What Is Resistant Starch

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Have you heard about resistant starch? It seems to be popping up on social media a lot so I thought it worth talking about!

What is it? What are the benefits? Is it something you should know about? Because obviously, everyone's talking about gut health at the minute, everyone's talking about carbohydrates and whether they're good, bad or ugly at the minute. So we need to put this thing into context.

Resistant starch describes a type of dietary carbohydrate that are resistant to normal digestion within the small intestine. Most carbohydrate digestion takes place within the small intestine. Pancreatic enzymes, pancreatic amylase, etc, start to actually attack these more simplistic carbohydrates and cleave them into their smaller sort of disaccharide units, monosaccharide units that we can absorb and put to use, the most obvious one being glucose. Glucose is that thing that we use to convert into ATP in our cells.

Most of the more simple carbohydrates are broken down and digested in the small intestine, but there are a certain category of carbohydrates that are almost completely resilient to this type of digestion. And instead they get broken down by means of fermentation. They're actually fermented by the bacterial colony that live in the gut. These are the resistant starches. Now they're not all the same. There's four main groups of resistant starch. Okay. So type one resistant starch, these are the ones that are found in grains, in seeds, in legumes, these kinds of things.

These are the ones that are found in these very, very high fibre foods. It's not that the actual carbohydrates within them are particularly complex. They are relatively simple, but it just means they're very, very tightly bound in this network of dietary fibre, of types of polysaccharides that aren't broken down, what we would call insoluble fibre. Some people call it roughage. I think it's a terrible word. Anyway, these are so tightly bound within the dietary fibre that not a huge amount of them are released, but the fermentation process does liberate some of them.

Type two resistant starches are the ones that found in some of the starchy staple foods such as raw potatoes. The carbohydrates in potatoes, the starchy potatoes are highly, highly resistant when the potato is raw. Obviously raw potatoes, absolutely revolting. You know, that kind of sensation you get from eating one, if you've ever done it. But as soon as you cook it, you get degradation of some of the carbohydrates and fibre.  The complexity changes and all of a sudden those starches become much easier for your digestive system to actually liberate and to break down. So a raw potato, relatively low glycemic impact, a cooked potato, very, very high glycemic impact.

That's an important thing to know. When we talk about glycemic impact, what I basically mean is the capacity for a food to raise your blood sugar and the extent to which it does it.  So something like white rice versus brown rice, the white rice, that will raise your blood sugar very, very quickly because there's not much fibre there. It means the sugars are liberated very, very quickly. So they flood your bloodstream very, very quickly. Brown rice, you've got much more fibre. And as we talked about in the type one resistant starch, that fibre will slow down and will impede the body's ability to liberate the sugar from it. So it'll be more of a drip-feeding effect rather than a carpet bombing.

Why does this matter? Well, in the short term, a very, very high glycemic diet will send your blood sugar up and it'll come crashing back down again, which will make you feel quite heady, quite tired, quite fatigued. And you just end up feeling very, very sleepy. You get a carb coma. If this goes on day after day, I mean, you think about this as a normal dietary pattern. This isn't particularly abnormal at all. Someone may have like a bowl of cornflakes and a slice of white toast for breakfast. They might have a sandwich and a packet of crisps for lunch. In the evening, they may have a great big mountain of mashed potato or a big bowl of pasta, something like that.

None of these foods are bad. I'm not demonising individual foods. The pattern of consumption is the issue because blood sugar is constantly being pushed up, pushed up, pushed up beyond the level that the body can actually handle in a healthy way. Over time, this can raise cholesterol. This can actually increase risk of type two diabetes. It can cause visceral fat gain and it increases risk of cardiovascular disease in a second way, because it can exacerbate inflammation within the endothelium, which is the inner lining of blood vessels. So I am an advocate of following a low glycemic diet. Okay. So when I'm talking about glycemic, the glycemic impact that these things have, the lower, the better.

The other well-two known type resistant starch are green bananas. I don't know whether you've ever bitten into an unripened banana. You almost feel like you get a coating on your teeth and like your tongue dries out a little bit. That is the starch. That is that very, very complex starch that would be highly resistant that goes away as the banana ripens and they become sweeter. That's because those carbohydrates have become much less complex and much easier to liberate.

The type three resistant starches, these are formed when certain starchy foods like potatoes and white rice are cooked and then cooled. So when you first cook them, they have a very high glycemic value, but when they've been cooked and cooled, the resistant starch starts to form and they have a much lower glycemic impact. And then the type four, these are the manmade resistant starches that are sometimes added to functional foods, for example.

So what's the deal with these? Why are these potentially beneficial? Well, they are a food stuff for the bacterial colony that live in the gut. The more simple carbohydrates are broken down by the enzymes that are secreted in the small intestine, very easily, very rapidly. But these complex ones, the resistant starches, the starches that are resistant to those enzymatic processes, these actually get broken down by the gut flora within the colon. This fermentation process has several benefits. Firstly, it increases the number and the diversity of the bacteria that live within the gut. There's more of them and there's a more diverse range of them. The more diverse number of bacteria you have, the better. There's anywhere between 500 to 1000 different strains of bacteria that can live in our gut and they all have different roles to play.

That's the next thing that we should get into, why are these bacteria so important in the first place? Well, they've got some really important roles to play. They synthesise certain nutrients like vitamin K and some of the B vitamins. They also help to look after the health of the local environment of the colon, they keep the colon very, very healthy. But probably one of the most fascinating things from my point of view at least is the impact that they have on the immune system. They have a really, really interesting regulatory effect on our immunity. I you think about it, the digestive system is a very, very straightforward interface between the outside world and the inner workings of the body. It's a potentially easy route for opportunistic pathogens to gain entry into our body. We swallow them, in they go.

So this area obviously has to be very, very tightly policed. And they're policed by these little patches of tissue that are embedded in the walls of the gut called Peyer's patches and Peyer's patches are a little bit like a surveillance station. They're constantly monitoring gut contents and then relaying this information back to the rest of the immune system. And they have two distinct types of response. They need to determine whether tolerance takes place. Tolerance is basically where something enters the body and the immune system's like, okay, yep. That's a Pfizer chemical or a nutrient or whatever. That's important. We're going to let that in, don't react to it. Don't kick off. That's perfectly fine. His name's on the list, lets it in.

Then obviously the other kind of thing that they need to figure out is whether an immunological response needs to take place. So if something is pathogenic or potentially damaging, then the Peyer's patches and the cells that inhabit the Peyer's patches will determine the fact that an immunological response needs to be instigated. And then will send a whole range of chemical messengers to the immune system to tell it what type of response needs to take place when, where, and how aggressive. So, that's what the Peyer's patches do. And within those Peyer's patches, you've got T0 cells, you've got dendritic cells, you've got all sorts of different types of immunological cells, antigen presenting cells. The gut bacteria talks directly to this cell population and actually helps them to do their job more effectively, which I find utterly fascinating.

And then also, the final thing, I mean, you've heard me talk about the gut serotonin thing in the past. The serotonin in the gut has got nothing to do with depression whatsoever. Serotonin in the brain has, but we do know that there is a link between the gut and the brain. And we do know that a healthier digestive tract is related to improved mental health outcomes. But this has nothing to do with serotonin. This seems to be related to gut flora, again, a communication between gut flora and the nervous system. It's early days in the research, but that's where that link seems to be. So looking after the health of the gut bacteria is of vital importance.

So, that brings me to the second part of this discussion point. Should we be consuming carbs? So many people ask me, oh, should I be consuming carbohydrates? Should I go on a low carb diet? I am a big advocate of a low glycemic diet, which as I have discussed before. It is a diet that keeps blood sugar nice and stable and doesn't give you those peaks and troughs and it has so many protective effects on metabolic health. If we look at the things that are plaguing our health system at the moment, cardiovascular disease, type two diabetes, obesity, these are metabolic problems. So anything that looks after the health of many aspects of our metabolism is going to be a winner for so many different reasons. That's why I am an advocate of a low glycemic diet.

But I do eat carbs every day. I mean, last night I had an amazing vegan curry with courgettes, mushrooms, spinach, red onions, black beans. And I had it with brown rice, the black beans and the brown rice. These are dense carbohydrates, but they are real, real slow burners. They don't cause the massive spikes in blood sugar. And they have huge amounts of these resistant starches, long chain polysaccharides that feed the gut bacteria. Okay? My message is like, just keep away from the white bread, white rice, white pasta, sugary drinks, chocolate, and just keep away from the crap. We know what we need to be avoiding and instead, just switch over to a whole foods diet. That means the whole grains, pulses, those kinds of things. These will give you carbohydrates to maintain your glycogen stores and to actually fuel you through the day. But they will also have sufficient amounts of these key fermentable polysaccharides that support the health of the gut.


In conclusion

Resistant starches, and more broadly very complex low glycemic carbohydrates are an important part of a healthy diet. They help to feed and nurture our gut flora and improve multiple aspects of metabolic health. 

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