This article was first written for The Conversation - an independent source of news and views, sourced from the academic and research community and delivered direct to the public.

Only until relatively recently in human evolution have we eaten three meals plus snacks every day. Breakfast simply didn’t exist for large parts of history. The Romans, for example, didn’t eat it – usually consuming only one meal around midday – breakfast was actively frowned upon. Regular working hours following the industrial revolution brought structure to mealtimes to sustain labourers. And by the late 18th century the pattern of eating three meals a day in towns and cities emerged. But these days, people are eating more frequently than they ever have before – and often outside of meal times. New smartphone app data shows that we now have erratic eating patterns. Many of us are continually snacking rather than eating at defined times – which means we spend up to 16 hours a day in a “fed” state.

The Issue with eating

Designed to supply our energy demands and nutrient requirements, we primarily consider the gastrointestinal (GI) tract as a conduit for food. But the gut serves additional very important roles: housing the trillions of bugs that form our microbiome and is home to the majority of our immune system. The entire gut is lined with a barrier that is only a single cell thick - its a dynamic barrier between us and 'them' - bugs and germs that can easily enter through our mouth. How exactly the gut barrier lets food though and keep the bugs out is marshalled by the tight junction proteins. These acts as the doormen between the epithelial cells which line the GI tract. Most of the time, the tight junctions are kept tight, separating the gut contents from the rest of the body. But each time we eat, the gut barrier must become transiently permeable, known as 'leaky gut'. This permits the absorption of essential fluids and nutrients from a meal but comes with a collateral challenge - a transient inflammation. For around four hours after each meal, gut microbes and their components leak into our bloodstream – silently triggering inflammation by the immune system. This process is driven largely by the activation of a critical immune sensor of nutrients called the “inflammasome”, which releases an inflammatory molecule known as “interleukin-1β”. Inflammation is only ever meant to be a short-term protective assault by our immune system. But inflammation after eating – known as “postprandial inflammation” can be exacerbated by our modern lifestyles. This includes calorie dense meals, frequent eating, excessive fructose and fatty foods – particularly saturated fat.Leaky gut allows gut bacteria and their products to enter the bloodstream which is a problem for our immune system. Even the 'good' bacteria contain the immune triggering molecular bar-codes that switch on inflammation if they get into the wrong place. Unfortunately, this means that the act of eating is, in and of itself, inflammatory. This is known as post-prandial endotoxemia. For around four hours after each meal, microbial 'endotoxin' leaks into our bloodstream silently triggering the inflammatory immune system. Sounds very sinister, but this short-lived phenomenon is physiologically normal. It can be exacerbated by calorie dense meals, excessive fructose and fatty foods (particularly saturated fat) and is counteracted by a diet rich in fibre and plant polyphenols found in fruits and vegetables.

While leaky gut is a symptom not a cause, type ‘leaky gut’ into Google and you will quickly get the impression that it's a catch-all cause for long list of ailments. But post-eating leaky gut isn't a cause for concern in healthy adults eating at defined mealtimes. But it does trigger inflammation which is acute by design. Modern life often dictates the now normal erratic eating patterns, creeping us towards a continual snacking routine, rather than eating at defined times. This means we spend up to 16 hours per day in a post-fed inflamed state, nudging us into a persistent inflamed state and towards a potential chronic problem for our health. Low-grade chronic inflammation such as that arising from the post-fed state induces oxidative stress and reduces cellular antioxidant capacity. It has emerged as an important proxy to many lifestyle related diseases including heart disease and type 2 diabetes, preceding diagnosis by years. While the role for saturated fat in cardiovascular disease still remains heavily debated, meal frequency is seldom a consideration. We know that increased eating frequency can increase body-weight without a calorie surplus and erratic eating habits contribute to type 2 diabetes without obesity. Gut permeability is increased in patients with chronic heart disease and that silent inflammation from the gut acts upstream of traditional risk factors such as blood pressure, cholesterol or weight changes.

Stop the snacking

Considering the significance of post-eating inflammatory endotoxemia to human health, meal frequency guidelines are yet to translate into dietary guidelines. Current UK guidelines focus on calorie and saturated fat reduction strategies, emphasising consumption of a range of vegetables and whole grains. Recommendations for type 2 diabetics focus on consumption of five small meals a day to balance blood sugar, reduce hunger and total energy. Other studies stress the division of food intake should be frequent but based on individual preference, without recommendations meal frequency. There are few clear insights into the supporting evidence that informs these guidelines. We still don't know the cumulative impact on disease risk of healthy adults who longer periods of time in the post-fed inflammatory state. But what is clear, is that low-grade inflammation is the most important driver of age-related disease. Reducing frequency of eating through intermittent fasting or time-restricted eating also highlights the broadly beneficial effects reduced meal frequency has on human health. On the basis of available data, the fact that such a fundamental aspect of our dietary habits, the number of meals we eat every day, has not yet been subject to rigorous scientific investigation is remarkable.