As Worth in Progress, both the online publication and the video content, is about personal development, it would be counterintuitive to refrain from talking about weight loss. Losing weight, you see, is a big part of personal development for many people. Some want to lose weight to become healthy. Some want to lose weight to become the best version of themselves. And while losing weight is no longer a part of yours truly's life - after losing 22 lb last year - the topic is still worth discussing. I've found that there are two ways to lose weight, mutually exclusive, both based on the same principle.
Before we continue, note that the author or Worth in Progress in general have no degree in medicine or nutrition and that the following is based not on science but on the personal experience of the author and it should not be interpreted as medical advice. For medical advice, consult your doctor.
The basic principle behind weight loss is that you consume less energy than you spend; that your energy input is less than your energy output. This does not mean that all sources of energy are equal, nor does it mean that you need to exercise excessively. Some foods make you want to eat more, and some kill your hunger. And your basic metabolic rate is usually so high that any form of exercise is small in energy expenditure in comparison.
There are three kinds of macronutrients: proteins, fats, and carbohydrates. All food is composed of a combination of one to three of these. Red meat has protein and fat, but no carbohydrates. Lean chicken and tuna have basically only protein. Butter has only fat. Some vegetables have only carbohydrates. Processed foods have all of the three.
In order to lose weight, your diet should have a macronutrient ratio of EITHER
A) high carb, moderate protein, low fat, OR
B) high fat, moderate protein, low carb.
If you go category A, you're basically vegan: you eat a lot of vegetables that have a lot of carbs and only a little fat. You can eat a lot every day because vegetables tend to be low in energy.
If you go category B, you're more like a carnivore: you eat little to no vegetables (or very low carb vegetables) and a lot of fatty meat and fats. You must eat less because fat has a lot of energy, but the fat that you do consume keeps you satisfied for longer so your energy intake ends up at the same level as the vegan energy intake.
The key is that if you eat a lot of carbohydrates, you must keep your fat intake low, and vice versa - because it's the combination of the two that makes you gain weight. High fat + high carb together will make you fat. This is why TV dinners and other processed foods are generally unhealthy: they're high in both carbs and fat. (I like to think that the body, when given both at the same time, prefers the carbs for energy and stores the fat because it doesn't have to use it in the presence of carbs; I don't know if this is true, however.)
Both of the categories have their pros and cons: A is usually low in vitamin B12, and category B is low in vitamin C. Low fat products tend to have a lot of sugar that can cause diabetes and heart disease. High fat diets lack fiber. A balanced diet would be optimal with that respect. However, if losing weight is your goal, it may not help you get there.