The key to healthy diet and weight is a lifestyle change. You need to change your attitude about food
There are several approaches; counting calories, using a points system, or portion control being some of the most popular.
In my opinion, the simplest approach is portion control. Learn what you can eat unlimited amounts of; and keep those as the centerpiece of your diet. Then learn the proper portion size of other foods and how many portions a day you can eat. Learn which foods you really should not be eating at all , and if you do eat should be in very limited quantities.
What should you eliminate, what shouldn’t you eat? Empty calories. Sodas and juice drinks; prepared food (food in a box) with a long list of ingredients and high calorie to fiber ratio, fast food (since it is generally going to be calorie dense, high fat, high salt and sugar, and low fiber).
What can you eat virtually unlimited amounts of? Non starchy vegetables. Be careful what you put on them. Read dressing labels . They do make low calorie fat free dressings made with an acid (vinegar, or fat free buttermilk) and a soluble fiber (no calories even though they count as carbs on labels. Guar gum, acacia fiber…) or you can make your own (I have quite a collection of different vinegars , and always keep lemon and lime juice on hand). I like to keep some steamed vegetables (broccoli, green beans, cauliflower, summer squash, …) in the fridge front and center in a tupperware container. Also there are many low calorie high fiber fruits. Melons for example. I keep some prepped in tupperware in the fridge.
Now some portions
A portion of whole grain or resistant starch (starches which resist digestion and take a long time to break down , thus giving you a steady blood sugar level rather than a spike and sag which leaves you hungry). is about the size of a ball you can close your fingers around.(tennis ball) You get three total each day. You can eat them all at once, or spread out.
A portion of protein (meat, eggs, …) is about the size of your hand with the fingers and thumb removed ( a deck of cards) again three portions per day.
Fats, limited quantities. A portion is your thumb max , and really should be half that. Stick to ones that are liquid at body temperature. Avoid hydrogenated and partially hydrogenated (trans)fats.
Learn to cook and enjoy it. Learn to use more vegetables in dishes and learn to use techniques such as steaming , boiling, braising, broiling, grilling, baking, roasting …
When I say I am having spaghetti and sauce for dinner I mean I am having a big serving of sauce with lots of added vegetables (often adding sliced onions, bell peppers, cubed zucchini, broccoli florets, mushrooms, whole tomatoes squished in my hand…) to the sauce, minimal amount of lean meat and minimal amount of pasta.
Spaghetti with kale is a good example. I take a bunch of kale, and strip the leaves from stems and tear them and toss em in with about a third of an average “serving” of spaghetti and several cloves of garlic. When done remove the garlic and crush it or chop it and add back in. I toss them with a little (ounce or two) sliced up low fat turkey smoked sausage (shaved thin, slivered, warmed in microwave or a non stick pan) and lemon juice. A little fresh grated parmesan cheese and you have a meal.
Exercise is another problem area; the key in my opinion is to start off easy. Do something you can do and do it every day (even multiple times a day). Walking is one of the best. Start off with a walk around the block, gradually build on that until you are doing a mile or more.