There are roughly 75,000 enzymes that we know of. Without enzymes we couldn't properly break down food for digestion or properly metabolize food; in other words we would die without them. Even before food enters our mouth enzymes are being secreted. This is called the cephalic stage of digestion. There is a reason why we salivate when we smell and/or see delicious food. In saliva there is is an enzyme called amylase which breaks down carbohydrates in the mouth so we don't have to chew as much. Starches, which have one or more bonds between sugar molecules, need to be broken up before they can be digested and enter the Krebs cycle where they are used for energy.
Above is a disaccharide consisting of one glucose and one fructose molecule creating sucrose. Enzymes like lipase for fat and proteinase K for protein are also used to break down these macronutrients and make them readily available for storage and building, or for entering the Kreb cycle and producing energy in the form of ATP. Great so we all have these enzymes that breakdown our food and help us conserve energy. Well, this is isn't always the case. Diseases like PKU(Phenylketonuria), and Goucher disease are caused by enzymatic deficiencies. PKU is a hereditary disease in which the body cannot convert the amino acid phenylalanine into tyrosine. A buildup of phenylalanine in the blood is toxic and can lead to death if not treated. The missing link is the enzyme phenylalanine hydroxylase.
Enzymatic deficiency is more common than you may think. The words food intolerance may be more familiar to you which is synonymous with enzymatic deficiency. Food intolerance gets lumped in with food allergy and food sensitivity, but is very different. If you have a food intolerance, you feel sick because food is not being properly digested. This is not because of an immune response like food allergies and sensitivities. Lactose intolerance happens because of the absence or down regulation of the enzyme lactase. Around 65% of the world's population has some problem in digesting dairy. This isn't that surprising because mammals stop drinking milk once they begin eating other foods, except for us. We are still adapting to drinking milk at older ages because like other animals, we typically lose our lactase enzyme during infancy. Lactose, like sucrose, is a disaccharide consisting of glucose and galactose. Without lactase dairy isn't well digested. As dairy passes through to the large intestine, bacteria consume it and create methane as a byproduct resulting in gas, bloating, and indigestion. Dairy options that are better digested for those who may not tolerate dairy well are hard cheeses, yogurt, or even better kefir. These foods have already been partially digested by bacteria, so they typically won't cause as much discomfort as milk.
Unfortunately testing for food intolerance is very difficult. Genetic testing is the best option, but still isn't well understood. Hopefully in the near future we will be able to analyze all of our enzymes and understand how to get around deficiencies more efficiently. Nutritional genetics is a very interesting topic and I will delve into it more in another post. For now we can eat enzymes! Some foods that are high in enzymes include: papaya, mangoes, pineapple, avocados, bananas, and apples. If you do think you may have some sort of intolerance it is possible that you have an allergy or sensitivity instead. Because there are already several developed testing methods for these problems I would recommend getting tested for them first.