The gut microbiome is an essential part of the human organism, as has become abundantly clear from much research carried out over the last few decades. The International Scientific Association for Probiotics and Prebiotics declared several strains of probiotic bacteria to have definite health benefits, and fermented foods containing these organisms are said to be beneficial to health as a result.
However, since these do not come under the purview of drug regulation, the food industry is free to apply labels of varying accuracy regarding their benefits and the types and concentrations of probiotic bacteria they contain. This includes claims about the number of colony-forming units per gram (cfu/g) and viable bacteria content. Such claims do not have to pass the scrutiny of the US Food and Drug Administration (FDA).
A recent study in the journal JDS Communications reports the results of an analysis of five brands of kefir on the US market, indicating the need for stricter regulation of this field.
Mechanisms of benefit
Probiotics may produce health benefits due to their immunomodulatory functions, antimicrobial production, favorable interactions with host microbiomes, enhanced epithelial barrier integrity, and the production of enzymes required for normal metabolism. However, none of these apply to fermented foods such as kombucha and kefir.
Importantly, it is not necessary to record any definite health benefit from the consumption of a particular fermented product in order to sell it as a beneficial food. This means customers bear the burden of making sure they are spending wisely on fermented foods that actually can improve their health.
Kefir is a fermented drink made by fermenting water or milk with kefir grains containing bacteria and yeast. It is a low-cost health food, and the promise of improved health has lured many people into using it as part of their daily diet.
Indeed, kefir consumption has been associated with lower levels of fasting insulin, a drop in serum lipids in premenopausal women, lower inflammatory markers such as erythrocyte sedimentation rate (ESR), and lower C-reactive protein (CRP) levels in patients with Crohn's disease.
The study aimed at measuring microorganism density in the kefir products.
Earlier studies have shown, for instance, that almost two out of three commercial products containing probiotics do not make claims backed by research. Many have misleading content labels. This is inconsistent with the high demand for these foods. Thus, regulatory oversight is required to pick out the key microbes that must be present at a specific threshold before a fermented food can be sold as such.
Similarly, claims regarding cfu/g and bacterial strains must be verified by regulators.
The current study examined five brands of commercial kefir, from companies such as Maple Hill, Siggi, Redwood Hill Farm, and Lifeway. All five advertised their product as containing specific microbes, while three of them also claimed a minimum count of microbes in cfu/g.
Chobani yogurt was used as the control. All were measured the same way, and their composition was analyzed.
What were the findings?
The results show that 66% of the products failed to meet their guaranteed claims of cfu/g, by at least one log. One product claimed 1 × 109 cfu/g more than was actually present.
None of the three products that claimed a minimum count of viable bacteria met the cfu/g label standard when opened. Only one product out of five met this after incubation in anaerobic conditions for 14 days.
Bacterial sequencing showed that some degree of accuracy was achieved with regard to the bacterial taxa claimed to be present, yet species like Streptococcus salivarius, and Lactobacillus paracasei, were present in a majority of products above the minimum detectable threshold (0.001% relative abundance) despite not being present on the labels.
"All 5 kefir products guaranteed specific bacterial species used in fermentation, yet no product matched its labeling completely."
With product A, five of the ten named species were detected, with two other species not named on the label. The majority comprised Streptococcus thermophilus (85%). Product B had all four of the named genera, mainly Streptococcus (54%), Lactococcus (24%), and Lactobacillus.
Product C had four of 11 claimed species, including mainly Strep. Thermophilus and Lactobacillus species. With product D, again, the former predominated at 88%, but of two bifidobacterial claimed on the label, only one was found.
Finally, product E had three of 11 claimed species, mainly Lactobacillus species.
What are the implications?
Importantly, these kefir products meant for human consumption are meant to be labeled accurately, and, being cultured milk products, must disclose all added microbes. This demands better regulation of the quality and viability of the probiotic microorganisms added.
The researchers acknowledge that methodological changes may allow the isolation and identification of more taxa and varying cfu/g results. If nonviable bacteria were present, they might escape counting as they may not be cultured. However, the Chobani yogurt control showed close matching to product claims, boosting the reliability of these results.
"Regulatory agencies and consumers must continue to scrutinize these products and demand a higher level of accuracy and quality."