Do You Avoid Gluten? You Could Be Doing More Harm Than Good

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Coeliac disease is a genetic condition in which the immune system attacks the lining of the gut when gluten is ingested. Gluten is a protein found naturally in some grains like wheat and gives dough its stretchy properties. The only treatment for people with coeliac disease is to follow a diet that contains no gluten at all. However, many people without coeliac disease still seek out gluten-free products under the assumption that they are healthier. Is there any evidence to back this up?

Why Avoiding Gluten Might Be Beneficial

There is some evidence that gluten may cause problems for people without coeliac disease – an overview of this evidence can be found in this review. Some people develop various symptoms upon ingestion of gluten, which then go away when gluten is removed from their diet. These symptoms include gastrointestinal disturbances, rashes and even depression and altered cognitive function. These people do not have antibodies associated with coeliac disease, but still experience an inflammatory reaction upon gluten ingestion. This condition is known as non coeliac gluten sensitivity (NCGS). 

However, gluten itself may not always be responsible for NCGS – many grains contain other substances that have been found to trigger these symptoms, such as fructan. When people with NCGS were randomly assigned gluten or a placebo without being told which one they were getting, only 16% developed symptoms in response to the gluten and not to the placebo. 40% of patients who took a placebo treatment they thought was gluten still developed symptoms.

Our understanding of how gluten affects people without coeliac disease is still rudimentary, but here is a breakdown of the evidence concerning some of the conditions that may be associated with gluten consumption in non-coeliac patients.

Irritable bowel syndrome (IBS)

• Research has found that gluten consumption was associated with significantly more severe IBS in comparison to a placebo group after one week.
• Some studies suggest that gut permeability is increased (this is a bad thing) in people with IBS when they consume a gluten-containing diet compared to a gluten-free diet. However, other studies disagree.

Type 1 diabetes

• Type 1 diabetes is an autoimmune disease in which the immune system attacks insulin-producing cells in the pancreas. Coeliac disease and type 1 diabetes share a common genetic susceptibility. 
• People with T1D have a 10% chance of developing coeliac disease, but people with coeliac rarely develop T1D. Some people have proposed this could be because people who get coeliac first adopt a gluten-free diet, which somehow protects against T1D. 
• There is some data to support this, but not much is known about the mechanism involved.

Type 2 diabetes

• There is some evidence that gluten-free diets reduce the risk of type 2 diabetes, a disease characterised by resistance to the blood sugar lowering hormone insulin. This may be because of the way gluten shapes the gut microbiome and alters the permeability of the gut. 
• Diabetic mice on gluten free diets have improved insulin sensitivity.
• Most human data is observational, which means it is subject to confounding factors we will discuss later.

Chronic inflammation

• Some studies have found that a gluten-containing diet is associated with increased inflammatory markers in the blood.
• This could be explained by changes in the gut microbiome and intestinal permeability.
• Once again, this is mostly observational data and so we can’t yet rule out factors other than gluten as being responsible.

Depression

Some studies suggest that people have higher depression scores after ingesting gluten in comparison to placebo

Why Avoiding Gluten Might Be Detrimental

The evidence presented above is by no means conclusive – when considering much of the data, we always have to keep confounding factors in mind. Whether justified or not, healthy people avoiding gluten-containing products clearly care about their health and are more likely to engage in other healthy practices too, which can be hard to control for.

That being said, maybe you still feel that avoiding gluten is ‘erring on the side of caution’. However, before coming to that conclusion, you might want to take a look at this paper published in the British Medical Journal (BMJ). It looked at about 100 000 men and women without coeliac disease over a 26 year follow up, and collected data about gluten intake. They found that the 20% of people with the highest gluten intake were about 15% less likely to develop coronary heart disease than the 20% with the lowest intake. 

So, why does avoiding gluten suddenly look like a bad idea? There are a few possible explanations:

• People who avoid gluten-containing foods miss out on important nutrients like fibre, vitamins and minerals.
• Diets low in gluten tend to be more rich in saturated fats and carbohydrates. 
• Foods labelled as gluten-free may have undergone more food processing, which could be inherently detrimental. 
• Maintaining a gluten-free diet tends to involve the replacement of wheat products by rice, which is naturally gluten-free. However, rice contains minute doses of heavy metals. Although these metals are unlikely to pose a significant health risk to the average consumer, it’s possible that high levels of rice consumption as part of a gluten-free diet could have a negative health impact.

The take home message:

While gluten-free diets might help a minority of non-coeliac patients with specific conditions, the evidence for this is limited. It’s unclear exactly which people benefit from a gluten free diet, or whether gluten is even the problem in the majority of cases. The current scientific consensus is that most people have more to lose than they have to gain from pursuing gluten-free options.