Yogurt
Yogurt is cow's milk usually fermented using two synergistic bacterial species Lactobacillus delbrueckii subspecies bulgaricus and Streptococcus thermophilus. The amount of fat and even the bacteria used to ferment the milk may vary from study to study. The presence or absence of living bacteria must be kept in mind when evaluating studies which employ yogurt. There are few randomized studies in which yogurt (as opposed to lactobacilli or yeast in pure form) is administered in the developed world. Beniwal et al gave 109 American patients 227 grams of vanilla flavored yogurt twice daily for 8 days if they were receiving intravenous or oral antibiotics [32]. The yogurt contained L. acidophilus as well as L. bulgaricus and S. thermophilus. The control group of 97 patients received no yogurt. The mean number of days of yogurt intake was 6.6 days. Diarrhea as defined by 3 or more loose bowel movements per day was reported in 13% of yogurt ingesters and 23% of those not eating yogurt. The duration of diarrhea was not significantly decreased. Israeli soldiers eating yogurt with living L. casei did not have fewer diarrheal episodes than those soldiers eating yogurt containing no living bacteria [33]. The study had approximately 250 soldiers in each arm and the mean incidence of diarrhea was 14%. If there were an undetected effect, it would have had to be a small one.
While not a nutritional therapy per se lactobacilli are used by those who do not tolerate yogurt or find it unfeasible. Lactobacillus casei strain GG was administered in capsules (not yogurt) to American children receiving concurrent antibiotics. The living bacteria reduced the percentage of children with diarrhea (defined as more than one liquid stool/day) from 26 to 8% when compared to an inulin placebo [34]. A Finnish study using Lactobacillus strain GG found that recovery from diarrhea was one day quicker on average in those children that received living bacteria in capsular form as opposed to children who received a placebo [35]. The same Lactobacillus casei strain reduced the incidence of antibiotic-associated diarrhea in Finnish children from 16% to 5% [36].
When the effect of the same GG strain was used to prevent antibiotic associated diarrhea in American adults, the results were disappointing. A study analyzed 268 hospitalized patients and found almost identical diarrhea rates and frequencies in those receiving the live bacteria and in those receiving a placebo [37].
The "non pathogenic" yeast Saccharomyces boulardii has been shown to reduce antibiotic-related diarrhea in hospitalized Americans when administered in capsule form [38]. Enthusiasm for this therapy has waned due to reports such as that of 7 French patients who developed fungemia after ingesting this yeast in the setting of an intensive care unit [39].
The ability of yogurt or lactobacilli to prevent diarrhea is still in question. Should yogurt contain living bacteria? Do the species of bacteria matter? Can yogurt be made with skim milk? Does the flavoring matter? How much yogurt should be ingested? These questions probably will never be answered. At present, yogurt cannot be recommended as a proven method of diarrhea prevention.
Table 1 summarizes the effects of various nutritional interventions on infections in the general population and in institutionalized people.