After a month-long diet of (almost exclusively) eggs, ground beef, and liver, I'm sure that vegetables play some role in digestive health.
Why does eating vegetables make me feel good?
Soluble fiber? Folate? Nitrate? Some other micronutrient I'm missing?
Could be the vitamins and minerals, could be the antioxidants, could be the fiber, or could be (and probably is) some synergistic effect of all three. Check out Michael Pollan's "In Defense of Food." The point he makes is this: every time we think we've "solved" human nutrition, we later found out there was something we were missing. First it was the discovery of macronutrients in the mid-1800's, and so conventional wisdom of the time said, "as long as you're getting enough protein, you'll be fine." But people weren't fine--scurvy is a good example. Then scientists discovered vitamins, and said, "okay, okay guys--this time we've got it." But it turns out that's not the whole answer either. The latest cure-alls are antioxidants, fiber, and omega-3's. All good things, admittedly, but how good are they individually and how much does the whole package matter? Until that answer materializes, I will keep eating a rainbow of fruits and vegetables, because there's something going on there that's clearly working.
Vitamin C is a candidate http://www.wellnessresources.com/health/articles/vitamin_c_boosts_mood/
And now what have we learned? Don't go on restrictive diets that mess with your noggin, that's what. Glad you're feeling well.
For most people, extreme eating just isn't ideal. A sensible mix of meat, vegetables and fruit makes the most sense for a lifestyle, as opposed to a diet.
If you binge on junk food (as I used to) you won't feel good. If you choose vegan, that may not agree with you. If you choose fruitarian, that may not agree with you. If you go meat only, that may not agree with you.
Vegan, fruitarian and ZC each have people who swear the approach saved their lives, but I consider them all hardship diets we may adapt to--or even thrive with--for the short term but may not find optimal for a permanent lifestyle.
It's all about evolution. Our ancestors had periods of time when then could only eat meat, and periods of time when no meat was available and they ate mostly fruits and veggies. But this was only temporary, and over the long run their diet consisted of all the food groups, not just one. We're adapted to eating meat and veggies, not just one or the other like many animals are, that's why we have a shorter small intestine (like carnivores) and a longer large intestine (like herbivores). If you weren't eating veggies for fruits then you weren't getting vitamin C, which is needed for synthesis of neurotransmitters that improve our mood. It's not necessarily just veggies that are making you feel good, but probably any carbs. Carbs allow tryptophan to get into the brain, and it's converted to serotonin, the neurotransmitter responsible for making us calm and having a stable mood. Don't forget that good bacteria in the gut feed off of the fiber in veggies, and there's researching showing a lack of good bacteria can lead to anxiety and depression.
Absolutely. I became grain and Dairy free, and for the time being I am easy on protein until my gut heals, but I just ate a big plate (80%) of spinach with a little bit (20%) of chicken, and I feel so good. Not too full, and happy.