Researchers in the United Kingdom have been studying a fibrous material in seaweed or sea kelp known as alginate. They have found this material is quite affective at preventing fat absorption. Researchers performed laboratory studies that modeled fat absorption within the human intestine and demonstrated that alginate will bind the fat and prevent its absorption into the body. The researchers believe when this material is added into commonly consumed foods such as breads and other staples that up to 75% of dietary fat would pass through the intestinal system without being absorbed into the human body.
Anyone who has taken Xenical will know that blocking absorption of fat into the body means one thing: it passes out the stool, usually in the form of diarrhea or a special greasy form of diarrhea known as steatorrhea. The appeal of fat blockers stems from the fact that fat is a very calorie dense nutrient containing 9 calories per gram of food.
However, research that has focused on reduction of fat has lead to very disappointing results for the outcomes that matter: weight loss and resolution of obesity related conditions like diabetes. Research involving fat blocking drugs such as Xenical have shown very mild weight loss and to such a low extent that most professional weight loss physicians only recommend the drug (also sold as Alli over-the-counter) when a weight loss patient is suffering from constipation.
So seaweed might have an interesting role in cutting down some calories we absorb. Reducing fat calories will help the overall cause, however it is quite unlikely that reducing fat calories is going to solve obesity for most people. The epidemiological evidence points strongly toward carbohydrate over-consumption as the main culprit so unless we discover a seaweed that is a “carb blocker “then it is unlikely to make a dent in the obesity epidemic