How can the credibility of dietary recommendations of medical sciences and EBM be upheld in light of a history of radical changes of its claims?

Question

I know the typical argument is that science is a work in progress and is constantly self-improving.

However, self-improvement demands some continuity in claims. For example, relativistic physics was a generalization rather than negation of Newtonian physics.

This does not seem to be the case with regard to dietary recommendations. The history of outright U-turns makes it hard to claim self-improvement. For example, for quite a long time we were hearing that eggs were unhealthy and should be avoided, but now eggs turn out to be healthy. Similarly with tomatoes and coffee. Glucose, on the other hand, was once used as a medicine for heart diseases and headaches; now it is as detested as all other simple sugars. Fructose was considered a healthier alternative even after glucose had been banned, but is now considered exceptionally unhealthy as well.

A little background maybe... I have two people in my closest family whose views radically contradict these of the WHO¹. Worse, they are preaching "their medicine" to the rest of the family². This leads to numerous discussions. In one of these discussions I pulled the "evidence-based medicine" and "scientific method" card. This was countered with the above argument: "Your 'scientific method' today claims the exact opposite of what it was claiming yesterday, which was itself an outright denial of what it had been claiming ereyesterday. With no doubt, today's recommendations will also be completely invalidated tomorrow. Maybe we'll soon start hearing that sugar is very healthy, while fish should be avoided?"

Reluctantly, I admitted I had no answer for this. How to uphold the reliability of evidence-based medicine in light of this?

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¹ _{Their views also contradict each other, so it's kind of fun to watch them talk.}

² _{I don't want to start believing in what is considered outright quackery by mainstream medicine, however, in order to avoid cognitive dissonance I feel I do need convincing counter-arguments... At least convincing enough to stay convinced myself. (I don't believe I can convince anyone else.) And saying that "WHO said something, therefore it must be true" seems a surprisingly weak argument, especially when bombarded with (pseudo?)arguments originating from (pseudo?)scientists who oppose the WHO, which - sometimes - seem cleverly-crafted enough to convince the ignorant. After all, if they weren't, the (quacks?) behind them would've already went bankrupt.}

Answer 1

There are a few common argumentative strategies that defenders of science use in these kinds of cases.

One strategy is to blame hype. Someone has taken properly conducted, fallible, limited scientific findings and extended them beyond what the evidence actually indicates. Often the blame will be placed on journalists (see confused's comments). But scientists themselves engage in hype. And evidence is ambiguous. It doesn't actually say anything; it requires human interpretation and generalization. For instance, suppose we have a feeding study that used 60 labs rats and lasted 90 days. Do the results of this study tell us anything about humans and other mammals? Or do its results only apply to rats? Or, indeed, maybe its results only apply to these particular 60 rats. Because scientists can reasonably disagree about how far the evidence can be extended, it's often unclear where to draw the line between "responsible inference" and "hype."

Another strategy is to point to non-epistemic values. Epistemic values are factors such as simplicity that (we think) tend to lead us to true conclusions. Non-epistemic values are other factors, that (we think) don't tend to lead us to true conclusions, such as a concern to protect human health or to make a lot of money. One common view, the value-free ideal, holds that non-epistemic values have no legitimate role to play in evaluating hypotheses.

As a defense of science, we might say that non-epistemic values play a role in some cases, and this explains the few problem cases; but that, on the whole, scientists act according to the value-free ideal, so we should trust scientists.

Critics of science make a similar appeal to value-free science. But they might argue that non-epistemic values are widespread in science. You haven't told us much about your relatives. But, knowing the type, I suspect they might think non-epistemic values run rampant in "mainstream medicine." Namely, they might think that medical research and practice are dominated by the pharmaceutical industry, who want to sell us lots of expensive drugs and treatments in order to make a lot of money. Because "mainstream medicine" is saturated with these profit-seeking non-epistemic values, it shouldn't be trusted.

You might respond that, in the case of nutritional studies, we're typically talking about "whole foods" — eggs, coffee, meat — not highly processed foods, much less pharmaceuticals. Often this research is sponsored by the relevant industry — the egg industry sponsored a lot of the research showing that eggs don't raise our cholesterol, for example. But this industry influence has nothing to do with the influence of the pharmaceutical industry on biomedical research.

That's not a very compelling response, though. I think a better response is to question the value-free ideal. Why think that non-epistemic values are necessarily bad for science?

One useful alternative to the value-free ideal is called inductive risk. The framework was promoted by Heather Douglas, especially through her book Science, Policy, and the Value-Free Ideal. Inductive risk argues that we should take the non-epistemic consequences of a hypothesis into account when we evaluate it. Consider a breast cancer screening. A false negative result (there is cancer, but the test says there isn't) could lead to an avoidable death, while false positive results (no cancer, but the test says there is) could lead to unnecessary surgery and chemotherapy. We should take these consequences into account — which consequences are worse — when we evaluate the results of the screening. According to inductive risk, this is a legitimate way that non-epistemic values can influence scientific reasoning.

Inductive risk can help us interpret nutritional research. Suppose an (imaginary) study indicates that ketchup increases the frequency and severity of migraines. If we accept this finding, we would probably avoid or stop eating ketchup. If you, like me, don't like ketchup, then this wouldn't be a big deal. I might start avoiding ketchup a little more actively, just in case. Or, someone who's already prone to migraines and strongly wants to avoid getting more might avoid ketchup, even if they really like it. By contrast, if you LOVE ketchup and don't get migraines, you might reasonably reject this finding, or keep eating ketchup until we have more evidence.

In other words, the study's finding sets up a tradeoff between the pleasure of eating ketchup and the risk of migraines. Inductive risk says it's legitimate to interpret the evidence in light of where we stand on this tradeoff.

Now suppose the Ketchup Manufacturer's Association sponsors a study finding that ketchup does not increase the frequency and severity of migraines. From an inductive risk perspective, the Ketchup Manufacturer's Association probably has a very strong preference for people eating lots of ketchup, and probably doesn't care about migraines. But most people, I assume, would want more balance in their ketchup-migraine tradeoff. This means that most people would interpret the study's findings differently from the Ketchup Manufacturer's Association. Maybe the new evidence nudges us a little bit towards "ketchup is probably okay after all." But just a little bit; we might still try to reduce the amount of ketchup we eat.

Answer 2

"Evidence-based medicine" is a school of thought in doctors' offices and hospitals that was enunciated in major journals in the 1990s by Dr. David Sackett of Oxford:

Evidence based medicine is the conscientious, explicit, and judicious use of current best evidence in making decisions about the care of individual patients.

Evidence based medicine: what it is and what it isn't.

The WHO seeks to promote "evidence-based" practice with doctors around the world. A textbook example of "not evidence-based practice" is doctors in Africa using a particular drug against malaria even though the drug had lost its potency when the pathogen became resistant.

You should be able to see that the "evidence-based" standard for medicine has many subjective elements, such as "conscientious", "judicious", "best", "making decisions", "care", and "individual". It's not really different from saying "be smart about it!"

Also, and this is less obvious: the evidence-based standard requires care for individual patients. Uncontroversial, right? Not so! Doctors are faced every day with ethical dilemmas in which the interests of the insurers, the pharmaceutical manufacturers, the institutions, other doctors, themselves, patients' family members, non-government organizations, etc. etc. etc. compete against the interests of the patient. The evidence-based standard seeks to stamp out predatory prescribing for profit, unscrupulous research, and other health-system excesses.

Evidence-based medicine does not solve the problem of science's credibility, particularly with regard to a single study, paper, article, drug, etc. The person applying the science must make the best judgment that he or she can, and to do that will involve as much wit, discernment, care, and honesty as a person can muster.

Answer 3

The OP offers the following scenario:

I have two people in my closest family whose views radically contradict these of the WHO¹. Worse, they are preaching "their medicine" to the rest of the family². This leads to numerous discussions. In one of these discussions I pulled the "evidence-based medicine" and "scientific method" card. This was countered with the above argument: "Your 'scientific method' today claims the exact opposite what it was claiming yesterday, which was itself an outright denial of what it had been claiming yesterday. With no doubt, today's recommendations will also be completely invalidated tomorrow. Maybe we'll soon start hearing that sugar is very healthy, while fish should be avoided?"

One of the advantages of having a dietary based theory of disease is that it offers hope. If crippling diseases are the result of genetics or age there is little that one can do to avoid them. But if a theory of disease involves what one is putting in one's mouth, or exposing oneself to in the local environmental or even inappropriate exercise, there is hope that one can do something to prevent the disease. Preventing diseases not only benefits the person who is ill, but the family members who have to take care of them.

As the members of the OP's family note, recommended diets, what toxins to avoid or exercises to pursue change. Can one trust medical science to know what is best? No. One can't. If one could, we wouldn't have to worry about getting these diseases.

One needs to maintain one's skepticism without dismissing any empirical evidence. In other words if a relative follows a diet and loses weight one should take that empirical evidence seriously and perhaps follow that diet if one needs to lose weight. If one has other bio-markers, such as reported in blood tests, that are out of normal range, suggesting the onset of diabetes, dementia, auto-immune disease or whatever, one should take that empirical data seriously.

Given the above, let's consider the question:

Reluctantly, I admitted I had no answer for this. How to uphold the reliability of evidence-based medicine in light of this?

There is no need to uphold the reliability of any evidence-based medicine unless the evidence shows that it actually works.