Normal person depends on different foods. Juices take a short time and meat longer time. Most foods stay 3-4 hours in stomach for digestion except alcohol which is absorbed in the stomach.
Here is the problem. Some have cold, normal or hot stomach. Some could argue all stomach temperature is same, but it is not true. Another example is that someone who has headache might notice head is warm or hot. If stomach is cold or gastroptosis, food staying is longer. If stomach is hot, digestion is faster and food staying is shorter, making hungry easily.
Let's assume someone eat too much. We acupuncturists make stomach temperature cooler. Food will stay longer making less hungry. Western approaches are to operate stomach which means gastrectomy. Which one is more economical, a few acupuncture treatments or gastrectomy? We also try to find what make stomach warm or hot and eliminate that cause. Which one makes more sense to you?