A big, thick juicy steak may not be fully appreciated in every circle, but for some, it's barbecue bliss. Various cuts and sizes of steak exist, such as rib-eye, T-bone and filet mignon, but they are all digested in the same manner. Some cuts have more fat than others, although protein is the main nutrient you’re going to get from your steak. Protein from meat contains all the essential amino acids you need to build and maintain healthy muscle, skin, fingernails and many other structures.
It Begins in the Mouth
The initial digestion of steak, and all food, begins in your mouth. The act of chewing reduces steak into smaller pieces, which exposes more surface area to the various digestive enzymes that are in saliva and the stomach. Alpha-amylase is the most predominant enzyme in saliva and starts the digestion of starchy carbohydrates. Unless you’re eating a baked potato or rice, alpha-amylase will have no impact on your steak dinner while it’s in your mouth. However, another digestive enzyme called lingual lipase is released from glands in the mouth when you chew, which initiates the digestion of saturated fat within steak. From the mouth, chewed steak travels down the esophagus and enters the stomach.
Digestion in the Stomach
Once in the stomach, metabolism of protein begins. The main stomach enzyme is pepsinogen, which is quickly converted into pepsin by the acidic stomach juices. Pepsin starts to reduce the protein in steak into smaller building blocks called amino acids and peptide fragments. However, if your stomach isn’t acidic enough -- at least a pH rating of 4 or lower is needed -- less pepsin is converted and protein digestion is significantly reduced. Your stomach juices also contain some gastric lipase, which continues to metabolize the saturated fat in the steak. Steak spends much more time in the stomach, a total of about four hours, compared to grains, fruit or vegetables, which usually spend less than an hour or so.
Digestion and Absorption in the Intestines
When the partially digested steak enters the small intestine, your gallbladder releases bile to further break down fat, and your pancreas releases proteases to further reduce the amino acid chains. Further on down the small intestine, the amino acids, fatty acids, cholesterol, vitamins and minerals from the steak are absorbed. Many of the nutrients travel to your liver first and then out to the rest of your body via the bloodstream. The material left over, which is mainly fiber and indigestible gristle, passes into the colon, losses more fluid and then passes out of the body as feces. The total time it takes for a steak to be digested and passed is between 24 and 72 hours, depending mainly on your metabolic rate and intestinal motility.
Frequent consumption of steak and other forms of red meat can be harmful to your health. The high saturated-fat content is linked to higher risk of obesity and cardiovascular disease, whereas the charred material on the outside of steak contains compounds that are linked to various gastrointestinal cancers. In addition, beef sometimes contains hormonal and antibiotic residues.
- Human Biochemistry; Charles Dreiling
- Human Metabolism: Functional Diversity and Integration; J. Ramsey Bronk
- Public Health Nutrition: From Principles to Practice; Mark Lawrence and Tony Worsley
Sirah Dubois is currently a PhD student in food science after having completed her master's degree in nutrition at the University of Alberta. She has worked in private practice as a dietitian in Edmonton, Canada and her nutrition-related articles have appeared in The Edmonton Journal newspaper.