"What I mean is can you cycle the two ways of eating for max benefit?"

Hmmm...that last part makes the question not quite valid. You can mash paleo with the Zone, or mash paleo with Ornish. In fact, you could alternate days of paleo with any other diet. But I don't see any real benefit of so many all-fruit days. What exactly does that provide?

If you really want fiber, you can get it through vegetables and tubers. If you want sweet taste, eat a piece or two of fruit. If you want to carb cycle, you can still carb cycle. In fact, you can do anything with paleo! Come with me...and you'll be...in a world of pure imagination...

Sure there are some benefits to eating all fruit -- if what you were eating before was the SAD (in DurianRider's case, the Standard Australian Diet). If you eat all fruit you won't be eating any vegetable oil (Neolithic Agent of Disease #1) or any gluten (NAD #2). And if you happen to be an endurance athlete you'll be depleting your glycogen all the time and so the excess fructose (NAD #3) won't do as much damage.

But all of those benefits from eating all fruit are also benefits of eating paleo. (Again, taking into account the endurance-athlete technicality; on paleo you wouldn't have all the fructose in the first place.) That paleo will get you the same benefits is not surprising, since avoiding the three NADs is practically a definition of paleo. So you can think of an all-fruit diet as an odd subset of paleo: a sickly subset.

For the benefits of going a day without protein see Kamal and Nico: you can do protein restriction without eating just fruit. You could eat potatoes soaked in butter.

For the benefits of quicker digestion: I would never agree in the first place that constipation is a given "nuisance" of eating paleo. And even if you are constipated, then you could just eat some potatoes to restore the mucus in your digestive tract -- no need for fiber. (On the glucose idea (not necessarily the fiber idea) read Paul Jaminet at the Perfect Health Diet.)

And I've left aside the problems with vitamins and other longer-term issues that come from avoiding animal products, since you were asking about alternating days.

As for quirky, intangible benefits? I'm with Nico on this one: give it a go. You never know what will happen. But keep in mind that if you experience some positive effects there are plenty of potential confounding variables; e.g., as I said, you might just be experiencing the benefits of protein reduction, which you could have gotten from eating potatoes and butter -- and maybe eating potatoes and butter for a day would be even more beneficial than eating fruit for a day.

Well I suppose there's one other possible benefit. You might find the experience so distasteful you'll return to paleo with renewed appreciation. Absence makes the heart fonder?

I have some mostly fruit days when I'm fasting. Even Lustig says fruit is OK and there has never been a study showing that fruit is bad for humans. I've not gained weight and my triglycerides are great.

I've never seen any evidence that fruit is an anti-starvation fallback food for hunter-gatherers. In fact, many hunter-gatherers go out of their way to obtain fruit. That said, many such cultures have an idea that eating too much fruit will make you "hot." It's funny because Durianrider has said that the native Thai people he meets are horrified that he eats so much durian because its "too hot." Some fruits are "cold" though and can balance the intake of "hot" fruit. It would be interesting to look into whether there is some nutritional basis behind these beliefs. Meat is a "hot" food too though.

The fact that we need vitamin C and the enormous amount of trouble native peoples like the Sami, Yakut, and Inuit go to to procure berries is so indication that they might be important. I remember when I lived in the far north, berry season was very important and everyone went out to get some. Some berries were sour, but others were very sweet. There were enough in many places to get buckets and buckets of them.

Low-carb is a great diet for people with damaged metabolisms, but its prevalence in the paleo community has tainted paleo with all kinds of "just so" stories about carbs being bad. It has led to the idea that hunter-gatherers were low-carb, which is just not true at all.

You posted a link to Alan, which I disagree with on many points he berry Picks to and left out important information on dangers. Yet he claims that the safe daily amount would be less than 50g a day. A number that's commonly accepted as what a maximally depleted liver is going to absorb...

Meaning even the contentious article you posted, disagrees with fruitarian nonsense.

There are no societies that live on fruit exclusively, and hunter gatherers from everything I've read go for meat first.

Fruit is an anti starvation fallback and is not required for life.

I second Kamal. Eat starchy veggies and tubers, and some fruit, esp. berries.

I do have "low-protein" days where I eat mostly greens and starchy tubers like taro. I was moved to do this partially by what I've read, but also because, after three days of eating massive quantities of beef, I actually wanted a break. Of course, I always slather my veggies and tubers with butter/lard, or, like today, lamb fat.

As far as I can tell there is no reason to have a day where you'd eat all fruit. Until very recently, fruit was relatively rare and expensive, even in tropical areas, and no culture would have done this. These fruitarian types are eating massive amounts of imported tropical fruits.

I also know of no scientific basis for preferring a high-fruit diet. There's far more ancestral basis for occasional low-protein periods (not that that proves anything). Similarly, I've seen no basis for having low-fat periods. The research so far seems to suggest some benefit to protein fasting, however.

Of course, you can always give it a whirl and see what happens.

the warrior diet accomplishes both in the same day. fruit allowed during daytime undereating/fasting, and heavier foods for the evening meal. this is supposed to activate the sympathetic and parasympathetic nervous systems at the proper times. master cleanse lemonade is convenient during the day, though i use half the syrup.

It depends what your goals are if you want to blast and do athletic activities eating fruit and tubers is definitely a smart option.

Robert lustig thinks fruit in any quantity is fine because of the fiber, email for yourself.