Used to be a fatso here. Almost 200 LB at 5'8. Even developed type 2 diabetes. Since, I've lost almost 40 pounds. I'm now in the low 160s and continuing downward. Here is what I have learned through both lots and lots of research and personal experience.
(1) Blaming your overweight or obesity problem on metabolism is a cop-out excuse. Before you want to hang me to the alter of the fat-acceptance god, let me explain.
I used to use this excuse, too. Until this question came up in my mind during my research: What exactly is body metabolism? I don't mean the scientific definition of it. I mean specifically, what is a person's body metabolism to regular folks like you and me? Once I found out the answer, I realized blaming it on body metabolism has always been and will always be just a cop-out excuse.
Your metabolism is the total energy consumption of energy to maintain your current being. Seems simple, right? But think about it for a moment. Yes, it is true that the fat kid has a lower body metabolism than the lean kid, but why is that? If it was as simple as this, the fat kid should be dead. It cost real energy to keep a person alive at a normal temperature.
Let's take a step back. Have you ever noticed that fat people are always cold? Fat cells store fat. They don't really require that much energy to stay in being. Muscle cells, on the other hand, require a lot of energy to maintain. The bigger the muscle cells, the more energy they require to maintain themselves. Fat cells, on the other hand, require about the same energy to maintain whether it's got a lot of fat in it or not.
The totality of the energy consumption of your body to maintain itself is your body metabolism. In other words, the fat kid has a lower body metabolism than the lean kid because his muscle cells aren't as big as the lean kid's. There is no magic to this. And stop blaming it on your genetics. Anybody can have a higher body metabolism. Just gain muscle mass.
(2) Even though doing math with calories in and calories used is outdated, the concept is still useful to some degree. I know this because I used to eat like a fatso when I was fat. I ate until I was satisfied. The problem was over the years I had inadvertently trained myself to be satisfied on a much larger portion than I needed. Once I realized this, I started mentally train myself to pay attention to portion sizes. Nowadays, I still eat until I'm satisfied. But where I am satisfied nowadays is a lot smaller than where I was satisfied back when.
We have an aunt who is a little on the heavy side. She is always a mystery to us in that every time we eat together she always eats very little and usually only fruits and salads. My husband and I once talked about it and he could not understand why she is still big even though every time we see her eat she's always eating a tiny portion. I told my husband I absolutely don't believe that's how she eats normally. In other words, she's just eating that little in front of other people for show. Sure enough, since then we have had good authority on this that her normal portion size is probably bigger than both of ours combined. She just doesn't eat like that in front of most people. We gotta give it to her, though. She actually has the mental power to control her intake every time we go out together. Last time we went out together, she had a small salad and then said she was full. I thought I saw her husband rolled his eyes LOL.
I bring that up because of the leader of the fat acceptance movement Tess Holliday. She claims to not eat very much. I don't believe for a moment that she somehow breaks the laws of thermodynamics.
(3) What is more important than doing math is actually paying attention to what you are consumming. A sugar portion with X amount of calories will metabolize in a much negative way for your body than a non-processed meat portion with the same X amount of calories. And FYI to some people here, sugar is a type of carb. Even though Atkins wasn't the first researcher to figure out the correlation between carb intake and weight gain, he was the first to, I think, to publicize this widely.
Here is a problem that vegans have that most people don't know and they almost never talk about. Vegans have a lot of problems with rotting teeth. Why? Because they are essentially eating sugar. In a much less concentrated amount than sugar as we know it. But in order to support what their bodies need, they still consume enough sugar carb to affect their dental health.
In short, I don't believe for a moment that every single person with a weight problem has a genes problem or thyroid problem. Stop using such excuse and work on increasing your metabolism. How? By gaining muscle. And also watch what you eat. You CANNOT compensate a bad diet with exercise.
One more thing. Last month, we had some friends come and stayed overnight for our epic halloween party. In the morning, we all went to breakfast together. My friend, who is a little on the heavy side, said he noticed I've gotten a lot fitter. I thanked him for my compliment. At the time, I had finished my breakfast. I had only eaten half the portion they gave me. I wasn't consciously stopping myself. I was genuinely full. So was my husband after having only eating half the portion. My friend commented that we both look so fit because we seem to be starving ourselves. At the time, I didn't feel like explaining to him about eating healthy and whatnot, so I just smiled and agreed.
My point is there is a misconception, especially among fat people, that any restriction in portion size = starving oneself. We have people who 100-200 pounds overweight and yet are so afraid of starving to death. I blame this way of thinking on the culture. It is like a billionaire who is always afraid of becoming homeless so he keeps hording money and never spends it. Makes no sense to me, but that's how people think nowadays.
Added by edit.
Ever since I became fit, all my previous problems have gone away. Autoimmunity disorder has disappeared. Blood pressure is normal. I don't feel tired during the "midday slump" anymore. Type 2 is gone completely. Even my lactose intolerance has gone away, which not too long ago gave me explosive diarrhea on a regular basis.
So, please don't tell me you can be healthy at every size. Tess Holliday, you hear that?