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
A study comparing 44 long-term paleo dieters against 47 people eating a typical Australian diet found the paleo group had lower levels of beneficial fiber-fermenting bacteria and higher levels of bacteria linked to a heart-risk compound. This shift was directly traced to lower resistant starch intake, mostly a result of cutting out whole grains specifically.
The Italian study: a genuinely different result
A separate study on a "modern paleo diet," still cutting out grains and dairy but with generous fruit, vegetables, nuts, and seeds, found something notably different, fiber-loving bacteria were about the same as non-paleo Italians, and overall gut bacteria variety was actually higher than the comparison group.
What actually explains the difference
The key difference seems to be how much plant food volume and variety replaces the grains and beans that got cut out. The Australian paleo dieters had measurably lower resistant starch intake overall, while the Italian group's much higher fruit, vegetable, nut, and seed intake seems to have filled that gap far more effectively.
The heart-risk connection to whole grains specifically
The Australian researchers found higher blood levels of that heart-risk compound were specifically linked to lower whole grain intake, and concluded that adding whole grains back, even within an otherwise paleo approach, could meaningfully improve the diet's gut health picture.
If you're following or considering paleo, the lesson from these contrasting studies is that simply cutting grains and beans isn't automatically fine for your gut. It depends entirely on whether you're replacing that lost fiber with genuinely large amounts of other plant foods. Track your actual plant food variety, aiming for the 30-different-plant-foods-a-week target, since this seems to be the deciding factor between the two very different results these studies found. If cutting grains and beans entirely feels non-negotiable for you, prioritizing resistant starch from other sources, green banana, cooked-and-cooled potato, is a specific way to close the exact gap the Australian study found.
This content is for educational purposes only and is not a substitute for professional medical advice.