Vegan or Keto? Recent Study Reveals How Each Diet Changes Your Immune System

Nutrition headlines change every year, but a recent study from the National Institutes of Health (NIH) offers a reminder that might outlast all of them: Your immune system is listening to what you eat.

Researchers had participants follow two very different diets — a vegan diet (high in plants, low in fat) and a ketogenic diet (high in fat, low in carbs) — each for just two weeks.

Even in that short time, both diets caused dramatic changes in immune activity and gut bacteria.

Let's take a closer look.

How Two Weeks on Vegan and Keto Diets Changed the Immune System

In the study, the NIH researchers monitored twenty adults who spent a full month on-site so that every meal and variable could be controlled. For two weeks, each participant followed a vegan diet, then switched to a ketogenic diet for another two weeks.

Despite the short timeline, the changes were profound.

The vegan diet contained about 10% fat and 75% carbohydrates, while the keto diet flipped that ratio to roughly 76% fat and 10% carbohydrates. These differences didn’t just alter metabolism — they reshaped how the immune system functioned.

Blood, urine, and stool samples showed that:

• The vegan diet activated genes and pathways tied to innate immunity, the body’s first line of defense against infection.
  
  
• The keto diet influenced markers of adaptive immunity, the part of the immune system that builds long-term protection through exposure and antibodies.
  
  
• Both diets caused rapid shifts in the gut microbiome, changing the balance of bacteria linked to inflammation, metabolism, and mood regulation.

What surprised scientists most was how fast the body reacted. Within days, immune and metabolic pathways had already changed. This shows that diet doesn’t just shape health over time, but it can also influence immune activity almost immediately.

The findings suggest that our food choices are in constant communication with the immune system, shaping how we respond to stress, infection, and even how efficiently we detoxify.

What This Means for Your Body

When you change your diet, you don’t just change your weight or energy levels. You change the entire conversation happening inside your body.

In the NIH study, the immune system adjusted almost immediately. That means the foods you eat today can begin influencing inflammation, detoxification, and even how you handle stress within days.

This also explains why so many people feel better for a short time when they switch to a new diet. The body responds quickly to any shift in routine — especially when that change temporarily removes irritants or adds new nutrients.

But short-term improvement isn’t the same as long-term balance.
While both vegan and keto diets created measurable immune benefits, each one also pushes the body in a very specific direction:

• Vegan diets emphasize cleansing and lightness, but can weaken digestion or hormone balance over time if fats and minerals are too low.
  
  
• Keto diets provide stability and grounding, but can strain the liver and microbiome if fiber and fermented foods are missing.

Finding Balance Between Extremes

At Body Ecology, we’ve always taught that there’s no one-size-fits-all diet. The foods that heal in one season or stage of life can overwhelm in another.

The key is learning how to work with your body’s rhythms. That’s the foundation of the Principle of Balance, one of the seven core Body Ecology principles.

When you eat in balance:

• Your immune system stays alert but not overactive.
  
  
• Your digestion feels calm and efficient.
  
  
• Your energy remains steady rather than swinging between fatigue and stimulation.

As we can see in the NIH study, both vegan and keto diets capture one side of this principle. A vegan diet supports cleansing and lightness — something we often need in spring or during detox. On the other hand, the keto diet supports grounding and rebuilding — ideal during colder months or periods of stress when the body needs stability.

But living at either extreme for too long can create imbalance in the gut and immune system. That’s why the Body Ecology Diet blends the wisdom of both, combining high-fiber plant foods, fermented vegetables, healthy fats, and easily digestible proteins to create resilience year-round.

Bringing it Back to Your Plate

In practice, this looks less like “going vegan” or “going keto,” and more like combining their strengths.

Breakfast might be a warm grain-free porridge with coconut oil and a spoonful of cultured vegetables on the side. Lunch could be a salad topped with avocado and a small portion of fish or tempeh. Dinner might be a simple vegetable soup blended with ghee and sea salt, served with steamed greens and a probiotic-rich drink like coconut kefir or Cocobiotic.

Still, as the seasons shift, so should your meals. In summer, eat lighter and focus on hydrating, enzyme-rich foods that cool and cleanse. In winter, add grounding soups, root vegetables, and fermented drinks that keep digestion strong and the immune system alert.

This rhythm and listening to your body is how you create the steady internal environment that the study hints at. It’s also the foundation of the Body Ecology approach: not a rigid diet, but a living system that adapts right along with you.