Seaweed_satiety_web

Can’t kelp myself

Overweight and obesity are major health concerns in the modern world. The WHO estimates that by 2015 there will be 1.5 billion overweight people in the world. This is more than a cosmetic issue because being overweight is tied in to major health concerns like diabetes, heart disease, and even cancer. Reports are that seaweed supplements might be able to assist in weight loss but what in light of conflicting evidence what can seaweed do for you?

A sedentary lifestyle is doubtless a big part of the boom in obesity but so is the nature of modern eating. Lack of control of food intake, excess portion size, and frequency of meals are critical to the development of obesity. The problem is that we consume many empty calories these days and so mechanisms for feeling full are bypassed while we still pile in the food. Normally the stomach signals to the brain when you are full so finding ways to maximise that signalling may help reduce overall kilojoule and food intake. That is why alginates derived from seaweed may be part of an answer to the obesity crisis.

Alginates are cell-wall constituents of brown seaweed. They are polysaccharides made up of blocks of mannuronic acid and guluronic acid. Composition of the blocks depends on the species being used for extraction and the part of the seaweed from which extraction is made. Sodium alginate is widely used as a stabilizer or as an emulsifier, or both, and alginates are the preferred additive to ice-creams and dairy products in many countries, where they compete with carrageenans.

The theory goes that since sodium alginate forms a gel in the human stomach, if you take it pre-meals then it will make you feel full and you will consume less and thus you will lose weight. However, some recent studies have not demonstrated an effect of alginate on appetite.

For instance, researchers at the Mayo Clinic, Rochester, Minnesota, reported that alginate did not curb appetite, increase or decrease stomach emptying, or alter digestive hormone production in a ten-day study. Participants in the study, all overweight or obese adults, took six capsules of alginate 30 minutes before meals. Total calorie intake at the meals, in which volunteers had free choice of foods and quantities of food consumed, was not affected by alginate supplementation. The study was published in the journal Obesity (August 2010).

Against that however are quite a few trials showing that alginate will reduce hunger. In the same journal, Obesity (June 2011) alginate was shown to significantly reduce hunger . These authors concluded that strongly gastric-gelling alginates at relatively low concentrations in a low-viscosity drink formulation produced a robust reduction in hunger responses. It should be noted that this research was done by the Unilever Research and Development Team however, there is plenty of other research that supports alginate as a weight loss aid. The Journal Appetite (November 2008) reported a study where subjects were given sodium alginate prior to meals with the result of a seven per cent reduction in mean daily energy intake. This reduced energy intake involved significant reductions in mean daily carbohydrate, sugar, fat, saturated fat, and protein intakes.

So what is going on here? Does alginate from seaweed reduce appetite or not?

A new study has suggested that the key difference between the studies may have been the balance between mannuronic acid and guluronic acid in the alginate preparations used.

In this latest study (publishing in the May 2012 issue of Food Chemistry) University of Copenhagen researchers firstly showed that alginate with a low mannuronic acid:guluronic acid ratio (that is, they were higher in guluronic acid) formed a stronger gel than those with less guluronic acid (and therefore a higher mannuronic to guluronic ratio). They then tested giving subjects either an alginate with a mannuronic:guluronic ratio of 0.8, or one with a ration of 2.5. They found that the alginate with the lower ratio increased feelings of fullness and decreased appetite whereas the alginate with the higher m:g ratio (and therefore less guluronic acid) did not. The low ratio alginate decreased calorie intake by ten per cent.

In the end it seems that some alginates with the appropriate ratio of mannuronic to guluronic acid will increase feelings of fullness and reduce appetite. A high m:g ration however leads to a weaker gel that swells less in your stomach leading to less effect which is why some studies show no efficacy. It’s true then, all’s swell that ends gel.

Terry Robson

Terry Robson

Terry Robson is the Editor-in-Chief of WellBeing and the Editor of EatWell.

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