A low calorie mayonnaise product or margarine product comprising as a substitute for part or all of protein, carbohydrate, oil, fat or a mixture thereof, 0.7 to 10% by weight of paste-like konjak mannan hydrogel, based on total weight of said product and measured on the basis of dry konjak mannan, said konjak mannan hydrogel having a particle size of 5 to 80 .mu.m and a water holding capacity of at least 9 grams of water per gram of dry konjak mannan, obtained by mechanically pulverizing konjak gel in the presence of water and hydrolyzing the resultant pulverized mixture to partially decompose it, followed by centrifugation to form a centrifuged product.