New study casts doubt on the benefit of popular diets and supplements
A new study published in Annals of Internal Medicine suggests that low-fat and Mediterranean diets provide no proven benefit for cardiovascular outcomes or risk of death. This goes against much of the standard advice many health professionals provide, and thus the findings raise important questions.
In addition, the study suggests there is no benefit from taking vitamins A, B, C, D, E, calcium, iron and multivitamins, but there may be a small benefit from taking folic acid (at least in Asia) and omega 3 supplements.
How did they come to these conclusions? The authors evaluated 277 trials including almost 1 million people. A big strength of the study is that they included only randomized controlled trials or meta-analysis of randomized controlled trials, and they purposely excluded the much weaker observational trials.
Even when including only the highest level of evidence, questions still remain. For instance, they concluded there was moderate level evidence that low-sodium diets provided cardiovascular benefit. But we still need to understand who was included in these studies, what was their ethnicity, what was their baseline diet and their baseline metabolic health, and many more details that we don’t know. There is plenty of reason to believe that sodium intake as part of a real-foods diet is much different than salt intake as part of the standard American diet. Yet this trial does not help clarify that point.
They also found no evidence that low-fat diets improved cardiovascular outcomes or mortality. Thus, we have to ask how did the government and cardiology societies conclude that we all need to eat a low-fat diet? Those seemingly ancient conclusions were almost exclusively based on the much weaker quality observational data, something this trial excluded.
But just because this study only included randomized controlled trials, that doesn’t make it perfect. You see, the biggest problem with trials like this is that they assume people are all the same and we all respond the same to nutritional changes or supplements. They assume we can generalize findings to the population as a whole.
Given our different genetic makeups, different environmental exposures, and different baseline health challenges, it is crazy to think we can generalize findings to an entire population.
If anything, trials like these reinforce our need to approach each person as an individual.
They can provide a general framework, but that is all. We can assume low-fat diets don’t benefit everyone. We can assume blanket recommendations for vitamin D or vitamin B are not needed for everyone. And we can assume low-salt diets may benefit some people who are salt sensitive and follow standard Western diets.
However, these trials should absolutely not prevent healthcare practitioners from individualizing treatment plans, supplements, and dietary interventions to help each individual person.
Hopefully, if we all start from the baseline of a real-food, low-carb lifestyle, then supplements may be unnecessary as we can get all we need from our food. If we cannot, and we have obvious deficiencies, then we should address those accordingly.
Thanks for reading,
Bret Scher, MD FACC