OBJECTIVE: To determine change of weight, body composition, metabolic and hormonal parameters induced by different intervention protocols.
DESIGN: Randomized, controlled study including participants exhibiting a BMI between 27.5 and 35. Three different interventions containing lifestyle education (LE-G), or a substitutional diet containing a high-soy-protein low-fat diet with (SD/PA-G) or without (SD-G) a guided physical activity program.
SUBJECTS: A total of 90 subjects (mean weight 89.9 kg; mean BMI 31.5), randomly assigned to one of three treatment groups.
MEASUREMENTS: Change in body weight, fat mass and lean body mass measured with the Bod Pod® device at baseline, 6 weeks and 6 months; change in metabolic and hormonal parameters.
RESULTS: In all, 83 subjects completed the 6-months study. BMI dropped highly significantly in all groups (LE-G: −2.2±1.43 kg/m2; SD-G: −3.1±1.29 kg/m2; SD/PA-G: −3.0±1.29 kg/m2). Subjects in the SD-G and in the SD/PA-G lost more weight during the 6-months study (−8.9±3.9; −8.9±3.9 kg) than did those in the LE-G (−6.2±4.2 kg), and had a greater decrease in fat mass (−8.8±4.27; −9.4±4.54 kg) than those in the LE-G (−6.6±4.59 kg). In contrast, no significant intraindividual or between-group changes in the fat-free mass were seen. In all groups, metabolic parameters showed an improvement in glycemic control and lipid profile.
CONCLUSIONS: Our data suggest that a high-soy-protein and low-fat diet can improve the body composition in overweight and obese people, losing fat but preserving muscle mass.
In high-income countries, people are eating more and exercising less, resulting in an increase of body weight. In many developed countries, as much as half of the adult population are overweight and more than 25% obese.1 There are many conventional dietary approaches to weight management, recommended by the leading research and medical societies. However, only a few studies evaluated their long-term efficacy with respect to body composition, for example, changes in muscle vs fat mass.2, 3 The balance of macronutrients in a diet to lose weight is still in debate. Diets with a high proportion of carbohydrates may reduce the oxidation of body fat,4, 5 increase blood triglycerides6, 7 and reduce satiety.2, 8, 9 On the other hand, protein-rich diets may reduce energy efficiency and increase thermogenesis,10, 11 reduce the resting energy expenditure in response to a diet to a lesser extent,12, 13 spare muscle protein loss3 and enhance glycemic control.3, 14
We conducted a 6-month randomized, controlled trial to estimate the efficacy of a staged high-soy-protein and low-fat diet. The primary objectives were weight loss and a reduction in BMI of at least 2.5 kg/m2 after 6 months; a secondary objective was loss of fat mass and preservation of muscle mass.
Out of a group of more than 500 interested people recruited by public advertisement, potential subjects were excluded if they had clinically significant illnesses, including type II diabetes, were taking lipid-lowering medication, or were taking medications that affect body weight. From 114 eligible people, 90 pre-obese and obese subjects15 were randomized (see Figure 1) to participate in the study (mean weight 89.9±10.9 kg; mean BMI 31.5±2.26 kg/m2; mean fat mass 40.5±6.40 kg). All subjects completed a comprehensive medical examination and routine blood tests. Written informed consent was provided by all subjects, and the study protocol was approved by the local ethic review board.
The subjects were randomly assigned to three different treatment groups: the lifestyle education group (LE-G) attended three bi-monthly teaching sessions, and two individual visiting periods, 6 weeks and 6 months after enrolment; all sessions were led by experts in nutritional counselling. Subjects received a diet-overview handout, in accordance with the ‘German Society of Nutrition’ and the ‘German Society of Sports Medicine and Prevention’. A moderate-fat, balanced nutrient reduction diet was prescribed (1200–1500 kcal/day for women and 1500–1800 kcal/day for men, with approximately 60% of calories from carbohydrate, 25% from fat, and 15% from protein). The subjects assigned to the substitutional diet group (SD-G) were instructed to replace two daily meals by a commercially available soy–yoghurt–honey preparation (Almased®) for the first 6 weeks, followed by the replacement of one daily meal for 18 weeks. For the latter time interval, the dietary intake of fat should not exceed 60 g/day. This diet contained about 1000 kcal/day for women and 1200 kcal/day for men in the first 6 weeks, and then was aimed not to exceed 1500 kcal/day for women and 1700 kcal/day for men in the following weeks. In addition, a third group of subjects was motivated to attend two times weekly a 60-min endurance physical activity program, which was delivered by a sport physician, otherwise, they followed the rules of the substitutional diet group (SD/PA-G).
Data collected at enrolment and thereafter monthly were body weight, waist and abdominal circumference, self-reported medical history, blood pressure, glucose, insulin, serum lipids and inflammatory markers (C-reactive protein, IL-6). For measurement of body composition, the technique of the air displacement plethysmography was used (Bod Pod®).16 Dietary compliance was estimated by a 24-h recall of dietary consumption. However, the data derived from the self-reported 24-h recall showed a major under-reporting in all groups, so these data are not taken into account.
Testing for changes between examination at baseline and at examination after 24 weeks was carried out by paired sample t-test. For comparison of continuous variables between the groups, we calculated the change from baseline to 6 months in each subject and compared the mean changes in the three groups using analysis of variance with post hoc tests (Schiffé). Normality of all variables was tested before statistical testing. Leptin and insulin values were normalized by logarithmic transformation. All P-values were two-sided and a P-value of 0.05 or less was considered to indicate the statistical significance. Analysis was conducted using the SPSS software (version 220.127.116.11).
A total of 83 subjects completed 6 months of the study (28 subjects in the LE-G, 28 subjects in the SD-G, 27 subjects in the SD/PA-G); the differences in characteristics of subjects who dropped out of the study were not statistically significant.
With respect to weight changes during the 6-months study, there were differences between the three groups (F=4.292; P=0.048; ANOVA). Subjects in the SD-G and in the SD/PA-G lost more weight during the 6-months study (−8.9±3.9; −8.9±3.9 kg; NS) than did those in the LE-G (−6.2±4.2 kg) (P=0.048; post hoc analysis) (see Figure 2). The BMI, the second primary objective, dropped highly significantly in the LE-G (−2.2±1.43 kg/m2), in the SD-G (−3.1±1.29 kg/m2) and in the SD/PA-G (−3.0±1.29 kg/m2) (F=4.325; P=0.016; ANOVA). During the 6-months study, subjects had a greater decrease of fat mass in the SD-G and in the SD/PA-G (−8.8±4.27; −9.4±4.54 kg) than those in the LE-G (−6.6±4.59 kg) (F=3.049; P=0.053; ANOVA). In contrast, we did not observe significant intraindividual or between-group changes in the fat-free mass (LE-G: 0.4±1.76 kg; SD-G: −0.1±2.19 kg; SD/PA-G: 0.4±2.29 kg) (F=0.468; P=0.628; ANOVA). The biochemical changes are demonstrated in Table 1, exhibiting a significant improvement in glycemic control in all three groups; no adverse effects on serum levels of inflammatory markers were observed (data not shown).