Common issues I have heard of in 2 1/2 years participating in the online paleo community (but not experienced personally):

*Skyrocketing total cholesterol and LDL - jury is still out on long-term effects of super-high cholesterol from eating paleo and high in animal fats.

*Fat soluble vitamin poisoning (or just elevated blood levels of retinol, D) from high consumption through foods combined with supplementation.

*Worsened hypothyroid symptoms (likely from neglecting to find a reliable iodine source after no longer consuming processed foods with lots of iodized salt), or even development of hypothyroid after becoming paleo. Always seen with VLC/ZC (tons of meat)...

*Severe lack of appetite on a VLC diet higher in fat and protein, leading to chronic undereating and often to exhaustion, lack of endurance, and muscle loss.

*Serious exacerbation of OCD and eating disordered tendencies (usually pre-existing) leading to debilitating anxiety and guilt surrounding food, and/or to increasing amounts of self-deprivation (most commonly zero carb and/or 'fasting') which usually causes various serious health side effects (extreme weight loss to emaciation, depression/anxiety, and infertility/amenorrhea being the most common).

*Weight/fat gain due to believing the people who say calories don't matter and eating a high-cal, high-fat diet.

*Disturbed sleep/insomnia. Usually caused by ketosis.

*Constipation or diarrhea/extremely soft stool, or even both alternating. Caused by high protein/no starch.

For lean/thin individuals particularly, who eat low or zero carb though often higher in calories.:

*Muscle wasting, unintended weight loss to extreme/unhealthy levels

*Hormonal imbalances for both sexes, amenorrhea and infertility in women

*Exhaustion and lack of endurance, inability to recover from workouts

*Persistent hypoglycemic issues while in ketosis/eating low carb, no matter how long they try to tough out the 'low-carb flu'. Including low blood pressure/faintness, headaches/migraines, brain fog, slurred speech, irritability and anxiety, etc.

ETA: On a LC diet, thin people seem to experience one of either extreme of appetite: almost no hunger, or rather ravenous hunger which can't be satiated without starch. I've never been hungrier in my life than when I was VLC, but no matter how much I stuffed myself with fat/protein/veggies I never felt satisfied. Add a moderate amount of starch (say a minimum of 50g with my 2 or 3 daily meals) and I am totally satiated. It's literally the opposite effect that overfat people report on LC.

I have seen some real bad thyroid disease from a paleo diet high in iron from excessive muscle meats and the patient crashed on iodine, zn, and se. You got to be a total meat eater or you must supplement. There is no other option

If you consider that most of the dietary-related diseases paleo seems to address usually take decades to develop, most of us haven't been eating paleo long enough for any potential long-term negative effects to be evident.

Like a previous commenter, I'm also bordering on being too thin, but I couldn't say that's entirely blameable on paleo.

Im writing here mostly to confirm everything is better Paleo. As a person, I am not one to do any kind of diet! I had vowed to kill myself before ever following a diet! Here I am though and I can't really give it up because if I do, that means return of mental fogginess, skin problems, ADD, and less muscle tone. However, I write this everywhere, but I kept coffee as part of paleo for a long time and that was a big mistake. Going coffee free has been better than Paleo all together. So really, it's not Paleo that works/doesn't, it's knowing that food matters and your instinct is going to help you more than any doctor.

I have been more anxious and depressed lately. Mainly due to not cutting me enough slack. I have become too OCD about stuff. I guess i am prone to that. Its causing me to loose some (almost all of it) social life due to avoiding NADs. I will make cheats now but i will make them count), will make me feel better and less guilty. Take it easy :) Mental wellbeing is about the most important thing, if theres problems.

I've become way too obsessive about eating right, to the point where I lost a lot more weight than I needed to and have to gain some back or risk complications from being too thin. I don't think this necessarily stems from paleo, but it is a concern that people who are predisposed to becoming obsessive about food, or who have histories of eating disorders might have issues when switching to paleo since it restricts a lot of things. I got into trouble when I unnecessarily cut fruit and high-carb vegetables and started fasting daily. Now I am incorporating more fruits, tubers, and some white rice in an attempt to gain weight.

I was hospitalized because I fainted last year. Turned out it was very very low blood pressure which caused a syncope and severe cramping. It was a truly horrible experience because they didn't know what it was and I had to go through the gauntlet of tests to rule out things like epilepsy and brain tumors. Over a year later I have absolutely no more cramping, hypotension, or fainting issues. I upped the carb, calorie, and salt intake and watch mineral intake more carefully in general. I had been mostly paleo for about three years at that point.

I also had an issue with chronic stomach cramping and diarrhea while paleo and narrowed it down to brassica vegetables, which I don't eat anymore and it doesn't bother me at all.

Very good question, and I think that we need to be mindful of the data that are coming in on this. The full-scale and routine bashing, downvoting, etc. of others with different responses both on this site and others isn't conducive to good data collection. Personally, I haven't noticed that much of a change, but I wasn't eating SAD before. People I know who have abandoned paleo when it didn't work for weight loss or fit into their budget just added a few other foods, like some grains or peanut butter or non-grass-fed meat, but most of the people I know have seen other benefits that keep them on the diet.

The only issue I have encountered is trouble balancing electrolytes. I don't eat dairy for a lot of reasons and thus tried supplementing calcium since it's not in our drinking water as much as ancestrally, but I ran into cardiac arrhythmias, which I've had before off and on throughout my life, regardless of diet. When I remove calcium altogether and hope that there's enough in food I end up with muscle twitches. This is further complicated by the interplay between vitamin d, k2 and calcium. The way that sodium, chloride, magnesium and potassium play into this is difficult as well. Simply consuming the RDAs is too much, probably due to increased intestinal absorption from D3 and trying to get it from food is too little. I'm experimenting with dosages now but it's pretty annoying.

It's nowhere near as annoying as feeling sick all the time due to reactive hypoglycemia or actually being sick due to a compromised immune system that arose out of vitamin d and zinc deficiencies.

Also, remember that with so many people trying paleo, there are going to be certain portions of the population that do not react well to beef, eggs, etc. and if those people start eating more of those that could manifest in health problems. I'm surprised we haven't heard more of that, and that's the danger of anything that works.. even if it's only 1% for whom it does not work, that obviously gives those who are looking for problems something to latch onto.

Making a fundamental dietary change perturbs the body-mind's prevailing norms; homeostasis. Sometimes an existing diet/exercise regime can effectively mask symptoms, sometimes over a long period of time. This can be the case regardless whether the existing approach is sound or not. Making a change of any sort (including toward Paleo) can activate the symptoms. Thus one might conclude, "Maybe the change to Paleo is the CAUSE of these new symptoms." Basic truth: correlation is different from causation. Event A precedes B, which does not per se make Event A the cause of Event B. There is no off-the-top way to know whether there are elements of the Paleolithic lifestyle that may properly be understood as "causing health problems."

One possibility to consider is that the shift to Paleo might precipitate a "healing crisis," in the same sense as walking through the doors of the Betty Ford Center can kick an addict's symptoms into full bloom. Healing crisis as essential for genuine recovery. However, I don't recommend that you assume this is true in any particular instance. You should pay attention to the symptoms, and consider consulting a physician who's in sync with diet/nutrition, exercise, full-person perspective. Hint: most MDs do not fit this description.

The most common problem is constipation, although people are loath to admit. It is a problem. It continues to be a problem.

I think it's a good question.

I have/had these issues before and switching did not make them worse, BUT, my eczema has gotten worse, noticeably worse. It's finally calmer right now but hasn't improved much since it came out 'flaming' at about month 2/ now at month 9.

I think it might force issues to the forefront that perhaps were masked before clean eating. I'm assuming my eczema is another way my body is forcing out toxins and trying to heal. Healing is occurring for me so maybe this is just part of the process for me.

I started paleo very shortly after having my son so my issues could have been nutritional deficiencies caused by the pregnancy and SAD. BUT after starting paleo I had issues with constipation and psoriasis. The constipation I have since taken care of but the psoriasis has yet to go away. I'm trying some UVB therapy, zinc, and cutting night shades this month to see if that helps.

Elevated creatinine levels effect some, including myself, possibly due to the higher protein content inherent in the typical Paleo diet. Mine's higher than the person who started the linked thread below, although I may have been dehydrated at the time of the test (been Paleo for about a year and a half).

http://paleohacks.com/questions/6464/creatinine-paleo-paleos-effect-on-the-kidney#axzz1YjYoUKQE

Honestly, I walked away from Paleo over the last few months because I was becoming too obsessed with the details. Quite frankly I took a step back from other areas in my life where this was an issue. I'm definitely interested in coming back but I won't be approaching it the way I did in the past.

Medically: I had continuous soft stools while on Paleo.

Many of the above posts have to do with low-carb eating. I have one specifically related to taking grains and legumes out of one's diet. People with genetic mutations in their methylation cycle might rely on betaine (trimethylglycine) for recycling homocysteine back to methionine in the methylation cycle. After I went paleo, even though I was feeling better from a celiac perspective, I started getting mentally foggier and more tired. Eating paleo, high quality foods, without grains and legumes, can uncover methylation cycle defects in people with genetic susceptibilities (I'm not sure what percentage of the population would be affected: potentially around 10%, give or take?)

My eczema got a bit worst, I gained one small skin fungal spot, I sometimes have itchy eys and I have sugar cravings which I never had before in my life I think. Nothing serious comparing to what I gained. I don't know if all is related to my diet tbh, those are changes for the worst since I started it.

I've only been doing this for a few months, but I've found that my anxiety/panic symptoms have increased quite a bit. My sleep has also become more disordered (early waking--which is something I've never experienced before). And, I used to poo daily; now, I often go 2-3 days without a BM which definitely concerns me. I eat plenty of veggies, but I think the lack of legumes is a problem for me.

I'm keeping the grains out and I don't do dairy (which I know can cause that problem). But, I've decided to eat traditionally prepared (soaked/fermented/sprouted as per WAPF) legumes about once a week to keep everything moving. I came to paleo/primal from doing WAPF, so while I'm sure there are many of you who would have a problem with that, I feel comfortable that I'm making an informed decision. It seems to be working and my weight has started dropping again (it had stalled for a while).

While my diet is obviously lower in carbs than the SAD, I'm not doing VLC--I eat fruit, sweet potatoes, winter squash and nuts--so I don't think I could possibly be in ketosis (which can cause some of these symptoms). I get plenty of fat from grass-fed meats, pastured butter, coconut oil, and ghee.

The anxiety and sleep problems could be caused by perimenopause (I'm a little on the young side, but not by a lot and I have had some other symptoms that are definitely pointing in that direction). I'm not usually a believer in coincidence, but it is possible.

I haven't had any blood work since I started, so I can't comment on that. My numbers were all pretty good before I started, so we'll see what happens there when I repeat the blood work in the next month or so.

I have been doing a Paleo challenge with my crossfit gym and I have had almost all beneficial effects from this challenge. Those who report soft stool I wil concur. The issue may be coffee as it is for me I'm sure. My sister also drinks coffee and has the same side effects. I do have several days of normal stools in between, so that helps offset the other days. I have increased energy, sleeping better, improved skin (much less acne than I was having before). I have not been doing this long, just about 3 weeks, so someone who has eaten Paleo much longer could definitely attribute more. One important thing I would note is to never remove fruit from your diet totally for weight loss. There is too many vitamins and nutrients in fruits we need. Also when you cut out those natural sugars you will begin to crave carbs you do not need and is way more harmful to you than a banana. Be sensible with any food choices. Paleo is a bit of common sense. I feel that a 90% Paleo diet would be healthy and beneficial for anyone.