Is constant overeating and obsession with food a sign of dementia onset?

If she claims she eats very little but is eating continually and saying that she can't eat sweet things while eating a chocolate bar, then she has dementia.
Food obsession and anxiousness over when he next meal is coming minutes after finishing the last one is a very common form of OCD associated with some forms of dementia. It's not the same thing as a bored elderly person who has nothing to do except wait for the next meal. It's a type of OCD. I've seen the kind of food obsession you're describing with many different care clients who have been on my service over the years.
Talk to your mom's doctor. Explain the food obsession. The doctor can prescribe her medication to help with the OCD behavior too.

hugs!

dementia can do that. — but also some medicines. also boredom. one would have to analyze the specific case.

my LO went through that (extreme appetite).

we locked the kitchen and left a basket of fruits to snack on.

the phase lasted about 3 months, then the appetite returned to a normal level.

i hope your mother improves!!

Diabetic?
Thyroid problems?
I'd seek medical advice.

The same with my husband. He has gained 40 pounds in3 months and I’m buying as healthy foods as I can and I actually HIDE food and snacks to dole out slowly. I try to keep him moving. All of his clothes are too tight now. The neurologist said that part of the brain is “ broken” and he doesn’t feel satiated. He has Alzheimer’s/ vascular and is declining quickly. I as a nurse, know that at some point he will not be able to eat or swallow so honestly I’ll let him eat

I think you can help put this situation in perspective by considering that she's munching on " chocolates, cakes, ice-cream and whatever else is available."   That concentration of high sugar foods doesn't satisfy the body's need to nutrition, so she probably still feels hungry.   Chocolate and sugary foods can create a certain kind of "high" though,  a kind of temporary satisfaction.

I would as already suggested eliminate the sugary foods and substitute good, nutritional foods.    To Findel's list I would add carrots, celery, and fruits of the season (lower sugary ones if possible).   

The overeating and ensuing needed bed rest is alarming.  I think I would have one of her doctors check her for diabetes; that much sugar upsets the body.

If you have to, use the Indiana Jones approach:   remove the sugary foods but substitute them with something she can nibble on that's more healthy.   Protein foods could work.   I've always loved to nibble on turkey and chicken.

I think the lack of food satisfaction is contributing to the food and meal anxiety.

It could be a symptom of dementia. However it could also be a symptom of depression, which could also accompany dementia. I would get her to the Dr for a cognitive test and see what the Dr says. Be honest with the Dr about what she's doing. Good luck to you.

Take away the biscuits, sweets, processed food. Give her almonds, fruit and wholegrain. Yeast and sugar in foods create an addiction that is hard to break. That includes bread, chocolate, pasta. She can eat unlimited vegetables, buckwheat flour (great and easy pancakes), chickpea flour (also great crepes), eggs, yoghurt and olive oil. Condiments are miso, tahini, chilli oil, spices, sesame oil etc. Nuts are great to snack on. Lemon squeezed on everything.

You don't mention if your mother is showing early signs of dementia. My mother with dementia went through a phase like this when she had earlier stages of dementia. She put on a lot of weight, and then later lost it when that phase was passed and she had to switch to soft foods. Can you not have things around that your mother shouldn't be eating? Is she still doing her own shopping and cooking and taking food for herself or does someone have to get the food for her? If there are signs of dementia, you need to make sure all of her paperwork is in order and someone can take over for her if her judgment becomes impaired. This should be done as soon as possible, while her mind is still good and she can still sign legal papers. She needs Powers of Attorney to be set up for medical and financial matters, a living will with her medical directives, a will if she has assets. Be sure you or her POA is on file with Social Security and Medicare as someone who can speak on her behalf. Most financial insitutions (banks, credit card companies, etc.) also require their own POA forms. Regarding her anxieties, speak with her doctor about what you are observing. There are natural calming medications she could take like Melatonin.

TNtechie, excellent insight into how inadequate food supplies at an early age can affect eating and what some consider obsessions with food at a later age.  I recall my mother and father sharing insights into the sacrifices they had to make during the depression (and WWII),  how Mom studied by candlelight, when they had no coal for heat, and how Dad and his family used heat bricks in the bed as they had no central heating.    (I still haven't figured out how bricks could be used w/o creating a fire hazard, but they were so practical during those days that I'm sure they figured out something.

My grandmother also scrimped and saved, but from a different background and experience, the experience of fleeing the Turkish Massacres.

I’m sorry. I don’t think this is that uncommon. Look at the number of obese people in the US. And people often nap after eating large meals. Thanksgiving? Not everyone who naps has had turkey.

Stress, the thyroid, ghrelin and leptin disorders could all be at play here.
If you think about it, it’s really a form of ageism to decide that Bella’s mom has dementia.
She has been described as a sugar addict and it has hijacked her gut and brain is my hunch. When someone is an addict, they don’t easily give up that which they are addicted to. If she were 35 we wouldn’t consider dementia. Many don’t admit to themselves that they are addicted to shopping, gambling, working, eating, the computer etc.
I know that there is a certain ice cream that once it finds its way into my home will be whispering to me until it is all gone.
Those healthy snacks hold no allure for a sugar addict until they are detoxed. If you give her a little sugar in the form of a bowl of pasta, a slice of bread, a bowl of fruit, it is almost cruel as it keeps the addiction going.
It brings to mind the alcoholic saying “one drink is too many and a thousand is never enough”.
I think your mom is addicted and not necessarily demented.
Ask her doctor if Wellbutrin would help. It’s an antidepressant that is used to help folks quit smoking and to lose weight. It helps with compulsions. My 95 yr old takes it for depression.
The healthiest thing I ever did to break a sugar addiction was the 10 day detox by Dr Hyman author of the Blood Sugar Solution. My husband is diabetic and a foodie. He asked me to read it for him years ago after seeing him on PBS. No surprise, he didn’t want to follow Dr Hymans guidelines but when I did the 10 day detox, I no longer craved starch or sweets after the 3rd day. Your mom may need a little help letting go of the sugar. Once she has it out of her system and given her body a chance to recover she may be able to have sweets again in moderation, but at this stage no amount will ever satisfy her.
If you can video her eating and sleeping it off and show it to her, it might help her see for herself what she is doing. Videos are wonderful teaching tools for us to see ourselves and are much harder to ignore than someone telling us what we are doing wrong.