How Long Does it Take to Gain Weight After You Eat?

The Digestive Process

The human digestive system is about nine meters long, with many steps along the way that convert the food that you eat into nutrients, fat, muscle, and other important body necessities. The entire process can take between 24 to 72 hours before food is fully converted into waste and that which will stay on as body weight in some way, shape, or form. Before food even enters the body, the cerebral cortex is stimulated by the sight and smell of the food and acetylcholine, a neurotransmitter triggering a release of gastric juices in the stomach. When food enters the mouth, saliva is secreted and mixes with the chewed food by the tongue. The chemical breakdown of the food begins with saliva's enzyme, salivary amylase, as polysaccharides like starch are simplified into more simple sugars. The food next travels through the pharynx and oesophagus, where food is passed down into the stomach. Only around seven seconds elapse while food goes through the esophagus and into the stomach. The gastric phase follows which releases digestive enzymes like gastic acid and pepsin, triggers more hormones and lasts three to four hours. Some small molecules like alcohol become absorbed into the stomach and go directly into the circulatory system. The intestinal phase is divided into two phases. The first takes place in the small intestine where partially digested food fills the duodenum, intestinal gastrin, bile, pancreatic juices, and intestinal enzymes are released, and food is broken down into smaller molecules. Most digestion occurs in the small intestine, and it is here where the greatest amount of time is spent. It is at this point that the fat digestion occurs (discussed in section 2). The large intestine then absorbs water, stores feces, and prepares the waste for body elimination.

Fat Digestion and Storage

When fat is detected in the small intestine, hormones are secreted that bring forth bile from the gallbladder and lipase from the pancreas. Droplets of fat are mixed with the bile salts and become smaller droplets called micelles. The micelles are broken down even further by the lipases into their constituent parts, fatty acids and glycerol. The glycerol and fatty acids are absorbed by the intestine, reassembled into protein coated chlomicrons and released into the lymphatic system. The chlomicrons eventually enter the bloodstream through the veins, where they last about eight minutes in the bloodstream, as they are broken down into their fatty acids again. The lipases work rapidly if your insulin level is high, and hardly do anything at all if your insulin level is low. The fat cells, liver cells, and muscle cells in your blood then absorb the fatty acids and store them in molecules as fat droplets. Any extra carbohydrates and protein will also be converted into fat by the fat cells, but they are passed over until all fat has been dealt with, since fat is much easier for the fat cells to convert. 24 to 72 hours after the food is ingested, it has been converted to fat or muscle.

Protein and Glycogen

According to Dr. Michael Colgan of the Colgan Institute of Nutritional Sciences, the body has the ability to build about one ounce of muscle tissue a day. This is because the protein turnover rate in muscle cells takes about 180 days. Similar to fats, proteins are built in the blood stream from their amino acid components. There are thousands of different proteins in the body and the weight gain from the creation of these necessary proteins is limited. Another type of weight gain, known as "water weight," refers to the storage of extra carbohydrates in the body in the form of glycogen. Glycogen is formed in the bloodstream, and it is stored in muscle tissue and in the liver. Glycogen consists of simple sugars and water. Water weight is lost at the beginning of a trendy low carbohydrate diet like Atkins or South Beach because the body is low on sugar and needs to break down the glycogen stores to keep functioning. Since the loss of water weight is temporary, many diets are deceptive in their large initial gains. In order to truly be at a healthy weight, you should not care about gains and losses day to day, or week to week, but over months and years. Choosing a healthy lifestyle and sticking to it for a long time will be better for your body than quick crash diets. While it may take 24 to 72 hours to put on weight from your food, it is more important to monitor your weight on the scale of years, not hours.