Two Grams of Wakame Powder Blunts Blood Sugar Spikes After Rice and Curry

A single spoonful of powdered seaweed, stirred into an ordinary plate of rice and curry, was enough to measurably flatten the blood sugar and insulin spikes that follow a starchy meal. That is the central finding of a randomized, double-blind, placebo-controlled crossover trial published on 18 August 2026 in the Springer Nature journal Food, Nutrition and Health, which tested a calcium alginate-rich powder made from Undaria pinnatifida, the brown seaweed better known as wakame, in healthy Japanese adults. The study is small and short-term, and its authors are careful about generalizing the results, but it adds to a growing body of evidence that the dietary fibers in brown seaweeds can moderate the glycemic excursions that epidemiological research has linked to type 2 diabetes, obesity, and cardiovascular disease.

The trial enrolled twenty-two healthy Japanese individuals aged 20 to 59 years whose fasting blood glucose at a preliminary examination was below 125 mg/dL. Sixty-four volunteers were initially screened, and after one participant dropped out following vomiting during the first intake period and two others were excluded from the analysis because of suspected abnormal glucose metabolism or gastrointestinal tract defects, the final analysis covered the remaining participants. Their mean body mass index was 20.7 kg/m2 and their mean glycated hemoglobin level was 5.3 percent, consistent with a healthy, non-diabetic study population. The study was registered in the UMIN Clinical Trial Registry as UMIN000052681 and approved by the Ueno-Asagao Clinic Ethical Review Committee, with all participants providing written informed consent.

The design was a two-period crossover, meaning each participant consumed the test meal under both conditions on two separate days six days apart, in November 2023. On each test day, after fasting overnight and consuming only water for twelve hours following a standardized dinner provided by the researchers, participants ate 150 grams of packed rice and 100 grams of pre-packaged curry with 150 milliliters of water, a meal supplying 350 kilocalories and 55.8 grams of carbohydrates. In one condition the meal was supplemented with 2 grams of the calcium alginate-rich wakame powder; in the other it was supplemented with 2 grams of maltodextrin, color-adjusted so that participants and staff could not tell the conditions apart. Randomization was stratified by age, sex, and the two-hour glucose area under the curve measured during screening, and the allocation code was not opened until the database was locked.

The wakame powder itself was a carefully characterized ingredient rather than simply dried and ground seaweed. Dried wakame was washed with a calcium acetate solution, rinsed, and dried to produce a powder containing 54.9 percent dietary fiber, 39.4 percent alginate, 4.8 percent calcium, 27.5 percent protein, 6.5 percent lipids, and 50.0 percent carbohydrates. The 2-gram dose therefore delivered roughly 788 milligrams of alginate and 96 milligrams of calcium. The powder also had a very low salt equivalent, below 0.1 gram per 100 grams, and good water dispersibility, characteristics the authors note make it suitable for incorporation into a variety of processed foods. The dose was chosen based on previous studies indicating that between roughly 1.8 and 4 grams of wakame was effective and had produced no side effects in healthy individuals.

The results were strikingly consistent for a study of this size. Thirty minutes after the meal, blood glucose was 7 mg/dL lower and serum insulin was 7.5 μU/mL lower after the wakame-supplemented meal than after rice and curry alone, both differences reaching statistical significance at p < 0.05. Blood glucose and insulin rose from baseline after eating in both conditions, peaking at approximately 60 minutes, but the wakame condition blunted the early rise. The incremental area under the curve for insulin over the first hour was also significantly lower with the seaweed powder, while the insulin area under the curve over the full two hours only showed a non-significant trend in the same direction, at p = 0.15. Treatment compliance was complete, and no side effects related to the test meal were reported.

To probe the mechanism, the researchers also ran a cell-free artificial digestion experiment in which cooked white rice was digested with enzymes simulating gastric and intestinal processing, with or without wakame powder added at a final concentration of 6 grams per liter. After twenty minutes of simulated digestion, the free glucose concentration in the wakame samples was significantly lower than in the control, at 252 ± 8.9 milligrams versus 279 ± 6.7 milligrams. The authors point to prior work showing that alginate-containing wakame extract reduces glucose diffusion, and to a demonstration that alginate markedly inhibits α-glucosidase activity in vitro, as consistent with this finding.

Why would a viscous fiber from brown seaweed slow the appearance of glucose in the bloodstream? The authors discuss several non-exclusive explanations. Alginate is known to prolong the rate of gastric emptying, which increases satiety; wakame has previously been shown to increase the sensation of fullness and reduce hunger. Slower gastric emptying would naturally delay glucose delivery to the intestine and thereby lower glucose and insulin concentrations in the early postprandial period, which is exactly the time window where the trial saw its significant effects. A second candidate mechanism involves bile acids: dietary fibers can adsorb bile acids in a manner resembling bile acid-binding resins, drugs that improve glucose tolerance and insulin resistance in animal models. The authors’ own earlier work in rats found that wakame consumption lowered serum total cholesterol and increased messenger RNA levels of CYP7A1, the rate-limiting enzyme in bile acid biosynthesis. They also note that wakame contains magnesium, which has been associated in a dose-response manner with a lower risk of type 2 diabetes, so factors beyond fiber may contribute.

The context for this work is both nutritional and cultural. Seaweed is a traditional staple of the Japanese diet, consumed with noodles, soups, salads, and pickles, and an epidemiological study has reported that seaweed intake was inversely correlated with the risk of ischemic heart disease. Alginate, a naturally occurring anionic polymer isolated from brown seaweeds including wakame, konbu, and hijiki, has been associated in the literature with anti-inflammatory, hypolipidemic, antihypertensive, hypoglycemic, and anti-obesity properties. The authors’ own previous clinical trials found that consuming wakame as a salad or soup with rice, or before meals, could suppress postprandial blood glucose increases in proportion to the amount of wakame consumed. The new study extends that line of work by showing that a small quantity of a processed, low-salt, calcium-enriched powder, mixed directly into the meal, is also effective, which the authors suggest could offer a simple behavioral strategy for reducing glycemic excursions through everyday foods.

The limitations, which the authors state plainly, matter for how far these findings can travel. Selection bias cannot be excluded, the sample was small, and most participants were Japanese, so the results cannot be generalized; the authors call for further research in people in the prediabetic stage and in Western populations. The intervention was a single acute test rather than a long-term trial, so nothing can be concluded about sustained effects of daily wakame powder consumption. And the study only compared the supplemented meal with an otherwise identical meal lacking wakame, leaving open questions about which bioactive compounds in the powder drive the effect. Within those boundaries, the trial delivers a clean, controlled demonstration that 2 grams of calcium alginate-rich wakame powder taken with a standard rice-and-curry meal significantly lowered early postprandial blood glucose and insulin in healthy adults, and the authors conclude that consuming the powder with food staples such as rice and curry may help attenuate postprandial glycemic excursions.

Subject of Research: The acute effects of calcium alginate-rich wakame powder on postprandial blood glucose and insulin in healthy adults

Article Title: Effects of calcium alginate-rich Undaria pinnatifida (Wakame) powder on postprandial glycemia and insulin levels in healthy individuals: a randomized, double-blind, placebo-controlled crossover trial

Article References: Yoshinaga, K., & Mitamura, R. (2026). Effects of calcium alginate-rich Undaria pinnatifida (Wakame) powder on postprandial glycemia and insulin levels in healthy individuals: a randomized, double-blind, placebo-controlled crossover trial. Food, Nutrition and Health, 3(1), Article 29. https://doi.org/10.1007/s44403-026-00073-0

Image Credits: AI Generated

DOI: 10.1007/s44403-026-00073-0

Keywords: wakame, Undaria pinnatifida, calcium alginate, postprandial glycemia, blood glucose, insulin, randomized crossover trial, dietary fiber, seaweed, healthy adults, rice and curry, glycemic excursions