Are there ‘major doubts’ about the safety of keto?

keto diet doubts

Another day, another scary news story… Last Thursday, Business Insider whipped up concern with this catchy headline:

But are there really three huge new studies “casting major doubts” about keto and low carb? Let’s take a look.

Study #1: Prospective cohort study published in Lancet Public Health
Surprise! This is the same poor quality observational study for which Business Insider wrote a similar catchy headline in August. We wrote about the problems with this study last month. As did Nina Teicholz, with her op-ed in The Wall Street Journal. As did Dr. George Ede, in Psychology Today. As did functional medicine practitioner Chris Kresser, at length on his blog. If you prefer live TV, prominent cardiologist debunked this study’s claims as completely false on the BBC News. The common thread is that there is nothing new or newsworthy about this poorly designed observational study.

Study #2: Prospective cohort study, not yet published
The second study Business Insider cites is not really a study yet. Rather, it is a press release by the European Society of Cardiology about an abstract presented at its annual meeting. The lead author-to-be, Professor Maciej Banach, of the Medical University of Lodz, Poland, crunched through some NHANES data, along with another unidentified but much larger pool of outcomes, and found weak associations. Until we can see the complete study, we do not know enough to write a detailed critique. But much like the problems with the first study, weak observational associations are notoriously unreliable. More on that, below.

Study #3: Prospective cohort study published on PLOS Medicine
This third study (entitled Nutritional quality of food as represented by the FSAm-NPS nutrient profiling system underlying the Nutri-Score label and cancer risk in Europe: Results from the EPIC prospective cohort study) identifies a weak association between junk food consumption and cancer incidence. There are three problems with citing this as evidence that casts “major doubts” on ketogenic living. First of all, junk food is full of carbs, and a ketogenic diet is a low-carb real food diet, not a junk food diet. Secondly, the association was surprisingly weak, with a hazard ratio of just 1.07. This means that the study data shows that the highest consumers of junk food are only 7% more likely to get cancer than the lowest consumers. This association would have to be much more robust — a hazard ratio of 2.0 and up — to be taken seriously as stand-alone evidence. Finally, the authors mention the most obvious problem in the abstract: “The main study limitation is that it was based on an observational cohort using self-reported dietary data obtained through a single baseline food frequency questionnaire…” It is impossible to extract meaning from poor quality data.

The problem with prospective cohort studies
All three of the “huge new studies” promised in the catchy headline are prospective cohort studies, which are observational. No experiment of any sort was conducted; rather, the study authors look back at and analyze existing data. If you don’t fully understand the reason why observational studies are not reliable, you are not alone. Here are three really thoughtful longer posts that take the time to lay out, in detail, the problem with relying this type of science — also called nutritional epidemiology — to establish a causal relationship:

The first one might make you feel better about eating meat. The second may — or may not — make you feel better about your keto cocktail. Either way, you’ll learn more about confounders and selection bias and the confusing mess that is nutritional epidemiology.

Because of the inaccurate food frequency questionnaires and the weak associations that often have nothing to do with causation, Stanford scientist Dr. John Ioannidis recently suggested that journalists should no longer report on these types of findings. Perhaps we can hope for more restraint and fewer misleading, scary headlines in the future.


Nina Teicholz in WSJ: “Carbs, good for you? Fat chance!”

Should journalists avoid reporting on most food studies?

‘What the Health’ review: health claims backed by no solid evidence


The science of low carb

A low-carb diet for beginners

Low carb


  1. Susan
    All in all, the best eating plan is not something you do over the short term, it's something you can sustain as a way of life. Which is why, in every scientific study, the Mediterranean diet always gets the top score.
    Replies: #2, #3
  2. Ruth Gladden
    The diet you can sustain is one where you don't have to calorie restrict, such as the ketogenic diet.
  3. bill
    "...scientific..." Ha!

    There is no such thing as a Mediterranean
    diet. Never has been. Never will be.

    Reply: #12
  4. Ruth Gladden
    Those invested in the low fat plant based dogma are really getting desperate. First they say there is no longer term proof of the effect of keto. Then they try to manufacture studies going over all of the same old bad data. How can they be comparing keto, when the only ones eating low carb thirty years ago were those that didn't listen to any medical advice? Also the results get completely skewed and inflated by the media. Total click bait... How many of these opinion pieces are written by vegans?
  5. AJor
    What bothers me most is the rise of the "low-fat, plant based diet" "fad" coincides with the rise of obesity and heart disease. Not just in the United States, but world wide. Sure you can push the idea that fast food has made it harder to eat the "doctor approved" diet, but has it really? We as a society have pushed to eliminate as much fat as possible from everything we eat. We have called into question the ability for a person to eat butter and be healthy.

    I think there is something finicky going on in dietary science, and it isn't pursuing truth.

  6. Moose
    Business Insider is nothing but a click bait tabloid. I used to read their articles, but I got such of seeing such nonsense garbage coming from them, basically about whatever clickbait bullshit they can cash in on, that I've stopped reading anything they "publish"
  7. Julia Clare
    Part of the original Mediterranean diet has been pork. Lard. If the pigs are fed in the natural world, seasonal foods like acorns and not intensively farmed they make healthy fat and meat. You never see mention of this is all the contrived Mediterranean Diet info.
  8. Chris
    Population control crowd want us to eat plants only. This is all political.
    Reply: #13
  9. Maurice
    Been on LCHF lifestyle (float between strict, moderate, liberal) for nearly 3 years. Still waiting for something "unsafe" to happen.
  10. Tim H
    Study #2 is linked here:

    I am able to see the abstract but for full text it says, "You do not currently have access to this article". It is not clear whether that is because I am not a subscriber to the European Heart Journal or whether that is because it is not even published yet so no one has access to full text. I suspect the latter.

    Sidelight: The press release says "SOURCES OF FUNDING: No funding." Prof. Maciej Banach was an Undersecretary of State at the Ministry of Science and Higher Education of the Republic of Poland (2010-2012). His LinkedIn profile apparently lists 13 jobs. He is a member of numerous professional associations. So he obviously has complex financial and career interests. The possibility of indirect influence of this study remains.

  11. Michael
    The longer I eat Keto and do intermittent and prolonged fasting the more I see how wrong I was eating growing up. How could anyone want to go back to eating processed foods once progressing on LCHF. In the end the only good you are doing is lining the pockets of food manufacturers. Is that really good. I rather have my money go to fresh food farmers.
  12. Una
    Well I think a lot of my continental friends would disagree!
  13. Una
    My French dentist in London has been a vegan for nearly twenty-four years and forbids sugar, including wine. It suits him and he's not waving the flag per se for animal rights - too busy fixing teeth from excess sugar eaten in all forms by his patients!
  14. Donna
    I've been on keto for 3 years, long story short, my only personal issue I've had is that after a year my colonoscopy schedule went from every 5 years to every year because of the amount of polyps needed to be removed. Dr said it was because of the high amount of fat in my diet. Same exact thing for my husband ( we have our colonoscopies at the same time frame). This caused us to reduce our amount of fat and now we are both back on a 5 year schedule due to no polyps at our latest colonoscopy. Unfortunately I now have to wait 5 years to see if it really is the reduction of fat or just a fluke. The fat that I've cut back on is from fatty meats and mtc oil. Cut back, but not cut out. Have you encountered this before? Thank you

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