How Sugar Impacts your Gut: What your 4pm Chocolate Fix is really Doing

Photo credit: Getty Images
Photo credit: Getty Images

From Women's Health

From supporting your mental health to keeping your immune system in shape, your gut has had unicorn status bestowed on it over the past few years. Why?

Well, the scientific studies supporting the theory that a thriving digestive system is a crucial part of your overall wellbeing are seemingly endless.

  • Researchers in Belgium found that people with low levels of Coprococcus and Dialister bacteria in their gut, had a higher risk of depression

  • An association between the gut microbiome and the immune system’s ability to fight cancer has been identified by a study, published in Nature Communications

  • Lupus was shown to be linked to abnormal mix of bacteria in the gut by NYU School of Medicine scientists

What is the gut and why is gut health so important?

To recap: the gut, aka the gastrointestinal tract, is essentially a food processor. It starts at the mouth, travels through the stomach and intestines and ends up at the anus.

Your own personal blend of bacteria is thought to be created while in the womb, with genetics and lifestyle behaviours then influencing how it develops after you make your way into the world.

It’s believed the gut and brain can ‘talk to each other’ – a relationship referred to as the gut-brain axis.

‘Research in this field is in its early stages – but is beginning to suggest that your microbiome may be affected by conditions that are linked by the gut-brain axis, says registered nutritionist and Healthspan Head of Nutrition Rob Hobson.

‘Psychosocial factors such as stress or depression can influence the actual physiology of the gut, affecting movement and contractions of the GI tract, increasing inflammation and even making you more perceptible to infection.’

And vice versa; there could be a potential connection between how happy your gut is and your likelihood of experiencing anxiety and depression.

So, what can sugar do to your gut?

‘Sugar is mostly absorbed into the body in the small intestine,’ says Ruairi Robertson, post-doctoral researcher for all-things-gut-health website, The Gut Stuff.

'Although there are some microbes in the small intestine, there are more than a million times more microbes in the large intestine, which follows after the small intestine. This means that if you are eating a moderate amount of sugar, most of it won’t interact with the microbiome in the large intestine.’

Say what? Eating sugar might not be so bad after all?

‘We need sugar function properly,’ continues Dr Ashton Harper from probiotic-makers Bio-Kult. ‘For instance, glucose is virtually the sole energy source used by the brain. However, it comes in different forms – some of which are more harmful than others.’

‘The most harmful sugar in our diets come from what is known as ‘free sugars’, which are those commonly found in processed foods (think cake, biscuits, carbonated soft drinks), as well as highly concentrated natural sources such as fruit juice and honey,’ says Dr Harper.

How much sugar is too much sugar?

Before you head happily to the frozen yoghurt aisle, it’s important to remember that a healthy gut is one that’s built around balance.

‘The small intestine can only process a certain amount of sugar,’ says Robertson. ‘Most of the studies of sugar and the microbiome have been carried out in mice, so it isn’t definitive that these results are the same in humans.

However, some of these studies have shown that if you eat the equivalent of roughly 30g of sugar in one go (approximately seven teaspoons), the small intestine can’t process all of that sugar meaning some travels down into the large intestine (and eventually into the liver through the blood stream).’ For context, a single can of Coca-Cola is already over this seven teaspoon threshold – so it's really not huge amounts to mess with your gut.

Which is bad, because…?

‘In the large intestine, there are certain bacteria that digest the fibre in fruits, vegetables and wholegrains into molecules that protect the gut barrier and feed other healthy bacteria.

Excess sugar may prevent this good bacterium from sticking in the intestine, leaving room for disease-causing bacteria to colonise and grow in the gut.’

Not all sugar is made equal

We’ve already mentioned that there are more than 50 types of sugar and, like box sets on Netflix, not all are as good as others.

Dr Harper makes the assessment.

1 medium (peeled) banana (approx. 120g)

27.5g ‘total carbohydrates’

14.5g sugars

3.1g fibre

107 calories


2 milk chocolate digestive biscuits (approx. 34g)

21g ‘total carbohydrate’

10.2g sugars

1g fibre

174 calories

Note: the additional 10g of unaccounted for carbohydrate in both options above is ‘starch’, which is readily digested in our gut into glucose so, arguably, you can effectively double the free sugar content.

At an additional glance, you’d be forgiven for thinking there’s not that much difference in the stats of the banana vs chocolate biscuits. However, reason to binge eat Oreos, this is not…

3 factors to consider when building a healthy gut diet

1. Added nutrients (vitamins and minerals)

‘Biscuits don’t contain these; whole fruits do,’ Dr Harper says.

2. Dietary fibre

‘The fruit option has more than three times the fibre content of the biscuits.'

Why is dietary fibre important? It helps prevent constipation, makes you feel full, slows digestion and the rate at which sugar hits the bloodstream, and may even reduce the absorption of dietary fat and cholesterol.

'Dietary fibre includes complex sugars such as plant polysaccharides, which are indigestible by our own human enzymes but are metabolised by our resident microbes into a number of important compounds such as short chain fatty acids.'

These are vital for the normal functioning of the cells lining the large intestine and are thought to help protect against inflammation, leaky gut and constipation.

'Indigenous populations on traditional high-fibre diets, compared to those on low-fibre Western diets, have a remarkably different gut bacterial profile which is associated with a near absence of type 2 diabetes and obesity.’

3. Addiction

‘There is strong evidence that refined sugar is addictive in a way comparable to narcotic drugs.

One or two biscuits per day are unlikely to cause serious long-term health issues, provided that they are part of an otherwise healthy, balanced, high fibre diet – however, can you restrict yourself to just one or two? The degree of your sugar addiction may be largely under appreciated, but it all adds up.

'If you normally consume high concentrations of refined sugars and then these suddenly become sparse, say during a period of dieting, the microbes used to the sugar may manipulate your eating behaviour through pain signalling – making you crave (and eat) more.’

Aside from getting a handle on the amount of sugar on your plate, gut health is influenced by other (easier to manage) factors.

Workload and physical activity, for starters. Keep your gut bacteria happy with a 360-degree approach, as outlined by our team of experts in seven simple steps. Take action today and notice the benefits in as little as three days.

7 ways to improve your gut health naturally

1.Eat a diverse diet

‘There are more than 1,000 different species of bacteria in the gut, which need lots of different foods to stay diverse and healthy,’ says Kristy Coleman, a registered nutritional therapist at The Gut Stuff.

‘Don’t just eat chicken and broccoli for lunch every day; aim for 30 different types of plant-based foods, in a variety of colours (fruits, vegetables, nuts, seeds, beans, legumes). Vegetable box subscriptions are a great way to get out of the supermarket rut and help you to experiment with different ingredients.’

2. Fill up prebiotics and probiotics


‘Some foods contain specific fibres that we are unable to digest,’ says Hobson. ‘These fibres are referred to as prebiotics and act as a food source for gut bacteria.

Gut bacteria break these fibres down by a process called fermentation, which produces short chain fatty acids that supply energy to the cells that line your colon.’

The different types are prebiotic foods include:

  • Onions, garlic, leeks, asparagus and bananas contain inulin and fructooligosaccharides that act as prebiotics

  • Oats and barley contain beta-glucans that act as prebiotics

  • Starchy foods such as pasta, rice and potatoes form resistant starches (resistant to digestive enzymes) once they’ve been cooked and then cooled. Resistant starches act as prebiotics


‘Probiotics are bacteria that have been shown to have a positive health benefit,’ Hobson says:

  • Live yoghurt is the most well-known probiotic food and contains strains such as Lactobacillus Acidophilus and Lactobacillus Casei

  • Probiotic supplements offer a way of delivering large doses of specific bacteria to the gut. Stick to preparations that contain well-researched strains such as Lactobacillus and Bifidobacterium in a dose of at least 10 billion bacteria per serving

3. Don’t forget fermented foods

‘Fermented foods contain live bacteria,’ says Coleman. ‘This live bacteria may support bacterial diversity in your gut microbiome – although research into this is limited.’

Great sources of fermented foods:

  • Plain natural yoghurt (look for live cultures on the back)

  • Sauerkraut

  • Kimchi

  • Kombucha

  • Kefir

  • Sourdough

(FYI: Although you can add these to your weekly shop, homemade versions are not only cheaper, but often contain more diverse healthy microbes).

4. Take time for you

‘Chronic stress, an all-too-common part of our busy modern lives, perpetually activates the release of the hormone cortisol, which tends to slow metabolism and increases the permeability of the intestine (‘leaky gut’),’ says Dr Harper.

‘This is implicated in inflammation and type 2 diabetes. Probiotics such as those from Bio-Kult have been shown in both animals and humans to suppress levels of the stress hormone cortisol and may protect against the negative influence of stress on the microbiome and our wider health.’

5. Get active

‘Studies in animals and humans have found that just six weeks of exercising can help to improve the bacterial diversity of the microbiome,’ Robertson says.

6. Enjoy everything in moderation

‘Whilst sugar may not be great in large amounts, a little is fine as part of a balanced diet,’ says Hobson.

‘You might think that artificial sweeteners may be a better option, but early research has suggested that the artificial sweeteners Splenda, aspartame and saccharin may actually change the diversity of bacteria in the gut.’

7. Listen to your body

‘Everyone’s microbiome is unique and can respond to different foods in different ways,’ says Robertson. ‘In fact, a recent fascinating study found that your gut microbiome is one of the strongest factors that controls how sugar is processed in your body.

‘Researchers found that the spike in blood sugar that people experience after eating certain foods (known as the glycaemic index) varied hugely between people even when eating the same foods. Some people had a huge blood sugar spike after cookies, whilst others didn’t. Some people spiked after a banana, whilst others didn’t.

‘The researchers found that the gut microbiome was controlling much of these blood sugar responses. In the future you may be able to test your microbiome to understand what foods will be best for you, personally, to control your blood sugar and other health outcomes.’