A reader asked, “Why do many woman with ME report a worsening of their symptoms just before or on the first day of their periods? (And why for me does fasting during this time seem to help mitigate the effects?)”
This is actually a very good question because the incidence of CFS/ME/FM/IBS for women is much higher than men.
- “The female to male incidence rate ratio of CFS/ME was 3.2″  i.e. 3.2 women for every 1 men.
- ” The incidence rate varied strongly with age for both sexes, with a first peak in the age group 10 to 19 years and a second peak in the age group 30 to 39 years.”
- “Prevalent CFS and/or FM were more common among women, adults aged 40 years and over, those with lowest income, and those with certain risk factors for chronic disease (i.e. obesity, physical inactivity and smoking).”  some of these may be consequences of CFS, for example income!
The obvious suggestion for this are hormone shifts. The literature supports an association.
- “Our results indicated significant relationships between interleukin-8 and ratings of pain catastrophizing (r=0.555, P<0.05), pain anxiety (r=0.559, P<0.05), and depression (r=0.551, P<0.05) for postmenopausal women but not premenopausal women (r,0.20 in all cases).” 
- Age-of-onset of menopause is associated with enhanced painful and non-painful sensitivity infibromyalgia.  ” These results suggest that an early transition to menopause (shortening the time of exposure to estrogens) may influence pain hypersensitivity and could be related to aggravation of FM symptoms.”
- “Nevertheless, it is likely that hormone disorders are involved in the symptoms genesis of most middle aged women with FMS.” 
- “The studies on the influence of the hormones on the symptomatology of the patients with fibromyalgia have not managed to establish a link of causal union between the hormonal climacteric decline and the development of the painful syndrome. Nevertheless, there are studies that relate the pain, the anxiety and the depression to the level of sexual steroids.” 
Now to the question of menstrual cycle. Since the model is a disruption of the microbiome, we can infer that studies dealing with IBS, IBD and CD are likely useful.
- “There were no significant differences in follicle stimulating hormone (FSH), luteinizing hormone (LH), estradiol and progesterone levels in both of menstrual phases of patients versus controls.” 
- “Mean values for progesterone and all of its metabolites were higher in CFS patients, the most marked being a 2.3-fold elevation in isopregnanolone (3beta,5alpha-tetrahydroprogesterone; p < or = 0.001). Progesterone levels were correlated with those of its metabolites, but even after controlling for progesterone by ANCOVA, isopregnanolone levels were still elevated (p < or = 0.001). These elevated levels of isopregnanolone could not be attributed to medications (antidepressants and anxiolytics).” 
- Menstrual cycle, sex hormones in female inflammatory bowel disease patients with and without surgery.  “the majority of healthy women also complain of worsening of GI symptoms either during the premenstrual or menstrual phase. Despite conflicting evidence, studies suggest that sex hormones may increase GI transit time during the luteal phase. Similar phenomenon is also observed in women with underlying inflammatory bowel disease (IBD).”
- “Gender-related physiological variations in gastrointestinal (GI) symptomatology have been observed in women of reproductive age. Many women experience cyclical changes in GI symptomatology during their menstrual cycle, particularly alteration in their bowel habits. Physiological studies of healthy women during the menstrual cycle showed a prolonged GI transit time during the luteal phase, either in the oro-cecum route or in the colon. Worsened GI symptoms, such as abdominal pain, bloating or diarrhea are observed in patients with irritable bowel syndrome (IBS) during menses…Women with inflammatory bowel disease (IBD) also have exacerbated symptoms during menses; however, it is unclear whether this relates to physiological variation or disease exacerbation in IBS or IBD. Studies examining the association of the menstrual cycle and GI symptomatology in patients with IBS or IBD, have not yet clarified the underlying mechanisms.” 
- “Changes in menstrual function occur frequently in the year before IBD diagnosis; therefore, screening for menstrual irregularities should be considered in women with newly diagnosed IBD.” 
- “Symptomatic improvement in cyclical IBD symptoms was reported by 19% of estrogen-based contraceptive users and 47% of levonorgestrel intrauterine device users. Only 5% of all hormonal method users reported symptomatic worsening.” 
- “Premenstrual symptoms were reported by 93% of all women but statistically more often by patients with CD (p < 0.01). CD patients were also more likely to report increased gastrointestinal symptoms during menstruation ( < 0.01), diarrhea being the symptom reported most often. All disease groups had a cyclical pattern to their bowel habits significantly more than controls (p=0.01).” 
- “Premenstrually, women with CD (46%) vs. UC (26%) were more likely to report worsening of their IBD symptoms (P = 0.0007), but there was no difference between CD (47%) and UC (39%) for reporting worsening during menses (P = 0.24).” 
Putting it all together
The reader’s observation appears to agree with studies. The increased in (prolonged) GI transit time means that bacteria can work more on food (think of grape juice fermenting) which results in additional production, which I term “double fermentation”. Fasting means that there is less food to “double ferment” and thus reducing the worsening of symptoms. Decreasing GI transit time (somehow) should also help.
- ” No known therapy is highly efficacious, safe, and cost effective for treatment of slow-transit bowel disorders.”  This review did report B. lactis HN019 being the most effective probiotic in those reviewed. This probiotic is available in UAS Labs UP4 Probiotics Senior on Amazon.Com for $24.00 (On Amazon.co.Uk it is an outrageous £64.45)
We did find a study reporting that using a levonorgestrel intrauterine device appears to reduce symptoms in almost 50% of patients.
The cause appears to the prolonged GI transit time happening with menses. This results in an increase of symptom-causing chemicals by the bacteria. Fasting is one approach to this issue. An alternative is to try to decrease the transit time.
Whether this pattern is seen, or explanation works for IBS-D, IBS with diarrhea , is unknown.