The truth about gluten
It is becoming more and more common for people to demonise gluten, with claims that cutting it out of your diet will help you shed the pounds and boost your energy. This proliferation of information online is making it difficult to sift the facts from the fiction, but this article aims to address many of the questions people have about gluten.
What is gluten?
Although gluten has gained a bad reputation, the majority of people would struggle to explain what it actually is. The word gluten has gained a mythical status as a dangerous substance to be avoided. However, the truth is that gluten is just a mixture of proteins found in the seeds of certain cereal plants: wheat, rye and barley. Gluten is stored in a tissue inside the seed called the endosperm, which surrounds the plant embryo and provides a dense source of energy as the plant starts to grow. In wheat, gluten is formed when the proteins glutenin and gliadin cross-link into a net-like structure that provides elasticity (stretchiness) and viscosity (thickness). The word gluten means 'glue' in Latin and gluten essentially has the role of sticking bread together, allowing pizza chefs to throw their dough around without it flying apart!
Digestion of gluten
Gluten is found in many of our favourite foods; including bread, biscuits, cakes, batter and even beer! Once food reaches the stomach it must be broken down by enzymes in the process of digestion. Large proteins are broken up into chains of amino acids called peptides. Normally these peptides are easily broken down further; however, the gliadin peptides in gluten are difficult to break down as they are part of a group of peptides called prolamins. Prolamins are made up of lots of glutamine and proline amino acids, which digestive enzymes have difficulty breaking up. This means that unlike most proteins gluten digestion can leave strands of amino acids intact in the small intestine. These strands can be up to 10 amino acids long and are known as oligopeptides. For the majority of people gliadin oligopeptides are harmless, however, a small proportion of the population will produce an immune response known as coeliac disease.
Coeliac disease is a genetic condition that affects about 1 in every 100 people. It is also an auto-immune condition, meaning that its symptoms are caused by the body's immune system mistakenly attacking itself. Unlike some genetic diseases coeliac is polygenic, meaning that it is caused by many different genes acting together. Currently over 30 different genes have been identified that are believed to contribute to coeliac. These genes can be inherited so that a coeliac has a 1 in 10 chance of passing the disease on to their children.
What causes coeliac disease?
The absorption surface of the small intestine is huge because the intestine wall is folded into millions of tiny finger-like projections called villi. If it was spread flat the small intestine would have a surface area of about 250 square metres - the size of a tennis court! The walls of the intestine are made up of cells which form a strong barrier to prevent things we don't want being absorbed into the bloodstream from getting through. In non-coeliac individuals the oligopeptides produced by gluten digestion have no harmful effects because they can't get through this defensive barrier and into the bloodstream. However, in individuals with coeliac disease the oligopeptides can sneak past the wall in two different ways:
1. Transcellular (through the epithelial cells): The immune system produces large, y-shaped proteins called antibodies that identify dangerous invaders in the body and latch onto them. The antibodies then escort these invaders through the intestine wall to the bloodstream where immune white blood cells are waiting to destroy them. However, in coeliac disease the immune system produces extra antibodies that mistakenly recognise gliadin oligopeptides as an enemy. The antibodies disguise the oligopeptides so that they are escorted through the wall like a Trojan horse being brought inside the city.
2. Paracellular (between the epithelial cells): Normally the cells of the intestinal barrier are held together by tight junctions, which act like cement between the cells in the wall. The levels of a chemical called zonulin increase when dangerous bacteria are detected in the intestine. The zonulin causes cracks in this cement so that the gaps between cells get bigger and the bacteria pass through to the waiting white blood cells. In coeliac disease the immune system recognises the oligopeptides as an enemy so increases the levels of zonulin as if an invader were present. The tight junctions open up and the cell lining becomes 'leaky', allowing the large oligopeptides to pass easily between the cells to the other side of the intestine wall.
Effects of coeliac disease
In individuals with coeliac disease lots of oligopeptides will reach the bloodstream where they meet an enzyme called TG2 that modifies them slightly. This then allows a special type of immune system cell called the antigen presenting cell (APC), to pick up the oligopeptides. The APC normally picks up broken up pieces of bacteria and shows them to 'fighter' white blood cells to activate them throughout the body. When the APC picks up oligopeptides the fighters are confused and start attacking TG2 and intestine wall cells that have come into contact with the oligopeptides. The symptoms of coeliac disease are caused by 'friendly fire' because the fighter cells are attacking the wrong targets. Over time, if gluten continues to be eaten, the intestine wall becomes more leaky and inflamed until the villi are completely destroyed and unable to absorb nutrients.
There are a wide range of symptoms of coeliac disease, caused by inflammation and nutrient deficiencies, for example:
- weight loss
- stomach pain
- diarrhoea or constipation
- anaemia (iron deficiency)
- skin rashes (dermatitis herpetiformis)
In the long-term, if coeliacs continue to eat gluten they can face an increased risk of cancer, infertility, osteoporosis (bone loss), and a reduced lifespan. Coeliac disease can be clearly identified through a blood test for gliadin antibodies, and if they are present this is followed up by biopsies of the small intestine to identify damage. Despite this, only about 24% of people with the condition are currently identified and the average time between the start of symptoms and diagnosis is 13 years.
Living with coeliac disease
The only treatment currently available for coeliac disease is life-long removal of gluten from the diet. This means no more cakes and biscuits, as well as looking out for hidden gluten in ingredients lists, making it harder to eat in restaurants. Coeliacs also have to be careful about cross-contamination with gluten when food is being prepared; using different pans and separate toasters in the kitchen. Although gluten seems to be found in all the best foods (pizza!), in the last ten years more and more gluten-free alternatives have become available in the shops. The good news for coeliacs is that by following a completely gluten-free diet they should have a full recovery of all their symptoms... and gluten-free bread doesn't taste completely awful!
Non-coeliac gluten sensitivity
One final trend spreading on the internet is the increasing number of people who describe a bad reaction to gluten despite having negative tests for coeliac disease. This is known as non-coeliac gluten sensitivity and is currently poorly researched. Although it is possible that some people do have a bad reaction not caused by coeliac disease, there might be other reasons for this trend. Two possible explanations have been suggested:
1. Symptoms may improve due to the placebo effect: individuals feel better if they believe strongly enough that the treatment will work. For example, giving someone a fake sugar pill that looks like a painkiller can help to relieve headaches.
2. Individuals may have more energy and fewer digestion problems just because they are cutting down on pizza and beer! A lot of tasty snack foods contain gluten and people may be replacing these with healthier alternatives, which end up making them feel better.
Further studies will be able to identify whether these explanations could be true. Currently, for individuals who do not have coeliac disease, cutting gluten from the diet has no clear benefits. In fact, despite the many health claims made about going gluten-free; gluten-free diets are often deficient in nutrients such as fibre, iron, vitamin B12 and calcium. Anyone worried about their reaction to gluten should visit their GP before making any changes to their diet, as going gluten-free can affect the results of coeliac tests.
If you are concerned about coeliac disease or simply want to find out more you can visit the Coeliac UK website.