I had opposite experience by switching to "eat all the meat you can" protocol from "hardly eat any meat at all" protocol.

There is probably nothing harmful in animal meat per se, except its low in some nutrients (so you have to eat organs or supplement). I find highly improbable that high meat usage can cause disease as most animals have similar evolutionary grounds and if meat protein is not poisonous to them, its not for us too (the same goes for saturated fat). The other thing is how animals are raised, but AFAIK most of the industrial toxins accumulate in fat, not lean meats, and that might be a problem for some people. Highly processed meats should be avoided.

So, you may have problems with

• High LDL cholesterol. Its highly genetic stuff and you probably shouldn't be concerned about it. If you are, test it, do not guess it.

• High protein load - its very hard to eat enough meat to get protein toxicity, if not impossible, but still its worth mentioning.

• If you have kidney problems, lots of protein is not advisable.

• Lack of Vitamin C if you are not eating enough plant stuff along with meat (VLC or low carb)

Vegetarian diet is not healthy on the long run, initially it might have positive effects, probably due to caloric restriction which is what most vegetarians probably end with (OK, it might be done correctly but its highly unlikely). First, you risk B12 deficiency (only analogs in plants), and low cholesterol is actually more harmful then higher one. Iron might be problem too (no oxigen and brain suffer first). Vitamin K2 (essential for teeth, proper calcium metabolism, coagulation) On the positive side, lack of protein will induce xenophagy which helps clear intracelular parasites (the same anorexic protocol body engage with some viral infections) so thats why its good on short run. The other positive effects are probably due to general "higher awerness of the food you eat" since beeing vegetarian is more like beeing in sect for most such people then anything else.

Lightness with the meat absence is probably due to failure of digestive system or improper food combining - you need to have good HCL levels in order to digest it well, plus it stays there in the stomach long time after eating. If you remove wheat and/or too much starches (potato, rice) you will fill light again, given that your GI is good - no dysbiosis, h. pylori etc.

I don't know what "more positive outlook of life" means. Is it lack of depression or lethargy? If that was the problem, low cholesterol, B12 and lack of fish meat or oils will make the things worst. Plant industrial oils will do that too (trans fats and industrial toxins) and soy is particularly harmful.

So, the only real problem might be lack of Vitamin C, depending on your other food habits, which you should supplement anyway with pure ascorbate acid powder unless you eat kidnies, adrenals, brainz, and eyes :) Vitamin C is required for dopamine synthesis which might influence your 'outlook'. Lack of it also impairs immune system giving chronic infections way to go. Depression is linked to infections. On the contrary, adding Vitamin C to protein meals will boost its absorption as some of it uses the same receptors as glucose (GLUT4, promoted by insulin, promoted by protein) and without glucose higher rates of C absorption are achieved which may promote infection clearance hence leading to better brain states. Industrial toxicity can cause bad fillings and C is potent toxin clearer. It can also potently fight toxic hard metals from fish meats, with some of them accumulating in the brain and causing depression.

=== EDIT ===

There was additional question in the comment, I believe something like how vegan diet can produce such great feelings biologically.

• As I mentioned, it could be due to xenophagy at least at the beginning.
• Vegan diet is high in carbs. Carbs might have seratonergic effect by boosting L-Tryptophan uptake which is precursor to serotonin.
• Carbs influence the opiate pathway. This means they can reduce pain which leads to happiness. Other then that, they change functioning of dopamine system since simple sugars are addictive (and all are simple, once amylase and friends do their work). Removing them will produce irritation for some time, until dopamine receptors are upregulated. This is actually one hypothesis of obesity and possible explanation of low carb flue. Also, plants might have some not-yet-understood chemicals that influence brain workings since their genome is large and they have to produce bunch of stuff from limited input.
• High w-6 PUFA are boosting anandamide synthesis. This one is responsible for "blissfull" state of the mind (THC from marijuana does the same thing, but better).
• Fasting, which is typically how vegetarian protocol is delivered religiously, at least in this part of the world most of the time means calorie restriction which promotes ghrelin synthesis. Ghrelin is addictive, boosts your intelligence and power, at least for short time.
• Placebo or positive thinking can influence brain state.
• Religion. Thinking that we are supposed to eat plants means that plants are not there to fight for their survival like everybody else but are of divine origin. Happy animal faces in minds of non-animal eaters add to that. I don't mind that, except its irrational - plants are living creatures too, not eating animals will not change anything and life doesn't function that way [if you really want to save animals, evolve enough so you can actually go to other planets and live them alone and/or produce your food synthetically and not starve yourself]. If elephant on Mars makes you happy, I am happy, just don't make me do it or call it scientific.

Humans are the only animals on the planet who feel "guilty" about anything. Perhaps your friends feel sorry for all of the cute, delicious animals, and they feel as though they're racking up good karma points by not eating them?

As for their sense of "lightness"--perhaps it's because they're not eating enough calories every day. Or, because all of that insoluble fiber is making them have to poo 3x/day, lol. I guess I'd feel pretty light too if food never stayed in my body long enough to digest properly.

i was vegetarian for 10 years and probably pushing for diabetes. If you avoid meat, you are inclined to raise your insulin levels over time. Soy is out, it's processed and robs the body of minerals, so do grains, mineral deficiency makes the body become unable to naturally detox which makes you feel junky. most women are protein deficient already bc they count every calorie, Just the nutritional imbalances alone will impact mental health in a negative way.

Going low carb has increased my energy and helped me fall in love with fitness. The proper work out will increase growth hormone naturally, the anti-aging hormone that keeps you feeling good and happy!

Animal protein has every vitamin, except C which is easy to get from other sources.

I'm sure I'm not the only one who had a lot of trouble with depression on a vegan diet. The brain is pretty hungry for minerals and fats that are only found in animals.

But I got caught up in the belief that doing a religious fast from animal products was a good idea some time ago again and I felt just awful. I had random bouts of crying all the time. I honestly feel like some religions encourage such fasts because of a misplaced gnosticism and also because you feel lightheaded and that can make one have mini-hallucinations while meditating or encourage that "Oceanic feeling" of infinity that Freud talks about. It also gives you a feeling of belonging and there is a placebo effect as well. If some guru tells you how great he feels and how it strengthens his meditations/prayers and you admire him...well you are liable to feel things because of that rather than because a no-animal diet is actually more spiritual.

Everyone is different though and if you do decide to devote yourself to being a monk, I think your diet matters less since life is more relaxing. And you know, everyone is different. My uncle has been vegan for quite a long time and it works for him. Other people...not so much. There are more ex-veg*ns than the veg movement would like to admit, plus the people who decide to become pescatarians.

Often you will feel more positive at first because you feel like you are doing something for the world, when in reality when it comes down to the economics of it, you aren't. Realizing that gave me the freedom to let go of the idea that veganism was doing something and to start eating to support my brain.

When I was a vegetarian, about 15 years ago, I gained about 20 lbs, became hypothyroid, and was anxious and stressed out, not to mention "munchy" all the time. Like, All. The. Time. Since becoming paleo/primal about a year ago, I've been more upbeat, even-tempered and optimistic.

My intuition about this stuff is that people's expectations about what you feel like after you eat meat are out of line with reality. Your friends expect a meat-heavy meal to make them feel weighed down because that is consistent with cultural truisms. But if they're anything like pre-paleo me, they're not paying much attention to how they actually feel after certain types of foods. If they did, in a systematic fashion, it's probable that they'd realize they're less likely to feel bloated/sluggish/weighed down after a meat/veggie meal vs. a grain/veggie meal.

(It is counter-intuitive for others probably. They assume that the vegetables digest through and the meat creates a heaviness. In my experience the veggies bloat me and the meat “lightens” me.)

Also paleo does not emphasize a lot of meat for all people—some people eat higher fat, a little meat and a ton of veggies—or any combination of macros.

As far as mental and spiritual…for me I get a brain fog without meat and animal fat—something is not working so well.

I wouldn't trust a word of it. Someone telling me they feel better eating this or that is as good as someone telling me they can fly...the human brain can convince itself of almost anything. This is especially true when someone "changes their life" for their "spiritual well-being" or for "a political cause," or even...no it can't be, "for health."

I would instead look at their face. Is it bloated? Look for signs of inflammation, watch their posture and body language. Are they overweight? Flabby? Gassy? Sick all the time? Sniffly/sneezing/etc...

I find that most people who poo-poo the Paleo WOE, when really observed, usually fall into the above categorization, regardless of their claims that "I'm drinking this muscle milk, and only eating quinoa and I feel so good right now, -giggle giggle-!" or "I'm not eating right now, I'm on a cleanse...I have to clean out my system." Try and catch people in candid moments, and you can usually see their feelings written plainly on their faces. It's what I call "real face." Some of the "happiest" people have incredibly depressing "real face."

I think there is a connection between whether or not people eat meat and their mental well-being. My experience (and the little research I've done) shows that a person's physical health/well-being directly affects their mental well-being.

As eating meat (or animal products...including fish) is an integral part to a person's full health, as I understand it, I can't imagine someone being in full physical or mental health when they refrain from eating it.

I do not know many long-term vegetarians, so my observations might not be universal. The ones I do know avoid animal products for a mix of religious/ethical reasons and also believe they are eating the healthiest diet that is possible.

They profess the same feelings of lightness and overall mental well-being that you say your friends speak about. Although they profess these feelings, they often have mood swings that remind me of sugar highs/lows, they are quick to exclaim the benefits of any food choice they make yet always seem to be looking for something better (as if they secretly feel like they're missing something), they often mention they are craving sweets or can't have sweets because they have no self-control around them, and one of them becomes easily confused and angry over small misunderstandings (adult temper tantrums?).

I don't know if these actions are part of these individuals' personality or if it's caused by some lack of nutrient in their overall diets. As I said, I only know a few long-term vegetarians, but it seems odd to me that they all have similar characteristics.

Perhaps it's not the vegetarianism itself, but a combination of SAD and vegetarianism that is showing in the individuals I know who are vegetarians.

The evidence is generally that meat is calming and happiness-promoting. That is why all of the supermarket fliers have a big roast or ribs on the front http://www.aolnews.com/2010/11/10/study-says-meat-is-the-key-to-male-tranquility/ Of course if you are already biased against it then I would expect things to be different. Oftentimes you get what you expect, like lobsterman said. Also if one feels as though one is better than other people by not doing something, then not doing that can be a contributor to self-esteem.

Here is a good video on meat: http://carnism.com

Vegetarian did nothing for my physical health, well I was a snackatarian lol. Then I was dx'd with gluten intolerance and discovered paleo, yay for me!!

when i was a vegan, i felt good about not eating animals because i thought i was a murderer if i did. as the years went by, my health went downhill. i eventually realized that it was either me or the animals, and i chose me. does that make me selfish? i'm sure some people would say so, but i now feel like i am being good to myself and that makes the trade off easier... not easy, but easier.