Digestion becomes weak.

Taking a shower reduces your body temperature. During which the arteries and veins dilate to increase the blood flow and hence moderate the temperature difference by transferring heat from your blood. If you take a meal before having a bath, your blood is pumped towards the stomach to help digestion, this blood would now be rushed to your arms and legs to moderate the temperature difference and hence, blood availability for digestion would be less during shower. After the shower, your body gets relaxed and drops the body temperature. The cooler your body becomes, the slower essential metabolic functions like breathing, pumping blood and digestion become. This affects the digestion and usually results in vomiting. These effects of taking a bath after meals are not evident enough in an average healthy human and is usually ignored as acidity, indigestion or a small gastric problem, but are quite clear in physically weak, ill or older people.