If you can motivate yourself to track what you eat "accurately enough" I can recommend just starting with that. There's a bunch of apps out there that let you

If you can motivate yourself to track what you eat "accurately enough" I can recommend just starting with that. There's a bunch of apps out there that let you track what you eat. They usually hook up to various databases on nutritional information, let you add your own recipes or new foods etc. Personally I could only bear it by starting to be reasonably good at estimating amounts/weights visually and not overthinking it or trying to be 100% precise. If you weigh every ounce of cheese you eat it can easily be overbearing. So I just stopped worrying about whether that's 50g or 60g of cheese. Some weighing to gain proficiency but that's it. From that you can get a 'good enough' idea whether you're eating 4000 calories from sugar and fat, get 0 Vitamin C or D or if you're in the ballpark of the 2k, not too much sugar etc. and adjust through tracking. Some apps will also give you food recommendations and such (usually for a fee). Most apps have the RDAs for most things already in the app and also let you adjust (in case you decide that science speaks for the carnivore diet or keto or a vegan diet or that you found a credible source that the RDA for sugar is bonkers and you want it to be lower etc). I think even without special sources you will have some data that allows you to make adjustments. My wild guess is that you will see too much sugar for example. My guess is that as soon as you eat a better diet your mood might automatically adjust. Not entirely sure what you mean by mood specifically. E.g. alcohol can have an effect on mood (through making you more irritable). If mood extends to being 'lethargic' then if it's the same thing I had, potentially probiotics can help.