<<Why is it that a person may not do well on a paleo diet?
The Ten Commandments also say Do Not Eat: Grains, Beans, Potatoes, Dairy,
and Sugar. Would taking any of these foods out of the diet make someone
sick? Jason >>

Jason, you ask some good questions.
I sincerely do not think there's any way that removal of the "Do Not Eat"
foods would make someone sick, other than temporary withdrawal to possible
allergic foods in this category. Once the withdrawal is over (between 3 to 7
days usually), if the person doesn't feel well I'd look for another
explanation. The "do not eat" foods are newer foods to which most people are
not well-adapted. Removal of these foods for anyone should not make them
sick. In the cases we've been discussing (tiredness) there are other things
to look for, besides the electrolyte issue that Todd brings up. One thing to
look at is: what IS the person eating? What is the ratio and amount of
carbohydrate/fat/protein and is this correct for the person's own
energy-producing metabolism? Another thing to look at is food allergies
(common!). Is the person eating an allergic food? Yet another thing is WHAT
types of foods is the person eating, and are they correct for this person's
inherited metabolic type? For example, some people of European descent may
have undesirable symptoms from eating lots of tropical fruits they are not
adapted to. Those people, depending on genetic inheritance,  may desperately
need a high level of purines (nuceotides) for their energy metabolism.
 You WILL be tired if you're eating the wrong foods or the wrong balance.
It's more complex than simply eating just anything in the paleo category.
Some people do better eating low-carb paleo with plenty of fat, others do
well with lots of energy from carbs. So there's tremendous variety within
paleo guidelines.
 If someone feels worse on paleo and is past withdrawal stage, then I'd
seriously consider them to examine further. Eliminating the newer foods and
anything processes should only promote health and energy. If you aren't
making energy, there's something you're eating or not eating that should be
modified.