I generally recommend against taking Lactobacillus probiotics. There are two reasons:
- They will not repopulate your microbiome — they will be rejected just like an organ transplant. Most are eliminated in a few hours and literally nothing is found the next day.
- They produce metabolites and antibacterials which will often suppress populations that you are low in.
On the flip side, I am in favor of feeding your native lactobacillus and bifidobacterium. The question is what helps them to grow????
LATEST INFORMATION (Constantly being updated)
There have been many studies on ITF,FOS,GOS etc, but results tend to be inconclusive [British Journal of Nutrition review]
I came across this 2017 study which compare the impact of three different types of protein source on bacteria.
The first table is shown below. It is very interesting because back in 2000 there was great interest and many reports of improvement. The thinking then was that it helped by providing glutathine levels [see Dr Cheney’s note from Oct’1999]. It seems that there may be an additional/alternative mechanism involved: increasing lactobacill and bifidobacteria (something off the radar of researchers back then)!
- ” Whey milk had a strong prebiotic effect on the gut microbiota …, showing a significant increase of Bifidobacterium (p < 0.05) with cow, sheep and mixed whey and increase in the Lactobacillus group, ” 
The second table is interesting because it does not list lactobacilli but lactic acid bacteria. Bacteria that produce lactic acid (which appears to be high with CFS patients).
A visual may help:
Pea is a pulse which I have mentioned before.
- “DNA microarray results suggested that feeding Pea Fiber diet inhibited 77% of genes (40 downregulated and 12 upregulated genes) related to colonic cancer, immune response, and lipid metabolism, involving in signal pathway such as intestinal immune network for IgA production, peroxisome proliferator-activated receptor signaling pathway and nutrient metabolism-related pathways. ” 
- ” The glycated pea proteins affected the growth of gut commensal bacteria, particularly lactobacilli and bifidobacteria, whose levels increased significantly.” 
- “The Firmicutes/Bacteroidetes ratio was reduced with oligofructose , yellow pea fiber , and yellow pea flour” 
- “Pea Fiber significantly decreased the plasma levels of isoleucine, leucine, lactate, and pyruvate as well as the urine levels of allantoin, bile acids, and trigonelline. Wheat bran Fibre significantly increased the plasma levels of acetone, isobutyrate, lactate, myo-inositol, and lipids as well as the urine levels of alanine, lactate, dimethylglycine, N-methylniconamide, and α-ketoglutarate. ” 
I have written about whey before (as source of Glutamine) and Whey, Colostrum and Goat Milk June 2017. Today, we need to look at Whey as the ideal food to increase Lactobacillus and Bifidobacteria.
IMPORTANT: We are talking about cow, sheep whey NOT soy whey or vegetable whey. We want the simplest ingredient list for it (no favoring or additives). Beware of Emulsifiers! Examples (not a recommendations) Wild Whey (from Australia)
, Naked Whey, and the favorite back in 1999, Imunopro.
Did whey cure anyone back in 1999? My memory is that there were a few that improved sufficiently to return to work, many that found some improvement, and a few that reported no effect. IMHO, the bad (overgrowth) bacteria need to be reduced concurrent with whey supplementation. Whey is not a cure by itself, it is fertilizer to help remission.