There are times when one finds self in adversity especially in shipwrecks or being stranded in remote locations without supplies. This is also common in conflict situations. You have to severely ration your food intake to survive with attendant loss in weight and the likelihood of developing a haggard emaciated look. This can be prevented by eating a packet of glucose before eating. The little food you eat afterwards will go into replenishing your energy reserves averting loss of weight.