Weight loss requires calorie deficit. That is the thermodynamic principal.
Now this can be done via two ways, reducing intake and/or increasing expenditure. The better option is to use both together in various ways.
Both have their difficulties and pitfalls. And as you will realize below, you cannot have a sustainable weight loss without using both together.
Before we begin the most important part to understand is that the body has a fat set point, which it will defend. To force the body to lose weight you have to change your diet/exercise regime. And to have sustainable weight loss you have to have a sustainable strategy.
Lets take the less complex part, increasing expenditure. This will have a feedback in increasing hunger, which causes more intake, due to the fat set point. Also there is the case of adequate rest, and avoiding repetitive stress injuries. You also want to avoid overusing very few muscles. The exercise needs to be overall body, with adequate rest, and a healthy diet.
Now for reducing intake. This can be done two ways.
Destroy your digestive system so that it cannot absorb the energy. For some reason bariatric surgeons favor this route, possibly because it makes them more money. You can also have it destroyed by overusing antibiotics.
The other more prudent way is to eat less. This strategy is pretty complex because of several reasons.
First the body has a set point which it wants to defend. So attempting to eat less will increase your hunger and temptation to food. The strategy of fighting your basic hunger will be a failing strategy. So your strategy has to reduce your calories but while achieving satiation.
Second the body can control its expenditure, by releasing or holding body heat. Basically the body needs to burn calories for doing work as well as maintaining body heat. So it can reduce the expenditure by slowing metabolism by reducing body temperature. This is the starvation response, the thyroid hormones are down regulated and metabolic rate is reduced. This happens when the calorie intake is low too for too long.
Third the diet must provide enough micro-nutrients for the body's upkeep. Your body can supply the energy by burning the excess fat, but it has limited stores of micro-nutrients. So these must be part of your diet in adequate amounts. This actually implies that the diet should be low in carbs and fats, as both are plain calories which you want to reduce. It is best to consume whole natural foods.
Fourth the diet must be highly satiating. This is the most complex and subjective part of the diet. It depends on every persons personal tastes and gut flora. There are a few generic ideas that would help.
Protein is more exothermic so keeps your metabolic rate higher, and is not readily used for energy, which makes it more satiating. Strive for protein intake between 15%-30%. The exothermic part of protein limits its intake during tropical summers. In extreme winters protein intake can get a lot higher and will be helpful to deal with winters. The body on an average has the ability to digest 250 gms of protein, which depends on the excretion of nitrogen from the body.
Fibers are more filling and good for the gut flora. The ability to digest fiber depends on the gut flora and the type of fiber. Generally you want a good mix. Normal humans can absorb 100gms per day, but you need to have adequate gut flora for it. It might take some time to build enough gut flora.
There are some foods which are highly satiating. The foremost example is the potato. The potato hack is the fastest way of losing fat. It is difficult to consume more than 1200kcal from boiled and lightly seasoned potatoes, if no fat or other caloric additives are added.
Lastly there is fasting. There are several fasting protocols which are used. The best seems to be eating in a small window. For example 16 hour fasting and 8 hour eating window. Another variation is fast5, which is a 5 hour eating window. Some people also do alternate day eating. The fasting protocol does not limit calories within the eating window, so you are never under eating for too long. It is generally good to sleep on a more or less empty stomach. ie Almost never have a big dinner.