet would increase pyy levels , serum fasting and postprandial auc pyy decreased by nearly 10% after weight loss by either diet .
subjects randomized to the low - carbohydrate diet lost 6-fold more weight than those randomized to the low fat - diet .
however , change in auc pyy occurred independently of dietary intervention and degree of weight loss .
few studies to date have evaluated the effects of dietary composition on pyy expression in humans . unlike our previous study ( 6 ) , this study showed no difference in postprandial pyy levels between low - fat and low - carbohydrate diets , likely because subjects prepared their own meals and were not as adherent to their assigned diets as subjects in the previous study .
the fact that some subjects did not achieve weight loss as expected with a 500 kcal / day deficit suggests noncompliance .
( 8) reported no difference in pyy levels with a high monounsaturated fat , low glycemic index diet versus a low - fat diet .
likewise , brownley et al . ( 9 ) reported that postprandial pyy levels were not affected by glycemic load in obese women .
an interesting finding of this study is that postprandial pyy decreased significantly after weight loss regardless of low - fat or low - carbohydrate diet .
( 8) reported that 8 weeks of a low energy diet resulted in lower pyy levels and increased appetite scores .
10 ) reported that short - term fasting over 4872 hours reduced fasting pyy levels . since lower pyy levels
are associated with increased appetite ( 5,7 ) , we speculate that reduced pyy levels following diet - induced weight loss represents a physiological homeostatic mechanism to preserve baseline body weight . reduced pyy levels would indirectly stimulate hypothalamic neurons containing neuropeptide y and agouti - related protein , which in turn would stimulate appetite and food intake
lastly , measures of hunger , appetite , and satiety were not evaluated . in summary , this study demonstrates that weight loss by either a low - fat or low - carbohydrate diet reduces postprandial serum pyy levels .
this finding suggests that low pyy levels may contribute to the high recidivism and weight regain with energy - restricted diets .
further investigation is needed to determine whether diets comprised of various macronutrient compositions may increase pyy levels and promote weight loss in obese individuals .
 objectiveto compare the effects of weight loss by an energy - restricted low - fat diet versus low - carbohydrate diet on serum peptide yy ( pyy ) levels.design8-week prospective study of 30 obese adults ( mean age : 42.8  2.0 years , mean bmi 35.5  0.6 kg / m2).resultsafter 8 weeks , subjects on the low - carbohydrate diet lost substantially more weight than those on the low - fat diet ( 5.8 kg vs. 0.99 kg , p<0.001 ) . 
 weight loss by either diet resulted in a 9% reduction in both mean fasting serum pyy levels ( baseline : 103.5  8.8 pg / ml , after weight loss : 94.1  6.5 pg / ml , p<0.01 ) and postprandial auc pyy ( baseline : ( 20.5  1.5 )  103 pghr1ml1 , after weight loss : mean auc pyy ( 18.8  1.4 )  103 pghr1ml1 p<0.001 ) . 
 there was a trend towards lower levels of pyy with greater degrees of weight loss.conclusionsreduced pyy levels after weight loss by an energy - restricted low - fat or low - carbohydrate diet likely represents a compensatory response to maintain energy homeostasis and contributes to difficulty in weight loss during energy - restricted diets . 
Objective
Design
Results
Conclusions
Introduction
Materials/Subjects and Methods
Results
Discussion