OBJECTIVE: The goal of this study was to evaluate the effect of two diets (‘food combining’ or dissociated vs balanced) on body weight and metabolic parameters during a 6-week period in an in-hospital setting.
SUBJECTS AND DESIGN: 54 obese patients were randomly assigned to receive diets containing 4.5 MJ/day (1100 kcal/day) composed of either 25% protein, 47% carbohydrates and 25% lipids (dissociated diet) or 25% protein, 42% carbohydrates and 31% lipids (balanced diet). Consequently, the two diets were equally low in energy and substrate content (protein, fat and carbohydrate) but widely differed in substrate distribution throughout the day.
RESULTS: There was no significant difference in the amount of weight loss in response to dissociated (6.2 ± 0.6 kg) or balanced (7.5 ± 0.4 kg) diets. Furthermore, significant decreases in total body fat and waist-to-hip circumference ratio were seen in both groups, and the magnitude of the changes did not vary as a function of the diet composition. Fasting plasma glucose, insulin, total cholesterol and triacylglycerol concentrations decreased significantly and similarly in patients receiving both diets. Both systolic and diastolic blood pressure values decreased significantly in patients eating balanced diets. The results of this study show that both diets achieved similar weight loss. Total fat weight loss was higher in balanced diets, although differences did not reach statistical significance. Total lean body mass was identically spared in both groups.
CONCLUSION: In summary at identical energy intake and similar substrate composition, the dissociated (or ‘food combining’) diet did not bring any additional loss in weight and body fat.
Obesity is nowadays commonly accepted as a chronic disease associated with known co-morbid conditions such as type 2 diabetes mellitus,1,2,3 hypertension, coronary artery disease, hypercholesterolaemia, arthrosis, gout and cancer,4,5,6 as well as a reduction in life expectancy. During the last decade a large amount of information regarding its pathophysiology, and more specifically the adipocyte's signalling mechanisms, has emerged. Despite several missing links in the aetiology of this complex and heterogeneous disease, most authorities agree upon a disequilibrium between energy intake and expenditure being a key factor in the development of obesity. Thus, total energy intake plays a pivotal role in the development and maintenance of obesity.
Patient education and dietetic counselling are mandatory as the first steps in the therapeutic approach to obesity. Concerning the influence of qualitative diet composition on weight loss, several authors7,8,9,10 agree that the total energy intake, and not its composition, determines the final weight loss. Nevertheless, when it comes to long-term follow-up, mixed, varied and individually tailored diets achieve better compliance.11,12 Once total energy intake has been adequately reduced and tailored to the patient's individual needs, compliance becomes an issue. Long-term outpatient dietary studies tend to show a decrease in compliance with time.13 The latter is difficult to assess on an ambulatory basis where the main source of information relies on dietary diaries.14 Theoretically, it should be easier to monitor and therefore improve patient dietary adherence in an in-hospital setting. Unfortunately these kind of studies require a multi-disciplinary approach, are time-consuming and are rarely attempted.
All sorts of different diets have been popularized by the media in recent years.15,16,17 Among them, dissociated diets, commonly known as food combining diets, have lately gained popularity and have gathered a full array of false beliefs concerning their potential benefits. Their main principle consists in spreading the intake of substrates (carbohydrate, fats and proteins) throughout daytime. Montignac18 states that carbohydrates and lipids should not be ingested simultaneously during a meal since the former, acting as a potent insulin secretagogue, would favour an increase in fat cell stores (i.e. insulin's antilipolytic and lipogenic effect). Interestingly enough this statement relies purely on a theoretical basis and is lacking scientific proof. On the contrary, Bobbioni-Harsch et al 19 have recently shown that energy expenditure and substrates oxidative patterns are identical after glucose, fat or mixed loads in normal weight subjects on a short-term basis (8 h).
The aim of our study is to compare the medium-term (6 weeks) effects of a low-calorie (1000 kcal/day) dissociated vs balanced (1000 kcal/day) diet in an in-hospital setting.
Material and methods
Fifty-four adult obese patients were studied before, during and after a 6-week period of hospitalization. These subjects had been referred to the Obesity Outpatient Clinic of the Department of Medicine at Geneva University Hospital for dietary treatment of their obesity.
During the first visit, it was decided on the basis of a failure to lose weight in response to ambulatory treatment that these individuals would benefit if they were hospitalized for the first 6 weeks of treatment. Criteria for admission included a body mass index >30 kg/m2 strong personal motivation, and the ability to participate in the requisite amount of physical activity. Patients with obesity secondary to endocrine disease, as well as those with psychiatric diagnoses were excluded from the study. The protocol was submitted to and accepted by the ethical committee of the Department of Medicine at Geneva University Hospital. In addition to a low calorie diet, subjects participated in a structured, multidisciplinary program that included physical activity, nutritional education and standard behavioural techniques. Exercise consisted of 1 h of aerobic exercise training per day and 1 h of exercises in a swimming pool per day. Nutritional education was provided by a registered dietitian twice a week (once in a group session and once individually). The cognitive–behavioral approach consisted of six sessions, during which issues of self-control, cognitive restructuring, reinforcement, and relapse prevention were addressed.
On admission to the hospital, patients were randomly assigned to two groups whose baseline characteristics are listed in Table 1. After baseline metabolic data were acquired, the patients were assigned to receive one of the two experimental diets whose composition is listed in Table 2. Both diets consisted of natural foods. Recipes and menus of various food items were standardized. A 7 day rotational menu was employed. The menus provided similar protein composition but offered diverse foods. Itemized composition of meals from one day of the rotation menu for the balanced and dissociated diets are given in Table 3. Protein intake was fixed to be at least 25% of the total daily energy intake (1.2 g of protein/kg of ideal body weight)7,20 in order to avoid muscular wasting. Group 1 (n=28, 21 F/7 M) received a balanced diet while group 2 (n=26, 20 F/6 M) received a dissociated diet. Both experimental diets had identical energy content (4.5 MJ/day, 1100 kcal/day). The balanced diet's composition was 42% carbohydrates and 31% lipids. The dissociated diet's composition was 47% carbohydrates and 25% lipids. Both diets contained similar amounts of saturated fat (14 g/day) and cholesterol (230 mg/day). Daily energy intake was distributed between breakfast (22%), lunch (33%), dinner (33%) and bedtime snack (12%). Energy intake was carefully measured for each patient. All subjects were instructed to eat all foods and a dietitian was present during each meal to improve compliance and education. To verify compliance with the diet and mainly for education purpose, patients completed a one day food record once a week during the 6 weeks of the study. These food records took the quality and the quantity of the consumed food into account. The software PRODI3+ was used to calculate meal plans and food records.21 The food composition tables used were from Souci et al 22 and Renaud and Attil.23 The balanced diet associated the three substrates during each meal, while dissociated diets did not allow simultaneous consumption of lipids and carbohydrates. Blood was drawn after a 14 h overnight fast before and after 2, 4 and 6 weeks of both balanced and dissociated diets for measurements of plasma glucose,24 plasma immunoreactive insulin,25 total cholesterol,26 high-density-lipoprotein (HDL)-cholesterol, and triacylglycerol concentrations.27 Nitrogen balance was measured to compare the protein-sparing effect of both diets. Urinary nitrogen was measured by the Kjeldahl method.28 Twenty-four-hour urine samples were collected every week and average urinary loss was computed on the basis of these six collections. Integumental and stool losses were estimated on the basis of previously reported studies; 5 and 10 mg/kg body weight, respectively.29 Daily nitrogen balance was calculated by subtracting total output (urine, stool/and integumental losses) from dietary input.
Body fat composition and percentage of adiposity were determined by bioelectrical impedance analysis.30 Data are expressed as means statistically significant (95% confidence)±s.e.m.s and were analysed with the Statview4 software package. To evaluate the differences the two groups of obese patients, before and after weight loss, data were analysed by two-way analysis of variance, with the multiple-comparison approach of Scheffe.
As depicted in Table 2, daily protein intake and average protein losses were very similar in both groups. Being equally low in energy, both diets were similarly catabolic. Values for age, systolic and diastolic blood pressure values, total body weight, BMI, waist and hip circumferences, and waist-to-hip ratio before the diets are given in Table 4. These values were perfectly comparable between the two groups at baseline. Total body weight, body mass index, waist and hip circumferences (as well as their ratio) decreased significantly in both groups and the magnitude of the changes did not vary as a function of the type of diet; nevertheless the group receiving the balanced diet showed a tendency to lose weight more than the group on the dissociated diet (7.5±0.4 kg vs 6.2±0.6 kg, P=NS).
Both systolic and diastolic blood pressure values decreased significantly in the group receiving balanced diet, but not in the other group. However, there were no differences between two groups.
Table 5 lists values for fasting plasma glucose, insulin, cholesterol, HDL-cholesterol and triacylglycerol concentrations before and after 6 weeks of dietary intervention. At baseline there were no significant differences in either group. In both groups plasma glucose, cholesterol, HDL-cholesterol and triacylglycerol concentrations decreased significantly. Similarly, insulin concentrations decreased in both groups at the end of the study.
In this study we evaluated the effects of two low-energy diets (balanced and dissociated) on both weight loss (total and fat body weight) and various metabolic parameters. The amount of weight loss was similar in response to the two diets (which had similar energy and macronutrients contents (Table 2)) and was apparently independent of the substrate distribution within meals, being principally related to total energy intake, in accordance with previous works from our group and others.7,8 The theoretical energy expenditure with each diet was calculated using the Harris–Benedict formula. According to the latter, the expected fat loss would be 4.5 kg in 6 weeks. The theoretical fat loss was then compared to the fat loss assessed by electrical bio-impedance. Therefore, dietary compliance was maximal in the group receiving the balanced diet (100%), while it was estimated to be 84% in the group receiving the dissociated diet. These differences in calculated compliance may account for the differences in observed weight loss. The small, not significant, difference in body fat loss may also be due to inaccurate determination by bioelectrical impedance.
Systolic and diastolic blood pressure values fell significantly in the group receiving balanced diet, but there were no differences between the groups in the change in blood pressure. Interestingly dietary salt content was similar in both diets and none of the patients in either group were on anti-hypertensive medications. In opposition to popular beliefs, variations in the daily distribution of substrates did not add any supplemental metabolic benefit. More specifically, both diets allowed a significant improvement in fasting plasma glucose, cholesterol and triacylglycerol values. At the end of the study there were no significant differences in plasma glucose, insulin, triacylglycerol or HDL-cholesterol between the two groups. In conclusion, our results substantiate the lack of benefit of dissociated (food combining) vs balanced diets in terms of weight loss and further support that it is energy intake, not energy composition or distribution throughout daytime, that determines weight loss in response to low-energy diets.
We are grateful to the members of the Dietary staff of the Department of Medicine for their assistance, in particular to P Rigoli, C Bussien and J Duffey.