We hear a lot about various deficiencies; iron deficiency in women, vitamin D deficiency in the winter; hell, half of the country thinks they're protein deficient. But nobody stops to think about how much fibre they're getting.
Stick a side of peas or broccoli on your plate and you're good, right? You eat wholemeal toast and brown pasta and call it a day. Or maybe you're on the low-carb bandwagon with these punks.
Well, just hold the phone a second. The RDA for dietary fibre isn't 30g/day just for shits and giggles (the NHS actually suggests 30g/day is the minimum we should get). Most people in the UK get about 18g/day, give or take. A slice of that wholemeal toast, has about 2g. A side of broccoli? About 2g. Peas. Yeah, 2g. So, you see where this is going. And, just by way of evolutionary comparison, our Palaeolithic era relatives got an estimated 100g of fibre PER DAY. In other words, people on the original Paleo diet ate more than 3x times the amount of fibre than the current RDA, and more than 5x the amount the average Briton eats.
But, a fibre deficiency isn't just going to keep you backed up for days. I mean, it will, but it's also linked to weight gain, obesity, type 2 diabetes, and even some cancers. As fibre goes up, risk of metabolic syndrome goes down, there's less inflammation in the body, and the risk of obesity drops. A study from the University of Leeds found that for every additional 7g/day serving of fibre, cardiovascular disease risk lowered by 9%. Yeah, I bet you didn't read that on your favourite socialite's pseudo-nutrition blog. Amongst other things (like lowering cholesterol, blood glucose levels, and blood pressure) fibre feeds our gut bacteria. So, let's take a look at what's really going on down there.
Insoluble fibre is not people food. Humans can't digest and absorb it like sugar or fat or vitamins. We don't have the enzymes that can break it down, so it stays intact, until it hits the colon where it becomes bacteria food.
There maybe as many as a million different species of bacteria living in our gut, not to mention the fungi, viruses, and other microorganisms living down there. It's estimated that there are around a HUNDRED TRILLION microbial cells in or on our bodies, outnumbering our own cells 3:1 (whatttt??). Collectively these microbes are called our microbiome, and their genetic capacity is 100 times greater than our own (mind blown!), meaning they can produce proteins and enzymes that we can't. Ergo, why they can digest fibre and we can't. You can learn more about the human microbiome here.
What are these little guys doing down there? Well, they're not just chilling, that's for sure. They help boost the immune system, improve digestion and absorption of nutrients, they SYNTHESISE vitamins, (I'm sorry, but that's f*cking cool) and they help prevent pathogenic bacteria taking hold and turning the whole thing into a shit show. Literally. Lastly, and most importantly our microbiota produce a chemical called butyrate; this is what feeds the cells that line our colon and keep them healthy and prevents local inflammation.
We've evolved a pretty kushy symbiotic relationship with our microbiome; they'll watch our back and keep them healthy. There's just one caveat; you have to feed them fibre!
Remember that what you eat, is also what they eat. Long-term diet shapes our microbiome. If you're eating a high fat, high sugar diet, you promote the growth of bacteria that can make use of those foods, and as a result shift the composition of the mirobiome towards a less healthy one i.e. one with less microbial diversity and that produces less butyrate.
This imbalance of the communities in our gut is call dysbiosis. Although scientists are still trying to figure out exactly which bacterial species make up a healthy/unhealthy microbiome, there are a few things they're pretty sure about 1) less bacterial diversity = worse human health 2) without enough food to feed the microbiome, the gut confuses the lack of butyrate production with pathogenic (bad) bacteria being present, and effectively begins to attack itself, resulting in inflammation.
Unlike a healthy microbiome that produces vitamins and boosts the immune system, an unhealthy one is linked to carcinogen production, intestinal putrification (usually of protein), toxin production, diarrhoea, and constipation. Obesity, metabolic syndrome (like that associated with polycystic ovary syndrome), some cancers, and inflammatory bowel disease have all been linked to low bacterial diversity too.
But fibre is only one side of the story, what about the stuff you're eating when you could be eating more fibre? Milk protein has (experimentally at least) been linked to colitis. It's thought that milk causes a bloom in the colitogenic bacteria Bilophila wadsworthia. Likewise, oral iron intake may exacerbate experimental colitis through the action of the micriobiome. Diets high in choline (from eggs and meat), and carnitine (from meat, some energy drinks and supplements) select for bacteria that convert these compounds into TMAO. Elevated blood concentration of TMAO is a risk factor for major cardiovascular events, and surprise, surprise, blood levels increase after eating foods containing carnitine and choline due to bacterial action in the gut. Interestingly enough, people on plant based diets select against a microbiome that can metabolise carnitine. Instead, their microbiomes support the growth of butyrate producing bacteria because, spoiler: they eat more FIBRE!
So if wholegrain bread and pasta aren't cutting it in terms of fibre, where the eff should you be getting it from?
- 40g (1/2 cup) bowl of porridge with a tablespoon of flaxseed and a serving of blueberries or a small sliced banana is > 7g fibre
- A baked sweet potato (skin on) is around 5g fibre; have it with one of my chipotle black bean burgers for an extra 4g.
- A medium portion of quinoa (145g) has 5g fibre, add some broccoli for another 3g.
- This bean spicy bean chilli has 9g per portion add brown rice for 2 more grams
- Snack on pears (4g) or carrot sticks and hummus (10g)
Some of you might be wondering if you could just add a probiotic yoghurt into the mix to increase your number of 'good' bacteria. But unless you're feeding the bacteria that are already there, what's the incentive for new ones to stick around? Save your money and eat more whole grains, vegetables, fruits, and legumes instead.
Don't f*ck with fibre.
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