Legumes are Bad for You? What you Need to Know

From my quick search of “legumes are bad for you”, I came across several articles with similar claims about why legumes are bad. Is there any truth to these claims? What does science have to say about why legumes are bad?

Some claims against legumes are specific to a single type of legume (ex. phytoestrogens in soy, aflatoxins in peanuts) and I won’t be covering these in this article. Instead, I’m focusing on more general claims as to why legumes are bad for you.

This article covers:

Lectins
Saponins
Phytic acid
Carbohydrates
FODMAPs

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Lectins are Bad for You?

The first and most popular reason people claim legumes are bad for you is that they contain lectins. There’s no research to sufficiently support the theory that eating a diet high in lectins is harmful to health ¹.

On the contrary, foods high in lectins including legumes, whole grains, and vegetables, are some of the most health-promoting foods you can eat ³^,⁴^,⁵^,⁶^,⁷.

Eating Raw Legumes Can be Harmful because of the High Lectin Content

One specific claim against lectins is eating raw or undercooked legumes can cause nausea, vomiting, diarrhea and bloating ¹. There is some research to support that eating raw legumes isn’t the best option.

So, it’s best to avoid eating raw legumes because of the high lectin content.

However, in properly cooked legumes, the lectins are destroyed ². This is the main reason why claiming legumes are bad due to lectins is not a strong argument. The lectins are destroyed by proper cooking (not to mention most people aren’t eating raw legumes anyways).

If cooking legumes at home, it’s best to soak them overnight then drain away this water and rinse the legumes before cooking. Cook at a high heat (full boil or pressure cooker) until the legumes are soft throughout.

Peanuts and green peas are legumes that are ok to eat raw if you like and don’t have a medically necessary reason to avoid this.

Lectins Cause Leaky Gut Syndrome?

A main reason lectins and legumes are said to be harmful to health is that they cause leaky gut syndrome.

Leaky gut syndrome is a poorly defined diagnosis which is apparently caused when substances from food damage the lining of the intestine wall ⁸^,⁹. This leads to “holes” in the walls of your intestine (what scientist call increased intestinal permeability), allowing bacteria and other “toxins” into your blood stream ⁸^,⁹.

Lectins are stated to be one of the foods that can cause leaky gut syndrome, with gluten and refined sugars being the other two commonly reported substances.

While many people report having leaky gut syndrome, it’s not yet a medically diagnosable condition and significantly more research is needed on increased intestinal permeability.

What you Need to Know about the Science Behind Leaky Gut Syndrome

Leaky gut syndrome is not a diagnosis recognized by traditional medical practitioners because there is not enough research to define, correctly diagnose or develop a clear plan of action for treating the condition ⁸^,⁹.

Furthermore, there is debate on whether leaky gut syndrome is the cause of other health issues, or a symptom of other ailments.

Research supports that people with certain gastrointestinal disorders have increased permeability in their intestinal lining (Celicac disease, IBS, IBD) that leads to inflammation in the gut itself ⁸^,⁹. But there is significantly lacking evidence to suggest whether other conditions originating elsewhere in the body cause leaky gut, or if leaky gut can cause issues outside of the intestinal tract ⁸^,⁹.

Some alternative health practitioners state that leaky gut is the cause of many health problems including type 1 diabetes, lupus, multiple sclerosis, chronic fatigue syndrome, fibromyalgia, arthritis, allergies, asthma, acne, obesity and mental health disorders. Research does not support any of these claims ⁸^,⁹.

Be wary of anyone online promising to “cure” or “heal” your gut (or anything else) because these are often false claims and, if the person isn’t a medical doctor, they may be in violation of healthcare practice laws.

Saponins

So if lectins aren’t truly a harmful component of legumes, there must be another good reason why legumes are bad and we must avoid them, right? Let’s take a look at another commonly touted “anti-nutrient” found in legumes: saponins.

Saponins are a group of chemical compounds found in many plant-based foods, and are found in the highest concentrations in legumes, some vegetables (garlic, asparagus, green peas), whole grains (oats, quinoa), and red wine ¹⁰.

Saponins get their name from the word soap because they have foaming properties due to how the structure of saponins interacts with the structure of other molecules and cells in the body.

Just as lectins are said to be an “anti-nutrient”, saponins are often placed in the same category by people who bash legumes as being a harmful food to eat.

It’s funny because, just like foods that contain high amounts of lectins are actually health-promoting, foods containing saponins are also found to have many health benefits.

What Saponins do to the Human Body

Saponins have a wide range of effects in the human body including anti-inflammatory activity, cholesterol-lowering ability, anti-fungal and anti-parasitic properties, blood vessel protection activity, impact on lowering blood sugars, and immunomodulatory (modifying the immune system) effects ¹¹.

Since saponins are found in hundreds of plant species, we need to be careful when looking at saponin research to identify the source of saponins used. Some are edible while others are not.

New saponin molecules from different plant species are often being discovered and having their chemical, physical and physiological properties defined by researchers.

One major area of research regarding saponins is their cytotoxic effects. This sounds like a bad thing right? Toxic can’t be good?

The cytotoxic effect of saponins generally refers to saponin molecules’ ability to kill cancer cells ¹¹. Dozens of articles describe different saponin molecules’ ability to kill cancer cells in a petri dish ¹¹.

Although this is interesting research, studies are needed in humans, not petri dishes. Also, many of the saponins in these research studies are extracted from non-edible plants ¹¹.

Regardless, it seems very odd to me that compounds that have the potential to kill cancer cells are targeted as a harmful component of foods we eat.

To summarize: saponins are shown to have many positive impacts on human health and have the potential to kill cancer cells in a petri dish ¹⁰^,¹¹.

A Quick Rant about Saponins and Evidence-based Nutrition

I found one site that states saponins damage red blood cells, interfere with thyroid function, and inhibit enzymes in the body. They only provided one reference for this claim and it linked to an article that showed saponins kill leukemia cells.

That’s right, far from having damaging effects on red blood cells, saponins were found to help stop leukemia cells from growing, and this article is being used to promote a “saponins are dangerous” message.

This is a clear example of why you need to check the sources of information you read, especially about nutrition.

So many unqualified people spread messages that have absolutely no basis in science. Simply stating something as fact, and providing an inaccurate reference (which I assume they don’t intend for anyone to check) is unethical, dangerous and frankly shouldn’t be allowed.

They also didn’t provide any references for saponins interfering with thyroid function or inhibiting enzymes, so I’m not sure where they pulled that information from other than a mistaken understanding of science and nutrition.

This type of thing happens all the time with people promoting certain diets, especially by people who don’t have a background in nutrition or have something to sell you like a book, program, supplements, etc.

I also frequently find people using references for petri dish or animal model (ex. rat) studies while making claims about humans and human nutrition. While these studies may be interesting, they don’t “prove” anything about humans or human nutrition (FYI we aren’t rats).

Legumes Contain Phytic Acid and are Therefore Unhealthy?

Phytic acid is the storage form of phosphorous in many plants including legumes, grains, nuts and seeds ¹².

Phytic acid is another compound that is considered an “anti-nutrient” because in the digestive tract it binds with minerals like iron, zinc and calcium. This binding prevents these minerals from being absorbed ¹², so even though legumes, grains, nuts and seeds contain important nutrients like iron, zinc, and calcium, we don’t absorb the full amount.

Phytic acid is not metabolized by humans because we lack the enzyme needed to break it down ¹². Luckily, there are ways to overcome some of the effects of phytic acid and increase nutrient absorption.

Firstly, soaking and cooking legumes and grains shows a reduction in phytic acid, and subsequent increase in mineral absorption ¹²^,¹³^,¹⁴.

Second, fermentation has been show to help lower phytic acid content of grains and the same could hold true for legumes ¹²^,¹³^,¹⁴.

Third, germination, aka sprouting, of grains can reduce phytic acid content by up to 40% ¹².

Specifically looking at iron absorption, addition of vitamin C to a meal can increase iron absorption and overcome some of the effect phytic acid has on decreasing iron absorption ¹⁵.

Are there Health Benefits to Consuming Phytic Acid?

Phytic acid can be a concern for decreased mineral absorption, but many common cooking methods for legumes (soaking and cooking) can help overcome this ¹²^,¹³^,¹⁴. Eating vitamin C with a meal can also overcome decreased iron absorption ¹⁵.

Foods that contain phytic acid are an important source of nutrition for humans, especially those on a plant-based diet. And, just as with lectins and saponins, phytic acid has been shown to exert positive effects in humans.

In short, phytic acid has been shown to be an antioxidant, and may protect against kidney stones and some types of cancer (more research is needed) ¹²^,¹³. Phytic acid may also help lower risk of cardiovascular disease, and could have a blood sugar and lipid (cholesterol) lowering effect although more research is needed in humans ¹².

So once again, the claims that phytic acid in food is harmful, unhealthy, and a reason to avoid eating legumes, does not hold true.

Legumes are Bad for Us because They are High in Carbohydrates?

Legumes do contain carbohydrates; however, they contain complex carbohydrates along with fibre and significant protein content.

Fibre and protein both help mediate the absorption of carbohydrates from food into the bloodstream. The fact that legumes contain high levels of both these mediating factors makes them an ideal source of carbohydrates because you don’t have to think about adding fibre or protein to your meal to help with keeping blood sugars more stable.

For people concerned about the amount of carbohydrates they eat (ex. people with diabetes), legumes are still a perfectly acceptable food to add to your diet. However, there may be some work required to figure out how your body reacts to carbohydrates and what this might mean for taking insulin or other diabetes medications. Please work with a dietitian to help you navigate this.

Legumes Contain FODMAPs and High FODMAP Foods Need to be Avoided?

FODMAPs are yet another hot topic in the nutrition world.

FODMAPs (Fermentable Oligosaccharides, Disaccharides, Monosaccharides and Polyols) are a group of carbohydrates that are poorly digested or absorbed in the small intestine of some people.

If left undigested, they travel into the large intestine where they ferment by the good bacteria there. This can cause gas, bloating, and other unpleasant gastrointestinal symptoms especially for people with a digestive disorder.

A trial of a low FODMAP diet can help determine the trigger foods and tolerance levels of people who have difficulty digesting foods that contain FODMAPs. This type of elimination diet should always been done under the supervision of a dietitian.

Low FODMAP diets are also not intended to be life-long; rather, it is a trial of elimination with a reintroduction phase to help identify problem foods and assess tolerable levels.

If you are in the elimination phase of a low FODMAP diet, legumes are reduced in the diet for a while (a few weeks). But this does not mean that legumes are an unhealthy food, or that they should be avoided long-term, or that people who have no issues digesting FODMAPs need to avoid this higher FODMAP food.

Summary: Legumes are Bad for You?

Legumes are an incredibly healthy food. The many claims against legumes, primarily due to “anti-nutrient” content, do not hold up against currently available evidence.

There are many who gain from confusing people about nutrition. Please always check the source of the information you read online, especially as it relates to nutrition.

Registered Dietitians are a quality source of nutrition information as they are the healthcare profession with the most education and training in nutrition science. Dietitians are also a regulated profession which means they are held to high standards for the work they do.