Friday Favorites: Are Pre-Cut Vegetables Just as Healthy?

Below is an approximation of this video’s audio content. To see any graphs, charts, graphics, images, and quotes to which Dr. Greger may be referring, watch the above video.

Seven years ago I introduced the endotoxin theory literature, which sought to explain how a single meal of sausage and egg McMuffin could cripple artery function within hours of consumption. Maybe because such a meal causes inflammation by inducing a low-grade endotoxemia: endotoxins in the bloodstream within hours of consumption. Endotoxins are structural components of gram-negative bacteria like E. coli, and certain foods have such high bacterial loads, like ground meat, the thought was that it was the endotoxins in the food that was triggering the inflammation.

Critics of the theory argued that because we have so many bacteria already living in our colon, so many endotoxins just sitting down there in our large intestine, a few more endotoxins in our food wouldn’t matter much in terms of causing systemic inflammation. After all, we have like two pounds of pure bacteria down there where the sun don’t shine; so, there could be like a whole ounce of endotoxin. And the lethal dose of intravenously injected endotoxin can be just like a few millionths of a gram; so, we could have a million lethal doses down there, but the apparent paradox is explained by compartmentalization. It’s location, location, location.

Poop is harmless in your colon, but shouldn’t be injected into your bloodstream, or eaten for that matter—particularly with fat, as that can promote the absorption of endotoxins up in the small intestine, even well-cooked poop.

You can boil endotoxins for two hours straight with no detriment in their ability to induce inflammation. You could easily kill off any bacteria if you boiled your poop soup long enough, but you can’t kill off the endotoxins they make, just like you can’t cook the crap out of the meat. The consumption of meat contaminated with feces doesn’t just cause food poisoning. It can spill out onto the skin during the evisceration process, when the digestive tract is ruptured.

Even when slaughterhouse workers trim off the visible fecal contamination, the trimming itself can, ironically, sometimes lead to an increase in certain fecal bacteria, thought to be caused by cross-contamination from one carcass to the next. Then, even when properly stored in the fridge, endotoxins start accumulating, along with the bacterial growth.

What about other foods? The highest levels of endotoxins were found in meat and dairy, and the lowest levels in fresh fruits and vegetables. But that was testing whole fruits and vegetables. “Most spoilage organisms cannot penetrate the plant’s surface barrier and spoil the inner tissues.” That’s why fruits and veggies can just sit out there all day in the sun in the fields. Once you cut them open, though, and bacteria can gain access to the inner tissues, within a matter of days, your veggies can start to spoil. So what does that mean for all those convenient pre-chopped veggies these days?

While endotoxins were not detectable in the majority of unprocessed vegetables, once you damage “the protective outer layers of vegetables,” you diminish their resistance to microbial growth. So, while freshly-chopped carrots and onions start out with undetectable levels, day after day, even kept chilled in the fridge, you start to get the growth of bacteria, and along with them endotoxin buildup. Not as much as meat, but not insignificant. Enough to make a difference, though? You don’t know, until you put it to the test.

What would happen if you switched people between a diet expected to have a lower endotoxin load to foods containing more endotoxins, like going from intact meat like steaks and whole fruits and vegetables, to more like ground beef and pre-chopped veggies and more ready-made meals? After just one week on the lower-endotoxin diet, people’s white blood cell count, which is an indicator of total-body inflammation, dropped 12 percent, but then bumped back up 14 percent after just four days on the higher endotoxin diet. And, they actually lost a pound and a half on the lower endotoxin diet, and slimmed their waist a bit.

But they weren’t really eating otherwise identical diets. Looks like they were eating more meat and cheese overall on the higher endotoxin diet, and maybe getting more food additives in the ready-made meals. So, how do we know endotoxins had anything to do with it? That’s where the onion study comes in. A new study was designed based on two meals that differed in their content of bacterial products, but which were otherwise nutritionally identical. So, they compared freshly chopped onion to pre-chopped onion that had been refrigerated for a few days. It wasn’t spoiled; it was still before the “best before” date. So, would it make any difference?

Within three hours of consumption, the fresh onion meal caused significant reductions in several markers of inflammation. That’s what fruits and vegetables do; they reduce inflammation. But these effects were not observed after eating the prechopped onions. For example, here’s one inflammatory marker. Three hours after eating fresh-chopped onions, a significant drop in inflammatory status, but three hours after eating the exact same amount of pre-chopped onions, no significant change. So, it’s not like the pre-chopped onions caused more inflammation, like in the meat, eggs, and dairy studies, but they did appear to extinguish some of the anti-inflammatory effects of the onion. In conclusion, the modern trend towards eating the pre-chopped vegetables rather than whole intact foods is likely to be associated with increased oral endotoxin exposure. It’s definitely still better to eat pre-chopped vegetables than no vegetables, but chopping your own might be the healthiest.

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Image credit: fruitnet.com via flickr. Image has been modified.

Motion graphics by Avocado Video