A fat man’s penis does get bigger after he loses weight, but it is mainly the visible part of the penis that increases in size, not the penis that grows bigger again. When men develop obesity, a large amount of adipose tissue accumulates in the perineum due to growing fat, which can bury the penis under the fat and cause it to look relatively small. Some obese people may even develop an invisible penis, which is when the body of the penis is completely retracted within the fatty tissue and only part of the foreskin is exposed. When a man loses weight, the penis buried in fatty tissue can be effectively exposed to the surface of the body, which can effectively improve erectile function and make the penis look larger. But losing weight will only make the exposed portion of the penis larger, not really bigger. If you have an abnormal penis size, you should still seek medical attention and treatment under the guidance of a medical professional.