Does Eating Beans W/B4 Meals Have the Same Blood Sugar Lowering, and Fat Loss Promoting as ‘Carb-Blockers’?

Reader’s question from the SuppVersity’s Instagram page: “I wonder if just having a small serving of beans before a meal would have good effects also. Red velvet, black, etc.” – Johan

Those of you who already follow the SuppVersity on Facebook will have seen the news item (in the infographic section) about the latest bean-carb-blocker study. Some may even have seen that there were a lot of comments, comments in which you repeatedly found the question whether, instead of the stupid bean extract, one wouldn’t be able to simply eat a bunch of beans before or with the meal and see the same potentially weight-reducing effects that were reported in the study.

Well, it turns out it is not that easy to find an answer to this question – especially not one that is workable, i.e. “eat exactly X grams of THIS type of beans at timepoint T to improve your glucose metabolism by Z and lose BETA kg of weight in GAMMA weeks.” What I could come up with, however, is the following review of relevant studies and data and a bottom line in which I will at least try to formulate the aforementioned workable answer to the question.

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In my quest for some concrete advice, I will start by addressing the “why?”, i.e. why do certain substances in beans significantly improve the glucose response to a meal? Well, the answer is not as simple as it may seem. In contrast to what most people believe, the benefits are mediated only in parts by the inhibition of the amylase enzymes your body needs to ‘digest’ (=break down) complex starches like those in pasta or rice – it is this ability to block, or at least hinder, the enzymatic breakdown of complex carbs, that makes Phaseolus vulgaris an attractive ‘carb blockers’.

Mechanism? Wait, there’s more… probably

As already hinted at, the ‘carb-blocker’ effect is part of it, but there’s more: Lentils are also high fiber foods, and full of antioxidants, all of which contribute to the well-established health, body-comp, and metabolic benefits that have been observed (albeit with high heterogeneity in terms of the effect sizes). One such example is Luhovyy et al.’s 2015 study in N=14 overweight/obese subjects.

Figure 1: Metabolic changes in overweight/obese subjects after consuming 5 cups of canned navy beans per week for 4 weeks / no other mandatory dietary changes (graph created based on data from Luhocyy 2015)

As you can learn from the caption of Figure 1, Luhocyy’s (2015) study did not rely on Phaseolus vulgaris extracts. The subjects were simply fed meals that contained 5 cups of canned navy beans. The benefits are quite pronounced but the fact that they were cumulative (i.e. occurred over the course of the 4-week study) tells us: It’s not all just about carb blockin’.

In fact, a closer look at the data reveals that some of the benefits may be mediated by nothing else than measurable (but not significant) changes in the baseline diet; dietary modifications the subjects undertook without even realizing it, modifications such as reduced intake of classic side dishes like rice, pasta, bread, and co, and a surprising increase in fruit and vegetable intake.

Eating beans goes hand in hand with an extra serving of fruit & veg + lower intakes of grains.

Furthermore, the Luhocyy (2015) shows that benefits in the blood lipid department are at least as significant as those related to glycemia (obviously, you’d expect insulin, glucose, and, of the lipids, at best triglycerides to be the primary benefactors of a ‘carb blocker’). In conjunction with the lack of improvement in HbA1c the study clearly questions the notion that beans work their metabolic health magic or he 2.5 and 2.1 cm reduction waist circumference in female and male study participants, respectively, by ‘blocking carbs’.

Figure 2: Number of studies (total 20) showing health/metabolic benefits in the latest meta-analysis by Ferreira (2020).

What’s important to point out is that the Luhocyy study is not the only one that would support the conclusion that there’s more than just ‘carb blocking’ going on here. Similar results have been observed by Ferreira et al. (2020) who calculated significant improvements in blood lipid profile, blood pressure, inflammation biomarkers, as well as, body composition in people who consumed ~150g of cooked pulses per day (minimum-maximum: 54-360 g/day).

What is important to remember is that both the Luhocyy as well as the studies that were included in the 2020 meta-analysis by Ferreira et al. used whole beans (or other pulses), no flour, powder or extracts.

Not all “common” beans are equal but the following overview of the “effect of bean colour on α-amylase inhibitory activity of P. vulgaris” should calm your fears of missin’ out: they are all similarly effective and it’s not like one is useless while the other brings your CHO digestion to a screeching halt (data from Lajolo & Genovese 2002)

How are carbohydrates digested, anyway? Barrett & Undani (2011) describe the process in their review of the “clinical studies on weight loss and glycemic control” in response to the use of the best known ‘bean-based’ carb-blocker: the common white bean (Phaseolus vulgaris) quite nicely: “Digestion of carbohydrates begins in the mouth, with amylase secreted by salivary glands. This action accounts for only about 5% of the breakdown of carbohydrates. The process is halted in the stomach due to the high acid environment destroying the amylase activity. When the food enters the intestine, the acidic pH is neutralized by the release of bicarbonate by the pancreas and by the mucous that lines the walls of the intestine. Amylase is secreted into the small intestines by the pancreas. Alpha-glucosidase enzymes are located in the brush border of the small intestines. Amylase breaks down the carbohydrates into oligosaccharides. The glucosidase enzymes (including lactase, maltase and sucrose) complete the breakdown to monosaccharide units. It is only the monosaccharide units that are absorbed into the body.” What the enzymes cannot digest – like the previously discussed resistant starches will be passed from the intestine to the colon”, where they are fermented by colonic bacteria to produce short-chain fatty acids, carbon dioxide and methane” (ibid)… I what you’re thinking not: #cow-farts, #climateChange

The previously referenced studies are thus of particular relevance to finding an answer to the question Johan and Amaan asked on the SuppVersity’s Instagram page:

“I wonder if just having a small serving of beens before a meal would have good effects also. Red velvet, black etc.” – Johan

So, yes this could work, but it is unlikely that there are acute benefits of timing the beans/pulses before a meal. It could be that the glucose spike is further reduced as this may guarantee that the amylase inhibitors will already be present in your gut when the spaghetti start their journey from stomach to colon to… you know where 😉

Warning: The bean trick works for starchy foods like pasta (polysaccharides Ü broken down by amylase which is blocked by bean proteins), it won’t work for sugary foods like Ben & Jerry’s (mono-/disaccharides Ü disaccharidase, not blocked by ‘carb blockers’ in )!

On the other hand, the previously discussed studies leave little doubt that the inhibited complex carbohydrate intake cannot fully explain all the benefits. To add the missing piece to the puzzle it’s worth taking a look at (a) the high nutrient density of pulses, and the largely ignored fate that’s awaiting the largely undigested spaghetti chime in your large intestine.

Let’s talk dirty… about what happens to your spaghetti if they survive the upper gastrointestinal tract – keyword: #resistantStarch 😮

So, the most likely candidates for the benefits of increased pulse consumption are their high (micro-)nutrient content and their potent prebiotic effects (Siva 2019), which are based on (a) fermentable fiber the beans themselves contain, and (b) the previously mentioned spaghetti which will not be properly broken down to simple sugars before they are ‘fed’ to the myriads of gut bugs in your colon.

Figure 3: SEM images of starch granules of (top) cooked, (middle) cooled, and (bottom) reheated pinto beans. Plus: Resistant starch (RS) concentrations of different common bean (a and c, respectively) and chickpea (b and d, respectively) market classes after cooking, cooling, and reheating (from Siva 2019).

As the data in Figure 3 shows, this overall (probiotic and metabolic) health effect can be increased by cooking and cooling your beans – a process that has been shown to increase the content of resistant starch, i.e. starch that is not broken down and make it to the large intestine where they are then fermented and act as prebiotics the postbiotics (products they are transformed to by the gut microbiota) have  been linked to significant health benefits (Snelson 2019).

Indeed, resistant starches #RS could contribute significantly to the benefits

As a SuppVersity veteran, you know about the way heated/cooled/reheated starches contain higher amounts of that from previous SuppVersity articles as well as news items. Nevertheless, I was still pretty sure you’d appreciate the inclusion of Table 1, which shows the RS content (percentage dry matter basis) of a selection of repeatedly heated/cooled foods; and yes, there are beans (kidney beans) and its relatives (lentils and peas) on the list.

Table 1: RS content (percentage dry matter basis) of heated/cooled foods (Yadav 2009). Even higher RS values can be achieved if you repeat the process twice or thrice – with lentils being the unchallenged #1 that will double it’s already high RS content of 4.89% to 9.21% over 3x heat-/cooling cycles 😮.

For all of them, the #RS increase is significant after only one heating/cooling cycle (which will significantly reduce the ‘load’ on your taste-buds). The study I borrowed the table from did yet also show that you can increase the RS content of kidney beans by another >2% if you heat/cool your beans thrice… whether you’ll be left with anything that you will be voluntarily eating, let alone enjoy, wasn’t accessed by Yadav et al. (2009) but my personal experience would say… “NAH! 🤢”

What you should have realized by now is that kidney beans are by no means the only ‘carb blocker’ option you have… there are alternatives like lentils and, as you can see in Figure 3 other, more exotic beans – often with even higher resistant starch content to maximize the non-carb-block benefits.

You have to be careful, though two of these rather ‘exotic’ beans actually show a paradox reaction to the heating and cooling. Beans like “small red” aka Adzuki beans or “cranberry” aka Borlotti bean, to be precise show a decline in RC content when you apply the cooling/(re-)heating trick 😪.

Whether or not you benefit will also depend on the food matrix the beans are part of | learn why!

Benefits could be the largest/smallest for… people with (A) low fiber intake, who get a large fraction of their energy from ‘slow’, starchy carbs and lowest for the health-conscious (B) low-carber who fibers up his diet with veggies, fruit & co. Why? Easy: (A) If your fiber intake is already high (~30g/d or more) the effects on the microbiome as well as downstream effects on your metabolism won’t be as pronounced and if (B) you’re not eating significant amounts of starchy carbs, the alleged ‘carb-blocker’-effects are useless because sugar(s), HFCS and other carbs that come as mono- or di-saccharides don’t need to be broken down by the enzymes that are ‘blocked’ by the ‘carb blocker’ in beans, peas, and other pulses.

I just realize we’ve deviated from the initially introduced carb-blocker quite a bit. So, let me remind you: The “blocking” of carbs is facilitated by molecules in the beans that can block the enzyme that would normally dismantle the starch granules to simple(r) sugars (monosaccharides) that will then be transported by various transporters right into the portal vein and into the liver. In conjunction with (micro-)nutrient density, resistant starch and unconscious changes in dietary habits this ‘carb blocker’ effect produced the initially referenced ‘magical’ weight loss of -2kg in about a month Wang et al. (2020) report in their initially cited paper in Food Science and Nutrition.

Overall, we seem to be able to answer the main question of whether you “cannot simply eat a serving of beans instead of using a bean extract similar to the one in the Wang study” affirmatively and based on a plethora of research – not all in well-controlled human studies, though.

 The whole idea that beans could have a unique effect on body weight that goes beyond a satiating effect and reduced energy intakes dates back to the 1990s when scientists such as Pusztai et al. (1998) observed that fat rodents that were fed with a diet containing 18% raw kidney beans had such profound effects on the digestibility of a low-fat diet that the fat Zucker rats in the ‘bean group’ of the study ended up being significantly leaner, not just lighter than their peers – with the highest dose of raw beans yielding a 7% lower total body fat content compared to the standard diet – or, as the scientists write: They “deposited essentially no body fat in 10 d” (Pusztai 1998). Even if it was not for the ill effects on the rodents’ pancreases that were observed in the long term, no one would be able to stomach that amount of raw beans and, if you look closely at the body composition data, you will realize that, unlike the total lean mass, the gastrocnemius weight (=proxy of muscle weight) was reduced by 11%… 😱

Note: ‘Carb blocking’ and existing (enhanced) resistant starch content are two pairs of shoes which -just like real shoes – serve practically the same purpose: feed your gut bugs! And since those excrete digestible short-chain fatty acids, the energy is at best partly lost. So, yes – the CHOs in beans and even more so of those meals you use them with as a ‘carb-blocker’ count… at least a significant %-age of them. On the other hand, try stuffing yourself with beans before your next spaghetti meal: I bet you’re gonna eat less and hence reduce your total energy intake, as well.

So, based on what we knew at the turn-of-the-century about simply eating copious amounts (including non-deactivated lectins due to the raw nature of the beans the rodents were fed) the verdict would be something between “not possible” and “not healthy”. This very inability to consume “enough” beans is probably also the reason that today, roughly 22 years later, we have only very limited data from #humanStudies in which subjects consumed their beans/peas/lentils as whole foods. The few human RCTs are yet in line with the 2nd generation rodent studies showing similarly huge benefits of feeding chow based on cooked (and dried) pulses – essentially the same flours and powders that also caught the food industry’s interest (Patterson 2010).

Yes, beans (or rather pulses in general) work – Meta-analysis: ‘It takes 1 serving per day (132 g/d), or more to make a difference…’ – with no evidence that more pulses help more

One of the most recent meta-analyses that went beyond the often-reported improvements in blood lipids and quantified the effect of “dietary pulse consumption on body weight, waist circumference, and body fat by conducting a systematic review and meta-analysis of randomized controlled trials” (Kim 2016). Overall, Kim et al. analyzed data from 21 trials with 940 participants, who were even locked up in metabolic wards in n = 5 studies, so that compliance shouldn’t have been an issue (not sure about methane production, though 😋). The researchers’ analysis of the data revealed …

“[… ]an overall significant weight reduction of −0.34 kg (95% CI: −0.63, −0.04 kg; P = 0.03) in diets containing dietary pulses (median intake of 132 g/d or ∼1 serving/d) compared with diets without a dietary pulse intervention over a median duration of 6 wk” (Kim 2016). 

What is particularly interesting is that significant benefits were observed in both, studies where the subjects were in a matched energy-deficit (weight-loss diets | P = 0.02; N=5) and those in which the subjects were on energy-balance balanced diets (weight-maintaining diets | P = 0.03; N=17).

Nutrient timing in general contexts.

So, 100-150g/day, pulses in general work, supplements are not necessary?! That’s at least what the not exactly overwhelming evidence suggests. That’s also in the range of the 5 servings kidney beans per week the subjects of the initially discussed study by Luhovyy et al. consumed with quite satisfying metabolic results. In that, it is no coincidence that the studies discussed align so well with each other (and the rest of the literature). After all, Kim et al. highlight in their meta-analysis that there’s “low evidence of between-study heterogeneity” (Kim 2016). Moreover, the very same low inter-study heterogeneity was observed for the “6 included trials [which] suggest that dietary pulse consumption may reduce body fat percentage” (Kim 2016).

❕All in all, this review of the albeit astonishingly scarce non-supplement and hence relevant research in humans suggests that Johan’s & Amaan’s question must be answered affirmatively: “Yes, you can eat beans instead of taking bean extract supplements!” It also suggests that you don’t need to pound raw beans like the rodents in the earliest studies to see results on the scale.

👨‍⚕️The corresponding workable advice is thus: ‘Make beans, chickpeas, and other pulses a regular part of your diet. Aim for 100-150g of these nutritional powerhouses per day and consume them with or, probably even better (no good evidence available to confirm this hypothetical advice), 30-45 minutes before a starchy meal (not a sugary meal | see 1st red box). If you can’t imagine eating beans that often, just eat them regularly and consider one or two or even three (if you can still tolerate their taste and texture by then) heating > cooling > reheating cycles to further increase their already significant resistant starch content.’ I guess that’s it … may the farts be with you!


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