Protein Slows Digestion? Nope.

By Jordan Feigenbaum MS, Starting Strength Staff, CSCS, HFS, USAW Club Coach

In response to this gem of an article. I answered this on the Starting Strength nutrition forum, but I thought I’d repost it here. The article’s claims are italicized and my responses are in bold. 

The food that we consume is absorbed and its nutrients are subsequently sent to different organs through the blood.

The food that we consume is absorbed and its nutrients are subsequently sent to different organs through the blood. Not really the case literally. Protein and carbohydrates get absorbed as amino acids and monosaccharides through the small intestine’s brush border> into the enterocyte (cell)> into the portal vein> to the liver first before going anywhere else, then they get distributed based on lots of factors.

Fats get absorbed as fatty acids directly into the enterocyte (cell) and packaged into the chylomicron (with cholesterol, phospholipids, etc.)> into the lymphatic system> into the venous circulation and then go to some tissues, but mainly those who express high levels of mitochondria for beta oxidation or peroxisomes for long chain fatty acid oxidation. Principally, these are the liver and skeletal muscle.

However, a slow or sluggish digestive system isn’t able to perform its assigned function effectively. That is why a person experiencing a bout of slow digestion is bound to feel extremely uncomfortable post lunch or dinner. Nausea, bloating and vomiting are the most common symptoms of sluggish digestive system that occur after having meals.

Notice they do not define a normal GI transit time for a mixed meal, a slow GI transit time for a “bad” meal, nor do they distinguish between a pathologically slow state like gastroparesis or ileus or obstruction and a “slow” transit time occurring due to a specific meal composition. Yes, there is a marked difference.

Constipation or common digestive problems like diarrhea and irritable bowel syndrome can make the digestive system sluggish.

Diarrhea is actually the GI contents moving too fast. IBS has physiological symptoms of a combination of diarrhea, constipation, abdominal pain, and abdominal bloating. Seems like it might not make the digestive system sluggish, right? Though if you’re constipated, sure (and fiber and/or some probiotics tend to improve symptoms by increasing motility and osmotic pressure in the intestine to propel the contents)

Although protein is good for health, excessively high amounts of protein in the diet can slow down the digestive health. This is because, the body has to really work to digest protein.

Not the case at all. Proteins are initially broken down via the acidic pH of the stomach (and further in the small intestine by pancreatic enzymes that are all part of our normal physiology) and are absorbed very rapidly into the portal circulation. Whey, for instance- spikes blood plasma levels of amino acids (digestive end products of protein) within 20 minutes of ingestion.

Mixed meals confound the “speed” component, i.e. what is the fat content (slows gastric emptying), fiber content (soluble slows, insoluble speeds), total kCal content (larger is slower), tonicity of the meal (isotonic empties faster than hypo or hyper tonic from the stomach to the small intestine), etc. In addition, the hormonal milieu at the time with respect to previous meals also influence gastric transit time. Ghrelin, for instance- increases when you’re hungry and increases the motility of the gut.

Don’t forget about existing food in the GI tract. See how this is quite complicated to talk about? Let’s not forget about drugs….

At any rate, Carbohydrate rich and protein rich foods empty at about the same rate, but normal gastric emptying following a meal is 2-6 hrs….so yea- perhaps this whole article is a bit silly, eh?

Unlike simple carbohydrates, proteins are heavy, hence are not easy to digest and so when its presence is alarmingly high in everyday meals, the consequence is a slow digestive system.

Now this is easy to see that this is wrong…

People with intestinal problems such as Crohn’s disease tend to have a sluggish digestive system besides bowel dysfunction (diarrhea or constipation), vomiting and stomach pain. In this condition the lining of the small and large intestine are inflamed. However, in most cases, the swelling infiltrates in the inner layers of the bowel tissue. This chronic inflammatory disease considerably slows down digestion as the food tends to move at a very slow pace through the intestine.

Fuark. Crohn’s is, currently, a dysregulation of inflammation in response to bacteria in the walls of the GI tract, which results in proinflammatory substances causing direct mucosal injury.

Crohn’s usually presents with diarrhea, fatigue, weight loss, and crampy abdominal pain plus oral ulcerations, perianal fissures, perirectal abscesses, and malabsorption BECAUSE THE FOOD CAN’T BE ABSORBED BECAUSE IT’S MOVING at a normal speed but the mucosa can’t absorb it.

A point to note that although food is digested in the stomach, most of the digestion occurs inside the intestine. Experts say that the intestine is the place where nutrients are observed and eventually circulated in the bloodstream to various parts of the body. However if the food stays for longer time in the stomach, this can affect the digestion process. This condition is known as gastroparesis, in which the stomach takes more time to transfer the ingested food to the intestine. This happens because the stomach muscles that are assigned the task of pushing the food to the intestine, lose their ability to work efficiently. Gastroparesis is the result of malfunctioning of the vagus nerve that regulates movement of muscles lining the stomach wall.

Most common KNOWN causes of gastroparesis:

1) diabetes mellitus
2) idiopathic
3) post-surgical (especially if vagus nerve damaged)

Other causes:

-meds
-etoh and tobacco, weed
-surgery
-infection (mono, chagas, rotavirus)
-CNS injury like a tumor or cerebrovascular event
-PNS pathology (parkinson’s or guillan barre)
-other issues (cancers, hypothyroid, lupus, intestine obstruction, portal hypertension, HIV, stroke and migraines)

So…yea, protein is UNLIKELY to be the cause of “slowed” gi emptying….

-thefitcoach

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2 thoughts on “Protein Slows Digestion? Nope.

  1. Jordan,

    I’m going on a backpacking trip this summer. High Sierras, 8 days, mostly off-trail, mostly over 10,000 feet. Historically, I have lost a LOT of weight on trips like this–7 pounds in 7 days despite drinking enough water to pee every hour, IIRC–and my strength has dropped too. It occurs to me that this rapid loss probably includes a fair bit of lean mass. You have any ideas for packable dietary steps I can take to remedy this? Would BCAAs help?

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