Paleo, eating like our Paleolithic ancestors supposedly did, fruits, vegetables, meat, fish, eggs, nuts, seeds, while cutting out grains, beans, dairy, and processed food, is one of the more contested diets in gut health research. Two real studies looked at essentially the same diet idea and found meaningfully different results, and the difference between them is instructive.
The Australian study: a real concern
Researchers compared 44 long-term paleo dieters against 47 people eating a typical Australian diet, and found the paleo group had lower levels of beneficial fiber-fermenting bacteria along with higher levels of bacteria linked to a heart-risk compound.[1] That shift traced directly back to lower resistant starch intake, mostly from cutting whole grains out entirely.
The Italian study: a different result
A separate look at a modern paleo diet, still cutting out grains and dairy but loaded with fruit, vegetables, nuts, and seeds, told a notably different story.[2] Fiber-loving bacteria came out about the same as in non-paleo Italians, and overall gut bacteria variety came out higher than the comparison group.
Australian paleo dieters (44 vs. 47)
Lower fiber-fermenting bacteria, higher heart-risk-linked bacteria, tied to low resistant starch intakeItalian paleo dieters
Fiber-loving bacteria unchanged, overall variety higher, thanks to heavy fruit, vegetable, nut, and seed intakeWhat explains the difference
The key difference comes down to how much plant food volume and variety replaces the grains and beans that got cut. The Australian paleo dieters were eating measurably less resistant starch overall, while the Italian group's much higher fruit, vegetable, nut, and seed intake filled that gap far more effectively.
The heart-risk connection to whole grains specifically
The Australian researchers linked higher blood levels of that heart-risk compound specifically to lower whole grain intake, and concluded that adding whole grains back in, even within an otherwise paleo approach, could meaningfully improve the diet's effect on gut health.
What to do with this
If you're following or considering paleo, these two contrasting studies teach a clear lesson: cutting grains and beans isn't automatically fine for your gut. It comes down entirely to whether you replace that lost fiber with large amounts of other plant foods. For a diet that leans the opposite direction on grains, see how the Mediterranean diet fares, or compare against the stricter carnivore approach. Track your actual plant food variety and aim for 30 different plant foods a week, since that seems to be the deciding factor behind these two very different results. A hearty paleo-friendly meal like our slow-cooked pot roast with carrots can help you work whole vegetables back in.
This content is for educational purposes only and is not a substitute for professional medical advice.
- Australian paleo dieters vs. regular eaters, gut bacteria comparison: pubmed.ncbi.nlm.nih.gov/27110483
- Modern Italian paleo diet and gut bacteria: pubmed.ncbi.nlm.nih.gov/28225384
