"Neanderthin" claims that obesity comes from allergies - may be -
because allergies put everything in disorder.
Besides that
I know at least one more mechanism and I'd like to share that thought.

Obesity comes from cravings, caused by deficiency of any vitamin.
Vitamins are essential, and your body will keep on giving you
cravings and keep you eating _until_ a minimum supply is achieved.
If your average food composition doesn't supply enough of _any_ of the 40
essentials you need, you will find yourself over-eating in terms of calories.
Compensating by quantity what lacks in quality.

Many food compositions of today give a very low vitamin yield
compared to both the proposed paleolithic nutrition,
and the scientific recommended values.
Especially food compositions with "processed" items (shugar...)
and compositions high in meat result in some or many lows on vitamins.
That's - in short - reason for obesity, as well as for many other "civilatory"
deseases  which can be considered also vitamin deficiency deseases
(cancer, diabetes, heart deseases).

Now, check (for example) how much Vitamin B1, how much folic acid,
how much K,C, A you get.
Are _all_ of them at least approaching the proposed needs?

If not, you're not paleo.
In paleolithic times unmodified and fresh food items
had a very high vitamin content and composition.
Nuts and seeds' contents resemble the proposed needs very good.

regards
Amadeus