A healthy diet is a diet that:
— is organic
— is seasonal
— is local
— isn't excessive in any of the macronutrients (most diets are excessive in carbs, especially processed carbs such as pasta, bread or pizza)
— contains non-starchy vegetables as the main source of carbohydrates
— is defective in any of the micronutrients (everyone is deficient in magnesium, most people are deficient in other minerals, vitamins and antioxidants, generally you need a value much higher than what most medical doctors recommend because we have deficiency and those recommended values are for healthy people, not people who've been deficients for years or decades)
In your case that you're trying to lose fat, limiting foods with high glycemic index is fundamentals. When you do eat those, be sure to pair them with healthy fat and protein sources.
High GI foods (70 and above): glucose (dextrose, grape sugar), high fructose corn syrup, white bread (only wheat endosperm), most white rice (only rice endosperm), corn flakes, extruded breakfast cereals, maltose, maltodextrins, white potato (83).
Medium GI foods (56-69): white sugar or sucrose, not intact whole wheat or enriched wheat, pita bread, basmati rice, unpeeled boiled potato, grape juice, raisins, prunes, pumpernickel bread, cranberry juice, regular ice cream, banana, sweet potato.
Low GI foods (55 and below): fructose; beans (black, pinto, kidney, lentil, peanut, chickpea); small seeds (sunflower, flax, pumpkin, poppy, sesame, hemp); walnuts, cashews, most whole intact grains (durum/spelt/kamut wheat, millet, oat, rye, rice, barley); most vegetables, most sweet fruits (peaches, strawberries, mangos); tagatose; mushrooms; chilis.
Fruit should be considered as your dessert, because it's a natural dessert and you modern desserts are mostly unhealthy, while fruit is very healthy.
I'd advise a ketogenic diet but that's not for everyone (taste-wise) and it's not budget-friendly. Furthermore, no one who has talked about it here in other topics seems to know anything about it, even those who supposedly tried it but didn't actually eat a ketogenic diet as can be seen by everyone who has sufficiently studied what a ketogenic diet is like and it's not certainly bro-science as it has existed for centuries and it has been used to treat pathologies like epilepsy, seizure, stroke and related, as well as cancer most recently. Furthermore, to be bro-science it would need to be actually promoted by people who attend gym, when it actually is barely heard of in gym and between athletes. I know athletes, military athletes, soldiers and many specific categories in the field, instead of just guessing or "googling" like many people here do.
For the rest, use the search function and also don't neglect to have an active lifestyle with no excuses.