While researching intermittent fasting for my talk a few weeks ago, I was able to find quite a bit of data, but only a fraction of that data was from human studies. It’s not surprising that this should be the case when you consider that fasting was a fringe health topic until recently. With fasting of all sorts becoming better known, the body of scientific research on the topic is increasing. This review, conducted in 2014 outlines the mechanisms involved in fasting and the evidence available in everything from single celled organisms to humans. I’ll be providing more information on the contents of this article and other cool studies in my fasting series, but first: let’s talk about human vs. animal data.

Humans vs. Animals

It’s not that the only good data is human data. All research has a place in the scientific process. However, the key difference between animal and human data is the applicability of that data. Animal data gives us a hint of what the results might look like in humans, and allows us to justify performing similar work in humans. This is necessary because in modern medical research we have these things called ethics committees. They are responsible for approving studies before they’re done and are quite helpful in avoiding the sorts of things one might see in sci-fi movies. The ethics board would really prefer that before you start mucking about with humans, you muck about with animals first (sorry PETA). If the animal data appears promising, and doesn’t show anything terribly dangerous, we move on to designing similar trials in humans.

So testing things with animals is good, and necessary. But how does that data stack up against human data? Well, the whole reason that we test in specific animals, like rats, is that they have a lot of similarities to humans. But of course, a rat is not a human, and the differences are greater than just whisker size and tail length! This has implications in both the kinds of data we can obtain, and the way we can apply this data to humans.

Humans vs. Animals; Designing trials

As mentioned above, human trials need to clear an ethics evaluation before being approved. People tend not to care all that much if we propose to genetically modify a group of mice to determine how that gene plays out in disease development. Not so much the case if the same were proposed with humans. By studying animals we can really speed up our drug discovery and testing process. The other difference between humans and lab animals is the number of confounding factors present. In the lab, you can take a group of animals and control for just about everything. When you look at the results of your study, they’re pretty clean. Humans on the other hand, have many confounding factors (ex: socioeconomic status, diet, lifestyle etc). Hence trials are more complex and thus, more expensive. It’s best to try the intervention in animals first, before spending all your R&D money on a failed human trial.

Humans vs. Animals; Hierarchy of evidence

The evidence based medicine pyramid, pictured below, shows how different evidence is ranked for weighting in clinical decisions. Before studying pharmacy I thought that randomized control trials (RCTs) were the be end of the end all. Turns out there’s a lot of really poorly done RCTs out there! That’s why we weigh reviews of many RCTs, and meta analyses more heavily than a single RCT (more heavily weighted=at the top of the pyramid). Where does animal data fit in there? Well, if we’re making clinical decisions about that animal, it would go right in the spot corresponding to the type of study done. But if we’re making clinical decisions about humans, the animal data should probably go in the background information section. We can use it to inform further research, but not to inform clinical decisions in humans.

https://guides.library.utoronto.ca/evidencebasedmedicine

How can you tell the origin of a statement or piece of evidence?

Ideally the information will be clearly referenced. Use caution when consuming health information that isn’t sourced. (An exception to the rule: Sometimes an expert in a topic might feel that a piece of information is obvious because they deal with this stuff so regularly. While it may be novel information to you, they may not feel the need to source it.) But even if the information has not been explicitly referenced, there are some clues that can point to the origin of the data:

Clue 1: The data is from a study that would not have been ethical in humans

Again with those pesky ethics boards!

Clue 2: The data pertains to prevention of disease vs treatment of a disease

A classic case of confounding factors. Photo stolen from this website.

As mentioned above, the number of confounding factors in a population of humans is enormous. It is difficult to isolate the effects of a single intervention since so many of them are linked together in behavioural patterns. For example: smoking and drinking go hand in hand, but it’s clearly the smoking that causes lung cancer, not the drinking. Similarly, there are different diets that show promise in preventing chronic disease. But is it the diet itself, or is that diet a proxy for a more health conscious lifestyle?

What can you expect from me?

What you can expect from me in my blogging is evidence based health information that is clearly referenced and described with enough detail such that you don’t need to go to that article and waste your time fact checking me. I won’t shy away from animal studies because sometimes that’s all we have (ex: drug use in pregnancy and lactation), and often animal studies pertain to cutting edge concepts which is pretty cool! However, in the case that I cite an animal study, I will clearly indicate that fact. But for the purposes of providing health information tailored to individual humans, the best studies are indeed human studies and I’ll always choose the unfavourable results of a human study over the favourable results of an animal one.

Happy learning!

xo Kimberley

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