I wrote about d-ribose in a post from 2012. I recommend it strongly then. Dr. Myhill writes favorably on her website – “Therefore I recommend that my CFS patients use 5 grams (1 scoop) three times a day”.
- “Ribose was added to the existing treatment regimen of a woman with fibromyalgia, resulting in a decrease in symptoms.” 
- “D-ribose significantly reduced clinical symptoms in patients suffering from fibromyalgia and chronic fatigue syndrome.” 
A reader asked me today “Is d-ribose bad for leaky gut and candida?”. I can understand the logic leading to the question:
- Sugar is bad for leaky gut and candida.
- D-Ribose is a sugar.
- Thus D-Ribose may be bad!
The fallacy is that “All sugars is bad” is an over generalization! The statement is true for normal household sugar, we need to be careful not to extend this without evidence.
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” These excretion patterns correlated well with the excessive oral ingestion of dairy products, artificial sweeteners and sucrose. Eliminating excessive use of these foods brought about a dramatic reduction in the incidence and severity of Candida vulvovaginitis.” 
According to WebMD, “Ribose is a kind of sugar that is produced by the body. It is used as a medicine… it has also been used to improve symptoms of chronic fatigue syndrome (CFS), fibromyalgia, and coronary artery disease. ”
WikiBooks writes ” D-ribose supplements improved their conditions [CFS,FM] because it helps the patients produce more ATP in the body, because their body cannot produce a sufficient amount of ATP needed…D-ribose is a molecule that is naturally produced by the human body and is not found in food sources. However riboflavin[B2], a component of d-ribose that helps aid in the production of d-ribose, is found in a plethora of food… Convert B6 vitamin into a form the body can use.”
According to Wikipedia “In biology, D-ribose must be phosphorylated by the cell before it can be used. Ribokinase catalyzes this reaction by converting D-ribose to D-ribose 5-phosphate. Once converted, D-ribose-5-phosphate is available for the manufacturing of the amino acids tryptophan and histidine, or for use in the pentose phosphate pathway. The absorption of D-ribose is 88–100% in the small intestines (up to 200 mg/kg/h)”
Answers to the Questions
- If almost 100% is absorbed, then it feeding candida is very suspect. I could find nothing supporting that it increases candida.
- Reduced levels of histidine is associated with IBD flares  as is Tryptophan , both would be expected to increased with d-ribose. So reduced leaky gut would be expected from adding d-ribose.
There can be side-effects, it is used by E.Coli (low in CFS patients) so a shift in the microbiome may happen — which could produce diarrhea, stomach discomfort, nausea, headache. When you add it, add is slowly!
D-Ribose continues to be on my recommended list — especially with Mutaflor (E.Coli Nissle 1917) . It is on my frugal list of supplements – although I cite just 1 gm/day instead of the 15 grams/day of Dr. MyHill ($66/month).