(Note - the SCD is only part of the answer for me. I sometimes stray slightly from the diet, so don't feel my example is typical or useful in judging the SCD. There are many more glowing SCD testimonials out there.)
I have been mostly on the SCD for 1.5 years for an undiagnosed problem like leaky-gut/celiac/parasite/citrobacter with colitis. Initially it firmed my foul and loose stools quickly, which was a big relief from visiting the toilet after almost every meal. It also greatly reduced red skin bumps on legs/arms. However after 6 months I was still getting bloating/gas/rumblings from even small amounts of fruit. Also honey and homemade yoghurt (tho I never experimented much) gave diarrhea. Raw fibre from nuts, fruit skins, and non-tender vegetables also still gave colitis.
I switched to very low-carb for next 6 months which relieved bloating/gas wonderfully. However diarrhea, previously seldom, increased: heavy fat meals gave nausea and diarrhea. Cheddar and more low-carb veggies (fibre?) reduced the diarrhea to tolerable cramps. Most of this time was low-fibre tho, for the purpose of resting the colon to allow some healing from colitis inflammation/irritation.
After this my colon felt stronger with less pain. I reintroduced fruit with much less gas/bloat. I broadened my diet to be mainly peeled fruits - yellow & red pawpaw/papaya, soft rockmelon, browned bananas, pears, apples & stone fruits (raw, cooked, and canned), fish (whitefish like nile perch, & salmon), lean beef, avocado, cheddar (Farmland semi-matured, or a mild cheddar - both have less salt), and some cooked veg (carrot, swede, brocolli). I still get diarrhea from foods like butter, oils, fatty meat & eggs. Drained homemade yoghurt is now OK. Too much fruit brings gas/loose stools. Nuts still give colitis except small amounts, ground (except pine nut butter which i can eat freely). Also sometimes eat homemade cottage cheese. I also have food allergies, particularly chicken & turkey: I limit these. The SCD has my gut now fairly stable, although my range of foods is somewhat limited. My remaining problem is chronic fatigue, which persists despite my weight being normal - so I'm looking at other means to improve further. I expect the SCD will be central to whatever I do.
I have been slack with the vitamins - more off than on. In hindsight I would have taken them at SCD dose from start.
Also got rampant white scalp deposit (uric acid/calcium?) which is worse on high protein (seemingly high purine foods like mackerel & sardines). Fruit also gives itchy arms and legs. Both these conditions are helped by Max EPA.
Prior to SCD, briefly tried natural medical doctor in Sydney. But supplements like UltraClear Maintain intestinal repair supplement (with rice fibre), Uva Ursi and Paracea gave colitis. I think its the raw fibre. Testing suggestive of (Great Smokies) severe dysbiosis: Citrobacter Freundi infection (1+ on low-carb diet [which was dumb during the stool test]), no good bacteria, no secretory-IgA, low pancreatic output, no parasites, no yeast, (Live ) leaky-gut, incomplete protein digestion/sticky , (EFA profile) EFA deficiency, (standard test) high uric acid/urea, eosinophilia, IgE (i think) off the scale, gliadin part positive (the part that takes longer to return to normal) some months after gluten-free, and endomysial -ve some year(s) after gluten-free, (2 standard stool tests) negative
Fatigue is now my major problem: I'm only fit for part-time work at the moment. This is despite my weight being healthy. I cant do my normal job of computer programming due to fatigue/inability to concentrate. I need to sleep long hours and wake up still tired.
More to do...
Vitamins I have taken with no problems:
A - Nature's Own Vitamin A 5000IU
A & D - Nature's Nutrition A 4000IU & D 400IU
C - Nature's Own Calcium Ascorbate Powder
C - Melrose Calcium Ascorbate Non-Acidic Crystalline Powder
B - Macro Mega B capsules
Multi - Pluravit Multi Vitamins & Minerals capsules (incomplete: no biotin or folic)
E - Golden Life Natural Vitamin E (in soya oil base) gel capsules
E - Chemline Natural Vitamin E Wheat-Free capsules
Biotin - Nature's Own Biotin 300mcg capsules
B12 + Folic - Nature's Own B12 100mcg + Folic Acid 400mg? tablets
Magnesium - Nature's Own Amino Acid Chelated Magnesium 500mg tablet
EFA's - Nature's Own MaxEPA 1000mg gel capsules
All hard tablets were crushed into a powder.
Magnesium (& Potassium) - brand? Caused mild colitis.
ChemWorld Vitamin Big B with C Complex - suspected of causing red skin spots that i get with gluten and starch ingestion. The label reads "no added ..." rather than "free from ...".