Thinness occurs either from the absence of a fattening substance in food, or from the abundant consumption of thinning nutrients, from which much blood is not generated, or the diet is limited to substances from which pure blood is not formed. This also happens from the weakness of the force that disposes of the nutrient, that is, the digestive force or the force that attracts food to the organs, and weakness arises either from a disorder of nature, most often cold, or from frequent being at rest, in which the attracting force sleeps, especially if this happens after physical work, which has taught the nature to attract nutrients with its help, when the work is stopped, the nature does not attract even a naturally balanced nutrient.
Thinness also occurs for the reason that blood is contrary to nature - bile blood is more contrary to the attracting force than liquid, watery - or because the spleen, having become large, presses on the liver, attracts most of the blood to itself and weakens the power of the liver due to the struggle between them, or due to the fact that worms are crowded in the body, or due to the narrowness of the pores, clogged with juices or closed from compression caused by cold, heat or dryness alone - all this you can recognize by the corresponding sign. The reason for this is also the constant wearing of a bandage, which clogs the pores and passages into which the nutrient is not drawn, especially edible clay, which clogs the pores. Or the cause of thinness is strong dissolution, due to which the nutrient substance drawn into the organs is not retained there, but is dissipated, as happens during rapid physical work, during worries and sorrows, or during diseases that dissolve nutrients.
A body that loses weight in a short time can return to fullness in a short time, but a body that loses weight over a long time can gain weight only through careful care, because the natural strength is too weak to use the abundant nutrient. The body that is best suited to fattening is the one with the softest and most stretchable skin.
A person who is weak, highly susceptible to cold and heat, who reacts sharply to skirmishes, clashes and emotional experiences, fatigue, hardship, insomnia, evacuation and copulation, should avoid losing weight; nutrients are retained in his vessels, do not pass further and rot.
Obesity also has harmful sides, which we will mention later, and there is nothing better than moderate obesity. As long as obesity does not cause harm, do not abhor it, for life is rooted in moisture, but you must be careful and avoid the path of excess, even if trouble is not visible, for trouble strikes unexpectedly and suddenly, as it is said in its place. If the body and air dry out, thinness appears.