As a 29yo woman who started Paleo with a BMI outside any medical chart and no gall bladder, I did not experience this. I "detoxed" off carbs/sugar, but with salads, meat, nuts and coconut as my only foods for a month, I had PERFECT "BMs." It might be the fish oils, the actual foods or "sneaking" gluten once clean (that does the same as above for me) but from my experience not her body composition.

FWIW, I stuck with it and am feeling amazing at 111lbs lighter 9mo later.

I second this ... motion. [WARNING: MILD TMI ALERT] BMI 41. Pānu since 12 February; STRICTLY VLC; STRICTLY twice as many grams of fat as grams of protein; NO fruit (juice of ONE slice of lemon on some days); Kwaśniewski's obesity macro-ratios. And the first week was diarrhea every day. Steak, coconut oil, pastured eggs, Kerrygold butter, avocados, romaine, lemon or lime juice, cherry tomatoes, sardines, heavy cream. Last coupla days have had some solidity (sorry), but I just wanted to let your wife know she is NOT alone. It has been disconcerting me as well - I better lose weight with all this!!! :+}

Is she missing her gallbladder? If she is, and she eats a lot of long-chain fatty acids, it doesn't matter where they come from, they'll give her the runs. Medium-chain fatty acids (also referred to as medium-chain triglycerides) do not have the same effect.

I don't know if there's a real difference between grass-finished and grain-finished in terms of LCFAs or MCFAs. I do know coconut oil's a great source of the latter. Maybe she could go for lean cuts of meat and then add in the coconut oil as her dietary fat.

Seconded on the fruit if she's eating a lot of it. Plus there's the fructose angle. With her being that overweight she might also have fatty liver (it can occur in non-alcoholics); in that case the last thing she wants large quantities of is fructose. But fruit can cause GI upset even if her liver's healthy. I'd say stick with no more than a serving (maybe 1/4 to 1/2 cup) of berries or low-sugar melon (think cantaloupe or honeydew) per day. She needs to be cutting back on sugar intake anyhow, natural or not.

[Side note: Just in case she's dealing with fatty liver (it shows up on lab tests as elevated liver enzymes sometimes, though not always), choline will help. Liver and egg yolks are excellent sources.]

There's something to be said for yogurt or kefir if the gut flora are out of whack. I know they're not "Paleo" but they are traditional. The brands you find in the average health food store (Whole Paycheck maybe) will probably be a better bet than Yoplait. They're more likely to be organic or grass-fed and they're more likely to be full-fat. If you just can't do dairy, look into kombucha. Raw is best. They're re-formulated the major brands so they are lower in alcohol. It's not as bad as it sounds--a little bit like drinking cider. Which is sort of Paleo. :) I tend to be mistrustful of all these so-called "probiotic blends" the big food companies are coming out with. At least in a food or a drink you know the germs are probably live. The ones that make lactic acid will survive the stomach and populate the intestines.

That is quite a bit of fish oil to take all at once - especially if you never have before- maybe she is having a reaction to the oil. Maybe try to take less oil and ramp up to that amount.

Try adding in a pro-biotic like Culterelle to add good bacteria back into her gut.

My advice would be for her to attempt a more gradual transition to paleo. Give her body time to adapt. Cut out some of the worst right away like wheat and sugar. But let stay lots of potato and maybe some rice. Leave in some of the borderline stuff at first. Coast in more slowly and just don't slam her body with a whole new world all at once. See how it goes. Make changes gradually and see any particular change causes any particular probs.

And I agree to not do the fish oil supplement at first. See how she does without it. You guys have probably been living all your lives without fish oil pills so a bit longer won't matter hugely in the overall scheme of the universe. PLus it may not be a good quality one or it may have gone bad. If you pop open a pill and it smells very fishy, then it may have gone rancid. Fresh fish actually does not smell fishy. Only old fish does. And some people just seem to do badly on fish oil pills in general. If you do decide to do fish oil later, ramp up the dose slowly and watch for side effects. Remember that fish oil is a blood thinner and large doses of fish oil are somewhat controversial in the paleo community.

Are you eating lots of nuts? Nuts, almonds especially, tend to have the same effect on me.

I'd guess that it is a gall bladder issue. The gall bladder emulsifies any fats that are eaten. If the fats are not emulsified they can give you the runs. It will take some time for the gall bladder to get up to speed. In the meantime, she can adjust her fat intake. Divide the fat intake over the day, so the gall bladder can produce less at a time, and possibly emulsify any oils. Instead of eating a really fatty steak, rather eat a leaner steak with some home-made bernaise sauce, where the butter is emulsified with eggs.

See this for Kurt Harris' take. http://www.paleonu.com/panu-forum/post/992321