(Source: The science of staying well  Dr Jenna Macciochi)

High dietary fibre consumption comes with a 30 per cent decrease in death from all causes, particularly some of the top killers globally, including heart disease and type 2 diabetes. Not only that, eating a fibre-rich diet is linked to reduced risk of colon cancer and can reduce inflammation associated with joint pain and arthritis.

Yet despite now having a clear picture that fibre is good for us, there are still some misunderstandings around how much we need. A good rule of thumb for the biggest impact on health is to aim for over 30 different plant foods per week, while eating 10 or fewer has a potentially damaging impact on the microbiota. There are over 100 different types of fibre found in foods such as fruit, veg, nuts and seeds, legumes and whole grains. Aim to include some resistant starches - so called because they are resistant to digestion in your gut, but not for your gut bugs. These include cooked and cooled white potatoes, oats, lentils and rice.

Butyrate - A special chemical.

From our point of view, butyrate is a wonderful chemical. It helps control the growth of our gut wall cells which protects us against bowel cancer, it has powerful anti-inflammatory effects, and recent research has shown that it kills bad bugs such as Salmonella. 

Inflammation is one of the ways your body defends itself. If you get flu you will probably become hot and inflamed, with achy joints, as your body tries to destroy the viruses. That's fine. The problem comes when inflammation persists. Just as having a chronically infected tooth is a bad thing, having persistently inflamed guts can lead to pain, bloating, gas, constipation and eventually bowel cancer. 

One way to counter this is to boost your butyrate levels by eating food with lots of fibre in it. The undigested bits of fibre will reach your colon and give your 'good' bacteria plenty to chew on. Well fed, these 'good' bacteria will provide you with lots of lovely butyrate.

As well as lowering inflammation, butyrate helps to maintain your gut lining, the barrier that keeps bacteria and other toxins from escaping into your blood. If this barrier starts to break down, you get a condition known as 'leaky gut syndrome' which can lead to all sorts of distressing problems, including IBS. 

​(Source: the Clever Guts diet -Dr Michael Mosley)

If our immunity is beholden to the health of our microbiome, it follows that we need to feed those bugs well. After birth and breastfeeding, nothing matters more than giving them the right food. Fibre is good for you and now science knows why: fibre not only helps keep our bowels regular but provides some great fodder for your microbiome and might just be the lifesaving food 90 per cent of us aren't eating enough of. Although not often considered an important 'immune booster', through feeding our microbiome, fibre plays a vital role in the overall capacity of the immune system to do its job. The preferred food for our gut bugs, dietary fibre is the most accessible tool to nurture our gut microbiome and put our immune system on the right track from the start.

What we eat can change the balance of microbes in our guts - and as their relative numbers change, they secrete different substances, activate different genes and provide us with different nutrients. Our modern-day diets are inherently lower in fibre than our ancestors'. This has led to a loss of our ancestral microbial heritage - a mass extinction, if you will. This is seen with immigrants from traditional cultures who lose valuable gut microbes when they move to industrialised nations, correlating with a rise in Westernised diseases in these populations.

Resistant Starch (RS).

​Resistant starch is a type of starch that, as the name implies, resists digestion in your stomach and small intestine and reaches your colon largely intact. You are unlikely to get big blood sugar spikes after eating RS, and you won't hold onto many calories from it either. Once it reaches the large intestine, it feeds the 'good' bacteria which digest it and release butyrate. 

You'll find lots of resistant starch in grains, seeds and legumes. You also get it in unripe bananas and green peas. But one of the more surprising places you will find some of it is in pasta or rice that has been cooked and cooled.

In an experiment at the University of Surrey, volunteers were asked to eat pasta with tomato sauce either hot, cold or reheated. Their blood sugar levels were measured after each meal. It was found that eating cold pasta led to a smaller spike in blood glucose and insulin than eating freshly boiled pasta. That's because cooking and cooling pasta changes the structure of the starch in the pasta, making it more resistant to digestion.

But then we found something that we didn't expect - cooking, cooling and reheating the pasta had an even more dramatic effect. Or, to be precise, eating reheated pasta resulted in an even smaller effect on blood sugar levels than eating cooled pasta. In the volunteers it reduced the rise in blood sugar levels by 50 per cent.

A group in Sri Lanka have done something similar with rice. They found that if they boiled rice with a bit of coconut oil, cooled it down, then reheated it in the microwave, they could increase the levels of resistant starch in it roughly 15-fold. They think that eating rice this way probably halves the amount of calories your gut will absorb from it.

And by the way, the claim that reheating rice is dangerous is an almost total myth. Unless it has been sitting out in a warm place for many hours it should be absolutely fine.

(Source: the Clever Guts diet, Dr Michael Mosley)

Forgotten Fibre

Sorry, low-carb dieters, your microbes are just not that into you!

While many people report wonderful results from a low-carb diet, the effect on the gut microbiota is not well understood. A potential challenge of eating a low-carbohydrate diet, if implemented improperly, the resulting low fibre intake and knock-on impact on your fibre-loving gut microbes.

When we eat a fibre-deficient diet, our gut microbes starve, with a knock-on negative impact on out immunity that could open us up to illness down the line. This is especially true if the few remaining dietary carbs contain a limited amount of fibrous food for gut bacteria, which means they have less to eat and less to do.

High-fat diets are interesting because the organisms in the gut that love fat are not those organisms believed to be the most beneficial for the microbiome. So while there have been dramatic health effects in people on a high-fat diet devoid of complex carbohydrates, the research is just getting started on what this does to the gut microbiota and the long-term impact on our health. But early indications show that unless a complex carbohydrate intake is maintained while eating low carb, exclusive consumption of a high-fat diet is pretty destructive for the diversity of the microbiome.