Study in mice links heat-damaged DNA in food to possible genetic risks
Study in mice links heat-damaged DNA in food to possible genetic risks
Researchers have newly discovered a surprising and potentially significant reason why eating foods frequently cooked at high temperatures, such as red meat and deep-fried fare, elevates cancer risk. The alleged culprit: DNA within the food that's been damaged by the cooking process.
Bullet point summary of the full paper
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"The consumption of foods prepared at high temperatures has been associated with numerous health risks."
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In previous studies, high heat has specifically been examined with its ability to transform harmless molecules into small-molecule metabolites that can interact with DNA such as "polycyclic aromatic hydrocarbons (PAHs) and heterocyclic amines (HCAs)... aldehydes, acrylamide, and N-nitroso compounds"
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When such species interact with DNA, "mutations when replication specificity is altered by modified nucleobases and in genotoxicity and chromosomal rearrangements when strand breaks occur during repair"
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The amount of DNA seems to be reflective of how many of these small metabolites are formed. For example, in animal products, often associated with health concerns, we see high amounts of DNA content (cows = 5.3-19.5g/kg, pigs = 6.9 - 21.2g/kg). But in plants, we see a far lower amounts with grains, starches, fruits, and legumes the lowest (wheat = 0.6g/kg, lentils = 0.7-0.8g/kg, potatoes = 1g/kg, avocado = 0.6g/kg), and vegetables being higher (spinach = 2.6g/kg, cauliflower = 2.8g/kg, broccoli = 5.1g/kg)
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This study notes that the link between small-molecule agents and health concerns are not yet proven. They primarily focused on examining connection between individual parts of said DNA hypothesis.
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They note that if their findings continue to be held up as true, frying/grilling/smoking are probably the worst, roasting being similarly bad, and boiling being the least harmful. With raw and non-heat processed foods being the best.
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The authors note they are not yet clear on why many plant foods seem to have protective effects in other studies for cancer, but they do write "starch may contribute to some protection against reactive oxygen species" which is common in many unprocessed plant foods like legumes and tubers.
TL;DR: Food products still contain DNA from their sources. When consumed, the DNA must be broken down and utilized by our digestive system. When exposed to high heat, DNA from foods may break down into harmful molecules. When we consume said DNA in our food, it can be harmful to our existing DNA causing deleterious mutations. Some foods have less DNA content and speculated protective compounds such as starch which may prevent some of damage to us including many plant foods, but specifically tubers, legumes, fruits, vegetables, and grains. The study reinforces previous studies showing diets high in said protective foods and low in animal products may result in positive health impacts including lower rates of cancer.
Damn I eat meat almost everyday. I guess I should start a vegetarian diet .-.
Or just reduce your meat consumption. Daily sounds like a lot. I love meat but I don’t think I usually have it more than 2-3 times a week.
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"eyebrow raising" indeed. Makes me think of the following questions:
- Why is the amount of DNA in plants so much lower than in animal tissue? Is this because plant cells are larger? (some plants like wheat have very large genomes, I wonder how that affects it too)
- Are cells lining the intestine replaced frequently? and which population of stem cells do they come from? this would reduce the affect, but I suppose, not eliminate it. If a mutation still occurred in a checkpoint gene, could that cell still become cancerous, even if it is terminally differentiated?
thanks for posting
Why is the amount of DNA in plants so much lower than in animal tissue? Is this because plant cells are larger? (some plants like wheat have very large genomes, I wonder how that affects it too)
They are quoting the DNA concentration in g per kg of dry matter.
Plant cells have cell walls of cellulose, hemicellulose and pectin, which adds some dry weight that is absent in animals.
In addition, these seeds and tubers etc. we eat tend to be energy storage organs with a whole bunch of starch vs. not very much regular cell mass. It would be the same way if you ground up bone tissue and measured the DNA concentration.
Thanks for the detailed points and clarification :)
A few things that caught my attention:
- Heat damaged meat had more damaged DNA than a heat damaged vegetable.
- Lab grown meat really soaked up the damaged DNA from meat/veggies
The article does reinforce the commonsense that being a vegetarian is healthier for you than eating meat... But eating fried veggies still absorbs that damaged DNA into your system.
I think you misunderstood the article. About your points:
1 - "...potatoes, for instance, incurred less DNA damage at higher temperatures than meat for unknown reasons."
It's only at higher temperatures, and they only tried two kinds of meat and one veggie (potatoes).
2 - It doesn't talk about lab-grown meat at all. It mentions lab-grown cells, which are
probably bacteriavarious types of human cells that they exposed to the heat-damaged DNA, and they absorbed the damaged DNA. (thanks @appel@whiskers.bim.boats for the correction)Also I don't see how "being a vegetarian is healthier" is commonsense, but that's besides the point. The article doesn't reinforce any of that. It just says that:The study does reference another study about how low meat consumption can lead to less cancer. And they say this would support their findings of less damaged DNA in plant material, therefore causing less genetic damage.In summary (see @higgsbi@beehaw.org's comment here for a much better one):
a) Food gets DNA damage when heated up (even boiling).
b) That DNA damage can be absorbed by lab-grown cells and also by mice
c) They speculate cancer and genetic diseases are more probable because of the damaged DNA.
They have a very small food sample size, and didn't try many methods of cooking (they admit all of this). Which is to say: they have no idea yet how this impacts people, if at all.
I wanted to check which cells they used, because using bacteria would give it no power at all, as bacteria have very different uptake, DNA damage tolerance and DNA repair mechanisms. they used:
- SW620: a epithelial cancer cell line from a 51 yr old male's colorectal cancer
- HEK293 an immortalised cell line from a human embryo kidney
- MCF-7 a breast cancer cell line.
- HeLa the infamous HPV cervical cancer cell line.
So they are all human cells, and the SW620 cells would be somewhat similar to our gut epithelial cells, as they once were the same. It's hard to be certain though, because immortal cell lines can accumulate many differences since they were isolated.
The SW620 cells did take up the damaged nucleosides, and more so than HeLa or MCF-7.
I think what they meant by "being a vegetarian is healthier" is from the point of conclusion from this study referencing lower cancer (and all cause-mortality in referenced analysis) rates for plant based vs animal containing diets. I agree it's a tough claim to make since a vegetarian diet could literally just be oreos for 3 meals a day, but if I had to guess what they meant, it's probably what I mentioned.
More info from actual study here
So, what about slow cooking meat? I guess that's still in those temperature ranges, huh?
Given that heat-induced deamination producing dU in isolated DNA continues to proceed over extended times (Figure 2b), (18) hours of roasting or smoking could potentially result in higher levels of damage, although this was not tested here. For dU in briefly roasted beef, the amounts found here correspond to milligram quantities in a serving of cooked meat, as much as 1000 times greater than concentrations of HCA or PAH molecules in cooked meats
Summary here
Yeah I'd love to know whether to cook my food
Same. I mean I'll eat it raw if it helps.
Forgive me if I'm reading sarcasm into your comment where it wasn't intended, but raw food diets are definitely a thing, and there are people who choose to abide by them. It's not a diet I would personally choose, but it for some folks it works.
Seems potatos were less a risk cooked at high temperatures. more reason to be vegan for me! lol. Also, if you want to eat a raw food diet (not me) - much safer to keep it vegan and not eat raw meat lol. I dont agree that everyone can easily meet a balanced diet eating nothing but raw foods. I need beans! you'll never take my beans away from me
If you want some cool potato facts, you might be best off boiling and then cooling your potatoes before eating. There is some preliminary evidence that cooling the potato instead of eating it directly from heat may lower its glycemic index and thus limit blood sugar spikes. The mechanism is still uncertain, but there is thought that the crystallization of the gelatinized starches from cooking may lead to a slower break down of sugar in the small intestine.
I am calling this an overall win for potato salad lovers everywhere.
So maybe eat more cold potato salads? I think I can make that sacrifice, for my health of course. Thank you!
How high is too high? Didn’t early humans unlock the next tier by basically burning meat?
We do not really know how cooking helped us evolve, but there are many theories. It could have been that cooking our food allowed us to have smaller digestive tracts (compared to our ancestors) meaning we had a better ability to grow our brains. Or possibly it was because cooking allowed for a break down of plant and animal matter which allowed us to have more energy/access to nutrients giving us an evolutionary edge. Or if you want to examine a possible psychological reason, may fire specifically allowed us to think, examine, and memorize for longer periods of time including night.
As for why it was good then and bad now, we have to understand the split in what kills us. Prior to the invention of common sterilization methods, clean drinking water, and antibiotics/antifungals/antivirals, you were far more likely to die of some disease than some chronic disorder like you are today. Now, most people are living well past their 60s in some impoverished countries and many in rich countries far higher in their late 70s, 80s, or even 90s. This gives a lot more time for other factors like cancer to be an issue. Considering cancer is developed because of mutations in our DNA, the longer we live, the more chance said mutations will occur before we can stop the deleterious effects Additionally, our tools are far more extreme than they used to be. Boiling is a fairly new (in the broad scheme of things) invention with things like frying or smoking being even newer. That doesn't always mean its going to be a bad thing, but in this case, newer cooking methods just involve a higher heat which does indeed present issues.
As far as how high you can cook food without seeing damage, there is no answer for a specific no-no temperature. Just that higher temperatures result in more damage as I discussed here. Boiling seems to be the least bad compared to roasting, grilling, or smoking considering boiling stays around 100C compared to > 200C in other methods. Plant matter seems to be far better than animal matter likely due to the high content of other molecules with less DNA although the authors of the study note that future studies should be undertaken to learn more about these effects with a wider food pool.
TL;DR: we don't really know all of the specifics for why we evolved. Cooking was likely part of it. Today, there is no correct temperature to cook at, but lower temperatures seem to be better for this particular issue.
Would I be correct in assuming that milk and yogurt wouldn't be affected by this?
The study did not specifically test said products, yet they note future studies ought to do so.
However, given that dairy products do indeed have DNA from the cow they are taken from and are pasteurized at 280-320C, a temperature range far greater than anything tested in this study, it stands that the conclusion could be the same. I am unfamiliar with the specific heating practices in common yogurt brands, so I cannot even begin to speculate there.
This would match up with some initial evidence that cancer, especially prostate cancer, may be linked with higher dairy consumption. However, the authors in these studies speculate that the cancer risk is from high consumption of IGF-1 (insulin-like growth factor 1) which is especially high in dairy products. The linked study looked at direct comparison between soya milk and dairy milk which can be troublesome because soy products have been shown decrease risks of cancer. Other studies comment on the effects of milk on cancer risk from several linked papers.
To gain deeper understanding of whether dairy milk may influence cancer risk, more research is needed to clarify whether there are plausible biological mechanisms, including how different dairy products relate to the IGF system, to other hormones and to other bioactive constituents.
This is especially important with the original post here. There may be future studies that expand on the relative risks of both IGF-1 and damaged DNA in dairy.
