Proteins and carbohydrates -- of which lactose is one -- are both types of macronutrients. These are energy-providing molecules that you consume as part of your diet. Your body processes them through similar but distinct mechanisms, both with regard to digestion, and with regard to the metabolic processing of the digested products for energy and to serve other purposes in the cell.
Protein
Protein is an important component of every cell, and is also a critical part of the diet. Your cells use protein for both structural and functional purposes, and the protein in your diet provides the building blocks -- called amino acids -- for cellular proteins. To take up the amino acids from the proteins you eat, you break down protein through digestive processes that require both acid and enzymes, explains Dr. Lauralee Sherwood in her book, "Human Physiology."
Lactose
Lactose is a sugar, and more generally, is a carbohydrate. You consume carbohydrates in many foods each day, but lactose specifically comes by way of dairy foods. You digest lactose in the same way by which you digest other carbohydrates. As with protein, this requires both acid and digestive enzymes. You can then take up the components of lactose and use them to generate cellular energy or store them for later use.
Digestion
You must digest both protein and lactose before absorbing them into your blood -- this is the first part of processing. While both require enzymes for digestion, the enzymes aren't the same. You use enzymes in the stomach and small intestine to break down protein; these are called proteolytic -- protein-breaking -- enzymes. Lactose, on the other hand, you break down in the small intestine using the enzyme lactase, explain Drs. Reginald Garrett and Charles Grisham in their book "Biochemistry."
Further Processing
After you absorb the amino acids from protein and the smaller sugar constituents of lactose, you process them on a cellular level. In both cases, you can generate large amounts of energy, or you can convert the components of proteins and lactose into fat. There are some things you can do with protein that you can't do with lactose, however, including building new cellular proteins. Similarly, you can burn the components of lactose in the absence of oxygen, which you can't do with lactose.
References
- "Human Physiology"; Lauralee Sherwood, Ph.D.; 2004
- "Biochemistry"; Reginald Garrett, Ph.D. and Charles Grisham, Ph.D.; 2007
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