selection of carbohydrate food and drink

I’m not telling you anything new here: sugar isn’t very good for us.  You’ll already know that a high-sugar diet contributes to:

  • weight gain, which contributes to other health conditions
  • energy and mood fluctuations
  • dental problems.

But, did you know sugar can cause problems in your gut, which may also affect other aspects of your health?

Carbohydrate, Digestion and Energy

To start with, let’s take a quick look at carbohydrates and what happens during digestion.

During digestion, digestible carbohydrates (which include sugar), are broken down into their component parts such as glucose, a simple sugar.  We absorb glucose in our small intestine as part of normal digestion so that we can use it for energy.  Any glucose that we can’t absorb (i.e. the excess) continues on to the large intestine where the bacteria, etc that form our microbiome feed on it.

Therefore when discussing sugar in the body, we are generally talking about the output of digestion – glucose.  Of course, the more digestible carbohydrates we consume the higher our level of glucose will be, and the greater the amount of excess that travels to our large intestine.  And sugar itself is one of the easier types to reduce our intake of.

Complex carbohydrates are discussed briefly later in this article.

If we do not consume enough carbohydrates to fuel our bodies, we can get energy from fat and protein.  Fats can be broken down into fatty acids and glycerol which the body then uses for energy, without the need to break it down into glucose (this is possible but is difficult for the body).  If there is insufficient energy available from food or stored fats, the body can breakdown protein to make glucose using the amino acids stored in muscle.

Gut Bacteria

While there are many types of bacteria in the gut, the main four have been found to be: firmicutes, actinobacteria, proteobacteria and bacteriodetes.  Each of these types have many sub-types.  When the proteobacteria, in particular, breakdown excess sugar that reaches the large intestine their number increases.  This leads to an imbalance of the bacteria in the gut (“dysbiosis”), which can contribute to health problems.

It should be noted that these imbalances have been identified in children as well as adults.  This emphasises the importance of encouraging children to have a healthful diet in childhood, not just when they grow up.

What are proteobacteria?

Proteobacteria are a type of gut bacteria that need to be kept in check.  They include many pathogens (things that cause illness in the body) and high numbers may therefore contribute to ill-health within the whole body and not just the gut.  They have been linked to inflammation* and there is strong evidence of their role in inflammatory bowel disease (IBD), metabolic disorders (disruption of the process where your body converts and uses energy from food) and mental health problems.

A high-sugar diet increases the risk that large amounts of glucose will reach the large intestine and increase the numbers of proteobacteria, and therefore increase the risk of ill-health.

*We need some inflammation in the body, but excess inflammation can contribute to chronic illness.

What are short-chain fatty acids?

If you saw my recent post about immunity, you will have seen these mentioned.  Short-chain fatty acids are produced by the bacteriodetes bacteria when they digest complex carbohydrates (carbohydrates that contain fibre).  Short-chain fatty acids have an anti-inflammatory affect on the body and support the health of the gut itself.

There is some evidence that insufficient butyrate can contribute to an increase in the less-favourable gut bacteria.

If we do not produce enough short-chain fatty acids it may impact on our ability to absorb nutrients, and reduce the gut’s immune functions.

Sugar and Vitamin C

Besides the effect on our immune system through the gut, studies have shown that vitamin C and sugar compete for absorption.  This means that sugar may also be weakening your immune system by reducing your ability to absorb the well-known immune-supporting vitamin.

Sugar and Heart Disease

You’ll have heard that people with high cholesterol should cut back on saturated fats, but did you know that sugar also plays a role in heart disease?  When we eat a diet high carbohydrates, the glucose not required for energy is stored.  In the liver, this can be used to produce triglycerides which increase the risk of heart disease when levels are high.  The risk is increased further if you have high LDL (‘bad’) cholesterol and low HDL (‘good’) cholesterol levels.

High triglycerides can also increase the risk of inflammation of the pancreas.

Sugar and the Liver: Non-Alcohol Related Fatty Liver Disease

As mentioned above, any glucose absorbed into the blood stream that isn’t needed for energy is stored as fat in the body.  One place we store it is in the liver.  High levels of fat in the liver can lead to non-alcohol related fatty liver disease.  This can prevent the liver from functioning properly leading to further health problems.

As you can see, a high consumption of sugar (or other simple carbohydrates) can have a negative effect on your body beyond the concerns we normally hear about.  Do you need to remove them completely from your diet?  Potentially not.  But, it is important to be mindful of what you eat and eat a good variety of fruit*, vegetables (including pulses and legumes), nuts, seeds and whole grains to support your gut.

*It is recommended that you do not consume more than two portions of fruit per day to help minimise the potential negative effects of the sugar in the fruit – some glucose along with fructose.

References/Further Reading