Beans are nothing new. What’s interesting is what happens after you eat them.

Beans brings together fibre, plant protein, slowly digested carbohydrates and resistant starch — a combination that can influence how quickly glucose reaches the bloodstream, how full we feel and what happens further down in the gut.

That last part is especially interesting. Because not all of the starch in beans is digested by us. Some of it ends up feeding our gut bacteria instead.

First, what exactly is resistant starch?

Starch is a type of carbohydrate found in foods like grains, potatoes, bananas and beans. Normally, starch is broken down into glucose in the small intestine and absorbed into the bloodstream. But resistant starch is different. As the name suggests, it resists digestion in the small intestine. Instead, some of it travels on to the colon, where certain gut bacteria can ferment it. During this process, short-chain fatty acids are produced, including butyrate. Butyrate is particularly interesting because the cells lining the colon use it as an important source of energy. Research suggests resistant starch can influence both the composition and activity of the gut microbiome, although the response varies from person to person. [1]

So, why beans?

Beans are particularly interesting because resistant starch doesn't come alone.

You also get fibre, plant protein and slowly digested carbohydrates, all packaged within the natural structure of the bean. That structure matters. It means the carbohydrates in beans tend to be digested and absorbed more gradually than carbohydrates from many refined foods. The result? Generally a slower, lower rise in blood glucose after eating.

Research on pulses — including beans, lentils, chickpeas and peas — has found beneficial effects on several markers of glycaemic control. [2]

And resistant starch itself has also been studied for its effects on blood glucose and insulin sensitivity. A meta-analysis of 19 randomised controlled trials found modest improvements in fasting glucose and insulin resistance. [3]

And what does insulin have to do with it?

When glucose enters the bloodstream, the pancreas releases insulin. Insulin helps move that glucose into our cells, where it can be used for energy or stored for later. That's a normal and essential process. But foods aren't all digested at the same speed. A rapidly digested carbohydrate can create a very different post-meal glucose response from a bowl of beans, where fibre, protein, food structure and slowly digested or resistant starch all come into play. This is one reason beans are so interesting from a metabolic perspective. It doesn't mean that keeping insulin as low as possible is the goal — or that lower insulin automatically leads to weight loss. The reality is more nuanced. But blood sugar regulation, insulin sensitivity, appetite and the types of carbohydrates we eat are all part of the bigger metabolic picture.

Then there's the gut

This might be the most interesting part of all. Because resistant starch isn't completely digested before it reaches the colon, it becomes available for certain gut microbes to ferment. And when they do, they produce metabolites including short-chain fatty acids.

Research suggests resistant starch can alter the gut microbiome and increase certain bacteria involved in its fermentation. But there's an important caveat: we don't all respond in exactly the same way. The type of resistant starch and the microbes already living in your gut both appear to matter. [1,4]

So when we talk about eating for gut health, it isn't only about adding bacteria through fermented foods or probiotics. It's also about giving the bacteria already there something to eat. And beans happen to be very good at bringing fermentable carbohydrates and fibre to the table.

Could that have something to do with weight?

Possibly. And this is where the research gets particularly interesting. In a 2024 randomised crossover trial, researchers gave resistant starch to 37 people with overweight or obesity for eight weeks. During the resistant-starch intervention, participants lost an average of 2.8 kg, improved their insulin resistance and experienced changes in their gut microbiome. [5]

The researchers also identified changes involving Bifidobacterium adolescentis, suggesting the microbiome may have played a role in the metabolic effects. It's an exciting study.

But there's an important distinction: the researchers used a specific resistant-starch supplement at a controlled dose. They didn't simply ask participants to eat more beans. So we can't say that eating beans will produce the same result. What the study does give us is another clue that resistant starch, the microbiome and metabolic health may be connected in ways we're only beginning to understand.

The easiest way to eat more beans

Make them easy to reach. One of our favourite ways is to make a big bowl of bean salad and keep it in the fridge. Then lunch doesn't require another health decision — you simply add a few spoonfuls to whatever you're already eating.

There isn't a magic amount you need at every meal.

And if beans aren't currently a big part of your diet, start with a smaller portion and gradually increase it. A sudden increase in fermentable fibre can mean a little more activity in the gut than you bargained for.

The Everyday Bean Salad

You'll need

2 cans black beans, rinsed and drained
1 small garlic clove, finely grated
3 tbsp extra-virgin olive oil
Zest of 1 lemon
Juice of ½ lemon
Sea salt
Freshly ground black pepper

Optional: chopped parsley, coriander or whatever fresh herbs you have around.

Mix everything together and keep it in the fridge and add a few spoonfuls to salads, eggs, roasted vegetables, fish, chicken or grain bowls.

The takeaway

Beans aren't new. Maybe that's part of what makes them so easy to overlook. But inside something incredibly ordinary is a surprisingly interesting combination of fibre, plant protein, slowly digested carbohydrates and resistant starch. Sometimes eating better really can be as simple as keeping a bowl of beans in the fridge.

References

[1] Baxter NT et al. Resistant starch: impact on the gut microbiome and health. Current Opinion in Biotechnology, 2019.
Read the study on PubMed

[2] Sievenpiper JL et al. Effect of non-oil-seed pulses on glycaemic control: a systematic review and meta-analysis of randomised controlled experimental trials. Diabetologia, 2009.
Read the study on PubMed

[3] Xiong K et al. Effects of resistant starch on glycaemic control: a systematic review and meta-analysis. British Journal of Nutrition, 2021.
Read the study on PubMed

[4] Chen R et al. Meta-analysis reveals gut microbiome and functional pathway alterations in response to resistant starch. Food & Function, 2023.
Read the study on PubMed

[5] Li H et al. Resistant starch intake facilitates weight loss in humans by reshaping the gut microbiota. Nature Metabolism, 2024.
Read the study on PubMed