Dear Aseem: nutrition has hijacked evidence-based medicine

My friend Aseem, 

early this morning you shared with me a sensationalistic news of a “Harvard professor” claiming that coconut oil is poison, and my first reaction was “let me look at the evidence, I know nothing about this oil”. Actually, I'm too lazy to look for this evidence. I already know the answer: coconut oil does not matter; neither for good, nor for bad. 

Apart from eating enough calories to become obese or drink alcohol pathologically, food specifics should not be a major cardiovascular concern. Specially coconut. In a scientific sense, the value of food is overestimated. It usually happens with medical opinion: we tend to overestimate the value of beneficial interventions or the harmful effect of risk factors (JAMA Internal Medicine). That’s how the human mind evolved, not much calibrated for “value”. I think it happened with the so called "Harvard professor".

Quality scientific research either fail to show specific dieting effects on clinical outcomes or show very small effects. In a peculiar systematic review from Ioannidis exploring the tiniest effect sizes in literature, nutrition was the field most prevalent; second, when randomised trials adjust for calorie intake and confounding variables, the type of diet does not show much impact on weight or clinical outcomes (PLOS ONE systematic review). The DIETFITS trial recently published in JAMA is one example of such evidence.

So we should not investe our time discussing efficacy of diets, meaning an explanatory concept or intrinsic property.

I know, it seems frustrating, skepticism is boring. By I am not a boring skeptical. I just found a solution to make dieting an interesting issue again: Aseem, let’s shift the discussion to effectiveness.

Efficacy is tested by randomized trials, in which allocation for intervention takes nothing into account (it is random). Thus, a randomized trial does not evaluate the effect of preferences on outcomes, it is a pure explanatory concept.

In the real word, preferences may be are taken into account for dieting decision. In this circumstances, if preference and choice match, effectiveness tend to be superior to efficacy, because patients get motivated to perform well with the intervention they prefer. Thus, if a type of diet is an easier match with general preferences, it should be a more effective diet. 

For example, in my non-scientific experience, I have a sense that people on low-carb diets are happier with the experience and results obtained, as compared with other diets. I claim the test of this hypothesis should be pursued. Studies should be planned to test effectiveness. 

Here are some ideas:

• Pragmatic randomized trials, in which just a general recommendation is given and we let people develop their eating habit, their meals in a pragmatic way. Just like a long-term diet takes place in the real world (habit). In this pragmatic circumstance, I suspect a low-carb individual will eat less calories, are happier, lose more weight.

• Observational studies with statistical adjustment for outcome predisposition, as opposed to propensity scores. The traditional propensity score should not be utilised for the test of effectiveness, because it adjust for the very preference that will improve result in a preference-matched choice. Observational studies lose opportunity to test effectiveness by focusing on the non-sense of pursing efficacy of life-style by adjusting for propensity.

• Cross-over studies, to measure the outcome happiness at the end of each intervention. Happiness improves effectiveness and if people are happier with a certain diet, the result will be better.  

Science is more about the right question as opposed to a platonic answer. Sometimes we ask the wrong questions in unfruitful debates. 

I am glad that you woke me up (considering our time difference) with your provocation on coconut oil. I know that, as a cardiologist, your concern is not coconut oil (maybe as a chef it is). You are really concerned with the “miscarriage of science” performed by fake scientific news of this type. To say that any specific food is poison is non-scientific. To use the title of a “Harvard professor” to make such a statement is a good example of eminence-based medicine, as opposed to evidence-based medicine. 

I think advocates should have a role to use the dieting issue to clarify the different values of these two complementary concepts: efficacy and effectiveness. The important issue here is science, not coconut oil.

Meanwhile, I have to confess: personally, I love the subject of dieting and I have my own preferences. Professionally, I should stick with evidence. We need effectiveness evidence.