Animal studies routinely appear in the scientific literature linking dietary factors to the overall health of the organism. For example, today I found this article investigating heart disease in fruit flies. Just a couple of the red-flags I found...
"Their study, published November 3 in the journal Cell Metabolism, also demonstrates that manipulating TOR protects the hearts of obese flies from damage caused by high-fat diets."
"In this study, flies fed a high-fat diet of coconut oil became obese and exhibited many of the same secondary symptoms as obese humans, including heart dysfunction."
It seems like a dangerous extrapolation to assume that these results translate to humans (No way I'm turning on coconut oil anytime soon!). Does anyone have references for studies indicating that animal metabolism is UNLIKE human metabolism? Forgive my lack of knowledge in this domain. A simple example being that cows eat grass, and we don't. Some researchers assume that results translate to humans but there must be evidence showing otherwise? Seems like a gray area to me!
asked bythemobiustrip (255)
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on November 05, 2010
at 02:38 AM
When they are trying out what certain genes do, they often use a very simple and well understood creature like drosophila to try to tract down effects. I have yet to hear anyone try to extrapolite food health from drosophila to humans though, hehe. But they do try to extrapolite potential gene function in one creature to another. The prob is there a bunch genes and at first, they are quite unsure what those genes do in the body. SO they start with a very simple animal and test. Then they move up to something like rats and see if the same thing happens or similar things happen. THen they test other mammals. Finally, they may eventually find some potentially theraputic uses for their knowledge, which are again tested on animals and then may finally be tested on humans. In this case, sounds like they were mostly just trying to get a handle on what that one particular gene codes for. And often, it will code for similar things in higher animals. The prob is that in higher animals, more and more complexity and ameliorating factors like other genes make the system more and more complicated so results become less and less cut and dry as that complexity goes up.
on November 04, 2010
at 02:26 PM
You've kind of hit the nail on the head in terms of the validity of animal studies in medical research. We use them out of necessity because we obviously can't subject humans to similar experimental procedures, but the data is often difficult to extrapolate to humans. I would be especially wary of extrapolating information from Drosophila (which I'm assuming was their model system) into humans, because we don't share a lot of features in common with fruit flies.
That said, it sounds like the target of their study wasn't to suggest that coconut oil was bad, but instead to investigate the genetic elements that might render individuals more susceptible to cardiac damage on a high-fat diet. Their use of coconut oil was probably due to its relatively easy availability and combination into fly food. Flies are a particularly useful genetic tool for things like this because there are vast libraries of flies with specific genetic defects; the authors hypothesized that the target of rapamycin (TOR) gene, which is a powerful central regulator of metabolic function, may play a role in the genesis of obesity-related cardiomyopathies. They found that TOR mutant flies had reduced incidence of cardiomyopathy compared to the control flies fed high-fat diets. This led them to evaluate the contributions of the insulin-TOR signaling axis to this process, and they found that inhibition of insulin-TOR signaling also protected flies from fat-related pathology.
Ultimately, what they found shouldn't deter you from coconut oil--they just used that as a model to make the flies fat quickly. They showed that, at least in obese flies, insulin signaling axes promote the development of cardiomyopathy and that interruption of those axes can protect against those outcomes. This probably is of importance in humans on some level, and as an early study provides some interesting groundwork for examination of patient populations and more complex animal models. Incidentally, it also fits in pretty well with what the paleo nutrition community already practices in terms of insulin level maintenance--that you should keep constant, low levels and not have spikes, as these can mess with your metabolism.
Hope that helps!
on November 10, 2010
at 02:40 PM
I think a lot of the confusion comes from the popular media stories that take preliminary animal studies and try to draw direct connections to human biology. When I was doing animal research, we were always very careful to be sure not to overstate the extent to which our results could be extended to humans. For example, if gene X is regulated a certain way in mice, and if humans have gene X and the same regulatory region in their genome, then it's worth seeing if humans have the same reaction. Some genes and gene regulation has been conserved for billions of years, others not so much. The similarity varies gene by gene and species by species.
Those nuances get lost in the popular media: as demonstrated here
on November 04, 2010
at 02:39 PM
Animal metabolism CAN be like human metabolism, but I don't think that's really the question here. It depends a lot on the animal and weather comparisons are correct. In this case there appears to be some evidence that fruit flys and human share certain gene sequences indicative of certain diseases.
One could be a little flippant and say that a watermelon and a cloud are basically the same because they're both mostly water; so I'm not sure how meaningful the genetic similarities are. We are possibly genetically similar to the Paranthropus branch of hominids, but given that branch went extinct and we did not, suggests important key differences. Point being, genetics is only part of the story.
I think more importantly we need to look through this evolutionary lens that we call paleo when applied to humans. I doubt fruit flies naturally get much of their nourishment from fat so feeding them a high fat diet and drawing conclusions is pretty questionable. This is similar to the T. Colin Campbell fiasco were rats and 20% casein diet showed more cancer than those on a 5% casein diet. While there are numerous layers to this particular onion (such as the fact that the 20% rats lived longer despite there cancer) rats aren't naturally adapted to consume 20% milk protien their entire lives.
Conclusion? Animal models can be useful, or not.
on November 04, 2010
at 02:27 PM
Ultimately, it depends on the animal. Some of them are very similar to us (If we were to compare digestive tracks, for instance, then dog's digestive tracks are very similar to ours). Some of them are a bit less similar. I'm not sure about metabolism but a lot of structures are VERY similar in both animals and humans (e.g the brain, nervous system, spine (in vertebrate)).
The beauty of evolution is that you can do comparison between species. I doubt we are all the same but we share a lot of similarities (which is why studies are done on animals...)