Eating kombu daily increases gut health and heart markers in men

Eating kombu daily increases gut health and heart markers in men

New research shows that eating kombu seaweed daily may help Japanese men lose body fat and improve their gut bacteria without affecting thyroid health or causing adverse effects.

In a recent article published in the JournalFood Science and NutritionResearchers evaluated whether consuming cooked kombu powder causes changes in gut microbiota and body fat reductions for Japanese adults. Their results suggest that kombu intake significantly reduced percentage body fat and increased serum adiponectin in men while reducing systolic blood pressure in both sexes. It also caused positive changes in gut microbiota without adversely affecting thyroid function, despite a daily iodine intake of 420 mcg.

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At week 12, waist circumference shrank significantly in female placebo participants, and in contrast to the temporary increase in the Kombu group. This suggests complex gender-specific responses to dietary changes.

Metabolic syndrome increases the risk of cardiovascular disease and is associated with problems such as insulin resistance, high blood pressure and abnormal lipid levels. Accumulation of visceral fat is thought to be a major contributor to this condition.

Diets that limit visceral fat accumulation could help prevent metabolic syndrome. Kombu, a type of edible seaweed, contains high levels of fiber, particularly sodium alginate, which has been linked to health benefits such as regulating blood sugar and reducing blood cholesterol. One proposed mechanism is that studies suggest that alginate forms a gastric gel that hinders the absorption of glucose and cholesterol.

These effects are also thought to occur through increased excretion of bile acid, changes in hepatic cholesterol synthesis due to fermentation products, and reduction in insulin secretion.

Kombu also slows digestion and nutrient absorption, which may help fight obesity. It also contains other fibers such as fucoidan and laminarin, which can clearly impact the gut microbiota.

No studies have examined the long-term effects of kombu on fat accumulation and gut microbiota in Japanese individuals through dietary (and not supplement) consumption.

About the study

Each kombu biscuit replaced a meal serving portentum of 200 g of rice, providing a convenient food swap that participants maintained with 100% adherence in 38 of 41 cases.

This 12-week, randomized, double-blind, placebo-controlled study aimed to evaluate the effects of cooked kombu powder on gut microbiota and body fat in Japanese adults with a body mass index (BMI) of 23 kg/m² or more.

Participants between the ages of 20 and 65 were required to have regular eating habits and were excluded if they disliked functional health foods, certain medications, kombu, consumed alcohol, had iodine restrictions, had serious medical conditions, or had recently donated blood.

A total of 44 participants were randomized into kombu or placebo groups balanced by BMI, age, gender, visceral fat area and low-density lipoprotein cholesterol levels.

The intervention included six cookies daily (replacing a staple meal) containing either cooked kombu powder or microcrystalline cellulose (placebo). Each test cookie contained 0.6 g alginate and 0.07 mg iodine (contributing to a daily intake of 0.42 mg or 420 mcg from the cookies).

The kombu was processed to reduce iodine before being dried and pulverized. Throughout the study, participants recorded their daily intake and diet. Dietary records were analyzed using standardized Japanese food composition tables.

Anthropometric data, blood and stool samples were collected at baseline and week 12. Visceral fat was measured using tomographic scanning and blood samples were analyzed for hormones and metabolic markers.

Stool samples were used for microbiota analysis. Genetic material was extracted from fecal samples and sequenced to identify microbial composition using gene sequencing. Bioinformatics tools were then used to classify and analyze microbial taxa and diversity.

Key Findings

The placebo group experienced a notable increase in serum uric acid levels, while kombu intake prevented this increase, indicating the broader metabolic benefits of kombu that went beyond fat reduction.

Of 44 participants, 41 completed the trial with kombu (cooked seaweed) cookies or a placebo. Baseline characteristics and nutrient intakes were similar between groups. LDL and high-density lipoprotein (HDL) cholesterol levels decreased in both groups with no differences between groups. Serum uric acid increased significantly only in the placebo group.

In men, Kombu intake resulted in a significantly greater reduction in body fat content and percentage compared to placebo. Such reductions were not observed in women; In fact, after 12 weeks, body fat percentage was significantly higher in the female Kombu group compared to the female placebo group, although a transient increase in weight and fat measurements had also been observed in women in the Kombu group at week 6. Systolic blood pressure decreased significantly at weeks 6 and 12 in both sexes in the Kombu group, and distal pressure from week 6.

Serum adiponectin increased significantly in men consuming kombu, but no changes were observed in women. Serum leptin levels and thyroid hormone levels remained unchanged, confirming that Kombu iodine intake did not negatively affect thyroid function. Except for one case of loose stools, no adverse effects associated with Kombu have been reported.

Visceral and subcutaneous fat areas did not differ significantly between groups.

Fecal microbiota in the kombu consuming group showed higher Agathobacter, Alistipes, Bacteroides, and Faecalibacterium; In particular, Agathobacter abundance showed a negative correlation with fat mass and body fat percentage in male participants. In addition, the Simpson's alpha diversity index, a measure of gut microbiota diversity, was significantly increased in the Kombu group compared to the placebo group. However, there were no significant differences in fecal short-chain (SCFA) concentrations between the groups, which the researchers suggest could be attributed to rapid absorption and utilization of SCFAs in the colon.

Conclusions

The study suggests that Kombu intake may reduce body fat in men and blood pressure in both sexes, without adverse effects or disturbances in thyroid function despite reported iodine intake. Its high compliance and safety support its potential as a dietary intervention.

A major strength was the controlled design and gender analysis, which revealed gender effects. However, the small sample size and short duration limit generalizability. The different results in women, including the transient changes and comparative increase in body fat percentage at the end of the study, as well as lack of significant effects on fat distribution or leptin, suggest that responses may differ by gender and warrant further exploration. The lack of change in fecal SCFA concentrations despite positive microbiota shifts also merits further investigation, perhaps through in vitro fermentation studies as suggested by the authors.

Future studies should include longer durations, larger samples, and a focus on underlying mechanisms, including hormonal and microbiome interactions.

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