Keto diets may cause ‘significant risks’ for pregnant women, physicians say

David S. Seres, MD, ScM, PNS, FASP

This article raises some important and legitimate concerns about the keto diet, but it should not be considered definitive. Rather, it tends to reflect the opinions of the authors.

Scientific credibility has been seriously challenged and we in science should do our best to explain how we do what we do so that the public will be better able to understand what they are hearing from the media.

Most of the authors are affiliated with and / or employed by the Physicians Committee for Responsible Medicine (PCRM), which funded the work. PCRM is a vocal advocate of a plant-based diet. This is a popular and probably correct philosophy – less meat is better. Keto diets rely heavily on meat for a high protein, high fat diet that is almost devoid of carbohydrates. If you’re anti-meat, anti-keto goes hand in hand.

The authors properly disclose their affiliations, but the reader should always be concerned with the objectivity of the authors and the strength of their conclusions when such a conflict of interest exists.

The Crosby paper is what is known as a narrative review. It is not direct research and there is no new knowledge. To build a narrative overview, authors often find studies that support what they believe to be true.

This is the least rigorous type of scientific publication as there is no systematic extraction of the available research. For any study included in a narrative review that reports a negative effect, there is a good chance that other studies that are not included will report a positive or no effect.

While the authors of the Crosby paper accurately detail the content of the various articles they review, the method by which their own article was written leaves a high risk of biased reporting.

Keto diets limit carbohydrates and require strict adherence to create a metabolic disorder that burns more fat. Instead of glucose, its usual fuel, the body uses ketone bodies, which are made by breaking down fat. This type of diet requires a lot of work. There are many unanswered questions as to whether a keto diet can even be maintained over the long term.

There are theoretical concerns about the keto diet. I emphasize that they are theoretical. Theoretical concerns should be weighed heavily, however, when the value of a keto diet has not yet been demonstrated in rigorous long-term randomized studies, except perhaps for controlling drug-resistant seizures, and is itself theoretical.

It is believed that the initial rapid weight loss on a keto diet is primarily due to water loss and may not be indicative of true weight loss. Also, people often feel bad for a long time, with dizziness, fatigue, pain and so on. High protein intake is linked to a higher risk of kidney stones and kidney dysfunction, and it is believed that long-term high protein intake may predispose people to osteoporosis.

So I agree with the authors that the keto diet won’t be ready for prime time until high quality randomized long-term studies to quantify these effects have been conducted. But I do not share the strength of their beliefs given the quality of the evidence.

Randomized studies of the effects of diets are difficult to conduct. You’d have to agree with a lot of people randomly assigned to stay on keto diets long enough to see, for example, how many heart attacks or how much cancer they have. Such a study may take hundreds, if not thousands, of subjects to adhere to the diet, likely for decades.

More importantly, before any of these nutrition studies can be conducted, we need to figure out how to motivate people to change their eating habits. In this era of personalized medicine and nutrition, behavior and motivation should be personalized first when trying to change the way people eat.

Find out what makes each individual change their behavior. For some, it’s a reward. For others, it means avoiding something punitive. When we learn how best to motivate behavior change, we may be able to study these things properly.

There needs to be a better balance between the public’s desire to know what to do and the transparency of science about the strength of our knowledge. While the overall conclusions in the paper agree with my own prejudices, the strength of the data does not deserve the strength of the conclusions of Crosby and colleagues.

David S. Seres, MD, ScM, PNS, FASP

Diet Section Editor, UpToDate

Former Chairman, Medical Nutrition Council, American Society for Nutrition

Professor of Medicine at the Institute for Human Nutrition

Director of Medical Nutrition, Associate Clinical Ethicist, Columbia University Irving Medical Center

Disclosure: Seres does not report any relevant financial information.

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