That's an interesting question, especially since 145 lbs. is considered light for someone who is 6'2." If I had to guess (and I'm not a dietician or a doctor, it's a guess) I would say that with such a tall body, you need that amount of fuel to rebuild cells and breathe and make blood and move around. In other words, just the effort it takes to run a body causes you to need food in a certain amount. 3500 calories is not surprising, you are 6'2" and also young (people burn their food off faster when they are young, which for most people begins to slow after a while). Have you ever had a pet who was long and lanky? We had a cat like that, no matter what we gave him, he simply could not gain weight -- he looked like a noodle. He didn't have worms, didn't have any digestive issues, he was just young. Only after he was a few years old did he begin to retain his food as visible weight. It wouldn't surprise me that as a matter of evolution, the youngest creatures (the reproducers of the species) needed to be programmed to be slim if they were also hunters, or they would be burning too much in order to catch food.
I agree that you, most likely, have a really high metabolism... As AnnieBrooke noted, that could be simply because you're young. There could also be a medical problem causing you to have a hard time maintaining weight.
The thyroid controls metabolism, so you might ask a doctor to run some tests to make sure that your thyroid isn't over-acting - aka producing too much thyroid hormone, also known as hyperthyroidism. Typically, there are other symptoms that go along with hyperthyroidism, but not always. Other symptoms can include tremors, rapid heart rate/palpitations, irrational behavior, fatigue, etc. Ask your doctor for Free T3, Free T4 and TSH tests. If any of those are out of range, ask for antibody tests to determine if you have an autoimmune thyroid condition that could result in hyperthyroidism.
In addition, blood glucose issues can cause difficulty maintaining weight. When my son was diagnosed with Type I diabetes, he lost quite a bit of weight, but again, there will be other symptoms that would indicate a problem. Initial symptoms of diabetes could include excessive thirst, frequent urination, weight loss, irrationality, etc.
As long as you don't have a medical problem, I don't think I'd worry too much... I have a brother-in-law who is well over 6' tall and he's 60 yrs old, but I'm not sure he weighs much more than you do, but he's healthy. That's the type of metabolism many of us would love to have - enjoy it as long as you're healthy. :-)
I'd say that first, calories aren't a very relevant measurement. While useful, the most important thing in weight is how your body metabolizes what you're eating. You don't mention the content of your daily diet; for example, if you're a vegan and eat pounds and pounds of celery you're still not going to gain a lot of weight, but if that large amount of calories are going to pork chops and French Fries and you're still that thin, then your metabolism is preternaturally high for someone who doesn't exercise much. If you were a marathon runner it might make sense, but you're tall and really really light in weight. That's not necessarily a bad thing; being thin has been associated in some not so well received studies but they are there with rats that being underweight leads to longer life. Now, the above are right, I'm a guy and from the time I was a teenager to the time I was nearly 40 I could eat as much as I could hold and not gain weight, but I was 5'11 and weighed 155 pounds. After that I started going to the gym instead of just doing cardio -- I did exercise a lot, I liked playing basketball a lot and ran -- and doing martial arts I got wider and stronger and just got a larger frame, more like the one my Dad had than the much thinner one I had than everyone else in the family. But that was added muscle. The only time I had a weight problem was when I was on an antidepressant that caused me to gain a lot of weight, and I've never lost al of it even after years off of it, and in my 40's I got a bit of a belly but I'm just saying this to show that what we eat, how much we exert ourselves physically, and simple aging does change our appearance and frame. I eat a lot better now than I did at your age but I also can't do what I could do physically. I have no idea if you have a health problem or not but it's worth looking into if this covid stuff ever ends -- I don't know how easily it is to get looked at right now with social distancing if you don't have a major health problem and apparently you don't feel sick. I do think if you had either a thyroid problem or diabetes you'd probably know it because you'd feel it, but in normal times it wouldn't hurt to see your doc and talk to him about it. But humans are peculiar, we're all different, and we're quite different at different ages. If your growth spurt in height, for example, happened recently, your weight might well catch up. A lot of taller folks are really really skinny when they're young and before they fill in the rest of their bodies. But I am concerned that you feel lethargic if you don't eat a ton of food and for that reason again if you can or when you can it's probably time to get a full checkup. By the way, when Barb mentions T3 and T4, do what she says -- if you don't ask for that the doc will only check you for Tsh, which won't tell you much about your thyroid. Peace.
Make sure that's FREE T3 and FREE T4 because they aren't the same tests as T3 and T4.
There are a lot of people who have autoimmune thyroid conditions for a long time and don't know it. I'm one of them. I was always one who could eat as much as I wanted without gaining weight, as well. There were times that I had such a hard time gaining weight that my doctors worried about how thin I was but I was never tested for autoimmune thyroid condition. As time went on, I went through short phases during which I'd gain 10-15 lbs for no reason, then suddenly lose that plus more, again for no reason. This happened multiple times over a period of about 20 yrs. It's pretty much been determined, now, that I had Hashimoto's long before I went hypo and that the times I lost weight or couldn't gain were, most likely, hyper phases of Hashimoto's. When my thyroid quit working and I went completely hypo, was when I finally gained permanent weight and had multiple other symptoms. The rest is a whole other story... :-)
I've also known people with mild Graves Disease that don't have symptoms, other than inability to gain weight.
Diabetes, on the other hand, will usually present other symptoms because when one's blood glucose becomes elevated due to lack of insulin, it doesn't take long to get very ill.
Hi! That does seem like a lot of calories. I find though, that we are all different and what makes one person feel best may just be unique to them. I wonder though if you couldn't still get the benefit of energy and feeling good with more quality calories instead of just a lot of them? I'm not really sure what you are eating to obtain the calories. For me, I find that if I have a lot of sugary food or caffeinated beverages I get in a cycle of ups and downs during the day. I feel great briefly but then I crash. I would describe it as lethargic too the cycle I can get in when my diet isn't quality. So, that would help us know if you shared what you are eating. I also have just found that for myself, taking a good multi vitamin helps with my energy. I'm not a huge vitamin person but this is something I did personally notice. Most dietary changes too take about 2 to 3 weeks to stabilize as during that period, our body is adjusting. Giving up sugar or caffeine for me is like giving up drugs. Ha, but really. Headaches, irritability, fatigue all are present. I will never fully give up sugar but I cut way down. So, making smart food choices is important. I also think that exercise has an effect that many don't expect. They feel 'too' tired go exercise. Don't do it and then are even more lethargic. But if they go ahead and take time to exercise, it pays off in additional energy. I'm not a morning person. But some do report that when they exercise first thing, they then have energy for the rest of their day. I used to do a class at my gym at 9:30 am which is early for me (ha ha) and is early enough that it would be a situation of getting my kids to school, cleaning up a little around the house and then getting dresssed and then getting to the gym so really was the 'start' of my day. When this was my routine 3 times a week, I absolutely had more energy during the afternoon. So, incorporating some exercise is important if you are allowed to.
Since you say you don't gain weight no matter what you do, I agree with Barb that it would be smart to investigate this to rule out any issues. We looked into graves for my son upon the suggestion from one of his coaches. He IS very thin but he's a competitive runner who does over 100 miles a week, so it is hard for anyone to put on weight with that. There are other symptoms of graves that might include fatigue and irritability, increased anxiety, issues with sweating, mild tremor, bulging eyes. A blood test will help identify this if it is the case. Some just have hyperthyroidism as well. https://www.mayoclinic.org/diseases-conditions/graves-disease/symptoms-causes/syc-20356240 It's worth ruling out.
You are currently a BMI of 18.61, and 3 pounds lower and you'd be underweight. My guess is that you have a very healthy metabolism and I would consider eating more healthy fats, such as olive oils in salads, coconut oil with your eggs. Doesn't sound like you eat much junk foods which contain an enormous amount of inflammatory seed oils such as canola, vegetable oils. I'm a retired pediatrician, and not providing medical advice, but would say give yourself a congratulations, but consider increasing your healthy fats to your diet and see what happens over a month... Keep in touch with us. All the best.