There is a lot to unpick here and I don't think it is a simple situation with one solution.
- The hiding creates a game out of finding and then eating the food.
- The eating until feeling sick - some children/people have poor interoception. This can lead to not recognising when they are hungry or full and can lead to eating out of habit, eating emotionally and eating out of boredom.
- These products are designed to be gorged. There have been studies that show that foods that are high in sugar and fat are more likely to be overeaten. There have been mice studies where they give them free access to as much high sugar, high fat, or high sugar and fat foods as they want. The mice that had access to either the high sugar or high fat foods ate a typical amount and didn't over eat. The mice with access to the high sugar and fat foods couldn't stop eating.
Other studies have found that these foods have been a design to require minimal chewing to eat and this means there is a delay between eating them and your brain registering that you have eaten them. By which point most of the packet has gone.
- The more sweetness you have in your diet you brain is reset to expect and need that level of sweetness. My partner spent a week in the US for work about 15 years ago and that was enough to reset his expectations of sweetness. He made dinner and i couldn't eat it as it was so sweet.
- Sugar and UPF foods are additive, it's not just the sweetness but the mouth feel and the texture and everything about them. This is compound if you have a sweet tooth - My dad has a ridiculously sweet tooth and used to eat pack of 4 mars bars for breakfast. He retired in the summer and with being at home more started eating more and more chocolate. Over November and December he managed to eat 4 of the Christmas chocolate tubs! He put on half a stone in two months and realised it had got a bit out of hand.
By hiding the biscuits there is a dopamine high to be gained from successfully outwitting you and finding the biscuits.
The biscuits high sugar and fat UPFs which creates another dopamine high. They are designed for you to eat more than you realise and to override your bodies "off" switch.
It really isn't a shock that what happened happened.
I would be somewhere between annoyed and furious but would recognise that these emotions teach through fear and sham and that wouldn't be appropriate here. I find approach these situations with firm boundaries and compassion usually helpful. Compassion that she is a child and many people will eat the whole packet but firm that it was wrong to seek them out knowing that they were for another day and by eating them all others have lost out.
I would do a radical assessment of the amount of high sugar and fat UPFs in your diets and make some sensible swaps. Assess each food based on it "eatability" are they one bite and they are gone? Are you grabbing at the packet for the next one before finishing the first? Darker chocolate is less likely to be over eaten. Buy based on expectations - if it's a product that is likely to be hitting the big red dopamine button repeatedly buy enough for one sitting and at a frequency that you would be happy for them to be all eaten at once. For the day to day look at snacks that gives that sweet fix and the feeling of a treat that has more of an off switch.
I would do some gentle proding to assess the awareness she has for the feelings of full and hungry. Identifying other emotions and bodily functions. Many people and children alike can't tell the difference between being hungry and thirsty. They eat not recognising they are thirsty but because they haven't had a drink then thirst doesn't go. What is she thinking and feeling when she is eating like this? Snacking is so often more emotion driven than hunger.
Bring in rules about when and how everyone is allowed snack foods. I have a 5 yo and she asks before she has anything to eat. She is the opposite and has poor interoception for hunger. She has dropped two percentiles in weight over the last 18 months as she will only eat if she is properly hungry so even an apple half an hour before dinner would be enough to stop that hunger and mean she would then refuse to eat dinner. At the same time we need to make the most of times when she is hungry to get some calories and nutrition in her so rather than her having free reign on the cracker draw and fruit bowl we monitor what she wants and if she is clearly hungry hungry we do her a balanced meal sized snack plate of various bits. She has food allergies so on a limited diet because of that too.
If we weren't having to make sure that she was eating a balanced diet and not only eating apples and bread sticks we would have different rules. It's about working out what is right for your family. She gets a cup of oat milk with each snack as well.
We do pudding after every evening meal but it varies from yoghurt with some fruit and nuts to sweets or cake. Sweet foods with protein causes less of a sugar spike and it means the brain is already expecting something sweet so on the days when it gets the cake it doesn't have as much of a yippee this is the best thing in the world I want and need more!