An anti-oxidation technique for treating raw foods, such as nuts and seeds, so as to make them oxidation-resistant. In the technique of the present invention, foodstuffs such as nuts, seeds, etc., are heated under pressure in a tightly closed vessel, so that the texture of the raw food materials is slightly softened, and so that the moisture activity value is at the same time adjusted to a value in the polymolecular-layer moisture region of approximately 0.3-0.4. As a result, the water molecules are absorbed on the surfaces of the lipid molecules so that a polymolecular layer of water is formed and strong bonds between the water and proteins act synergistically to prevent penetration of oxygen into the interior texture of the foodstuff, such as nuts, thus conspicuously hindering oxidation.