The present invention relates to a composition in the form of a powder or a viscous paste, said composition comprises at least one low viscosity alginate having a viscosity of less than about 100 mPaS in a 1 wt% aqueous solution, and at least one high viscosity alginate having a viscosity of more than about 100 mPaS in a 1 wt% aqueous solution, and wherein the composition further comprises at least one suspending agent, and thereby providing a composition, which is readily soluble in water such that an aqueous preparation can be prepared without substantive mixing. Said aqueous preparation is suitable for use in the treatment and/or prevention of overweight for both therapeutic and non-therapeutic purposes.