Eat heat-killed bacteria for health?

Two human studies investigated health effects of heat-killed lactic acid bacteria. The first from 2019 found:

“One hundred healthy subjects with a body mass index from 23.0 to 29.9 (51 men and 49 women, mean age 41.4 years) were enrolled in this randomized, double-blind, placebo-controlled, parallel group study. Subjects were randomly assigned to daily administration of a tablet containing heat-killed Lactobacillus plantarum L-137 (HK L-137) (10 mg) or a placebo tablet for 12 weeks. This study was conducted at Higashi Koganei Sakura Clinic (Tokyo, Japan) from December 2017 to March 2018.

HK L-137 improved TC and LDL-C levels, especially in subjects with high serum CRP, an indicator of total inflammation. Seasonal increases in levels of TC and LDL-C were observed in the control group, but not in the HK L-137 group, resulting in significant differences between groups at 12 weeks.

HK L-137 decreased aspartate aminotransferase (AST) and alanine aminotransferase (ALT) biomarkers of hepatic inflammation. Daily intake of HK L-137 enhanced T-cell responses and suppressed hepatic inflammation and serum cholesterol in overweight subjects.” “Daily intake of heat-killed Lactobacillus plantarum L-137 improves inflammation and lipid metabolism in overweight healthy adults: a randomized-controlled trial”

Four individuals in both the control and treatment groups – 8% – came down with influenza during the 12-week trial period.

Researchers of a 2020 study cited their previous work in mouse models and in a preliminary clinical study. Let’s start with their comment on the first study:

“Reduction in high-sensitivity C-reactive protein (hsCRP) or pro-inflammatory cytokines, the most important biomarkers of systemic chronic inflammation, was not found.

We selected Lactobacillus plantarum OLL2712 as an optimal anti-inflammatory LAB strain among hundreds in our LAB library. Administration of heat-treated OLL2712 cells alleviated chronic inflammation by suppressing pro-inflammatory cytokine levels in visceral adipose tissue and the serum and improved hyperglycemia in mouse models with obesity and diabetes.

In the present study, we conducted a randomized, double-blind, placebo-controlled, parallel-group trial to examine whether the 12-week ingestion of a test yogurt containing heat-treated OLL2712 cells is effective in improving glucose metabolism-related parameters in human prediabetic participants. Prediabetic adults (n = 130, age range: 20–64 years) were randomly assigned to either the placebo or OLL2712 groups (n = 65 each) and were administered conventional yogurt or yogurt containing more than 5 × 109 heat-treated OLL2712 cells, respectively, daily for 12 weeks in Minato-ku, Tokyo, Japan between July and December 2018.

HbA1c levels were significantly reduced in both groups at week 12 compared to baseline. 12-week reduction of HbA1c levels was significantly greater in the OLL2712 group.

Fasting blood glucose (FBG) levels did not change significantly in both groups. Fasting insulin levels were significantly increased in both groups compared to baseline due to seasonal fluctuations from summer to winter. However, they continued to increase consistently throughout the study only in the placebo group.

Increased chronic inflammation marker levels and insulin-resistant index (HOMA-IR) levels were higher at week 12 than at baseline in the placebo group but not in the OLL2712 group. HOMA-IR = fasting glucose (mg/dL) × fasting insulin (μU/mL)/405.

Overall, the only significant difference between groups was found for HbA1c levels. Effect size was very small compared to that of clinical trials of antidiabetic medication that target patients with severe diabetes.

Placebo yogurt used in this study contained some effective ingredients including more than 1011 cells of Lactobacillus bulgaricus and Streptococcus thermophilus, which might provide glycemic improvement and might affect benefits of OLL2712 cells.

Postprandial glucose excursions contribute more to HbA1c in participants with lower FBG levels. Ingestion of OLL2712 cells might reduce HbA1c levels in participants with lower FBG levels by suppressing postprandial glucose excursions.” “Effects of 12-Week Ingestion of Yogurt Containing Lactobacillus plantarum OLL2712 on Glucose Metabolism and Chronic Inflammation in Prediabetic Adults: A Randomized Placebo-Controlled Trial”

The placebo group’s Day 0 fiber part of their diet was 3% (11.0 / (11.0 + 232 + 62.6 + 69)). The treatment group was also 3%.

People are eating highly-processed food if fiber is only 3% of their diet. Can effects from other gut microbiota interventions be expected when basic soluble fiber requirements aren’t met?

Also, humans have 1014 gut microbiota. They outnumber the second study’s treatment “5 × 109 heat-treated OLL2712 cells” by 20,000 to one, and its placebo group by 1,000 to one. Could either group reach effective levels?

I’m not overweight or prediabetic, don’t have metabolic syndrome or diabetes. Like Day 70 results from Changing to a youthful phenotype with broccoli sprouts, it’s hard to make personal comparisons to populations represented by these two trials.

I eat less than half the fat, and several times more than the fiber shown above. If I took heat-killed lactic acid bacteria, would it have any measurable effects?

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