The case for coming to conclusions based on weak evidence

I want to make a case for the way science should be done in the health sciences–in a way that is totally different from physics–and I want to make this case using some of the evidence available on the link between animal protein and cardiovascular disease. I will use this as a particular example of the use of scientific inference, as is used in medicine to make a case that many might find persuasive, but which would be dismissed in other so-called hard sciences. I want to explain in particular why this kind of scientific inference is necessary for medicine–owing to its practical orientation–as compared to such other sciences.

Rabbits LDL levels increase with animal protein. Rabbits get atherosclerosis with animal protein via LDL. Humans increase LDL with animal protein (here and here). Humans get atherosclerosis via LDL.

We might infer therefore that animal protein causes atherosclerosis in humans.

To be clear, I’m not suggesting that animal protein definitely causes atherosclerosis in humans. But if it doesn’t, and if one accepts the lipid hypothesis, one would need to postulate some protective factor from animal protein that could counter its LDL-producing effects.

It follows that the more parsimonious (simpler) explanation is that animal protein is atherogenic in humans, and that is why an association between animal protein and cardiovascular disease is found in many (but not all) epidemiological studies.

This interpretation as far as I can tell is the simplest explanation comporting with the evidence. Again, I’m not saying it is true or that the evidence is strong. Clearly, the evidence is weak; direct human evidence in RCT would be strong. But it is the evidence that we have.

And here’s where the philosophy of science comes in. The health sciences (which includes nutrition science) are not like cosmology. In cosmology, conclusions don’t much matter, because nobody has to make decisions based on these conclusions. One can be agnostic and reserve one’s judgment on many issues.

However, in the health sciences, one must make a decision: do I take X action or not-X? What about Y? And Z? In the case of nutrition science, one must eat and thus while one can be scientifically agnostic, one must come to some practical conclusion. Because one cannot choose not to eat.

In such muddy sciences as the health sciences, it is not that we should be scientific idiots and go with any weak evidence to form some loaded and unjustified conclusions–some popular writers look to portray us in exactly in this way.

It is that as practical people who live in the real world, we must make decisions.

In medicine, we must make a decision based on incomplete information.

If the question of animal protein were a cosmological question with no practical relevance, I would be coming to a conclusion based on insufficient evidence to justify it. My conclusion would in fact be partly speculative: I am filling in the gaps in evidence (specifically, an RCT demonstrating an effect of animal protein on cardiovascular disease risk) with logic. In a formal sense, that isn’t science.

However, because this is about life and death and a decision I must make one way or the other, what constitutes good or bad reasoning in this particular domain is entirely different than what constitutes good or bad reasoning in cosmology.

Let us use an example to illustrate the case, and to more clearly illuminate what health science is, compared to a science like cosmology.

What if all politicians based their policy decisions on RCTs, with perfect design, generalizability, power, etc.? No decisions would ever be made.

This is exactly the situation in many areas of health science, medicine, nutrition science, etc.

That is why comparing medicine to physics and decrying the former for not measuring up to the latter is asinine. It totally misses the point of what medicine is about: making practical decisions.

When the point is making practical decisions, evidentiary standards radically shift: they go from a) austere scientific principles to b) making use of whatever is at hand to accomplish the task in the most competent way available.

I’m not the first person to say these things. They are obvious.

As a final note, this does not mean that we should abandon careful scientific principles. On the contrary, the difficulty of coming to good conclusions because strong evidence is so often absent requires us to double down on rigor and try to produce more of it–to ground the decisions we must make in increasingly strong evidence. It is precisely because we often have such little good evidence that we should take good science so seriously.

But given the flaws in the science, how do we deal with it scientifically *now*? This is a philosophical question and a lot more comes into play than I have just addressed. But I wanted to make a bare-bones case explaining one point of view.

Also: I’m not saying that the effect of animal protein in rabbits is the basis of my views. Rather, I’m saying indirect evidence such as that suggested by animal models has a greater role to play in forming conclusions in the health sciences than one like cosmology or physics. In the latter, such evidence would be frustrating. In health science, such evidence is sometimes necessary!

It’s nothing mind-blowing, but I guess these things sometimes need to be said–or rather, these assumptions about the way we approach science should be articulated because that’s the first step to understanding–both of each other and ourselves–and discussion at a deeper level.

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Help me communicate good science–and how to think about it–by supporting me at https://nutritionalrevolution.org/support-me/.

— Kevin

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