Regular consumption of diets with increased protein or fibre intakes may benefit body weight and composition and cardiovascular disease risk factors. Lupin flour is a novel food ingredient high in protein and fibre.
To investigate the effects of a lupin-enriched diet, during and following energy restriction, on body weight and composition and cardiovascular disease risk factors in overweight individuals.
Participants (n=131) were recruited to a 12-month parallel-design trial. They were randomly assigned to consume lupin-enriched foods or matching high-carbohydrate control foods. All participants underwent 3 months of weight loss, 1 month of weight stabilization and 8 months of weight maintenance. Body weight and composition and cardiovascular disease risk factors were assessed at baseline, 4 and 12 months.
Lupin, relative to control, did not significantly influence (mean difference (95% CI)) weight loss at 4 months (0.1 kg (−1.2, 1.4)) and 12 months (−0.6 kg (−2.0, 0.8)), maintenance of weight loss from 4 to 12 months (−0.7 kg (−1.83, 0.48)) or measures of body fat and fat-free mass. Relative to control, 24-h ambulatory systolic (−1.3 mm Hg (−2.4, −0.3), P=0.016) and diastolic (−1.0 mm Hg (−1.9, −0.2), P=0.021) blood pressures were lower at 12 months but not at 4 months; fasting insulin concentrations and homeostasis model assessment (HOMA) scores were significantly lower at 4 months (−1.2 mU l–1 (−1.3, −1.1), P=0.004 and −0.6 units (−1.0, −0.19), P=0.004) and 12 months (−1.3 mU l–1 (−1.4, −1.1), P<0.001 and −0.7 units (−1.1, −0.24), P=0.002).
A diet higher in protein and fibre derived from lupin-enriched foods does not enhance weight loss or improve the maintenance of weight loss. However, such a diet may provide cardiovascular health benefits in terms of insulin sensitivity and blood pressure.
Data suggest that a higher protein or fibre diet can enhance satiety and reduce energy intake acutely, and contribute to body weight loss in the longer term.1, 2, 3, 4 Increasing both protein and fibre in the diet can be difficult because popular low-carbohydrate, high-protein diets tend to have quite low fibre intakes.5 Thus, there are limited data on the effects of regular consumption of diets higher in both protein and fibre at the expense of starch. Protein and fibre can independently increase satiety,1, 2, 3, 4, 5 and these effects are likely to result via different mechanisms. Fibre appears to have a role in satiety and satiation through energy dilution, increased mastication, gastric distension, delayed gastric emptying and changes in orexigenic hormones.3 The mechanisms for the effects of protein are less clear but protein may influence satiety via orexigenic hormones.6 Therefore, it could be anticipated that their combined effects on body weight and composition would be additive. A practical approach to increasing both protein and fibre content of processed foods is to incorporate high protein and fibre ingredients into commonly consumed high-carbohydrate foods. There is evidence that this approach could also improve cardiovascular disease risk factors such as blood pressure7 and blood lipids.8, 9
Lupin flour is a novel food ingredient derived from the endosperm of lupin. It contains 40–45% protein, 25–30% fibre and negligible sugar and starch.10 It is commonly used as a minor food ingredient in baked foods, but can be used to partially replace wheat flour in foods such as bread and pasta, resulting in significant increases in protein and fibre levels.11, 12 These foods remain palatable and are acceptable to consumers.12
We have previously shown that high protein and fibre lupin flour-enriched bread, with 40% wheat flour replacement, significantly reduced appetite and energy intake acutely.8 We also showed that the lupin-enriched meal acutely suppressed plasma ghrelin,8 an orexigenic hormone thought to stimulate appetite.13 If consumption of lupin flour-enriched foods has similar effects on energy intake in the longer term, such effects could translate into weight loss. Diets higher in plant protein and fibre may also benefit blood pressure,14, 15, 16, 17 serum lipids18, 19 and glucose and insulin metabolism.20, 21 In a previous 16-week trial, we showed that consumption of lupin flour-enriched bread reduced 24-h systolic blood pressure by 3.0 mm Hg.22 Lupin-enriched diets have also been shown to reduce blood cholesterol concentrations in animals23, 24, 25 and humans.26 Furthermore, acute reductions in postprandial glucose and insulin have been demonstrated with lupin flour-enriched bread consumption,12, 27 but longer-term effects are not clear.11 The effects of a lupin-enriched diet on body weight, body composition and cardiovascular disease risk factors in the setting of weight loss and longer-term maintenance of weight loss have not been investigated.
Therefore, the objective of this study was to investigate the effects of a lupin-enriched diet, during and following energy restriction, on body weight, body composition and cardiovascular disease risk factors in overweight men and women.
Subjects and methods
Overweight and obese (body mass index 27–35 kg m–2), otherwise healthy volunteers aged 20–71 years were recruited from the Western Australian (WA) population through newspaper advertisements from August 2007 to May 2008, into a single-site study. Exclusion criteria included history of cardiovascular or peripheral vascular disease, diabetes, history of asthma, renal disease, liver disease or gout, a psychiatric illness, history of major gastrointestinal problems, other major illnesses such as cancer, hypertension (systolic blood pressure >150 mm Hg or diastolic blood pressure >95 mm Hg), use of antihypertensive agents, total cholesterol >6.2 mmol l–1 or triglycerides >2.0 mmol l–1, use of lipid-lowering medications, women who were pregnant or intended to become pregnant, history of food allergies, current/recent weight loss/gain (change of >6% body weight over last 6 months) and alcohol intake >140 g alcohol per week for women and >280 g alcohol per week for men. In addition, individuals with no history of diabetes, but with fasting plasma glucose concentrations ⩾6.0 mmol l–1 were excluded. Of the ∼800 telephone respondents screened by questionnaire, 231 were eligible and willing to attend the Research Unit for a screening visit. Of those 231 participants, 134 met the inclusion criteria and 131 were randomized and commenced the study (68 men and 63 women). All procedures followed were in accordance with institutional guidelines. The study was approved by the University of Western Australia Human Research Ethics Committee, and all participants provided written informed consent. The study was registered with the Australian New Zealand Clinical Trials Registry ACTRN12607000434493.
A randomized, controlled, double-blind parallel design trial was performed. Eligible participants were randomized into either a control group (consuming control foods) or a lupin group (consuming foods enriched with lupin flour). Eligible individuals were matched for body mass index, age and gender and randomly assigned (1:1) using computer-generated random numbers to either the control or lupin group. The randomization was performed by an independent person and group allocation was sealed in opaque envelopes. Participants and researchers responsible for dietetic intervention and assessment of outcomes measures were blinded as to group assignment. The researcher responsible for food distribution was not blinded to group assignment.
After randomization, participants commenced on a 3-month weight loss program (∼35% energy restriction) designed by a dietitian to achieve an average weight loss in all participants of between 7 and 8% of body weight. This incorporated the consumption of the assigned foods, monthly dietetic visits and fortnightly dietary phone consultations. This was followed by a 1-month weight stabilization period where participants ceased weight loss and maintained body weight within 1.5 kg. During the following 8-month weight maintenance stage, participants followed an ad libitum diet incorporating the assigned foods. The aim during this period was to maintain the weight loss achieved. The primary outcome variable was weight, with the secondary outcomes being body composition, analysed by dual-energy X-ray absorptiometry, including body fat mass and fat-free mass, and cardiovascular disease risk factors including blood pressure, fasting blood lipids, glucose and insulin. All assessments of outcome variables were undertaken at baseline, 4 months and 12 months. The study was run with two cohorts: the first cohort completed the study from October 2007 to November 2008, and the second cohort completed the study from April 2008 to May 2009.
Lupin or control foods were provided to participants and were consumed in place of other cereal-based food products normally used in the diet. The three foods provided were bread, biscuits and pasta. The bread and biscuits were baked at Bodhi's Bakery (Fremantle, Western Australia, Australia). The bread was sliced and supplied fresh or frozen to the participants every month, commencing from baseline. Participants were required to freeze the bread. The biscuits were provided fresh every month starting at the 4-month appointment. The pasta was produced at Belmar Foods (Balcatta, Western Australia, Australia) and was provided fresh every month starting at the 6-month appointment. The food introduction was staggered to keep the initial weight loss period of the study simple, and to aid retention in the later phases of the study by increasing variety.
The lupin flour in the lupin products was substituted for wheat flour, primarily wholemeal, in the control products. The incorporation rate of lupin flour into lupin products was 25–40% by weight. The two sets of food products were matched as closely as possible in colour, taste and texture, and sensory acceptability and energy, fat and sodium content in order to assist in blinding of participants to their treatment group allocation (Table 1).
Dietary intake was assessed using a 3-day food diary designed by a qualified dietitian, based on a previously validated 3-day estimated food record.28 Participants were given both verbal and written instructions on its completion using household measures to quantify intake. The food diaries were completed on two weekdays and one day of the weekend. A weekly log of alcohol intake was included in the food diary, where participants were asked to record their alcohol consumption over 7 days. Food intake data were analysed using FoodWorks Professional 2007 Software (Xyris, Brisbane, Australia) based on the Australian Food Composition Database to determine average daily energy, protein, total fat, cholesterol, carbohydrate, dietary fibre, mineral and alcohol intake.
Physical activity assessment
Participants were instructed to maintain their current physical activity levels for the first 4 months of the study (during the weight loss period and stabilization). During the 8-month weight maintenance stage, participants were free to alter their usual physical activity if they wished. Physical activity was assessed using the Stanford 7-day Recall Interview29 and the International Physical Activity Questionnaire, which has previously been shown to have an acceptable test-retest reliability and criterion validity.30
Body weight and composition
Body weight was determined using Wedderburn digital scales (20–200 kg) (Wedderburn, Perth, Western Australia, Australia). Participants were weighed with minimal clothing, without shoes, and weight was recorded to the nearest 0.1 kg. Body composition was measured with dual-energy X-ray absorptiometry (GE Lunar Prodigy, GE Lunar Corporation, Madison, WI, USA) by a trained researcher.11 The exclusion criteria for the dual-energy X-ray absorptiometry scan included a chance of pregnancy, a recent barium test or nuclear medicine scan. At the start of each session, quality assurance and quality control tests were performed. Participants removed jewellery/metal objects, and wore minimal clothing or a hospital gown. Participants were supine on an X-ray bed, centred within the scan line with their head 3 cm from the top border. The dual-energy X-ray absorptiometry scanner reliability is high with coefficients of variation of 0.6% for fat tissue and 4.5% for lean tissue.31
The 24-h ambulatory blood pressure measurements were performed using Spacelab monitors (Model 90217; SpaceLabs Medical Inc., Issaquah, WA, USA). The monitor was programmed to take an oscillometric reading every 20 min during waking hours and every 30 min during sleeping hours. The monitor cuff was fitted to the non-dominant arm approximately 2.5 cm above the antecubital fossa. The Spacelab machine was calibrated by taking a reading with Spacelab monitor connected to a mercury sphygmomanometer and at least three readings recorded by the monitor were within ±7 mm Hg of the readings observed on the sphygmomanometer after correcting for bleep stop value. A valid 24 h recording was defined as a minimum of 80% successful readings, with hourly mean blood pressure recordings missing for <4 h of the 24 h period. The 24-h ambulatory blood pressure provides greater statistical power than casual (clinical) measurement. Small effects on blood pressure may be missed using single clinical measurements. This is partly a result of increased power with multiple measurements over 24 h, but may also be the result of measuring a different parameter not influenced by the ‘white coat’ effect.32
Venous blood samples were collected following a 12-h fast from the antecubital vein of the forearm. Blood was collected into BD Vacutainer (Franklin Lakes, NJ, USA) serum separator tubes and EDTA tubes. All biochemical and haematology analyses were performed in the PathWest Laboratory at Royal Perth Hospital (WA, Australia). Analyses of lipids, insulin and high-sensitivity C-reactive protein were performed on sera stored at −80 °C in a single batch to reduce variability.
Full blood picture was performed on venous blood collected into an EDTA tube on an Abbott Cell-Dyn 4000 (CD4K) instrument (Abbott Laboratories, Abbott Park, IL, USA). Serum total cholesterol, high-density lipoprotein (HDL) cholesterol and triglyceride concentrations were analysed with a fully automated analyser (Architect c16000; Abbott Laboratories). The assay coefficients of variation were 0.9% for total cholesterol, 1.7% for triglycerides and 2.6% for HDL cholesterol. Serum low-density lipoprotein cholesterol was calculated using the Friedewald equation.33 Serum glucose was measured using a hexokinase/G-6-PDH method (Abbott Laboratories) using a fully automated analyser (Architect c16000). The assay coefficient of variation was 2.7%. Serum insulin was analysed by immunoassay (Abbott Laboratories) using a fully automated analyser (Architect c16000), with an assay coefficient of variation of 1.5%. The homeostasis model assessment (HOMA) score was calculated with the following formula,34 (serum glucose (mmol l–1) × serum insulin (μU ml–1)/22.5), to estimate changes in insulin sensitivity. High-sensitivity C-reactive protein was analysed using BN Systems (Dade Behring, Germany) with a BNII analyser, assay coefficient of variation of 4.4%.
Statistical analyses were performed using SPSS 15.0 software (SPSS Chicago, IL, USA) or Stata 11.0 software (StataCorp, College Station, TX, USA). The sample for this study was calculated on the primary outcome of body weight. With α=0.05, 50 participants per group provided >80% power to detect a 2-kg difference between groups. This would also provide >80% power to detect a 10% difference in fasting glucose and a 10% difference in low-density lipoprotein cholesterol. Secondary outcome measures included body fat mass, fat-free mass and fasting serum concentrations of cholesterol, triglycerides, glucose and insulin. To allow for dropouts, we planned to recruit at least 130 participants to this study. The primary analysis included participants who completed the intervention. Intention-to-treat analysis was also performed. For descriptive data, results are presented as mean±s.d., except for insulin and triglycerides that were log-transformed and are reported as geometric mean and 95% confidence interval (CI). The baseline-adjusted 4- and 12-month values and between-group differences are presented as mean (95% CI) with P<0.05 being the level of significance in two-tailed testing. At baseline, characteristics of participants in the two groups were compared using the independent-samples t-test and the χ2 test for categorical variables. The Stata ‘xtmixed’ and ‘margins’ commands were used to assess baseline-adjusted between-group differences at 4 and 12 months. Fixed effects in each model (except for 24-h blood pressure) were baseline value of the variable, an indicator variable for month 4, month 12, and for treatment group, a treatment group × month 4 interaction term and a treatment group × month 12 interaction term. A subject-specific random intercept term was also included. For 24-h blood pressure, fixed effects were treatment group, month (as a categorical variable—that is, with values 0, 4 or 12), month × treatment group and hour (as a categorical variable). A subject-specific random intercept and a subject-specific random slope for hour (treated as a factor using the R.hour notation in Stata) were included as random effects.
A total of 131 participants (63 control, 68 lupin) aged 22–71 years were randomized and commenced the study. In all, 110 (55 control, 55 lupin) participants completed the trial to 4 months and 93 participants (47 control, 46 lupin; 71%) completed the trial to 12 months (Figure 1). The reasons for withdrawal from the lupin group included: not able to commit to time requirements of study (n=10), relocation to other city (n=5), commencement or change in medication or health status (n=4), inability to consume foods provided in required amount (n=2), and one participant failed to disclose a pre-existing condition prior to randomization and was withdrawn immediately. The reasons for withdrawal from the control group included: not able to commit to time requirements of study (n=11), relocation to other city (n=1), commencement or change in medication or health status (n=3) and inability to consume foods provided in the required amount (n=1).
The two groups (control and lupin) were well matched at baseline (Table 2). There were no significant differences in baseline characteristics between the participants who completed the trial to 4 months or 12 months and those who withdrew. There were no reported adverse effects from eating either the control or the lupin foods during the 12-month study.
Energy and nutrient intake and physical activity
Energy and nutrient intakes and levels of physical activity were well matched between groups at baseline (Table 3). During the 3-month weight loss period, both groups were placed on ∼35% energy-restricted diet. During the 8-month ad libitum weight maintenance period, the energy intakes of both groups increased but remained below baseline energy intake. Estimated energy intakes during the weight loss and weight maintenance periods were not significantly different between groups (Table 3). At both 4 and 12 months, there were higher protein and fibre intakes and lower carbohydrate intakes in the lupin group relative to control. At 4 and 12 months, respectively, mean protein intake was higher by 19 g per day (95% CI: 8, 29; P<0.001) and 15 g per day (95% CI: 3, 28; P<0.001); fibre intake was higher by 9 g per day (95% CI: 6, 12; P<0.001) and 14 g per day (95% CI: 10, 18; P<0.001); and carbohydrate intake was lower by −26 g per day (95% CI: −47, −5; P=0.016) and −27 g per day (95% CI: −54, −1; P=0.041). The differences in protein, fibre and carbohydrate intake are close to those estimated to be observed based solely on intake of the lupin flour-enriched food provided. Differences in energy, fat and alcohol intakes, sodium and potassium excretion and physical activity at both 4 and 12 months were not significant (Table 3).
Body weight and composition
Body weight and body composition measurements were not different between groups at baseline (Table 2). The baseline-adjusted body weight and body composition measurements in the control and lupin groups at 4 and 12 months and the between-group differences are presented in Table 4. There were no significant differences between treatment groups in body weight, fat mass, fat-free mass, android and gynoid fat percentages at 4 or 12 months. Furthermore, there were no significant differences between treatment groups in the maintenance of body weight loss (−0.7 kg; 95% CI: −1.8, 0.5) and fat mass loss (−0.4 kg; 95% CI: −1.4, 0.6) during the weight maintenance period (from 4 to 12 months). Subgroup analysis according to gender and baseline age (above and below 50 years) and an intention-to-treat analysis did not alter the interpretation of these results (data not shown).
Cardiovascular disease risk factors
Blood pressures, and fasting blood lipids, glucose and insulin concentrations were not significantly different between groups at baseline (Table 2). Baseline-adjusted blood pressures, and fasting blood lipids, glucose and insulin concentrations at 4 and 12 months are presented in Table 5. For lupin relative to control, mean 24-h systolic and diastolic blood pressures were significantly lower at 12 months, but not at 4 months. There were no differences between groups in total cholesterol, low-density lipoprotein cholesterol, triglyceride and glucose concentrations at 4 and 12 months. HDL cholesterol was significantly lower for lupin relative to control. This difference was almost entirely because of an increase from baseline to 12 months in HDL cholesterol within the control group (0.07 (95% CI: 0.01, 0.13) mmol l–1, P=0.03), with no change within the lupin group (0.00 (95% CI: −0.06, 0.06) mmol l–1, P=0.94). At both 4 and 12 months, the lupin group had significantly lower fasting insulin concentrations and HOMA scores relative to control (Figure 2). Subgroup analyses according to gender, baseline body mass index (above and below 30 kg m–2) and baseline total cholesterol (total cholesterol above and below the median of 5.3 mmol l–1) and an intention-to-treat analysis did not alter interpretation of these results (data not shown).
We have investigated the effects of 12 months of regular consumption of a lupin-enriched diet, during and following energy restriction, on body weight, body composition, and cardiovascular disease risk factors in overweight and obese men and women. The higher protein and fibre lupin-enriched diet did not significantly influence body weight and body fat and fasting total cholesterol and glucose concentrations. However, the lupin-enriched diet resulted in significantly lower fasting insulin concentrations by 16 and 21%, and HOMA scores by 30 and 33% at 4 and 12 months, respectively. We also found that the lupin-enriched diet resulted in lower blood pressure at 12 months.
There is now strong evidence that increasing the protein and fibre content of the diet can reduce appetite acutely.2, 3 In line with this, we have previously shown that increasing the protein and fibre content of bread with lupin flour significantly reduced appetite and energy intake acutely.8 In addition, lupin fibre-enriched foods have been shown to increase satiety.35 Data from studies using ad libitum diets with increased protein36, 37, 38 or fibre3 intake are limited. We recently reported that an ad libitum lupin flour-enriched diet higher in dietary protein and fibre consumed over 4 months did not significantly influence body weight or composition in overweight individuals.11 There is some evidence that longer-term regular consumption of increased protein36, 37 or fibre39 diets can assist weight loss with energy restriction in overweight individuals. However, several intervention studies have failed to demonstrate benefit.
We have shown that a lupin-enriched diet did not significantly influence body weight, body fat mass or weight regain. The lack of a significant between-group difference in body weight suggests that effects of lupin-enriched foods on satiety may be, in part, counterbalanced by other dietary, lifestyle and/or environmental factors that influence energy balance in the longer term.40 The observed differences in body weight in our study were small (<1 kg). Although effects of this magnitude may be important for long-term maintenance of healthy body weight, our study was only powered to detect a 2-kg body weight difference between the groups. A recent meta-analysis suggests a small benefit of higher protein diets on fat-free mass retention (∼1.2 kg), but not on body weight or fat loss.4 The observed differences in fat-free mass in the current study were not significant. The difference in protein intake of 15–19 g per day in our trial was modest compared with most previous trials in which differences have usually been >30 g per day.2 However, the higher protein intake was concurrent with higher dietary fibre intake (additional 9–14 g per day), which would be regarded as considerable.3 The total fibre intakes of ∼35 g per day during weight loss and ∼39 g per day during weight maintenance in the lupin group would also be regarded as high and substantial enough to impact satiation and satiety.3 The type of fibre present in lupin may also be important. Lupinus angustifolius, the species of lupin used in these studies, contains ∼70% insoluble fibre.41 Insoluble fibre may be less effective than soluble fibre in reducing appetite.3 However, the results of this trial when taken together with results of our previous trials11, 12 bring into question the importance of acute effects of dietary nutrients on appetite and energy intake for longer-term effects on body weight and composition.
In the current study the lupin treatment resulted in a significant reduction in fasting insulin concentrations and HOMA scores following weight loss at 4 months. These differences were maintained during weight maintenance to 12 months. In a recently published study, involving a similar population of overweight men and women, we found that 4 months of regular consumption of an ad libitum lupin-enriched diet did not alter fasting glucose or insulin concentrations.11 This suggests that weight loss in overweight individuals may be important to attain improvements in insulin sensitivity with a lupin-enriched diet. If a lupin-enriched diet can improve insulin sensitivity, the components responsible remain uncertain. It is possible that both the fibre and protein in lupin flour could contribute to improved insulin sensitivity. We and others have previously shown that lupin flour-enriched foods can acutely reduce postprandial glycaemia and insulinaemia.12, 27 Such effects, if maintained in the longer term, may contribute to improved insulin sensitivity. Data from the Framingham Offspring Cohort study suggest that an extra 14 g of dietary fibre per day would improve HOMA scores by 0.6 units.42 In the present study the difference in fibre intake at 12 months was 14 g per day and the difference in HOMA score was 0.7 units. Acutely, dietary protein enhances insulin secretion,43, 44 leading to increased glucose disposal. Although data from epidemiological studies indicate that this may not result in improved insulin sensitivity,45, 46 positive effects of higher protein intakes have been observed in some intervention studies.21, 47, 48 The lack of effect on glucose concentrations in the current study may be because of population selection. All participants were non-diabetic and had otherwise normal fasting glucose concentrations at screening of <6.0 mmol l–1.
Regular consumption of lupin flour-enriched foods resulted in lower systolic and diastolic blood pressure at 12 months, but not at 4 months. Available data suggest that higher plant protein15 and dietary fibre17 intakes, and substitution of carbohydrate in the diet with protein and fibre can benefit blood pressure.22 We previously showed that 4 months of regular consumption of an ad libitum lupin flour-enriched diet resulted in lower systolic blood pressure by 3 mm Hg in overweight individuals.22 The lack of difference in systolic blood pressure at 4 months and the estimated systolic blood pressure difference at 12 months of 1.3 mm Hg indicates that weight loss resulting in lower blood pressure may have obscured some of the effects of the lupin flour-enriched diet. Another possible explanation of the smaller observed effect size is that the lupin flour was substituted primarily for wholemeal wheat flour. Most previous trials have used a refined carbohydrate as the control.14, 15, 16, 22
Limited data from human and animal studies suggest that a lupin-enriched diet may benefit serum lipids and lipoprotein.24, 49 However, we previously showed that an ad libitum lupin flour-enriched diet over 4 months also had no benefit on the serum lipid profile.11 The lack of effect on blood lipids in our studies may be because of a number of factors. Most of our participants had normal lipid profiles at baseline. Nevertheless, subgroup analyses in participants with baseline total cholesterol above or below 5.3 mmol l–1 (median) failed to show any between-group differences, which is a result similar to our previous trial.11 The lack of changes in serum lipids may also be because of the physical and structural characteristics of the lupin fibre, which is primarily insoluble.41 It is primarily soluble/viscous fibres that have been found to significantly reduce total cholesterol concentrations.41 The findings of a significant increase in HDL cholesterol from baseline to the end of intervention in the control group, with no change in the lupin group, are also consistent with our previous study.11 The mechanism for this is uncertain.
Our study was designed to investigate the functional effects of 12 months of regular consumption of a lupin-enriched diet. The study design did not allow demonstration of the effect of lupin per se, independent from any generic effects of increasing protein and fibre. However, the use of lupin flour is a novel approach to increase the consumption of both protein and fibre in significant amounts with a single food ingredient. This may be more difficult using more than one ingredient, or using selected high-protein and high-fibre foods. In addition, most of the available evidence for effects of protein and fibre on weight management and cardiovascular disease risk factors derives from studies investigating these dietary components independently from one another. The current study is therefore unique in studying the functional effects of a higher protein and fibre lupin-enriched diet, following both an energy-restricted weight loss diet and an ad libitum weight maintenance diet.
In conclusion, regular consumption of lupin flour-enriched foods during and following energy restriction did not significantly influence body weight. The changes in insulin concentrations and insulin sensitivity at 4 and 12 months indicate that even among non-diabetic individuals with normal blood glucose levels, lupin flour-enriched foods may improve insulin sensitivity in overweight individuals when combined with weight loss. The observed effects on blood pressure are consistent with a growing body of evidence suggesting that diets higher in plant proteins and dietary fibre lower blood pressure.
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This study was funded by The Western Australian Government, Department of Industry and Resources. We thank Dr Kay Cox for her assistance with recommending appropriate physical activity assessment tools. We also thank Bodhi's Bakery, Fremantle, WA, for baking the bread and biscuits and Belmar Foods, Balcatta, WA, for manufacturing and providing the pasta.
The authors declare no conflict of interest.
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Belski, R., Mori, T., Puddey, I. et al. Effects of lupin-enriched foods on body composition and cardiovascular disease risk factors: a 12-month randomized controlled weight loss trial. Int J Obes 35, 810–819 (2011). https://doi.org/10.1038/ijo.2010.213
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