Scientists Prove Western Diet Quickly Harms the Body—Here’s the Better Option

A diet packed with processed food, excess sugar, and salt can start to harm the body in as little as two weeks, according to new research from Radboud University in the Netherlands and KCMC University in Tanzania.

The study, published in Nature Medicine, shows how a Western-style diet can weaken the immune system and trigger early indicators of chronic diseases—even over a short time.

The research team observed men from northern Tanzania who swapped their traditional diets for a Western one.

The results were immediate: elevated inflammation, poor immune response, and biological signs pointing toward future lifestyle-related diseases.

“We show how harmful and unhealthy the Western diet can be,” said Quirijn de Mast of Radboud University in a press release.

A Two-Week Diet Switch

The study involved 77 African men who altered their diets under supervision.

One group replaced their usual meals with Western-style food—characterized by high-calorie, highly processed ingredients heavy in refined sugars, fats, and sodium. Blood tests taken during and after the two-week period revealed immune changes.

The men’s immune systems became less responsive to threats, and inflammation markers surged. Inflammation is closely linked to chronic illnesses such as diabetes, heart disease, and certain autoimmune conditions.

But when another group moved away from Western food and adopted a traditional African diet—rich in legumes, fermented foods, vegetables, fruits, and whole grains—the outcome was quite the opposite. Their inflammation markers dropped, and immune health improved measurably, even weeks after the diet period ended.

Short-Term Eating, Long-Term Effects

Perhaps most striking is that the body didn’t immediately bounce back or forget.

Researchers found that four weeks after the dietary changes, both the positive and negative effects were still visible in participants’ immune systems. This indicates that even short-term diet shifts can have long-term impacts on health.

“This gives us hope,” researchers noted, explaining that improving your diet for even a brief period could help “reset” the body’s immune response.

Why This Study Stands Out

Previous studies comparing Western diets with Mediterranean or Japanese eating patterns have reached similar conclusions about processed food and inflammation.

But this new research takes a fresh approach by focusing on African diets, which are less studied and offer unique insights into how traditional, plant-forward eating can bolster the immune system.