- Click here for explanation of classification scheme.

• To test the effect on weight loss of a diet incorporating one or two servings per day of foods equal in energy but differing in energy density
• The clinical trial consisted of a six-month weight loss phase and a six-month maintenance phase; the main outcomes were weight loss and change in diet composition at the end of one year.

• 20 to 65 years old
• BMI of 26 to 40kg/m²
• Participants provided written informed consent and were financially compensated for their participation. The protocol was approved by the Office of Research Protections of The Pennsylvania State University, and the study was conducted at the General Clinical Research Center located at the University Park campus of the university
• Potential subjects who met the inclusion criteria were instructed in keeping a detailed record of their food and beverage intake for three non-consecutive days.

• Blood pressure higher than 140/90mmHg
• Serum triglycerides higher than 400mg per dL
• Total cholesterol higher than the 90th percentile for their age and sex
• Had a serious medical condition that precluded participation
• Any condition limiting physical activity
• Were pregnant or lactating
• Had symptoms indicative of depression or an eating disorder
• Followed a sodium-restricted diet
• Were unwilling to regularly consume soup or savory snacks.

Recruitment

Potential subjects were recruited by flyer and newspaper advertisement and their eligibility for the trial was determined by a telephone interview, a physical screening session and questionnaires that assessed symptoms of depression, symptoms of eating disorders and the ability to safely engage in physical activity.

Design

Randomized controlled trial (RCT).

Blinding Used 

For study completers, the three-day diet records were coded by a dietitian who was not involved in the trial.

Intervention 

• Individuals who completed a baseline three-day diet record were assigned to an intervention group; a stratified randomized scheme was used to balance the distribution of subject sex and age across groups
• Subjects were instructed by dietitians to follow an energy-restricted diet; in addition, subjects were randomized to one of four intervention groups
• Subjects in three of the groups were provided a meal plan with dietary exchanges that provided 55% of energy as carbohydrate, 30% of fat and 15% as protein; the meal plan incorporated the provided food (soup or snack food)
• These subjects were given supplies of commercially available food that was low in energy (100kcal per serving) and fat (less than 4g per serving)
• During months one to three, subjects participated in a weekly individual counseling session with a dietitian and completed three-day diet records every two weeks; during months four to six, they had a counseling session every two weeks and completed three-day diet records monthly
• During the weight maintenance phase in months seven to 12, subjects met with a dietitian monthly and completed a total of two three-day diet records
• Each subject attended a maximum of 27 counseling sessions that lasted approximately 15 to 30 minutes each
• The study foods had a similar energy content (mean 100kcal per serving) and fat content (less than 4g per serving) but different in energy density (mean 0.35kcal per g for soups and 4.2kcal per g for snacks). Thus, although the study foods had the same energy content per serving, they had very different weight, volume and water content per serving
• Subjects in the soup groups could select from 18 kinds of commercial soups (six of which were also available in a low-sodium version) and were given a mug that held one serving of soup (300g;10.5 fl. oz.)
• Subjects in the snack group could choose from 18 varieties of commercial snacks (crackers, baked potato chips, baked tortilla chips, bagel chips and pretzels) that were provided in packages containing a single serving (24g)
•  In the dietary exchange system followed by the subjects, each serving of soup or snack replaced one grain exchange, so that the energy level of the assigned diet was not altered
• Subjects in all groups were told that the purpose of the trial was to test the inclusion of different food in a weight loss diet and were not given any specific information related to energy density or other qualities of the soup and snacks. 

Statistical Analysis

• Continuous outcomes were analyzed with a linear mixed model, which took into account auto-regressive nature of the repeated measures
• Intervention group, subject gender and study week were treated as fixed effects
• Anthropometric and physiological outcomes were analyzed for subjects who completed the study and also for all randomized subjects (testing the least-squares means from the linear mixed model)
• Food and nutrient intake data from the diet records were available only for study completers. Multivariate ANOVA was used to test macronutrient intakes as a percentage of energy intakes.
• Categorical outcomes from the questionnaires were analyzed using  X² test; where there was no effect of study weeks, outcomes from all available study week were analyzed together
• Step-wise regression analyses were performed to predict weight loss based on intervention group, subject characteristics and dietary and activity measures
• Differences were considered significant at P<0.05, except for post hoc pair-wise comparison between groups, for which modified Bonferroni adjustment was used (P<0.025). 

Timing of Measurements

• Body weight was measured at each counseling session
• Blood pressure was measured monthly using a standard method
• Fasting (12-hour) blood specimens were collected at baseline at baseline and at three, six and 12 months
• Dietary intake measured at baseline and one, three, six, nine and 12 months
• Physical activity assessed at each counseling visit.

Dependent Variables

• Weight measured with the subject wearing light clothing without shoes, using a scale that was regularly calibrated
• Blood pressure was measured using a standard method
• Fasting (12-hour) blood specimens analyzed for measurements of serum lipids and lipoproteins, performed at the Lipid Laboratory (Mary Imogene Basset Research Institute, Cooperstown, NY), which participates in the Center for Disease Control Lipid Standardization Program.
• Change in diet composition. 

Independent Variables

• Intervention group (either one or two servings of low energy-dense soup, two servings of high energy dense snack foods or no special food)
• Food records were analyzed for nutrients and food group servings using U.S. Department of Agriculture food comparison data supplemented with data from commercial sources
• Food energy density (kcals per gram) were calculated as the ratio between food energy and food weight, both excluding beverages; soup was calculated as a food in this calculation
• Eating occasions were categorized either as main meals (breakfast, lunch or dinner) or as between-meal snacks, based on the time of day and type and amount of food eaten
• Subjects in the soup and snack intervention groups were asked to complete daily records for their study food intake and were told that it was preferable to consume their servings of provided foods just before their lunch and dinner meals
• The Diet Satisfaction Questionnaire assessed subjects’ satisfaction with their food plan using seven-point scales
• The Eating Inventory measured dietary restraint (the tendency to consciously restrict food intake to control body weight), distribution (the loss of control over eating in response to emotional or social cues) and hunger (tendency to subjective feelings of hunger)
• The Food Preference questionnaire assessed preference for the taste of low-and high-fat versions of common foods
• Leisure–Time Exercise Questionnaire was used to assess physical activity during the past week.        

• Initial N: 200 overweight and obese women and men (154 females, 46 males), 50 in each group
• Attrition (final N): At the end of 12 months, 147 subjects remained in the trial (74%); these subjects were referred to as study completers. The most frequent reasons for withdrawal were inability to attend counseling sessions and difficulty in complying with the requirements of the diet or the record-keeping. 37 subjects in the Two Snack group, 39 subjects in the One Soup group, 34 subjects in the Two Soups group and 37 subjects in the Comparison group completed the study 
• Age: 20 to 65 years old
• Anthropometrics: There were no differences among intervention groups in baseline demographic, physiological or psychological characteristics, but there were some differences in dietary intakes. At baseline, the Two Soup group reported a greater mean daily intake of fruits and vegetables (P=0.024) and a greater sodium intake (P=0.028) than the other three groups
• Location: University Park, Pennsylvania.

Baseline Characteristics (Mean±SE) of the 200 Randomized Subjects 

	Intervention Group
	Two Snacks	One Soup	Two Soups	Comparison
Characteristics (N=50)
Age (years)	44.5±1.2	45.1±1.2	43.8±1.2	45.2±1.2
Height (cm)	168.4±1.1	167.4±1.4	169.5±1.3	167.8±1.1
Body weight (kg)	89.2±1.9	86.5±1.9	88.4±1.8	88.1±1.7
BMI (kg/m2)	31.4±0.4	30.9±0.5	30.8±0.5	31.3±0.4
Activity score*	272±29	367±42	400±40	356± 44
Energy expenditures (kcal per day)¶	2,073±39	2,049±44	2,046±35	2,052±36
Energy intake (kcal per day)§	1,978±82	2,209±82	2,191±113	2,056±94
Energy goal for weight loss	1,323±39	1,299±34	1,296±35	1,302±36

*From the Leisure-time Exercise Questionnaire (19).

^¶Estimated from sex, age and activity level (15).

^§From three days of diet records for study completers only (N=147).

Mean (±SE) Weight Loss and Reported Dietary Intakes for 147 Study Completers at Major Time Points

	Baseline	Six Months				12 Months
	All Groups	Two Snacks	One Soup	Two Soups	Comparison	Two Snacks	One Soup	Two Soups	Comparison
	(N=147)	(N=37)	(N=34)	(N=39)	(N=37)	(N=37)	(N=34)	(N=39)	(N=37)
Weight loss
Weight loss (kg)	NA*	6.1±0.7a	7.9±0.9ab	7.6±0.8ab	9.0±1.1b	4.8±0.7a	6.1±1.1ab	7.2±0.9b	8.1±1.1b
Percentage weight loss (% initial weight)	NA	7.0±0.8a	9.1±0.9ab	8.4±0.9ab	10.2±1.2b	5.5±0.8a	6.9±1.2ab	7.9±1.0b	9.2±1.2b
Dietary intakes
Soup intake (servings per day)	0.10± .02	0.25± .06a	1.09±0.09b	1.72±0.09c	0.40±0.07a	0.11.± .04a	0.90±0.09b	1.33±0.12c	0.10±0.04a
Snack food intake (servings per day)	0.16±0.03	1.93±0.06a	0.20±0.06b	0.13±0.04b	0.20±0.05b	1.90±0.15a	0.26±0.07b	0.18±0.06b	0.13±0.05b
Total energy (kcal per day)	2,110±47	1,430±45	1,557±82	1,390±57	1,538±90	1,441±26	1,496±42	1,443±32	1,496±0.42
Food weight (g per day)	1,013±25	830±33a	1,214±65b	1,226±47b	1,001±44c	859±30a	1,125±55b	1,244±67b	955±41a
Dietary energy density (kcal per g)¶	1.86±0.03	1.61±0.05a	1.23±0.05b	1.03±0.04c	1.40±0.05d	1.73±0.06a	1.32±0.06b	1.23±0.06b	1.54±0.05c
Fruit and vegetable group (servings per day)	5.8±0.2¶	4.7±0.3a	6.1±0.5b	6.4±0.3b	5.8±0.3ab	5.2±0.3a	5.9±0.5ab	6.8±0.4b	6.0±0.05ab
Grain and cereal group (servings per day)	7.5±0.2	6.5±0.3a	6.1±0.5a	4.8±0.3b	5.8±0.4ab	6.7±0.3	5.8±0.5	6.2±0.5	5.8±0.4

At a given time-point, means with different superscript letters are significantly different (modified Bonferroni comparison, P<0.025).

*NA, not applicable. 

^¶Energy density of food only, excluding beverages.

^§Fruit and vegetable intake differed by group at baseline; subjects in the Two Soups groups had a greater intake than the other groups (P=0.024).

Other Findings

• All four groups showed significant weight loss at six months that was well maintained at 12 months
• The magnitude of the weight loss, however, differed by group (P=0.006)
• At one year, weight loss in the Comparison (8.1±1.1kg) and Two Soup (7.2±0.9kg) groups were significantly greater than that in the Two Snack group (4.8±0.7kg); weight loss in the One Soup group (6.1±1.1kg) did not differ significantly from other groups
• Weight loss was significantly correlated with the decrease in dietary energy density from baseline at one and two months (P=0.0001), but not at six and 12 months.

 

• The hypothesis that changes in daily energy intake were caused by differences in satiety attributable to the dietary modifications remained feasible. The variations in reported food energy density and food weight that resulted from changing only two servings of food per day were striking; at six months, food energy density was 1.6kcal per day in the Two Snack group and 1.0kcal per day in the Two Soup group
• This randomized trial of modification of an energy restricted diet resulted in substantial weight loss in all intervention groups after six months, which was well-maintained for a further six months and resulted in improvements in blood pressure and blood lipids
• The magnitude of the weight loss, however, varied among groups
• The main evaluation of the trial demonstrated that consuming two servings of soup daily led to greater weight loss than consuming the same amount of energy as two servings of a dry snack food daily
• After one year, weight loss in the two groups was 50% greater than in the snack group(7.2 vs. 4.8kg). Thus, substituting a type of food that was low in energy density for one that was high energy density increased the magnitude of the weight loss
• These results extend the findings of single-meal experiments showing that consuming a food low in energy density increases satiety and decreases energy intake compared with consuming a food high in energy density
• The responses to the Diet Satisfaction questionnaire provided evidence that satiety played a role in the differential weight loss among groups; a greater percentage of subjects in the Soup group reported feeling very full and not hungry during the intervention. The regression analysis showed that the decrease in food energy density was the most significant predictor of weight loss at one and two months, when subjects were the most motivated and compliant and achieved most of the weight loss
• Weight loss in the trial was predicted by scores from the EATING Inventory. The decrease in the dis-inhibition score and increase in dietary restraint score predicted the mount of weight loss at six and 12 months
• The diet followed by the subjects in the comparison group was a standard one used for treating obesity. Because subjects in the comparison group were not required to eat a special food and record this intake each day, it is possible that they were able to concentrate on the dietary advice with fewer distractions
• These findings provide support for regular consumption of food low in energy density, such as soup, as a strategy for weight management.

Government:	NIH Grant MO1 RR 10732
Industry:	Campbell Soup Company Food Company:
University/Hospital:	General Clinical Research Center of the Pennsylvania State University

• High dropout rate of 26%; it was unclear if withdrawals from groups were similar 
• Differences in dietary intake between groups at baseline. 
• Authors note the following limitations:
  • Although they expected differences in satiety to affect compliance with the diet, the authors were unable to demonstrate differences in reported energy intake that would account for differences in weight loss among the groups
  • The most likely reason for this finding is that the diet records were insufficiently precise to measure the differences in daily energy intake that were involved (less than 120kcal per day).