Obesity Research & Clinical Practice (2008) 2, 101—110

ORIGINAL ARTICLE

Perceived hunger, palatability, and adherence: A comparison of high- and low-fat diets ˚berg a,∗, Gunnar Edman b, Stephan R¨ Gun A ossner c a

Psychiatry Karolinska Northwest, Stockholm, Sweden Department of Psychiatry, R&D Section, Danderyd Hospital, Sweden c Obesity Unit, Department of Medicine, Karolinska Institute, Karolinska University Hospital Huddinge, Sweden b

Received 23 September 2007 ; received in revised form 3 February 2008; accepted 2 March 2008

KEYWORDS Adherence; Low-fat diet; Palatability; Perceived hunger; Weight reduction



Summary Objective: To investigate whether there is a difference in palatability and perceived hunger between high- and low-fat diets, and furthermore to see if any such differences are correlated with the degree of adherence to a diet and with weight reduction. Design: Randomised, parallel, two-arm, open-label 10-week dietary intervention study comparing two hypocaloric (−600 kcal/day) diets with a fat energy percent of 20—25 or 40—45. Subjects: Obese (BMI ≥30 kg/m2 ) but otherwise healthy adult subjects (n = 100). Measurements: Perceived hunger, palatability of diet, difficulty of following dietary instructions and adherence to diet by visual analogue scales, and body weight loss. Results: There were no significant differences between the low- and high-fat groups in perceived hunger, palatability, difficulty of following instructions, nor adherence to the diet. There were significant trends towards lower perceived hunger during the trial [F(1, 86) = 49.99, p < .001], towards increased perceived adherence [z = 2.851, p = .004], and towards less perceived difficulty of following both diets during the second and third week [F(1, 86) = 23.51, p < .001]. Median weight loss was 7%. The patients who reached at least median weight loss decreased their perceived hunger significantly more than the group who did not [F(1, 85) = 4.12, p = .046], and had less difficulty of following instructions throughout the treatment period [F(1, 85) = 4.35, p = .040]. There was a strong negative correlation between perceived hunger and palatability [−.55] as well as between difficulty of following instructions and palatability [−.45], and a strong positive correlation between difficulty of following instructions and perceived hunger [.63] with both diets.

Corresponding author at: V˚ ards¨ atrav¨ agen 163, S-756 55 Uppsala, Sweden. Tel.: +46 70 6015120. ˚ berg). E-mail address: [email protected] (G. A

1871-403X/$ — see front matter © 2008 Asian Oceanian Association for the Study of Obesity. Published by Elsevier Ltd. All rights reserved.

doi:10.1016/j.orcp.2008.03.001

˚ berg et al. G. A

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Conclusions: The perceived hunger during the diet intervention and palatability of the diet are important factors for succeeding with weight reduction. The fat proportion of the diets was not important for determining perceived hunger and palatability. These findings suggest that the ability to compose a palatable and satiating diet may be important for successful weight reduction. © 2008 Asian Oceanian Association for the Study of Obesity. Published by Elsevier Ltd. All rights reserved.

Introduction Obesity is a major, global health problem. Obese people often experience a lower quality of life, and have an increased risk to suffer serious complications such as cardiovascular disease, type 2 diabetes, and some cancers [1]. Even a minor weight loss of 4—6% in obese individuals with impaired glucose tolerance is associated with a reduction of the risk of type 2 diabetes by 58% within 3—5 years [2,3]. The two major factors that are conducive to weight gain are reduced level of physical activity and excess energy intake [4]. There is a lively debate on the optimal composition of macronutrients (carbohydrate, fat, and protein) in the diet for restricting total energy intake and succeeding with weight reduction [5]. The predominant view during the past few decades has regarded a low-fat diet as the best choice [6]. Major arguments are that fat is less satiating than carbohydrate and protein per calorie [7] and that fat is the most energy-dense among macronutrients (9 kcal/g as opposed to 4 kcal/g for carbohydrate and protein). This suggests that a high-fat diet could lead to over-consumption of energy, in particular if food volume is regulated [8,9]. On the other hand, a low-fat diet need not have low energy density; many commercially promoted low-fat foods, based on sugar or highly refined carbohydrates, have a similar energy value to their high-fat counterparts; a salad with oil dressing can provide a high percentage of energy from fat but have a low energy density [10]. Other arguments are based on randomised controlled trials (RCTs). In a metaanalysis of RCTs [11—14], Astrup concludes that a reduction in dietary fat of 10% will lead to a weight loss of about 4—5 kg in subjects with a BMI of 30 kg/m2 [15]. These conclusions are challenged by a meta-analysis of six RCTs by Pirozzo et al. [16], who conclude that low-fat diets are no more efficacious than other weight-reducing diets for achieving sustained weight loss, and also by other recent studies [17—22]. Willett [23] and Pirozzo et al. [16] have argued that the studies used in a meta-analysis by Astrup et al. [11] cannot ascertain the longterm effect of low-fat diets, since they are short-

or medium-term (up to 6 months): a common observation in studies is that weight loss plateaus after 3—6 months [11], and that subjects have regained some of the initial weight-loss after 12 months [24]. Another shortcoming is that the intervention group (on a low-fat diet) often receives state-of-the-art instruction and support, but the control group does not; a study which offers similar coaching to both a low-fat diet group and an energy-restricted-diet group reports comparable weight losses for both groups [25]. Our conclusion from the studies cited above is that adherence to a prescribed diet over a longer period (several years) may be among the most important factors for long-term weight-reduction, more important than the ratio of dietary fat. An argument for a low-fat diet is that fats are often considered to lend greater flavour and palatability to foods, which could thus increase their consumption. On the other hand, high palatability may perhaps be the most important factor for long-term adherence to a low-energy diet. A study by McManus et al. [20] reports better long-term (18 months) weight loss from a moderate-fat Mediterraneanstyle diet compared to a low-fat diet. The study attributes the better weight loss on the moderatefat diet to superior participation and adherence. As a possible explanation, it suggests that the low-fat diet was less appetizing. However, the study did not actually measure the palatability, or some similar property, of the diets. Although many would agree that palatability exerts a powerful influence on eating behaviour, there is no systematic body of data to explain the strength or the limits of the effect [26]. Hence the aim of our study was to investigate how perceived hunger and palatability of the diet affect adherence and weight reduction, and whether the fat content of the diet makes a difference in this respect. Most previous studies on hunger, eating behaviour, food choice, etc., have been performed under laboratory conditions during a few days. Our study was carried out on freeliving subjects. For numerous logistical reasons the NUGENOB study was limited to 10 weeks. This is not enough to demonstrate persistent changes, but it may better transfer to medium-term effects for

Perceived hunger, palatability, and adherence: A comparison of high- and low-fat diets free-living subjects than most previous studies on hunger and eating behaviour.

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Subjects and methods

two hypocaloric diets, including 100 obese subjects of both genders. Inclusion criteria were body mass index ≥30 kg/m2 and age 20—50 years. Exclusion criteria were weight change >3 kg within the 3 months before the start of the study, hypertension, diabetes or hyperlipidemia treated by drugs, untreated thyroid disease, surgically or drug-treated obesity, pregnancy, participation in other trials, alcohol or drug abuse. Inclusion and exclusion criteria were assessed by measurements and questionnaires at a pre-study screening one week before start of the study. Participants were recruited through the media. Recruitment of subjects was undertaken from May 2001 until September 2002. The study was carried out during 2002 at the Obesity Unit, Huddinge University Hospital, under supervision of Prof. Stephan R¨ ossner and Dr. IngaLena Andersson. The study is a subproject within the larger project NUGENOB (Nutrient-Gene Interaction in Human Obesity: Implications for Dietary Guidelines), a European Community project with the objective to improve understanding of the role of interaction between nutrition, especially fat intake, and genetic variation, in obesity. Some results of the larger NUGENOB project have been reported by Peterson et al. [27].

Protocol and participants

Assignment and participant flow

The study was a randomised, parallel, two-arm, open-label 10-week dietary intervention study of

The 100 subjects were randomly divided into two groups of 50 subjects each. Stratified block ran-

Aims of the study The main goal was to study whether there is a difference in perceived hunger and palatability between high- and low-fat diets, and furthermore to see if possible differences are correlated with the degree of adherence to a diet and with weight reduction. The study was carried out on free-living subjects. The primary question of the study was thus to study • how perceived hunger, palatability, and adherence is related to the fat content of isocaloric diets for free-living obese subjects. Secondary questions were to study • how adherence is related to perceived hunger and palatability of the diet for free-living obese subjects, and • how perceived hunger, palatability, and adherence is related to weight-reduction for free-living obese subjects.

Table 1

Clinical and demographic characteristics of patients with a low and high fat diet

Variable

Diet 25% fat (n = 48)

Diet 45% fat (n = 52)

Gender

Male Female

10 (21%) 38 (79%)

10 (20%) 41 (80%)

Age (years)

M (median) S.D. Range

37.9 (29.0) 6.22 25—47

38.2 8.29 21—51

Smokers

11 (26%)

10 (23%)

Height (cm)

M S.D. Range

171 10.0 158—197

170 8.9 154—193

Weight (kg)

M S.D. Range

107 17.8 76—1629

106 16.1 73—153

BMI (kg/m2 )

M S.D. Range

36.6 4.45 30—49

36.5 4.55 29—46

Waist circumference (cm)

M S.D. Range

112.3 11.95 90—143

111.8 9.75 95—141

˚ berg et al. G. A

104 domisation was used with gender and three age groups (20—29, 30—39, and 40—50 years) as strata and a block size of 12. One group received a low-fat diet and the other group received a high-fat diet. Table 1 summarises clinical and demographic data of the two subject groups.

Diets The target macronutrient composition of the two diets was as follows: low-fat diet —– 20—25% of total energy from fat, 15% from protein and 60—65% from carbohydrate; high-fat diet —– 40—45% of total energy from fat, 15% from protein and 40—45% from carbohydrate. Both diets were designed to provide 600 kcal/day less than the individually estimated energy requirement based on an initial resting metabolic rate multiplied by 1.3. Subjects were given oral and written instructions relating to these targets based on an educational system, previously used by e.g., Verdich et al. [28], consisting of four colour-coded isocaloric interchangeable units (60 kcal each). Each colour represented a different nutrient composition: blue counters for food rich in protein, green counters for food rich in complex carbohydrate and fibre, yellow counters for food rich in simple carbohydrate, and red counters for foods rich in fat. Subjects were requested to adhere to a diet, such that the number of counters represented their target energy intake, and so that 20—25% or 40—45% respectively should be red counters. Subjects received a booklet with a description of the systems and with about 700 different foods divided in 15 groups, and also received a counter-diary to fill in every day. Instructions were also given to minimise differences between the two diets in other components such as sources and type of fat, amount and type of fibre, type of carbohydrate, fruit and vegetables, and meal frequency. Subjects were requested to abstain from alcohol consumption. All food items were purchased by the subjects themselves. The dietary instructions were reinforced weekly. At each session, a dietician gave individual feedback on how close the actual diet was to the prescribed diet, both in terms of energy and macronutrient composition.

Measurements of food intake and body weight

analysed using a food-nutrient database published by the Swedish National Food Administration.

Measurement of perceived hunger, palatability, difficulty, and adherence During the study, each subject was asked to assess his/her perceived hunger, palatability of the diet, difficulty of following dieticians instructions, and adherence to the prescribed diet, by rating each factor daily on a VAS scale. VAS scales, developed by Hill and Blundell [29], are commonly used to measure satiety and other feelings in studies on food intake. The questions were end-of-the-day questions, and subjects were asked to estimate the average ‘‘opinion about the day’’. The four questions were, in order (translated from Swedish): ‘‘How hungry have you felt today?’’, ‘‘How did the food taste today?’’, ‘‘How difficult was it to adhere to the dietary instructions today?’’, and ‘‘How well did you adhere to the dietary instructions?’’ Subjects were instructed to make VAS ratings as part of their daily evening routine, from the start of the intervention period. In order to distinguish between adherence as measured by food records, and adherence as rated by subjects on VAS scales, we will refer to the former as ‘‘reported adherence’’ and to the latter as ‘‘perceived adherence’’.

Anthropometry and metabolic rate Body weights were measured on calibrated scales. Body height was measured with a calibrated stadiometer. The mean of three measurements was recorded for each variable. Resting metabolic rate was measured by a ventilated hood system (Deltatrac II, Datex-Ohmeda, Finland).

Statistical analysis Power analysis The project has included 100 obese patients divided into two diet groups of equal size. This number of patients is enough to discover a medium effect size of .54 in any variable [30] based on a two-tailed test, a significance level of 5%, and a power of 85%.

Evaluation A 3-day weighed food record of two weekdays and one weekend day was performed before the study and during the last week of the intervention. Oneday-weighed food records were completed in the 2nd, 5th, and 7th weeks. The dietary records were

Outcomes were: perceived hunger, palatability, difficulty of following instructions, and adherence to diet, as measured by answers to the VAS scales. Also measured was weight loss, as well as reported

Perceived hunger, palatability, and adherence: A comparison of high- and low-fat diets

105

Table 2 Correlations between perceived hunger, palatability, difficulty of following diet instructions, adherence to diet, and weight loss

Perceived hunger Palatability Difficulty of following instructions Perceived adherence to diet * ***

Palatability

Difficulty of following instructions

Perceived adherence to diet

Weight loss

−.55*** —

.63*** −.45*** —

−.11 .02 −.03

−.16 .18 −.21* .14

p ≤ .05. p ≤ .001.

adherence to diet obtained from the weighed food record. Outcomes were correlated with age, sex, and level of education.

fat group. This difference in drop-out rate was not statistically significant (2 = .22, p = .640).

Relationships between ratings Statistical methods Because of sporadic missing values the day-to-day ratings of perceived hunger, palatability, difficulty of following instructions, and adherence to diet were averaged over weeks. Thus, 10 means were obtained per variable. If there were less than five mean weekly ratings missing, the method of last value carried forward was applied for replacing missing values. In the correlation analyses, the recordings during the fifth week were entered. This decision was based upon an analysis of the intercorrelations between every group of ratings, i.e., a factor analysis, where it was shown that the ratings during the fifth week had the highest mean correlation with the other ratings. All observations were summarised using standard descriptive statistics (e.g. mean and standard deviation). The ratings of perceived hunger, palatability, and difficulty of following instructions were approximately normally distributed, while perceived adherence was positively skewed. Thus, perceived hunger, palatability, and difficulty of following instructions were analysed with analyses of variance for repeated measurements (group × time), and perceived adherence was analysed with a nonparametric Mann—Whitney U test. Relationships between normally distributed variables were expressed as Pearson’s product-moment correlation coefficients, and for non-normally distributed variables Kendall’s rank correlation coefficients. The level of significance was set to 5% (two-tailed) in all statistical analyses.

Results Twelve patients did not complete the ratings, five from the low-fat group and seven from the high-

Four ratings of the diet were made — perceived hunger, palatability, difficulty of following instructions, and adherence to diet. The correlations between the ratings are shown in Table 2. A strong inverse relationship was found between perceived hunger and palatability — patients who experienced less hunger tended to rate the diet as more palatable. It was also less difficult to follow a diet which is highly satiating (i.e., giving low score for perceived hunger) and more palatable. Although highly significant relationships between the variables were found, there was a high proportion of unique variance, i.e., for a correlation coefficient of .50 the proportion of common variance was 25% and 75% was, thus, unique.

Perceived hunger and fat content of isocaloric diets The mean VAS-ratings of perceived hunger during the two diets — low and high fat — are shown in Fig. 1. As can be seen, the perceived hunger was rated low throughout the treatment weeks. There was a significant trend towards a lower effect with time throughout the trial [F(1, 86) = 49.99, p < .001]. This trend was similar in both groups with no significant difference [F(1, 86) < 1.00, p = .973]. There was no significant systematic difference in how the two diets were experienced [F(1, 86)) < 1.00, p = .416].

Palatability and fat content of isocaloric diets In Fig. 1, also the mean ratings of palatability are presented. The pattern was opposite to that of perceived hunger. A general linear trend in increasing ratings of palatability with time was observed [F(1,

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˚ berg et al. G. A

Figure 1 VAS ratings of hunger and palatability for subjects with high-fat and low-fat diet. The figure shows weekly averages of end-of-day ratings for weeks 1—10 during the intervention.

Figure 3 VAS ratings of perceived hunger and palatability for subjects that did and did not attain median (7%) drop in BMI, respectively. Weekly averages of end-of-day ratings for weeks 1—10 during the intervention.

86) = 9.93, p = .002] with no significant differences between the groups [F(1, 86) < 1.00, p = .728] and [F(1, 86) < 1.00, p = .963] for the interaction and the systematic effect, respectively.

significant [F(1, 86) = 23.51, p < .001]. No significant differences were found between the groups in trend [F(1, 86) < 1.00, p = .893] and no significant systematic difference [F(1, 86) = 1.28, p = .261].

Difficulty of following instructions and fat content of isocaloric diets

Adherence to diet and fat content of isocaloric diets

The mean perceived difficulty of following instructions, and perceived adherence, of the two diets are shown in Fig. 2. The perceived difficulty of following instructions was highest during the first week (a mean rating of about 50) and decreased during the second and third week and was thereafter stable. The change in rating was statistically

The mean ratings of perceived adherence to the diet, as measured by VAS scaled, remained high and stable during the treatment weeks with a significant increase over time [z = 2.851, p = .004]. There was no significant difference between the two diets in change over the treatment period (z = .01, p = .993), and no significant systematic difference (all z-values were nonsignificant after Tukey corrections for multiple comparisons). The reported adherence to the diets, as measured by fat content and carbohydrate content of weighed food records at weeks 0, 2, 5, 7, and 10, is shown in Table 3. It can be seen that the reported adherence follows quite well the prescribed diet for each group. The measurement at week 0 was performed before the intervention, and should therefore not be influenced by the dietary prescriptions of the study.

Outcome vs. ratings of hunger, palatability, difficulty of following instructions, and adherence to diet

Figure 2 VAS ratings of adherence and difficulty of following instructions for subjects with high-fat and low-fat diet. Weekly averages of end-of-day ratings for weeks 1—10 during the intervention.

The patient group was split according to the median change in body weight (7% drop or more). The ratings of perceived hunger, palatability, difficulty of following instructions, and adherence for both groups are shown in Figs. 3 and 4. Patients who

Perceived hunger, palatability, and adherence: A comparison of high- and low-fat diets Table 3

107

Compositions of the diet, the low and high fat diets Diet 25% fat (n = 46)

Diet 45% fat (n = 45)

M

S.D.

M

S.D.

p

672 458 399 649 344

2,193 1,619 1,617 1,650 1,676

604 382 361 430 349

.3985 .7097 .8242 .8709 .0473

Energy intake (kcal/day) Baseline 2,080 Week 2 1,586 Week 5 1,600 Week 7 1,631 Week 10 1,530 % Total intake from carbohydrate Baseline 49 Week 2 53 Week 5 54 Week 7 54 Week 10 54

6.9 6.7 7.4 5.8 5.0

48 40 39 38 37

6.3 6.9 5.5 5.4 5.1

.4242 .0000 .0000 .0000 .0000

% Total intake from fat Baseline 35 Week 2 26 Week 5 25 Week 7 26 Week 10 25

7.0 6.2 7.0 6.9 5.0

36 41 41 42 44

5.9 6.7 5.3 6.3 5.0

.5265 .0000 .0000 .0000 .0000

% Total intake from protein Baseline 16 Week 2 21 Week 5 20 Week 7 20 Week 10 21

3.5 3.5 3.6 3.9 2.9

16 20 20 20 19

3.2 4.1 3.8 3.6 2.0

.7208 .1381 .8099 .5639 .0012

accomplished to reach the median change of 7% tended to decrease their perceived hunger during the treatment period more than the group with a worse outcome [F(1, 85) = 4.12, p = .046]. Patients who reached the median change had a slightly

greater increase in perceived hunger, although not significantly, during the first week [F(1, 88) = 3.13, p = .080]. Patients who reached the median change also tended to increase their perceived palatability more than the group with a worse outcome, but the difference was not significant [F(1, 85) > 1.00, p = .498]. Both outcome groups decreased their rating of difficulty of following instructions, but the group with a better outcome seemed to have systematically less difficulties throughout the treatment period [F(1, 85) = 4.35, p = .040]. An analogous difference was obtained for perceived adherence (most of the z-values of the Mann—Whitney U test was significant at less than the 5% level).

Age, sex, and educational level vs. ratings of hunger, palatability, adherence to diet and difficulty of following instructions

Figure 4 VAS ratings of adherence and difficulty of following instructions for subjects that did and did not attain median (7%) drop in BMI, respectively. Weekly averages of end-of-day ratings for weeks 1—10 during the intervention.

Younger patients (

Perceived hunger, palatability, and adherence: A comparison of high- and low-fat diets.

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