Cheat meals taste so good — new evidence suggests they are so bad for your body

So much for weekends of caloric abandon.

New research confirms that just two days of eating a high-fat diet can compromise critical immune cells in the gut and weaken the intestinal barrier, suggesting the impact of our daily dietary choices is more immediate than previously believed.

Published this month in the journal Immunity, the research followed mice fed a regular diet, a high-fat diet and specialized diets enriched with saturated and unsaturated fats.

The high-fat diet led to the rapid suppression of specialized immune cells called ILC3s, which produce a protective substance called interleukin-22 (IL-22). This suppression is disastrous for the digestive system.

Within the gut, IL-22 typically shields the intestinal barrier by generating protective elements that prevent bacteria, toxins, undigested food particles and inflammatory pathogens from breaching the bloodstream.

When a high-fat diet limits the production of IL-22, that intestinal barrier becomes more permeable, a condition known, inelegantly, as “leaky gut.”

While not a formal diagnosis, leaky gut is known to cause bloating, constipation, indigestion, acid reflux and potentially intestinal pain.

What’s worse, when toxins leak beyond the gut, they trigger widespread inflammation, leading to issues like skin problems, brain fog, anxiety, depression, cardiovascular stress and even fertility challenges.

“The more saturated fats we eat, the more inflammation that builds up,” said study author Cyril Seillet from The Walter and Eliza Hall Institute of Medical Research in Australia. “This inflammation build-up is initially silent, remaining hidden in our bodies until years later, where it can present as chronic inflammation.”

Seillet and his team discovered that different fats have wildly different effects on overall gut health.

They found that unsaturated fatty acids, found in olive oil and avocados, helped support normal IL-22 production and gut barrier function.

In contrast, saturated fatty acids, present in palm oil, butter and fatty animal meat, deliver a one-two punch by seriously hindering immune cell function and increasing intestinal inflammation.

After just two days on high-fat diets, researchers observed that certain subtypes of ILC3 immune cells already exhibited reduced IL-22 production. A week into the high-fat diet, all ILC3 subtypes were compromised.

Further, within a week on the high-fat diet, the gut microbiome had rapidly shifted, exhibiting a decline in beneficial bacteria that produce short-chain fatty acids and a proliferation of harmful bacteria.

Using specialized equipment, the research team discerned that one week on a high-fat diet correlated to “leakier” mice intestines, a permeability that allowed more potentially dangerous substances to pass through.

There is a bit of silver (intestinal) lining to be found in this latest batch of research — the gut-compromising consequences of a high-fat diet aren’t permanent.

The research team found that after resuming a regular diet, gut function improved after just two days and returned to normal after seven days. This quick correction suggests dietary interventions could rapidly restore gut health.

In addition, researchers found that saturated and unsaturated fatty acids are processed in entirely different ways.

Saturated fats are processed through a pathway called fatty acid oxidation, which impairs immune function, while unsaturated fats like oleic acid form protective lipid droplets in the cells, helping to maintain proper immune responses.

To demonstrate how the processing of these fats influences intestinal inflammation, the research team induced colitis in the mice. The mice fed saturated fats showed greater tissue damage than those that ate unsaturated fats or adhered to a regular diet.

Results were similar when the team exposed isolated human immune cells to different fatty acids. Essentially, unsaturated fats support immune function while saturated fats suppress IL-22 production.

Researchers believe these rapid and profound changes in gut health could explain why people experience digestive discomfort when they veer from their regular diets during the holidays or on vacation.

Conversely, these results serve to explain why diets rich in olive oil and unsaturated fats, such as the lauded Mediterranean diet, are associated with lower levels of inflammation and improved gut health.

How important is gut health? Research reports that Parkinson’s disease may begin in the gut.

A 2022 study from New York’s Clarkson University even found a possible link between a person’s gut health and personality.