New research presented at the 2023 American College of Cardiology meeting shows that the popular ketogenic diet, which consists of consuming high fats, moderate proteins, and few carbohydrates, is linked to a nearly 2X increased risk of cardiovascular disease.
It is clear that diets come and go based on fads, mostly without solid scientific evidence supporting them, or promoters of the diet cherry-picking bad science while ignoring higher quality evidence that might not support the diet. I always have to remind people that weight loss (probably the number 1 reason to diet) is ALWAYS a simple equation — calories consumed must be much less than the calories burned.
These fad diets always try to invent reasons, without much evidence, why that basic equation doesn’t apply to them, but there’s no way around the basic equation of weight loss. There are no miracle foods that induce the burning of calories at a higher rate than other foods.
I write a lot about diets and nutrition (and vaccines, of course), and this research may be another reason to consider the Mediterranean diet as a better choice for long-term cardiovascular health while aiding in weight loss.
As I usually do, I will present the data and critique it for the reader. But I am here to teach, not profess that I have the Truth™ handed down from the ivory tower. The evidence does not support the healthiness of the ketogenic diet.
What is the ketogenic diet?
The ketogenic diet, sometimes called the keto diet, is a diet that is high levels of fats, moderate levels of protein, and extremely low levels of carbohydrates. Interestingly, it was originally developed not as a means of weight loss, but to treat epilepsy. It eventually was replaced by much more effective methods such as anti-convulsant medications.
The premise of the weight-loss ketogenic diet is that if the body is deprived of glucose obtained from carbohydrate foods, it will produce energy from stored fat, which is biologically plausible. A typical version of this diet for adults has about 50% of the food by weight coming from fat (70% of calories).
In 2021, the American Heart Association issued a scientific statement of guidance for diets that improve cardiovascular health. They stated that:
…there is insufficient evidence to support any existing popular or fad diets such as the ketogenic diet and intermittent fasting to promote heart health.
It appears that for the past few years, science is not supporting the efficacy of the ketogenic diet for weight loss or heart health. Now, if there was good evidence that the diet did reduce weight over a long period of time, that would incidentally improve cardiovascular health. Since long-term weight loss has not been observed, the quality of the diet itself has a negative impact on cardiovascular outcomes.
New ketogenic diet research
In research presented on 5 March 2023 at the American College of Cardiology (ACC) Scientific Session/World Congress of Cardiology (WCC) 2023, Iulia Iatan, MD, Ph.D., University of British Columbia, Vancouver, Canada, and colleagues demonstrated an association between a carbohydrate-restricted diet, such as the ketogenic diet and a greater risk of atherosclerotic cardiovascular disease.
For this study, Iatan and colleagues defined a low-carbohydrate, high-fat diet as consisting of no more than 25% of total daily energy from carbohydrates and more than 45% of total daily calories from fat. The carbohydrate intake was slightly higher than a typical ketogenic diet.
The researchers analyzed data from the UK Biobank, a large medical database with detailed health data from over half a million people living in the United Kingdom who were followed for at least 10 years.
On enrollment in the UK Biobank, participants completed a one-time, self-reported 24-hour diet survey. At the same time, each participant had blood drawn to ascertain their levels of cholesterol. The researchers identified 305 participants who indicated that they followed a low-carbohydrate, high-fat diet. These participants were then matched by age and sex with 1220 individuals who reported eating a standard diet (for the UK).
The researchers presented the following results:
- 73% of the participants were women and the average age was 54 years.
- Those on the ketogenic diet had a higher average body mass index (27.7 vs 26.7) and a higher incidence of diabetes (4.9% vs 1.7%). This does imply that those on the keto diet had a higher BMI or incidence of diabetes, it may mean that those participants who had a higher BMI or had diabetes chose to consume a ketogenic diet.
- Those on the keto diet had a significantly higher level of LDL cholesterol (known as bad cholesterol). LDL levels were 3.80 mmol/L (147 mg/dL) in the keto-like group vs 3.64 mmol/L (141 mg/dL) in the standard group.
- Those on the keto diet also had a higher level of apolipoprotein B (an indicator of “bad cholesterol”). Levels of apolipoprotein B were 1.09 g/L (109 mg/dL) in the keto group and 1.04 g/L (104 mg/dL) in the control group.
- After an average of 11.8 years of follow-up, 9.8% of participants on the low-carbohydrate/high-fat diet vs 4.3% in the standard diet group experienced one of these cardiovascular events — angina, myocardial infarction, coronary artery disease, ischemic stroke, peripheral arterial disease, or coronary/carotid revascularization.
- After adjusting for confounders, such as smoking, diabetes, obesity, and hypertension, the researchers found that individuals on the high-fat, low-carbohydrate diet had a 2X higher risk of a cardiovascular event compared to the standard diet group.
Before I get to my thoughts about this study, I need to give my standard disclaimer about nutritional studies — they are difficult to control and analyze. The diets of each participant was self-reported, meaning they were not locked in a building and fed only the diets described. This disclaimer applies to positive and negative studies about any diet.
Furthermore, this is an observational study. Again, it’s not a clinical study where we could control the diets of each participant.
All this being said, we have good evidence that a high fat diet can have deleterious effects on cardiovascular health. And there may be some unknown metabolic pathway that produces more bad cholesterol when consuming a high-fat diet. And we know that LDL cholesterol is linked to bad cardiovascular outcomes, like heart attacks.
The American Heart Association is generally opposed to these types of diets and is becoming more inclined to support the so-called Mediterranean diet which has moderate levels of “good” fats, higher levels of dietary fiber, and a broad amount of micronutrients that are necessary for good health.
For the time being, I’m giving this research 4 out of 5 stars, though a conclusive clinical trial would really be convincing (if it is even possible to do one).
Generally, I’m going to be highly skeptical of all diets because I understand how weight gain and loss work, and I am unconvinced of magical ways around the simple calories consumed < calories burned. Right now, the cardiologists who study nutrition are also highly skeptical of the ketogenic diet, so unless that changes, I’m sticking with the science and scientists on this subject.
- Freeman JM, Kossoff EH, Hartman AL. The ketogenic diet: one decade later. Pediatrics. 2007 Mar;119(3):535-43. doi: 10.1542/peds.2006-2447. PMID: 17332207.
- Lichtenstein AH, Appel LJ, Vadiveloo M, Hu FB, Kris-Etherton PM, Rebholz CM, Sacks FM, Thorndike AN, Van Horn L, Wylie-Rosett J. 2021 Dietary Guidance to Improve Cardiovascular Health: A Scientific Statement From the American Heart Association. Circulation. 2021 Dec 7;144(23):e472-e487. doi: 10.1161/CIR.0000000000001031. Epub 2021 Nov 2. PMID: 34724806.