The ripeness of the banana can change its digestibility.
This paper is useful for addressing this claim:
From the paper:
potatoes are used as a food, the starch granules
must be gelatinized before they become susceptible
to enzymic hydrolysis (2). This resistance
to digestion does not normally cause
any practical problems inasmuch as potatoes
are not eaten raw and the starch granules are
readily gelatinized by cooking. However, the
a-amylase resistance of some raw starches may
have importance for foods that are eaten
raw-such as bananas. Experimental studies
both in vitro and in animals suggest that
banana-starch granules are largely indigestible
However, there is a study showing that green bananas were useful for diarrhea:
- Green banana and pectin improve small intestinal permeability and reduce fluid loss in Bangladeshi children with persistent diarrhea.
Rabbani GH, Teka T, Saha SK, Zaman B, Majid N, Khatun M, Wahed MA, Fuchs GJ.
To evaluate the effects of green banana and pectin (nondigestible, dietary sources of colonic shortchain fatty acids [SCFA]) on intestinal permeability, 57 boys (5-12 months) with persistent diarrhea (> or = 14 days) were given a week's treatment with a rice-based diet containing either cooked green banana (n = 19), pectin (n = 17), or rice diet alone (n = 21). Intestinal permeability was assessed before and after treatment by giving a lactulose-mannitol (LM) drink and measuring urinary recovery after 5 hr. Treatment with banana significantly (P < 0.05) reduced lactulose recovery, increased mannitol recovery, and decreased the LM ratio, indicating improvement of permeability. Pectin produced similar results. Permeability changes were associated with a 50% reduction in stool weights which correlated strongly (green banana, r2 = 0.84, pectin, r2 = 0.86) with the LM ratio. Green banana-derived and SCFA-mediated stimulation of colonic as well as small bowel absorption is responsible for their antidiarrheal effects. The antidiarrheal effects of green banana and pectin are mediated by improvement of small intestinal permeability in addition to their known colonotrophic effects.
Here is another one:
- Green banana-supplemented diet in the home management of acute and prolonged diarrhoea in children: a community-based trial in rural Bangladesh.
Rabbani GH, Larson CP, Islam R, Saha UR, Kabir A.
SUMMARY OBJECTIVE: To determine the effectiveness of green banana in the home management of acute (<7 days) or prolonged (≥ 7 days) diarrhoea at the community level.
METHODS: A cluster randomized field trial was conducted among 2968 Bangladeshi rural children 6-36 months old. Wards (villages) were randomly assigned to either a standard care group or a standard care plus green banana group where mothers were instructed to add cooked green banana to the diets of diarrhoeal children. Through a village-based surveillance system, diarrhoeal morbidity data (severity, duration, compliance) were collected for 14 days. Treatment effects were determined by analysing cumulative probability of cure by testing Cox proportional hazards models and relative risk (RR).
RESULTS: The cumulative probability of cure was significantly (P < 0.001) different in children receiving GB for both acute [hazard ratio (HR) = 0.63 (95% CI: 0.56-0.67)] and prolonged diarrhoea [HR = 0.38 (95% CI: 0.26-0.59)]. The recovery rates of children with acute diarrhoea receiving GB (vs. control) were significantly more by day 3: 79.9%vs. 53.3% [(RR) = 0.47, 95% CI: 0.41-0.55], (P < 0.001) and day 7: 96.6%vs. 89.1% (RR = 0.32; 0.22-0.46), (P < 0.001). Children with prolonged diarrhoea receiving green banana had significantly higher recovery rates by day 10: 79.8%vs. 51.9% (RR = 0.42; 0.23-0.73), (P < 0.001) and day 14: 93.6%vs. 67.2% (RR = 0.22; 0.08-0.54), (P < 0.001).
CONCLUSION: A green banana-supplemented diet hastened recovery of acute and prolonged childhood diarrhoea managed at home in rural Bangladesh.*
Those with fructose malabsorption issues are advised to avoid green bananas and instead eat ripe bananas in this paper:
Shepherd S, Gibson, P., Fructose malabsorption and symptoms of Irritable Bowel Syndrome Guidelines for effective dietary management, J Am Diet Assoc. 2006;106:1631-1639
Kyaw MH, Mayberry JF., Fructose malabsorption is thought to be a variation of IBS:
J Clin Gastroenterol. 2011 Jan;45(1):16-21.
Fructose malabsorption: true condition or a variance from normality.
Fructose exists in food naturally or as a sweetening additive. It has been thought that fructose malabsorption may cause the gastrointestinal symptoms seen in patients with irritable bowel syndrome. However, fructose malabsorption is still poorly understood, and clinicians are still uncertain of its role.
The prevalence of fructose malabsorption may be aggravated by current american diet, according to this paper:
Fructose intake at current levels in the United States may cause gastrointestinal distress in normal adults.
Thus, the bananas' ripeness causing constipation problems is totally dependent on the state of your gut flora and whether you experience gastrointestinal distress with fructose.*
Constipation symptoms are listed as:
Pass fewer than three stools a week
Experience hard stools
Strain excessively during bowel movements
Experience a sense of rectal blockage
Have a feeling of incomplete evacuation after having a bowel movement
Need to use manual maneuvers to have a bowel movement, such as finger evacuation or manipulation of your lower abdomen
Some people may have lower abdominal pain with constipation that is sometimes followed by diarrhea. Other people have pain and mild constipation but no diarrhea.
Symptoms that are sometimes present include intestinal gas and passage of mucus in stools.
and IBS Symptoms are listed as:
Bowel movements may occur either more often (diarrhea) or less often (constipation) than usual, such as having more than 3 bowel movements a day or less than 3 a week.
Bowel movements may differ in size or consistency (may be hard and small, pencil-thin, or loose and watery).
The way stools pass changes. You may strain, feel an urgent need to have a bowel movement, or feel that you haven't completely passed a stool.
You may have bloating or a feeling of gas in the intestines.
IBS and constipation have many overlapping symptoms.
Thus, it is possible that green bananas could cause constipation, if one has IBS issues/ fructose malabsorption, and apparently the current American-type diet could aggravate this type of issue.