There are many dietary interventions available to counteract the epidemic of overweight and obesity which play a major role in the development of insulin resistance and type 2 diabetes mellitus [1
]. One strategy is based on lowering the excessive intake of carbohydrates, especially, the refined ones [2
]. This could be achieved by lowering the portions or replacing the carbohydrates with more fats or by adding soluble fiber to the diet which is thought to slow down the absorption of carbohydrates [3
]. Lowering the glycemic index through the usage of fiber in the diet is not favored by most people due to potential taste preferences and adverse reactions resulting in gastrointestinal problems such as gas and diarrhea. Therefore, another strategy becomes more and more promising to impact the carbohydrate absorption by using bioactive ingredients which block or slow the carbohydrate absorption in the gastrointestinal tract via inhibiting the necessary enzymes, amylase and glucosidase [4
]. Amylase breaks down complex carbohydrates, such as starch, into oligosaccharides and glucosidase enzymes further convert these to monosaccharides.
There are the different forms of amylase inhibitors, namely, Alpha-amylase inhibitor isoform 1 (Alpha-AI1), Alpha-AI2, and Alpha-AIL which can be found in in the embryonic axes and cotyledons in the seed of common beans (Phaseolus
]. These so-called glycoproteins bind to alpha-amylase non-covalently, mainly through hydrophobic interaction, by completely blocking access to the active site of the alpha-amylase [6
]. The Alpha-AI1 isoform is the one with anti-amylase bioactivity in humans, and therefore, inhibits the starch digestion [8
]. This blocking affect is also dependent on pH, temperature, incubation time and the presence of particular ions which have been optimized for the specific and proprietary product named Phase2®
brand Phaseolus vulgaris
White Bean product (Pharmachem Laboratories, Kearny, NJ, USA) [9
]. This particular dietary supplement has demonstrated its potential and ability to cause weight loss in numerous clinical trials in humans [11
brand Phaseolus vulgaris
White Bean extract is made by a standardized water extract of non-GMO (Genetically Modified Organism) whole dried beans (Phaseolus vulgaris
) which is made through a proprietary process. The white-to-beige powder consists of Phaseolus vulgaris
(~90%) and Gum Arabic (~10%). It has at least 3000 alpha-amylase inhibiting units (AAIU) per gram when tested at a pH 6.8 using potato starch as the substrate and pancreatin as the enzyme source. The Phase2®
brand products are used in dietary supplements in various forms, including powders, tablets, capsules and chewables for the application of weight control and weight loss. In addition, it is also incorporated in food products like chewing gum, mashed potatoes, yeast-raised dough (bread, pizza, etc.) without losing bioactivity or changing the appearance, texture or taste of the food [12
The aim of this meta-analysis was to examine the evidence for the effectiveness of a proprietary alpha-amylase inhibitor from white bean (Phaseolus vulgaris) supplementation interventions on modification of body weight and fat mass.
This review was performed according to the PRISMA (preferred reporting items for systematic reviews and meta-analyses) statement for quality of reporting a meta-analysis [15
2.1. Literature Search
Literature searches in PubMed, the Cochrane collaboration, and Google Scholar were undertaken using the following keywords: Phaseolus vulgaris, Alpha-amylase inhibitor/inhibition, Phase2®, White bean extract, kidney bean, starch blocker, weight loss, body weight, body fat, BMI (body mass index), anthropometric measures, obesity, overweight and safety.
In addition, the manufacturer was contacted for internal unpublished data, and finally, the reference section of relevant original research and review papers were mined for additional studies. No age, sex, geographic, time or publication status restrictions were imposed on the initial search.
2.2. Study Selection Criteria
Studies were eligible for inclusion if they met the following PICOS’ (Participants, Intervention, Control, Outcome measurements, and Study design) criteria: (a) Participants: overweight or obese individuals; (b) Intervention: Phase2® brand Phaseolus vulgaris white bean extract, at least 1200 mg per day, for at least 4 weeks; (c) Control: studies comparing the experimental group (Phaseolus vulgaris supplementation) with a control/placebo group (no Phaseolus vulgaris supplementation ), or against baseline; (d) Outcome measurements: studies needed to include measurements of body mass or fat mass; (e) Study design: Studies needed to be either randomized, double-blind, placebo-controlled parallel or crossover trial, or open-label studies.
2.3. Assessment of Risk of Bias
For the quality assessment of randomized controlled trials (RCTs), we used the Delphi list, which includes eight questions with three response options “yes”, “no”, or “do not know” depending on compliance with key methodological components, and produces a quality score of maximum 9 points that provides an overall estimate of RCT quality [16
2.4. Data Extraction and Quality Assessment
Two reviewers independently extracted the following data from the selected articles: publication year, number of participants (Phaseolus vulgaris and control group), baseline characteristics of the participants, methodological characteristics of the study, pre- and post-values and standard deviation for body mass and fat mass, and statistical information.
2.5. Statistical Analysis
A meta-analysis to estimate the overall treatment effect of Phaseolus vulgaris
supplementation relative to control groups was performed. Standardized Mean Difference (d) was used in the determination of effect size. In getting the Standardized Mean Difference (d), Cramer’s v
(which shows the magnitude size) and 95% CI (confidence interval) for each d was computed. The following guideline was used in reading magnitude effect size for Cramer’s v
< 0.1 small effect, 0.1 < v
< 0.3 medium effect, v
> 0.3 large effect. Weighted effect size on all studies was done using the Hunter–Schmidt approach. Weights are objectively assigned based from sample sizes of the studies. Hence, studies with bigger sample size (n
= 60 [17
]) had higher weight, compared to studies with smaller sample size (n
= 10 [18
-values of individual studies are transformed (logarithmic) and aggregated using Chi-square.
The aim of this meta-analysis was to determine the effectiveness of Phase2® (Phaseolus vulgaris) to support weight loss and to reduce body fat. The overall meta-analysis revealed a significant difference in change in body weight, and body fat between Phase2® (Phaseolus vulgaris) and placebo.
Barret et al. conducted a review of clinical studies with Phase 2 brand Phaseolus vulgaris
White Bean product on weight loss and glycemic control [29
]. The analysis identified ten clinical studies which have demonstrated weight loss over time following administration of Phase 2 when taken concurrently with meals containing carbohydrates. Three of these clinical studies revealed significant loss of body weight with Phase 2 compared to a placebo control in people who are overweight or obese. In addition, three clinical trials showed a reduction in serum triglycerides over time. Nine of these clinical studies reported by Barret et al. have been used in this systematic review and meta-analysis. The study by Vinson et al. was not taken into consideration due to its focus on glycemic index and blood glucose investigations without looking into weight loss parameters [30
While our meta-analysis revealed a significant difference in weight loss over placebo, a previous meta-analysis of Phaseolus vulgaris
] showed a non-significant difference in weight loss between Phaseolus vulgaris
and placebo groups. This can be explained by the fact that the Onakpoya et al. meta-analysis included not only studies performed with Phase 2, but all studies on Phaseolus vulgaris
. Both meta-analyses showed significant effects on fat loss. The importance of this work was to isolate the effects of the Phase 2 brand Phaseolus vulgaris
White Bean from the body of literature. By using unpublished data and all arms of all studies available to us, we were able to demonstrate statistically significant effects on weight and body fat. Part of this importance is in the supplement industry, there is an assumed “generic equivalence” which we know to be false. The prior meta-analysis assumed such a generic equivalence and therefore came up with negative results. In this case, by limiting to only Phase 2, it does appear that there is significant weight and body fat loss with an excellent safety profile.
Low carbohydrate diets have been linked to weight loss, even when not consciously restricting calories, improved triglyceride levels, a reduction in blood glucose levels and improved insulin sensitivity, a decrease in blood pressure. Very low carbohydrate diets (ketogenic diets), with fewer than 50 g of carbohydrate per day, have been linked to weight loss and specific health benefits including neurological disorders. Adaptations to a ketogenic diet is often difficult and nutritional aids have been shown to be useful for entering into nutritional ketosis [32
]. A recently concluded study indicated that both low-fat and low-carb diets can work for weight loss, and that there is no “best diet” when it comes to low-carb vs. low-fat diets. In total, 263 males and 346 premenopausal females were assigned to either a low-fat diet or a low-carb diet for 12 months. At 12 months, the low-fat group had lost 5.3 kg and the low-carb group 6.0 kg and this difference is neither statistically significant nor clinically relevant. The healthy diet that will work for you is the one you can stick to, and that varies by individual [33