The claimed health benefits of beans & legumes

Legumes and Type 2 Diabetes

The first claim is that it has beneficial effects on the treatment and prevention of Type 2 Diabetes. The study was conducted on 121 people with T2D for 3 months. The participants were split into two groups: One was “encouraged” to eat at least 1 cup of legumes per day, the other was supposed to more whole wheat products. They measured HbA1C to assess how the diet impacted diabetes. HbA1C below 5.7% is normal and 6.5% or above is diabetes. In between you are considered prediabetic.

First things first, this is an uncontrolled experiment. They “encouraged” people to eat more legumes, cool, but did the people actually eat more legumes? What else did they consume during the study period? And there was no real control group either, since both groups got an intervention. But that aside, people who ate legumes dropped their HbA1C by 0.5% and people who ate whole wheat dropped it by 0.3%.

The biggest question is what did the legumes replace in the diet. If they replaced high carbohydrate foods, the HbA1C is obviously expected to drop. But you can replace high carb foods with toilet paper, and your HbA1C will also improve. What I wanna say with this is that there is nothing magical in the beans per se, it’s simply eating less carbohydrates and sugars that does the trick. You do not have to eat beans for that, you can also eat meat instead and watch your HbA1C drop.

Hypertension

I quote: “In subjects who consumed slightly less than 1 cup of legumes each day for 10 weeks, both systolic and mean arterial blood pressure were significantly decreased.” Aha, significant! That must mean there was a big decrease in blood pressure… right? Of course not! What they meant is simply “statistical significance”, but regardless, they did observe a drop in blood pressure as following:

• Systolic: -2.25 mmHg
• Diastolic: -0.71 mmHg
• Mean: -0.75 mmHg

As an example: If someone with hypertension of ~160/105 would eat more beans, he would drop his blood pressure to ~158/104. Congratulations, now you still have hypertension and you fart more.

For reference, having to pee increases your systolic blood pressure by up to 10 and your diastolic by up to 7 points.

Hyperlipidemia

Hyperlipidemia is the fancy term for “high fat presence in blood” and refers to the classic blood lipids of cholesterol, LDL and HDL. I’m firmly of the believe that cholesterol is not the problem, but let’s ignore that for the sake of argument.

Cholesterol is considered normal if it’s below 200 mg/dL, anything above 240 mg/dL is considered high and anything between is borderline high. The legume intervention showed a reduction of ~12 mg/dL which, in my humble opinion, isn’t exactly a crazy change. Cholesterol in general varies from hour to hour by up to ±20% meaning these natural fluctuations are higher than the observed drop. This isn’t exactly convincing me.

Beans for weight management

Beans are associated with lower body weight and people who eat beans weight on average 3 kg less. Is that possibly useful for weight management? Sure, if you eat beans instead of junk food, it’s probably gonna do you a favor. But again, that’s not something magical about beans, that’s just what happens if you don’t eat trash foods.

Claim: Legumes are rich in iron

Of course we’re going to talk about the nutrition now. First up, iron. Now there are many different varieties of beans and legumes, so I’m gonna have to pick one. I’m going to pick lentils, which according to a vegan website are one of the top players in iron content. Lentils, according to the USDA food data central, contain 3.33 mg of iron per 100 g. That is not a low amount by any means, as this would cover 18% of a women’s daily requirement. (Women have higher requirements for iron)

But of course, bioavailability is extremely terrible, between only 0.84 to 1.91%. Those theoretical 18% just turned into actual 0.37% assuming the best case of 2% bioavailability. Honestly, this is worse than I expected. This is mainly due to Legumes containing phytates, lectins and oxalate that heavily impact iron absorption even at trace amounts. So are legumes rich in iron… yes, but you’re not getting any of it.

Additional note: Soy protein itself has an inhibiting effect on iron absorption.

Claim: Legumes are high in zinc

Do I have to bring out the oyster graph again? Of course I do. Phytates and lectins inhibit zinc absorption, resulting in about only 13% bioavailability of zinc from beans (and anything eaten with beans). Let’s go back to our lentils that clock in at 1.27 mg of zinc per 100 g. Adults need on average 12 mg of zinc per day, so bioavailability considered, this covers a meager 1.37% of daily requirements.

Claim: Legumes are high in phosphorus

Now this one is quite interesting. A large portion of the phosphorus in legumes is stored as… phytate. A major antinutrient in beans happens to be a storage form of phosphorus. Ruminant animals are able to actually digest phytate and derive phosphorus from it, because the bacteria in their guts make phytase (the enzyme that breaks down phytate). Humans lack phytase and as such are unable to digest it, and lectins further impact absorption of phosphorus, resulting in bioavailability of below 50%.

With our lentils containing 180 mg per 100 g at estimated 40% bioavailability, that means about 72 mg are absorbed, which would translate to ~10% of the daily requirement for an adult. Hey, that’s pretty good actually.

Claim: Legumes are rich in B-Vitamins

100 g lentils contain the following amounts of B-Vitamins:

• Vitamin B1 – Thiamin: 0.169 mg or ~15% of DR (daily requirement)
• Vitamin B2 – Riboflavin: 0.073 mg or ~6% of DR
• Vitamin B3 – Niacin: 1.06 mg or ~7% of DR
• Vitamin B5 – Pantothenic acid: 0.683 mg or ~13.5% of DR
• Vitamin B6: 0.178 mg or ~13% of DR
• Vitamin B9 – Folate: 181 µg or ~45% of DR

Hey, finally some good, solid numbers. The only thing to point out here is the distinct lack of Vitamin B12 – Cobalamin, which exclusively is found in animal foods. Some plants may contain Pseudo vitamin B12 which our bodies do absorb but cannot use at all. This actually poses the risk that consuming pseudo vitamin B12 could block the absorption of actual B12.

Claim: Legumes are a great source of protein

Legumes are generally not considered a complete protein, which means at least one amino acid is too low. In the case of lentils, Methionine is very low resulting in a low quality protein. This is called the Digestible Indispensable Amino Acid Score or DIAAS for short. It’s an estimate of protein quality and it’s digestibility. Whereas Eggs or Beef have a DIAAS of over 1 (= 100%), cooked kidney beans only have a value of 0.588 and cooked peas also only have 0.579. Chickpeas have a relatively high score of 0.83, but the major player are soy beans with a score of practically 1. This score can be increased by combining them with foods that “patch up” their shortcomings.

However, this score simply takes into account the overall makeup of the protein and doesn’t paint the whole picture. Unfortunately all beans and legumes contain protease inhibitors, meaning they mainly inhibit trypsin activity in the gut, impacting protein digestion. Soy for example specifically contains Kunitz STI protease inhibitor and Bowman–Birk protease inhibitor in high amounts in soy flours, soy concentrates and soy isolates. On top of that, phytates also impair protein digestability.

On that note, 100 g lentils on paper contain about 9 g of protein. This is an ok amount, but 100 g beef contains 26 g of complete protein without protease inhibitors.

Claims: copper, manganese and magnesium

I’m combining these 3 as I could find very little useful data regarding their bioavailability. Phytate does not inhibit copper absorption, but does impact manganese and magnesium. So bioavailability for these two could be similarly low as it is for zinc (~13%) but that is speculation on my part.

Beans and legumes contain lectins

I’ve already mentioned them further up, but they are the reason why beans in their raw state are very toxic. The only reason beans are edible is because cooking and other food preparation methods destroy lectins, but trace amounts are still left. If prepared correctly, lectins are reduced by a whopping 93.77–99.81%. This means boiling the legumes for an hour, which invariably will also destroy some nutrients though.

And again, there are usually still some active lectins left. Phytohemagglutinin for example can cause red blood cells to clump together. Lectins also bind to the gut lining for prolonged periods of time, potentially causing autoimmune responses. They are theorized to play a role in inflammatory conditions such as Type 1 Diabetes and rheumatoid arthritis.