It may not be a helpful answer, but I'd really recommend trying to look beyond weight as the only measure of health. I'd also be cautious of drawing conclusions about what other people are eating or doing when you don't see them.

I'm sure there is a genetic variation, but I also reckon that there's a big influence in your early life and if you set off down a wrong path then it can be hard to come back. But your body is capable of being healthy, so long as you don't impose too many constraints on what healthy means.

The key to eating whatever you want and staying thin is to change what you want.

You said 'young guy'. This is the key. I find that some people can get away with eating anything they want and stay very lean while they are young - up to about 30. Once people hit that age and they continue their all-you-can-eat diet they start ballooning like pigs. I think that unless you naturally have high metabolism in young age, you can't make your body to behave that way later in life.

I'm 50. Come from a long line of short, round, plough pony looking women. Somehow my mother and her sister seemed to escape that, but my mother died of cancer at age 54. My grandma spent a lifetime at Tops and WW and probably weighed 300 when she died with heart problems, dementia and Parkinsons.

At one time I could eat whatever I wanted, probably up until about age 28 or so. I started packing on pounds when I went back to college. Then I kept on weight with every child I had. Just a side note, my teenage daughters brought out my wedding dress when we had our 25th anniversary. My 12 year old was the only one who could wear it.

Was I healthy back then? No! I couldn't sleep because I drank too much caffeine. I also had chronic urinary tract infections from all the soda I consumed. I had lots of dairy, sugar, white bread and had problems with rebound hypoglycemia and PMS. I have degenerative disc problems which probably were not helped by my former bad habits.

I didn't hear about Paleo until recently, or I'd have done it lots sooner. It took me a year to lose 25# with weight watchers and I did it faithfully and worked hard at the gym. I started Paleo on Jan. 9, 2012 and lost 10# already and I could definitely use more exercise. But I've lost 4" off my waist, 3" off my hips and inches in other places as well. On two consecutive doctor appointments I went from a BP of 142/84 to 112/82. I reduced my migraine headaches by about 75%. The doctor told me to keep on doing what I was doing.

I agree with what was said above, to make health the goal. Right now I'm just over 200#. I'm working on weight loss but I want overall health. I don't have diabetes, high cholesterol, high stress level, cancer, heart disease, sleep apnea, GERD, Irritable bowel, or any of that. I've been married 27 years and my husband loves me for who I am, and not for who he fantasizes about. I enjoy camping, archery, canoeing, spending time with my kids and grandkids, I have an almost full time job, and I do step aerobics at 5:30 AM before work, so I'm not a couch potato. I suppose somebody seeing me might pigeonhole me into some type. I think genetics plays a role, but I don't believe that I'm stuck there. But if I do "get thin" I don't want to go back to "eating what I want" I want to stay healthy and be around for my hubby, kids and grandkids as long as I can.

I'm a small town girl and don't envy anyone who lives in NYC. Do real people live there too? ;)

I gain weight really easily. Right now I'm 5'3" and about 110 lbs. My older sister eats nothing but SAD foods and she's 4'11" and barely 100 lbs. And all she does when she's not working as a nurse is sit in front of the TV noming on Lay's potato chips, and Dreyer's coffee ice cream, and Stouffer's frozen dinners. And she doesn't gain a single pound. She has a flat tummy, slim face, etc. We're completely different--heck, we look nothing alike. When I ask her if she wants some of the food I've made, like beef ribeye with onions and mushrooms cooked in coconut oil, she goes "ew I don't wanna eat that healthy crap" and then proceeds to stuff her face with Krispy Kreme donuts or a meal from Burger King.

To me, weight really doesn't matter anymore. Sure, I may weigh more than my petite sister, but here's the kicker: my arms are more toned, I get complimented on my shapely legs, I could probably sit on my ass for a year and still beat her in a 5K, and I fill out clothes better (she has a hard time finding clothes that aren't too big). Plus, she has high cholesterol (so do I, but unlike her, I have a really high HDL and low triglycerides), supraventricular tachycardia for which she takes medicine for, urinary tract infections, and several other vague symptoms.

You say you want to be "that girl who can eat anything and not worry so much about it?" Trust me, you will be worrying about it. What's the point of looking pretty if you're just gonna die young? Being able to eat anything you want and not gain a single pound is cool, and I admit, I envy those who are that genetically blessed. But that is not an excuse to eat deep fried Oreos on a regular basis.

I've actually gotten thinner as I've gotten older, as I've trained my body to like healthy stuff like nutritious food + exercise.

I have noticed something similar to what you describe in terms of how much muscle people can put on, and how easily they get injured.

I definitely think some of it is predisposed and some of it is behavioral. I have bigger muscles than someone who doesn't work out, but much smaller than hubby (who doesn't work out as much as I do).

Well, I'm thin and have always been thin, and live in NYC. I work very hard to stay that way, watch what I eat & how much I eat, walk A LOT, exercise.

But when someone asks me what I do to stay thin and fit, I of course say nonchalantly "oh nothing, it's genetic and I'm just lucky". Who wants to admit they work so hard for their health, fitness and appearance?

I'm sure there are people who are just naturally thin, but probably not as many as we think.

I had a similar question here that may be of interest to you: http://paleohacks.com/questions/86511/are-we-pre-destined-to-our-genetic-body-type#axzz1n3jFIB00

Obviously, genetics play an enormous role in our body shape/size/weight. Poor health choices early in life could also be a factor (I was a vegan during my adolescence which probably did some damage...)

HOWEVER, I do believe you can achieve any body type with discipline/hard work. The question is how much, and is it worth it. What I'm learning now is to redefine my goal so that all the hard work I put in (which is alot) is in-line with my nature.

I've always wanted to have a super lean frame, do yoga, eat light, and never lift a weight. I never cared or even tried to bulk up. But I think my body is designed to put on muscle, it seems to come natural for me, so why try and fight it? I changed up my routine a bit and already see a difference.

The work and effort is still there, just in a different way.

I can't speak for you and your goals, but I live in NYC too, and if it's any solace, I bet the majority of the girls/guys you see who have the body of a model, probably have the brains/substance of one too :)

We all wish we could eat anything and not worry about it!

Of course I love meat and fruit and veggies, too, but I really wish I could eat anything (ice cream!!!) and still be slender, physically fit and in perfect health. But the truth is no one can. Those diets you describe might not make your friends fat, but they sure aren't making them healthy. Our culture has created a bunch of crap foods that taste fabulous to our ancestoral genes and that most people eat. It's really hard to say no over and over again. I think you've just got to believe that the health benefits (and not just how thin you are) are worth it to you.

I am not strict Paleo -- more like 90% -- but the health benefits so far have been amazing for me. As much as I wish I could eat anything, I continue to eat Paleo because I believe it's the healthiest way for me to eat and I really want to be healthy.

I was just like your best friend - could eat anything, and did, for years. I am a natural ectomorph as is my whole family, always thin and lean. I did a lot of running, too, for what it's worth, but I couldn't imagine doing a pullup or a pushup. But after I hit 45, I noticed my weight starting to creep up, my blood pressure also. My skin wasn't so great, either. It does catch up with everyone eventually. I'm only now cutting sugar and SAD foods, and I wish I'd done it so much earlier because I feel so much better. Think how much healthier I would be if I'd done it at 25 instead of 45? You're lucky!!

I can relate with your frustrations! I will say though...the same thoughts have led me recently to the whole weight set-point issue. I KNOW I naturally gravitate to a certain weight. People think I look slender at this weight even though it's 10 or so pounds over what I'd like. Everytime I go below it I DO get hungry and fall off track. I've been reading gnolls.org and Guyenet and Becker's Getting Stronger.org to try and discover the "secret" to getting a little leaner and also the hyper-palatable issue as it relates to me.

Anyway...yes I do wish I could eat whatever I'd like and not worry about it. But I do firmly believe that slim people end up with other ailments when they're living on bread and twizzlers. I think their teeth, joints and bones suffer. I believe their moods are sometimes worse. I also think they have a lot of stomach problems. The two very slender people I know are both on Prilosac. So yes they DO eat whatever they want and then they pop a pill.

I guess what I'm saying is...maybe we should count our blessings? We'll reap some benefits even if we have to eat the homemade coconut ice cream instead of the Ben and Jerrys. : )